Materials for electronics and optoelectronic applications away from silicon.G
Transparent conductive materials: from fundamental understanding to applications
Transparent Conductive Materials (TCM) play a pivotal role in many modern devices such as: solar cells, flexible light-emitting devices, touch screens and flexible transparent thin film heaters. This symposium aims at exploring the most recent ways to better understand the fundamental properties of TCMs and improve their integration in devices.
Transparent, electrically conductive materials (TCM) are important components of displays, touch-screen layers, thin film solar cells, organic light-emitting diodes (OLEDs) and transparent heaters. Conductive oxides such as ITO, AZO or FTO presently have the largest market share. Recent demands for mechanical flexibility and uncertainties in the availability of rare earths spurred the search for alternatives. This symposium aims to bring together research on traditional Transparent Conductive Oxides and emerging TCMs based on graphene, carbon nanotubes, metallic nanowire networks, metallic grids, and composites. The symposium will be concerned with both experimental and modelling approaches, and with the goal of improving their integration in devices.
A compromise between electrical conductivity and transparency imposes several specific requirements including for instance the design of appropriate interfaces and layers with defined microstructures and long-term stability. This symposium will bring together scientists and engineers from universities, research institutes and industries in order to comprehend TCMs properties and work with the target of fabricating stable state-of-the-art transparent electrodes. Deposition of layers containing one or more of the abovementioned conductive nanostructures and their characterization will be the main focus. Theoretical models that provide design rules for conductive layers based on anisotropic or isotropic nanostructures will be covered. Deeper experimental or theoretical insights into the materials will be sought and correlated to mechanisms responsible for key electrical and optical properties. Another focus will be on strategies to overcome limitations of the currently available technologies, and the integration of transparent conductive materials into functional electronic devices. Several keynote speakers will be invited to present their recent scientific contributions. We will also seek industrial contributions to give an insight into the growing commercial relevance of nanostructure-based TCM.
Hot topics to be covered by the symposium:
- TCO electrical and optical properties
- Mechanisms of, and limitations for, electrical conductivity in transparent materials
- Synthesis and processing of novel types of transparent electrode materials
- Optical properties of TCMs: experimental and modelling approaches
- Interface properties of TCMs
- n-type TCOs, p-type TCOs
- Metallic nanowire networks
- Carbon nanotube and graphene based materials
- Composites of metal nanoparticles and polymers
- Composites of carbon-based nanostructures
- Combinations of oxides, metals and carbon-based TCMs
- Diffuse transparent electrodes
- Electrical, thermal, chemical stabilities of transparent electrodes
- Upscaling and advanced large-area processing
- Integration of transparent electrodes into functional devices
- Mechanical flexibility of transparent conductive materials (TCM)
- Modelling and design
Invited speakers (confirmed):
- Delfina Munoz (INES, Bourget-du-Lac, France)
- Qiping Pei (University of California at Los Angeles, USA)
- Joris Proost (University of Louvain, Belgium)
- Thomas Riedl (University of Wuppertal, Germany)
- David Scanlon (University College London, UK)
- Yuzo Shigesato (Aoyama Gakuin University, Japan)
- Benjamin Wiley (Duke University, USA)
- Amelie Catheline (Linde Nanomaterials)
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Transparent Conductive Oxides Part 1 : Qibing Pei
Authors : Delfina Muñoz
Affiliations : Université Grenoble Alpes, CEA, LITEN, INES, 50 avenue du Lac Léman, F-73375 Le Bourget-du-Lac, France
Resume : Transparent Conducting Oxides (TCO) have been historically playing an important role on thin film solar cells technology as the play the double role of transparent /antireflection and collection layer. They have been widely improved on the front side of devices on the electrical behavior and transparency but also on the back side to improve infra-red management and light trapping. Nowadays, there is a growing interest on TCOs in the silicon solar cells development, especially on the so called amorphous/crystalline heterojunction technology (HJ) though the very thin amorphous silicon layers do not fulfil the electrical/optical properties to collect carriers on the front and back side. Improvements on the material, interfaces, deposition techniques and integration of different materials have been done the last years to reach very high efficiency devices over 23%. In this paper, a wide description of the interaction between TCOs and the HJ technology will be presented. Description on the optimization on front and back TCOs and integration on complete devices fabricated at CEA-INES will be shown. Finally a discussion on the large scale approach will be assessed.
Authors : Harald Scherg-Kurmes (1), Ahmad Hafez (1), Michael Siemers (2), Andreas Pflug (2), Rutger Schlatmann (3), Bernd Rech (4), Bernd Szyszka (1)
Affiliations : 1. Technische Universität Berlin, Einsteinufer 25, 10587 Berlin, Germany; 2. Fraunhofer IST, Bienroder Weg 54E, 38108 Braunschweig, Germany; 3. Helmholtz Zentrum Berlin, PVcomB, Schwarzschildstr. 3, 12489 Berlin, Germany; 4. Helmholtz Zentrum Berlin, Institute for silicon photovoltaics, Kekulestraße 5, 12489 Berlin, Germany
Resume : Hydrogen doped Indium oxide (IOH) is a transparent conductive oxide offering great potential to optoelectronic applications. Because of its high mobility of over 100 cm2/Vs, high optical transparency in the near infrared spectrum and a low electrical resistivity of approx. 300 µΩcm can be achieved. We have simulated the RF-sputtering deposition process of IOH by Particle-In-Cell Monte-Carlo simulation. At the surface of ceramic sputtering targets, negatively charged oxygen ions are created. These ions are accelerated towards the substrate in the plasma sheath with energies up to 150 eV. Particle energies in this order of magnitude damage the growing film, reduce crystallinity and should be avoided in order to achieve good material properties. The influence of a negatively biased mesh inside the sputtering chamber on particle energies and distributions has been calculated. We found that the mesh decreased the high energetic oxygen ion density at the substrate, thus enabling a more homogeneous IOH film growth with enhanced electrical properties. The theoretical results have been verified by XRD, 4-point-probe and hall measurements of statically deposited IOH films on glass.
Authors : Stephanie Weller, Manuela Junghähnel, Thoralf Gebel
Affiliations : Fraunhofer Institute for Organic Electronics, Electron Beam and Plasma Technology FEP;Fraunhofer Institute for Organic Electronics, Electron Beam and Plasma Technology FEP; DTF Technology GmbH
Resume : Flash lamp annealing (FLA) is a fast annealing method using xenon flash lamps with pulse times in the millisecond range. Therefore, only the surface is heated while the bulk of the substrate remains cold. Due to a reduction of heating and cooling times, this method is suitable for efficient in-line and roll-to-roll processes. We used FLA to improve the properties of transparent conductive oxides, which are widely used in display technology, transparent electronics, photovoltaics and OLED devices. Indium zinc oxide (IZO) and Indium tin oxide (ITO) thin films were deposited by dc magnetron sputtering in an in-line machine onto glass substrates at room temperature. The films were annealed by FLA at various energy densities and pulse times. We investigated the influence of FLA on the film properties in comparison to conventional annealing methods. The optical, electrical and structural properties were determined by optical spectrometer, four-point probe, Hall measurements, XRD and SEM. We achieved an improved conductivity and transmittance in the visible range for both materials. For 150 nm thick ITO films, the sheet resistance decreased from 42.7 Ω□ to 13.3 Ω□, which is comparable with annealing in air at 300 °C. XRD measurements showed an increased crystallinity of the ITO films while IZO stays amorphous. The carrier mobility in dependence of the structure will be discussed.
Authors : S. Prucnal1, Jiada Wu2, Raul Gago3, Kun Gao1, Fang Liu1, Shengqiang Zhou1, Hua Cai2, Dietrich R. T. Zahn4, Ovidiu D. Gordan4, and Wolfgang Skorupa1
Affiliations : 1. Institute of Ion Beam Physics and Materials Research, Helmholtz-Zentrum Dresden-Rossendorf, P.O. Box 510119, 01314 Dresden, Germany; 2. Department of Optical Science and Engineering, Fudan University, Shanghai 200433, Peoples Republic of China; 3. Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Científicas, Madrid, Spain 4. Semiconductor Physics, Technische Universität Chemnitz, D-09107, Chemnitz, Germany
Resume : Wide band gap semiconductors (> 3.0 eV) like ZnO and TiO2 are widely investigated in the field of optoelectronics for ultraviolet lasers, heterojunction solar cells, thin film transistors and light emitting diodes. Nowadays, the transparent conductive oxides (TCO) like Al- or F-doped ZnO (AZO or FZO) are basic materials for the front contact in thin-film photovoltaics. A highly doped n-type ZnO thin layer is an attractive candidate to replace the much more expensive indium-tin-oxide layer in the microelectronics industry. The optoelectronic properties of TCOs are determined by the type of doping and carrier concentration. The n-type conductivity of ZnO is easily achieved by substitution of Zn by group III elements (Al, Ga, In), or by doping with halogen elements (F, Cl or I) substituting oxygen in the lattice site. In the case of TiO2 the n-type material can be achieved by doping with Nb, Ta or F ions while p-type TiO2 can be realized by e.g. Cr doping. Here, we will present the utilization of highly non-equilibrium thermal processing of TCO/Si heterojunctions using millisecond (ms) range flash lamp annealing (FLA) techniques for the structural modification and dopant activation to form highly doped p- and n-type TCOs films on silicon substrate. The n- and p-type doping in ZnO was made by incorporation of Al and F or N and P into ZnO, respectively. While the conductivity of TiO2 films was controlled by efficient incorporation of Ta and Cr into the lattice side of titania. It will be presented that via millisecond range FLA treatment not only the optoelectronic properties but also the crystallographic orientation and phase formation of TCOs can be modified. The optical properties of fabricated TCOs were investigated using temperature dependent photoluminescence, Raman and transmission spectroscopy. X-Ray diffraction (XRD) and cross-sectional transmission electron microscopy (TEM) were utilized to study the microstructural properties while the electrical properties of the TCO layers and heterojunctions were measured using Hall Effect and current-voltage characterization, respectively. Moreover, it is shown that the annealing atmosphere, even during ms range annealing, can efficiently passivates the surface state and bulk defects in the TCOs significantly improving the near band gap emission.
Metallic Nanowires or Nanoparticles Part 1 : David Scanlon
Authors : Jiajie Liang, Shu-Yu Chou, Fangchao Zhao, Lu Li, Qibing Pei
Affiliations : University of California, Los Angeles
Resume : We have developed a flexible nanocomposite electrode comprising silver nanowires and substrate polymers that can replace ITO/glass and ITO/PET for a host of electronic applications. The mechanical properties of the electrode are determined by the substrate polymer and range from being flexible, elastomeric, shape memorable, to self-healable. The electrode exhibits low high surface conductivity, transmittance, and low surface smoothness. Light extraction efficiency of OLEDs employing the solution-processed transparent electrode is substantially higher than those on ITO/glass. Flexible OLEDs with high external quantum efficiency and luminous efficacy are being investigated for solid state lighting application.
Authors : Hugh G. Manning, Claudia Gomes da Rocha, Colin OCallaghan, Allen T. Bellew, Dave McCloskey, Mauro Ferreira, John J. Boland
Affiliations : School of Chemistry; School of Physics; Centre for Research on Adaptive Nanostructures and Nanodevices Trinity College Dublin, Ireland
Resume : Metal nanowire network (NWN) films have the ability to bring forward the next generation of devices based on flexible transparent conductors. Modelling NWNs correctly, to predict sheet resistances, involves taking into account the physical properties of the nanowires and the connectivity of the nanowire junctions. In AgNw systems the polymer coating formed during synthesis acts as a barrier to conduction where two nanowires overlap. Manipulating these junctions by electrical stressing allows for materials with tunable electrical conductivities. We report a method combining the controlled placement of nanomaterials with the surface uniformity and low volume of spray deposition to create user defined, isolated NWNs. This technique is employed to realize high transparency (>90%) and low sheet resistance (50-200 Ω) isolated Ag NWNs on transparent substrates. Through the use of a novel computational model these networks can be mapped wire for wire in simulations, avoiding costly configurational averaging of randomly generated networks. Incorporating experimentally measured values (material resistance, junction resistance, network transparency) and geometric analogues, provides the ability to predict network performances, display bottlenecks of conduction and highlight likely failure points in the network. More accurate modelling of these systems is invaluable in developing a reliable, quick benchmarking and binning tool to facilitate the design and integration into devices.
Authors : J.H.M. Maurer, L. Gonzalez-Garcia, B. Reiser, I. Kanelidis, T. Kraus
Affiliations : INM - Leibniz Institute for New Materials, Campus D2 2, 66123 Saarbruecken, Germany
Resume : Transparent Conductive Materials (TCMs) based on metal nanostructures are an alternative to ITO and used as transparent electrodes for flexible electronics, for example thin-film solar cells, displays, or touch screens. Wet-processed films of randomly arranged silver nanowire (AgNW) networks are commercially available and provide a good compromise between transparency and conductivity. Here, we use ultrathin gold nanowires (AuNWs) with diameters below 2 nm and large aspect ratios that provide mechanical flexibility, high optical transparency, and chemical inertness. After synthesis, AuNWs carry oleylamine as stabilizing ligand. The ligand shell causes high tunnel resistances at the nanowire junctions and must be removed to reach useful conductivities. We studied different soft sintering techniques and investigated their effects on conductivity, optical transmission, stability, and the structure of AuNW networks. Plasma treatments increased conductivity, stability, and left the optical transmission virtually unchanged. Optimal plasma treatments conditions reduced sheet resistances by 6 orders of magnitude up to 50 ohm/sq.  Guo and Z. Ren, Mater. Today, 2015, 18, 143  Sánchez-Iglesias et al., Nano Lett., 2012, 12, 6066  Chen et al., Adv. Mater., 2013, 25, 80  Maurer et al., ACS Appl. Mater. Interfaces, 2015, 7, 7838
Authors : Catherine Ainsworth, Brian Derby, William Sampson
Affiliations : School of Materials, University of Manchester, Manchester, United Kingdom
Resume : Transparent Conducting Electrodes (TCEs) are used in many modern optoelectronic devices such as solar cells, displays (OLEDs, LCDs) and touch screens. Silver nanowire networks are an attractive substitute for ITO as a TCE material because silver nanowires are highly conductive and the network allows good transmittance of light. Such networks can meet the industrial standards of transmittance T > 90% and sheet resistance Rs < 100Ω/sq. There have been many studies in the literature that have demonstrated correlations between the transmittance of a silver nanowire network and its sheet resistance. However, there is no agreed predictive model that couples these parameters, although it has been suggested that there are two regimes of behaviour where the network is modelled either as a percolating network or as a defective continuum. Here we demonstrate a relation that is effective in linking optical transmittance to d.c. sheet resistance that requires knowledge of two experimental measures: 1) mean aspect ratio of the nanowires and 2) mean network coverage. This relation is shown to accurately predict the relationship between optical transmission and sheet resistance for a range of silver nanowire networks with different nanowire aspect ratios produced by spray deposition. It is also shown to be consistent with data published in the literature.
Transparent Conductive Oxides Part 2 : Junjun Jia
Authors : David O. Scanlon
Affiliations : University College London, Kathleen Lonsdale Materials Chemistry, Department of Chemistry, 20 Gordon Street, London WC1H 0AJ, UK; Diamond Light Source Ltd., Diamond House, Harwell Science and Innovation Campus, Didcot, Oxfordshire OX11 0DE, UK
Resume : The most commercially successful TCO so far is tin doped indium oxide (Indium Tin Oxide ITO), which has become the industrial standard TCO for many optoelectronics applications; the ITO market share was 93% in 2013. Its widespread use stems from the fact that lower resistivities have been achieved in ITO than in any other TCO; resistivities in ITO have reached as low as 7.2 × 10-5Ω cm, while retaining >90% visible transparency. In recent years, the demand for ITO has increased considerably, mainly due to the continuing replacement of cathode ray tube technology with flat screen displays. However, indium is quite a rare metal, having an abundance in the Earths crust of only 160 ppb by weight, compared with abundances for Zn and Sn of 79000 ppb and 2200 ppb respectively, and is often found in unstable geopolitical areas. The overwhelming demand for ITO has led to large fluctuations in the cost of indium over the past decade. There has thus been a drive in recent years to develop reduced-indium and indium-free materials which can replace ITO as the dominant industrial TCO. Recent research has therefore focused both on developing alternative TCOs, such as SnO2, ZnO, and BaSnO3, which are all more abundant and less expensive. In this presentation I will focus on the electronic structure and defect chemistry of Sn-based TCOs, critically analysing them as viable alternatives to ITO.
Authors : Jakub Kaczmarski, Jakub Grochowski, Andrzej Taube, Aleksandra Treichel, Michał A. Borysiewicz, Wojciech Jung, Eliana Kamińska
Affiliations : Institute of Electron Technology, Al. Lotnikow 32/46, 02-668, Warszawa, Poland; Institute of Microelectronics & Optoelectronics, Warsaw University of Technology, ul. Koszykowa 75, 00-662, Warszawa, Poland
Resume : In the following study we report the fabrication of flexible IGZO MESFETs with transparent conductive Ru-Si-O and In-Sn-O, acting as Schottky gate electrode and ohmic source/drain contacts, respectively. The electrode materials were chosen to mitigate interfacial reactions with the IGZO channel. This allows to avoid the standard postdeposition annealing step, enabling MESFET fabrication on flexible PET substrates. The chemical composition of the Ru-Si-O Schottky metallization was optimized in order to achieve simultaneously a high oxygen content, low resistivity and high optical transmission. The nanostructural studies of the films were performed by means of XRD and TEM. No crystalline phases were recorded in X-ray diffraction patterns. However, high resolution TEM imaging revealed randomly oriented nanocrystalline inclusions embedded in an amorphous matrix. Devices were fabricated on PET foils in top-gate configuration, without neither annealing nor a-IGZO surface treatment. MESFETs exhibit on-to-off current ratio at the level of 1E3 A/A in a voltage range of 2 V, with subthreshold swing equal to 420 mV/dec. Channel mobility of 7.36 cm2/Vs was achieved. This research was in part supported by the Institute of Electron Technology statutory activities.
Authors : A. Gómez-Núñez, S. Alonso-Gil, P. Roura, C. López, A. Vilà
Affiliations : Department of Electronics, University of Barcelona, Martí i Franquès 1, E-08028-Barcelona, Spain. ; Department of Organic Chemistry, University of Barcelona, Martí i Franquès 1, E-08028-Barcelona, Spain. ; Department of Physics, University of Girona, Campus Montilivi, Edif. PII, E-17071-Girona, Spain. ; Departament of Inorganic Chemistry, University of Barcelona, Martí i Franquès 1. E-08028-Barcelona, Spain. ; Department of Electronics, University of Barcelona, Martí i Franquès 1, E-08028-Barcelona, Spain.
Resume : Thin films of ZnO are usually obtained by thermal decomposition of a sol-gel precursor film. Fabrication of ZnO-based electronic devices requires the high spatial control on film deposition achieved by ink-jet technology. Ink formulation must ensure that additives have no effect on the properties of the ZnO film. Although most of the papers published so far make use of Zinc Acetate Dihydrate (ZAD) as salt and Ethanolamine (EA) as stabilizer, the interaction of the latter with ZAD in the ink and its influence during thermal decomposition are not well understood. Previous work was devoted to identifying the molecular nature of the ZAD-EA precursor complex that constitutes the sol-gel film. In this communication, we will report on experiments (XPS, XRD, TGA, EGA ...) that elucidate the evolution of the film precursor to ZnO during thermal decomposition. Theoretical simulation of the ZAD-EA precursor complex has allowed us to identify unambiguously the volatiles detected by EGA at the various decomposition stages. So, our work contributes to the understanding of the decomposition dynamics and, especially, when N atoms leave the film. This information is crucial to improve the design of the ink for optimization of the thermal decomposition conditions and, ultimately, the ZnO properties.
Authors : D. Caffrey, E. Norton, L. Farrell, C. Smith, I.V. Shvets, K.Fleischer,
Affiliations : D. Caffrey; E. Norton; L. Farrell; I.V. Shvets; and K. Fleischer School of Physics and Centre for Research on Adaptive Nanostructures and Nanodevices (CRANN), Trinity College, University of Dublin, Dublin 2, Ireland D. Caffrey Advanced Materials Bio-Engineering Research Centre (AMBER) C. Smith School of Physics Trinity College, University of Dublin, Dublin 2, Ireland
Resume : The capacity to modulate the properties of Transparent Conducting Oxide (TCO) materials is of great importance for the optimisation of device efficiency. Tuning of the refractive index to reduce mismatch between two materials is highly desirable for the reduction of internal interface reflections. Previous works on ZnO:Al have utilised substitution doping with magnesium as a means to alter the bulk refractive index. However, the increased effects of neutral impurity scattering from the randomly distributed Mg leads to a reduction in both the mobility and carrier concentration of the material [1,2]. In our work, we create a superlattice structure of layered conductive amorphous InGaZnO (a-IGZO) and a dielectric material (SiO2) as an alternative method of reducing the refractive index without altering the carrier mobility significantly. These superlattice structures are grown with conventional RF magnetron sputtering from separate IGZO and SiO2 targets.  J. G. Lu; S. Fujita, et al., Appl. Phys. Lett. 89, (2006), 262107  K. Fleischer; E. Arca, et al., Appl. Phys. Lett. 101, (2012), 121918
p-type Transparent Conductive Materials Part 1 : Delfina Muñoz
Authors : İ. Cihan KAYA*, Hasan AKYILDIZ
Affiliations : Department of Metallurgical and Materials Engineering, Sel?uk University, 42075 Konya, Turkey
Resume : Delafossite type oxides have attracted considerable attention due to their unique properties, such as p-type electrical conductivity and transparency in the optical region , which makes them suitable for a variety of optoelectronic applications. In addition, delafossite oxides also showed promising thermoelectric, ozone sensing, photocatalytic hydrogen evolution properties and enhanced cathodic photocurrents in p-type dye-sensitized solar cell applications . Therefore, the synthesis of these oxides in the form of thin films, nanostructured bulk or nanometer size powders is critical for these applications. Among these oxides, Mg-doped CuCrO2 thin film has conductivity up to 220 Scm−1, which is the largest conductivity measured in the A M3 O2 systems . In order to improve functional properties, production of pure and doped CuCrO2 have been demonstrated in the literature using various methods such as conventional solid state synthesis, pulsed laser deposition, sputtering, sol-gel, and hydrothermal approach . Studies on the utilization of wet chemical synthesis-based techniques with flexible sample design showed that a variety of delafossite materials and sample geometries are possible with these approaches instead of using conventional solid state synthesis. Considering of diverse potential applications mentioned above, production of CuCrO2 nanostructures via hydrothermal approach is an alternative method with the added advantage of allowing an easy control of material chemistry and nanometer size particle processing. In this study, pure and Mg-doped CuCr(1-x)MgxO2 (x=0, 0.01, 0.03, 0.05) nanoparticles were synthesized via a well known low temperature hydrothermal method . The effect of Mg concentration on the structural, electrical and optical properties was investigated. The nanoparticles were synthesized via hydrothermal conversion of the reactants at 230 oC for 60 h in a custom made high pressure vessel. The precipitates were collected and cleaned with hydrochloric acid prior to drying. X-ray diffraction study revealed the formation of single phase CuCrO2 for all samples. The crystallite size of the pure sample was estimated to be ~11 nm using Scherrer formula. Electron microscopy examination implied a narrow size distribution for the nanoparticles. In order to understand the effect of Mg-doping on the optical properties of CuCrO2 nanoparticles, ultraviolet-visible spectroscopy was used. UV-Vis measurements revealed that, all nanoparticles exhibit a high transmittance (% 62-68 at 400 nm and % 82-90 at 700 nm) in the optical region. The optical bandgap was found to increase from 3.12 to 3.17 eV as the Mg concentration increases. We have also found that the room temperature electrical conductivity significantly increased with increase in the Mg-content and reached 0.01 Scm-1. Funding for this work was provided by (?YP) Academic Staff Training Program (Project no 2013-?YP-087), and Scientific Research Foundation (BAP) of Sel?uk University (Project no 14401104) which we gratefully acknowledge. 1. A. Stadler, Materials, 5, 661 (2012). 2. J. Ahmed, C.K. Blakely, J. Prakash, S.R. Bruno, M. Yu,Y. Wu and V.V. Poltavets, J. Alloy.Compd. 591, 275 (2014). 3 . R. Nagarajan, A.D. Draeseke, A.W. Sleight and J. Tate, J. Appl. Phys. 89, 8022 (2001). 4 . A.N. Banerjee and K.K. Chattopadhyay, Prog. Cryst. Growth. Ch. 50, 52 (2005). 5. M. Miclau, D. Ursu, S. Kumar and I. Grozescu, J. Nanopart. Res. 14, 1110 (2012).
Authors : Renaud Leturcq, Petru Lunca-Popa, Damien Lenoble
Affiliations : Materials Research and Technology Department, Luxembourg Institute of Science and Technology, 41 rue du Brill, L-4422 Belvaux, Luxembourg
Resume : In the field of transparent oxide semiconductors, one limitation for producing active devices is the lack of a p-type transparent oxide with good electronic properties. Cu-based delafossite materials are promising candidates, but applications are still hindered by the difficulty to produce it with large scale methods and the still limited electronic performances. Among them, Mg-doped CuCrO2 has shown the highest conductivity with high transparency, but the reported mobility is still two orders of magnitude lower than the expectations. Understanding the conduction properties could lead to the expected improvements for future applications. We have performed electrical measurements on back-gated CuCrO2 thin films in order to investigate the dependence of the conduction properties as a function of the carrier density. Pure CuCrO2 delafossite has been deposited by chemical vapour deposition and checked using X-ray diffraction. The film is deposited on a highly doped Si substrate covered by SiO2 gate oxide through a shadow mask. The conductivity of the thin film decreases when the gate voltage increases, a clear sign of the p-type conduction. From the transverse characteristics we evaluate the hole density at zero gate voltage to 6E18 cm-3, and the field effect transistor mobility of 0.04 cm2/Vs at room temperature. In order to understand the limitation of the mobility, we have further measured the transport properties as a function of temperature while varying the hole density.
Authors : Elisabetta Arca, Daragh Mullarkey, Igor Shvets
Affiliations : School of Physics and CRANN, Trinity College Dublin, Dublin, Ireland
Resume : p-type transparent conductors and semiconductors are still suffering from remarkably lower electrical performance in comparison with their more widely spread n-type counterparts. In this contribution we will present a comparative study on the defect chemistry of doping Cr2O3. Thin films of Cr2O3 doped with Zn, Mg, or Ni were deposited by Pulsed Laser Deposition. Conductivity as high as 20 S/cm were reproducibly achieved by Ni-doping, which represents an improvement of more than an order of magnitude in comparison to the conductivities previously reported for doped Cr2O3. A comprehensive characterization on the structural properties by X-ray Diffraction, on the electronic properties by X-ray Photoelectron Spectroscopy and on the electrical properties by DC resistance measurements have allowed us to shed some light on the mechanism responsible for the improvement.
Authors : M. Zubkins, R. Kalendarev, J. Gabrusenoks, R. Ignatans, K. Kundzins, K. Vilnis, A. Azens, J. Purans
Affiliations : Institute of Solid State Physics, University of Latvia, Kengaraga 8, LV-1063, Riga, Latvia
Resume : One of the obstacles to further developments of transparent electronics based on transparent conductive oxide (TCO) thin films is lack of p-type conductors. Polycrystalline spinel ZnIr2O4 thin films with appropriate acceptor defects are shown as p-type conductors by experimental and theoretical studies. Light ZnO doping with Ir has been studied only with first principles DFT calculation without any experimental investigation. This study investigates properties of ZnO:Ir thin films and how iridium incorporates in this system in these circumstances. ZnO:Ir thin films were deposited by reactive magnetron co-sputtering from a metallic Zn and Ir targets in an Ar O2 atmosphere. A set of samples was deposited at different Ir target (cathode) powers to vary the Ir concentration in the films. Composition and structural, optical and electrical properties of the ZnO:Ir thin films were studied by XRF, XRD, SEM, Raman, FTIR techniques, as well as Hall effect measurements and two beam optical spectrophotometry. XRD measurements showed that light doped (< 6.0 at. Ir %) ZnO thin films are oriented in the c-axis direction. Lattice constant c as well as strain and stress are increasing with iridium concentration. However, the grain size is not changing significantly. Above 7.0 at. % Ir concentration thin films become amorphous. Absorption in the visible range increases significantly with iridium concentration.
Authors : S. Brochen (1,2), L. Bergerot (1,2), W. Favre (2), V. Consonni (1,2), C. Jiménez (1,2), J.-L. Deschanvres (1,2)
Affiliations : (1) Univ. Grenoble Alpes, LMGP, F-38000 Grenoble, France (2) CNRS, LMGP, F-38000 Grenoble, France. (3) CEA, LITEN, INES, 50 avenue du lac léman, 73375 Le Bourget-du-lac, France
Resume : Cuprous oxide (Cu2O) and related compounds are considered as very promising materials as transparent p-type semiconductors thanks to its non-toxicity, earth abundance, low-cost fabrication, and direct band gap energy of 2.1 eV. In this study, temperature-dependent Hall effect and resistivity measurements were performed on p-type strontium doped Cu2O:Sr thin films, which were deposited on glass substrate by Metalorganic Chemical Vapour Deposition (MOCVD). Thereby, electrical properties of the sample, such as resistivity, carrier density and mobility, as well as the acceptor ionization energy, were determined as a function of the strontium content, quantified by wavelength dispersive X-ray spectrometry. The role of post-deposition annealing treatment on the residual compensating donor concentration, leading to an increase of the density and of the mobility of the free carriers (holes), was also discussed. Cu2O:Sr thin films obtained in this study present free hole densities higher than 1E17 cm-3 and resistivities below 1 Ohm.cm at room temperature, opening the way to their integration into optoelectronic devices.
Poster Session Part 1 : N.N.
Authors : Mehmet Ertugrul1, Zineb Benzait1, Demet Tatar2
Affiliations : 1.Ataturk University, Engineering Faculty, Department of Electric-Electronics, 25240 Erzurum-TURKEY 2.Ataturk University, K.K. Education Faculty, Department of Physics, 25240 Erzurum-TURKEY
Resume : ZnO has potential applications for a variety of optoelectronic devices because of its unique combination of physical properties. ZnO is a semiconductor material with a wide band gap energy of 3.4 eV. In addition, ZnO is an other candidate for high transparent contact material. Furthermore, Zn is non-toxic and occurs in many forms such as bulk single crystal, powder, thin film, nanowires, nanotubes, etc. ZnO has found a great deal of application in transparent electronics, UV light emitters, piezoelectric devices, chemical sensors, high-frequency wireless communication and spintronics. In the last few years, ZnO based chemical sensors have been investigated extensively, being considered as one of the promising candidates for chemical sensors due to their good adsorption characteristics, fast response and good selectivity towards flammable gases , ,  and . In addition, their low production cost, miniature sizes and simple synthesis process have made them frequent in sensing applications. Thin films of ZnO can be used as a window layer and electrodes on hydrogenated amorphous silicon based solar cells . In addition ZnO thin films offer a variety of applications in integrated piezoelectronic optics, gas sensitive devices , transparent electrodes  and Light Emitting Diodes (LEDs) . These materials have been prepared by numerous techniques. Among the various deposition techniques, the spray pyrolysis is the well suited for the preparation of doped tin oxide thin films because of its simple and inexpensive experimental arrangement, ease of adding various doping material, reproducibility, high growth rate, and mass production capability for uniform large area coatings. ZnO nanostructured thin ﬁlms with different dopants were grown by Ultrasonic spray Pyrolysis Technique (USPT). Figure 1 illustrates the schematic diagram of the equipment used in this work. A pneumatic nozzle made up of glass was used to produce and spray fine droplets of the precursor solution using compressed air as carrier gas, while a rotating plate was used to carry the substrates heated using halogen lamps with a control system to regulate the plate temperature. Before deposition, glass slides used as substrates were cleaned for 30 min using a piranha solution (H2SO4 /H2O2 = 3/1) then for 10 minutes with methanol and acetone in an ultrasonic bath, followed by rinsing with deionized water and drying at 150?C. The deposition was performed at a substrate temperature equal to 450?C during 30 minute of spraying. The evaluation of crystallinity of the the synthesized was carried out using an X-Ray Diffractometer (Cu Kα radiation (λ=0.154 nm), GNR APD 2000 PRO)) and the morphology and cross-section of the coatings were examined by a high resolution Field Emission Scanning Electron Microscope (Quenta 450 FEG FE-SEM; Erzincan University). Elemental analysis was carried out by energy dispersive X-ray spectroscopy (EDS) detector connected with SEM. In this study, we have developed zinc oxide thin films by the spray pyrolysis technique. Zinc oxide thin films were successfully grown by spray pyrolysis and they were characterized. The effect of ??? on the crystalline structure and optical properties of the as-deposited ZnO films was systematically investigated by X-ray diffraction (XRD), scanning electronic microscopy (SEM), atomic force microscopy (AFM), UV-vis spectrometer and photoluminecenc spectrophotometer. The X-ray diffraction patterns taken at room temperature showed that the films are polycrystalline. The XRD patterns shown in Figure X indicate that the films prepared possess polycrystalline hexagonal wurtzite structure of ZnO with peaks correspond to (100), (002), (101), (102), (110) and (103) planes [JCPDS data card (79-0206)]. SEM and AFM study reveals the surface of ZnO to be made of nanocrystalline particles.
Authors : J. Ramírez-Castellanos1, M. Taeño1, F. del Prado2, M. García-Tejedor2, D. Maestre2, A. Cremades2, J. Piqueras2 and J. González-Calbet1
Affiliations : 1 Dpto. de Química Inorgánica, Fac. de Químicas, Univ. Complutense de Madrid, 28040, Madrid, Spain. 2 Dpto. de Física de Materiales, Fac. de Físicas, Univ. Complutense de Madrid, 28040, Spain.
Resume : SnO2 is one of the most investigated semiconducting oxides due to its versatility and widespread applications in catalysis, gas sensing, photovoltaics, the chemical industry, energy storage, or as an alternative anode material  because of its high Li storage capacity. As most of these applications are highly dependent on the dimensions and the presence of dopants, during the last few years increasing research has been focused on the synthesis and study of SnO2 nanostructures doped with different elements, in order to optimize the response of SnO2. Different approaches are considered in order to solve problems such as the SnO2 volume expansion during charge/discharge processes, as the use of nanostructured SnO2 . In this work, different SnO2 based compounds have been prepared and characterized, with special interest focused on the effects induced by Li doping. Therefore, nanoparticles, rods and tubes have been fabricated following different methods. SnO2 nanoparticles doped with Li have been synthesized via a modified Pechini method, based on the use of polymeric precursors, which allows reaching high control in size and composition Moreover, low dimensional doped SnO2 structures in forms of nanowires and microtubes have been grown at 800-1400 ºC by a catalyst free evaporation-deposition method using either metallic Sn or SnO2 mixed with Li2CO3 as starting materials. The Li effect on the microstructure and luminescent properties of cassiterite SnO2 nanoparticles, nanowires and microtubes is studied by means of transmission electron microscopy (TEM), cathodoluminescence (CL), energy dispersive x-ray spectroscopy (EDS) and Raman spectroscopy. The thermal parameters and the corresponding precursor determine the morphology of the as-grown structures which dimensions vary from 5 nm to tens of microns width and up to hundreds of microns length. The incorporation of Li in SnO2 and its influence on the luminescence properties has scarcely been studied in nano and microstructures. The Li doping causes an enhancement of the conductivity of the samples. References:  Y.D. Ko, J.G. Kang, J.G. Park, S. Lee, D.W. Kom, Nanotechnology, 20, 455701 (2009)  J.Y. Huang, L. Zhong, C.M. Wang, J.P. Sullivan, W. Xu, L.Q. Zhang, S.X. Mao, N.S. Hudak, X.H. Liu, A. Subramaniam, H. Fan, L. Qi, A. Kushima, J. Li. Science, 330, 1515 (2010)
Authors : Saikumar Inguva 1, Rajani K. Vijayaraghavan 2, Enda McGlynn 1, Jean-Paul Mosnier 1
Affiliations : 1-School of Physical Sciences and National Centre for Plasma Science and Technology, Dublin City University, Dublin 9, Ireland. 2-School of Electronic Engineering and National Centre for Plasma Science and Technology, Dublin City University, Dublin 9, Ireland.
Resume : Deposition of transparent conductive oxides (TCO) films on thin flexible plastic substrates is presently of significant interest in research and technology. The majority of the works in this field focus on applications in optoelectronics and flexible displays in particular. In this work, we investigate the use of Zeonor (a brand of COP plastic) as a flexible substrate for the deposition of high quality ZnO and Al-doped ZnO (AZO: 3 at% Al) thin films. Films were prepared by pulsed laser deposition at room temperature in oxygen ambient pressures between 1 and 300 mTorr. The growth rate, surface morphology, hydrophobicity and the structural, optical and electrical properties of as-grown films with thicknesses in the range 65 nm - 420 nm were measured. The films obtained were highly reproducible, with high optical transparency (> 90%), and optically very smooth (RMS roughness ~ 4-8 nm for ZnO and ~ 1-2 nm for AZO). The films were also highly crystalline (average crystallite size ~ 4-22 nm for ZnO and ~ 3-18 nm for AZO) with strong c-axis orientation and in-plane residual compressive stress in the ranges 2-7 GPa and 0.5-4 GPa for ZnO and AZO, respectively. Their electrical properties showed low resistivities (10-2-10-3 Ω cm for ZnO and 10-3-10-4 Ω cm for AZO), high carrier concentrations (1020-1021 cm-3 for ZnO and 1021-1022 cm-3 for AZO) and reasonable Hall mobilities (4-35 cm2/Vs for ZnO and 1-18 cm2/Vs for AZO). All films displayed a marked hydrophobic behavior (water contact angle > 90°). Overall, the film properties were found to depend strongly on oxygen pressure and mildly on film thickness. Possible applications for these films are suggested.
Authors : Bedarev V.A, Merenkov D.M., Pashchenko M.I, Gnatchenko S.L. (1), Bezmaternykh L.N., Temerov V.L. (2)
Affiliations : (1) B. Verkin Institute for Low Temperature Physics and Engineering, 47 Lenin Ave., 61103 Kharkov, Ukraine; (2) L.V. Kirenskii Institute of Physics, Siberian Branch of RAS, 660036 Krasnoyarsk, Russia
Resume : The trigonal crystals of rare-earth TmAl3(BO3)4 and HoAl3(BO3)4 borate demonstrate a large magnetoelectrical effect. The nature of the magnetoelecticity of borates is related to the piezoelectric effect. And its well known that the Pockels effect is allowed in such crystals too. The main purpose of this work was the investigation of electric field induced optical linear birefringence of TmAl3(BO3)4. The single crystal plate with dimensions 4x4 mm and thickness about 200 μm was studied. In the experiment a quarterwave plate was used as the compensator to measure the birefringence. The measuring light beam of He-Ne laser (wavelength 0.633 μm) was directed along the trigonal c axis, and electric field was perpendicular to the c axis of crystals. It was found that the linear birefringence is induced by the electric field and depends on field orientation. In the electric field 106 V/m the value of this birefringence is ~ 10-5 at room temperature. The Pockels coefficient of TmAl3(BO3)4 is about 10-11 which is 10 times less than in well-known electro-optical crystal lithium niobate NbLiO3. Nevertheless, this result is a good reason to search and investigate new rare-earth aluminum borates with higher value of electro-optical effect.
Authors : Ching An Huang, Lin Tso Chiang, Kong Chen Li, Fu Yung Hsu*
Affiliations : Department of Mechanical Engineering, Chang Gung University, Taoyuan 333, Taiwan *Department of Materials Engineering, Ming Chi University of Technology, New Taipei 243, Taiwan
Resume : The microstructures and optical properties of the ZnO deposits were investigated, which were electroplated with direct- and pulse-currents on an ITO-glass in a zinc-nitrate based electrolyte. The surface morphologies of the electroplated ZnO deposits were examined with field emission scanning electron microscope, and their microstructures were detected with X-ray diffractrometer. Meanwhile the transparencies of ZnO-deposited ITO-glass specimens were evaluated. Experimental results show that the surface morphologies, microstructures, and optical properties of the ZnO deposits depend strongly on the plating bath temperature and current density. An amorphous structure of ZnO deposit was achieved when it was electroplated at a bath temperature of 30oC; while a crystalline ZnO deposit with hexagonal grains was observed at a plating temperature of 60oC. The crystalline ZnO deposits with a preferred orientation of  were obtained by using different plating current densities. With the same coating thickness, the ZnO deposits prepared at 30oC revealed higher transparencies than those prepared at 60oC. Moreover, the transparency of ITO glass can be markedly improved at a wavelength higher than 500 nm when it was coated a thin ZnO layer by using pulse-current plating at 30OC. Different energy band gaps can be detected from the ZnO-deposited ITO-glasses prepared with direct- and pulse-plating currents. The former is 3.16 eV and the latter increases to 3.47 eV.
Authors : Soo Hyun Kim,1 Woo Cheol Lee,1,2 Jung Joon Pyeon,1,3 Seong Keun Kim1
Affiliations : 1Center for Electronic Materials, Korea Institute of Science and Technology, Seoul 136-791, Korea 2Department of Materials Science and Engineering, Seoul National University, Seoul 151-742, Korea 3KU-KIST Graduate School of Converging Science and Technology, Korea University, Seoul 136-701, Korea
Resume : ZnO has attracted interests as a candidate for an active channel of thin film transistors (TFTs) because ZnO films can show ambipolar carrier transport by doping and good transparency. In particular, p-type ZnO could be obtained by doping nitrogen into the films. It was recently reported that the excess incorporation of nitrogen into ZnO significantly improved the mobility and photostablilty.  Here, we tried to grow ZnOxNy films by atomic layer deposition with DEZ, H2O and NH3 at low temperature. We varied the ZnO and ZnNx cycle ratio (RZnON) of [DEZ-H2O]:[DEZ-NH3] at the range from 1:0 to 1:9. Although Zn3N2 is known not to be formed by ALD using NH3 at low temperature (< 320 oC) because of the low reactivity of NH3, we achieved the growth of ZnOxNy films by ALD at 150 oC. The nitrogen contents in the films increased up to approximately 2 at.%. Interestingly, the growth per cycle of the ZnOxNy films increased with RZnON despite no growth of Zn3N2 at this temperature. In the presentation, we will show the detailed growth behavior and various properties of ZnOxNy films by ALD.  E. H. Lee, A. Benayad, T. H. Shin, H. G. Lee, D. S. Ko, T. S. Kim, K. S. Son, M. K. Ryu, S. H. Jeon, G. S. Park, Scientific reports. 4, 4948 (2014)
Authors : K. Elen, H. Damm, A. Kelchtermans, K. Schellens, A. Hardy, M. K. Van Bael
Affiliations : Hasselt University, Institute for Materials Research (IMO), Inorganic and Physical Chemistry, and IMEC vzw, division IMOMEC, Martelarenlaan 42, 3500 Hasselt, email@example.com
Resume : Aluminium doped zinc oxide (AZO) has attracted significant attention for replacing ITO. In the current work two approaches are presented for the wet-chemical processing of AZO. Chemical solution deposition of aluminium doped zinc oxide, by spin coating a 2-butoxyethanol precursor, yields TCO coatings with a transparency higher than 90 % and a resistivity of 1.3 mOhm cm after annealing at 450 °C in a reducing atmosphere. Furthermore, the potential of this precursor for large area coatings is demonstrated, by transferring the precursor to a spray coating system. Next, different synthesis routes for AZO nanoparticles are presented leading to particles with various characteristics. Minor modifications of the synthesis conditions have a profound impact in the particle morphology, the crystallographic position of the aluminium dopant and the generation of free charge carriers. Through an in-depth study of their characteristics, the most promising particles can be selected. Also, their potential as building blocks for transparent conducting coatings is demonstrated, providing a resistivity of 9.4 mOhm cm. In this work we demonstrate that through in-depth characterization we can correlate the synthesis conditions to the intrinsic properties of the obtained oxide, and come to functional, solution deposited TCO coatings. Acknowledgement: The presented research is conducted in the frame of the SoPPoM program and is financially supported by the Strategisch Initiatief Materialen (SIM).
Authors : D. Casotti1, A. di Bona2, S. Valeri1 2,
Affiliations : 1 Dipartimento di Scienze Fisiche, Informatiche e Matematiche, Università di Modena e Reggio Emilia, via Campi 213/a, 41125 Modena, Italia; 2 Centro S3, Istituto Nanoscienze, Consiglio Nazionale delle Ricerche, via Campi 213/a, 41125 Modena, Italia.
Resume : Nb-doped anatase TiO2 was shown to be a viable candidate for replacing indium-tin-oxide as a transparent electrode in several technological applications, like flat panel displays, thin film amorphous silicon solar cells or dye-sensitized solar cells. Transparent conducting Nb-doped anatase TiO2 films were grown at high rate by reactive DC magnetron sputtering from metal targets, using an active control of the oxygen gas flow in order to stabilize the plasma discharge voltage and to control the films stoichiometry. Electric transport and electronic properties of the highly conductive film are studied as a function of several process parameters, like plasma voltage, doping level and post-deposition reductive annealing temperature profile. Exposure of the films to ambient air, even at room temperature, either before or after the thermal process, has been found to play a crucial role in determining the resistivity of the material. In particular, air exposure times in the minutes range increases the resistivity of the film by one order of magnitude or more. Partial rejuvenation of the material could be obtained by thermal treatment.
Authors : M. Kormunda, A. Herwig, D. Fischer, U. Beck, M. Sebik
Affiliations : Faculty of Science, J.E. Purkyne University, Ceske mladeze 8, Usti nad Labem, Czech Republic; BAM Federal Institute for Materials Research and Testing, Division 6 4 Surface Technologies, Unter den Eichen 44-46, Berlin, Germany
Resume : The SPR gas sensors with sensitivity 0.5 ppm CO in air and 10 ppm methane in air were already demonstrated by our group [doi:10.1016/j.snb.2011.08.036]. The properties of the metal oxide transducer are the key element enabling future improvements in the detection. The dependences of the transducer properties to detection process have to be found. Therefore the properties the transducers have to be controlled. The control of the transducers properties is possible by the understanding to plasma deposition processes. The transducer oxide coating has to be uniform and thick about 5 nm used in prove of principle example earlier. The exact influence of the film thickness to detection process is still unknown. The primary investigated metal oxide is tin oxide doped by iron in low concentrations (about 1 at.%). The sputtering process was investigated by Hiden EQP plasma monitor. The SnO2 target was sputtered and mainly Sn and SnO ions were identified. The expected SnO2 ions were not identified. The ratio between SnO /Sn was about 0.5 for practically every parameters at DC pulsed plasma. In contrary the ratio SnO /Sn could be in range from 1.4 to 0.2 depending on plasma parameters. The energy delivered to growing films at floating potentials is influenced mainly by plasma potential which can be estimated from ion energy distributions for dominant ions. The DC pulsed plasma used repetition frequency 50 kHz therefore average values measurements were only possible.
Authors : E. Chubenko (1), V. Bondarenko (1), M. Balucani (2)
Affiliations : (1) Belarusian State University of Informatics and Radioelectronics, P. Brovka str. 6, Minsk 220013, Belarus; (2) Universita La Sapienza di Roma, Via Eudossiana 18, Roma 00184, Italy
Resume : ZnO nanostructures are useful element of perspective photovoltaic devices. ZnO nanostructures arrays can be used in thin film solar cells, photoelectrochemical cells and tandem solar cells. One of the key advantages of ZnO over other comparable wide band-gap semiconductors is that it can be deposited by the simple techniques of electrochemical and chemical deposition in the form of nanostructures arrays. ZnO is also can be easily doped directly during the deposition process by addition of corresponding additives to the solution. In this work we studied the electrochemical and chemical hydrothermal deposition of undoped ZnO and doped ZnO:Al and ZnO:Er nanostructures. The influence of temperature, solution composition, current density (in the case of electrochemical deposition), substrate conductivity and pH on the morphology and composition of deposited ZnO nanostructures were studied. Obtained doped ZnO nanostructures arrays showed enhanced conductivity compared to undoped ZnO and additional absorption bands in the IR range related to the presence of Er atoms in the ZnO crystal lattice. Their applications as a transparent conductive electrodes and energy upconversion layers are also discussed. This work is supported by Belarus Government Research Programs Crystalline and molecular structures, grant 1.09, Electronics 2015, grant 1.2.08 and Belarusian Republican Foundation for Fundamental Research grant X14MB-009.
Authors : Bongkyun Jang, Chang-Hyun Kim, Jae-Hyun Kim, Kwang-Seop Kim, Hak-Joo Lee, Byung-Ik Choi
Affiliations : Department of Nano-Mechanics, Korea Institute of Machinery and Materials
Resume : Graphene has outstanding physical properties that make it attractive for a variety of applications using excellent electrical, optical, mechanical properties. Among them, flexible and transparent electrode is one of the most promising applications. For a lot of applications for transparent electodes like solar pannel, touch screen, graphene should be transferred on the substrates with various materials, surface morphorlogies, surface energy and surface roughness. Transferring large area graphene sysnthesized on copper substrate by CVD process, is optimized by roll to roll transfer process. This process has advantages for the scailability and the compatibility for other roll process. In addition, graphene can be transferred on various substrate by roll transfer process. We used the carrier film for a protection of graphene film during copper substrate etching, handling, and transferring process. And finally it was transferred on various substrate like PET, silicon, and other polymer substrates. We compared to the qualities of graphene transferred on various substrates, and evaluated the effect of substrate. These results will be able to be directly used for fabrication of the devices with graphene transparent electrodes.
Authors : Hoang Ba Cuong, Ngoc Minh Le, Byung-Teak Lee
Affiliations : Chonnam National University
Resume : Effects of the oxygen flow ration within the Ar plasma on the structural, electrical and optical properties of sputter grown ZnMgO and ZnMgXO (X: Be, Ga) films, widely studied for the UV optoelectronic devices, were investigated in detail. The XRD results showed that the full width at half maximum values of the (0002) peaks drastically decrease with the small addition of oxygen into Ar plasma, but then increase with further oxygen addition. It was also observed that the optical bandgap (Eg) values of all the films substantially decrease with the oxygen addition. The Hall measurement data show the resistivity of ZnMgGaO films increase from 5x10-4 cm to 102 cm as the oxygen concentration increases from zero to 1. It was proposed that the bandgap change due to the combined effects of Brustein-Moss effect and the compositional change (Vegard?s law). It is suggested that the oxygen-rich condition may cause the formation of the compensating-defects trapping carriers such as oxygen interstitial, zinc vacancies and other complexes, which strongly reduce the carrier concentration in the Zn-based system. Further details on the operating mechanisms will be discussed during the presentation.
Authors : Seung Jae Baik
Affiliations : Hankyong National University
Resume : Random network of metallic nanowires is a well-known material for transparent electrode applications. They exhibit sufficient light transmittance-conductivity trade-off for the application such as front electrodes of solar cells, and moreover, they provide better bending reliabilities than other commercial transparent conducting oxides. The exceptional bending reliability provides various insights into flexible, wearable, or textile devices. We developed the random network of metallic nanowires encapsulated in ZnO, whose role is a chemico-mechanical protecting layer without a degradation of the electrical and optical property of the random metallic nanowire network. Considering wide applicability as a part of flexible, wearable, or textile devices; the processing temperature for ZnO encapsulation was limited below 150℃ by using a metal-organic chemical vapor deposition or a low temperature sol-gel methods. It was demonstrated that the fabricated hybrid transparent electrodes was well applied to flexible solar cell fabrication in case that the impurity of the metallic nanowire and its coating uniformity is well established. Other applications related to wearable or textile devices will be also introduced for a further discussion.
Authors : Chamorro William, Migot Sylvie, Miska Patrice, Soldera Flavio, Mücklich Frank, Horwat David
Affiliations : Université de Lorraine, Institut Jean Lamour, UMR7198, Nancy, F-54011, France Department Materials Science and Engineering, Saarland University, D-66123 Saarbrücken, Germany
Resume : Optical effects of noble metal nanoparticles (NPs) such as localized surface plasmon resonance (LSPR) or surface enhanced Raman spectroscopy (SERS) occurs when the NPs are in contact with the medium to be probed. This interaction could affect the size, distribution or shape of the NPs, changing their properties. If a temperature higher than room temperature is needed, the particles tend to grow by Ostwald ripening, which may lead to loss or weakening of the properties of interest. These problems can be solved using a thin oxide film to stabilize the NPs morphology. We report the synthesis by reactive magnetron sputtering and characterization of ZnO-Au nanocomposite thin films that show LSPR absorption by Au NPs in the visible region. Different gold loadings and reactive atmospheres were used to synthetize the films. The optical response of the nanocomposite films is connected to the change in local chemistry and microstructure. Those are set through the reactive deposition conditions and thermal annealing. Strong LSPR absorption and related effects such as SERS or improved photoluminescence can be obtained after an annealing process that leads to an increase of the NP diameter above 5 nm. Chemical analyses indicate that it is possible to form, in highly oxidizing conditions, NPs with a shell/core structure probably due to a change of the ZnO matrix from a reducing to an oxidizing character depending on the reactive conditions and the associated chemical defects produced.
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Metallic Nanowires or Nanoparticles Part 2 : Benjamin Wiley
Authors : John J. Boland
Affiliations : School of Chemistry and Centre for Research on Adaptive Nanostructures and Nanodevices (CRANN), Trinity College Dublin, Ireland
Resume : The seminar will discuss scaling and evolution of connectivity in inorganic nanowire networks exposed to different stimuli. Network junctions control the overall properties of any network and we show that all networks evolve connectivity in specific ways. In particular, we describe how junctions evolve from capacitor-like to resistor-like barriers in response to an applied stimulus and how the network self-selects connectivity paths by choosing the lowest barrier junctions. Continued stressing causes the selected junctions to strengthen and ultimately co-opts neighbouring junctions to reinforce the overall response to the stimulus. By engineering these junctions it is possible to control the properties and response of the network. Transparent materials with arbitrarily controlled connectivity and conductivity are demonstrated as are device with arbitrarily controlled multi-level memory, and single junctions capable of a learning response.
Authors : Bastien BESSAIRE (1,2), Mathieu MAILLARD (2), Caroline CELLE (1), Vincent SALLES (2), Arnaud BRIOUDE (2), Jean-Pierre SIMONATO (1)
Affiliations : 1) CEA-LITEN-DTNM-SEN-LSIN, 17 Rue des Martyrs, 38054 Grenoble, France 2) Laboratoire des Multimatériaux et Interfaces, UMR 5615 CNRS Université Lyon 1, 43 boulevard du 11 Novembre 1918, 69622 Villeurbanne Cedex, France
Resume : Conductive polymer and metallic nanowire based electrodes have been recently developed for their promising merit factor as transparent and flexible electrodes, i.e. low sheet resistance (R□) and high transparency (%T). We present the fabrication using electrospinning of conductive nanofibers and their characterization. This technique offers two main advantages compared to usual deposition techniques like spray or spin coating: a limited spreading constrain as the deposition is not surface energy dependent and the obtained fibers are highly conformable on non-planar surfaces. We successfully developed a process to obtain homogeneous conductive PEDOT:PSS nanofibers, using low humidity electrospinning technique, leading to highly conductive nanofibers with variable coverage and a sheet resistance of 340Ω. Our results on process optimization also revealed a strong humidity dependence on the final morphology of the electrospun mat. These conductive structures can be used as a template for metallic electrodeposition to further increase conductivity. Alternatively, electrospinning also allowed us to produce networks of composite coaxial fibers made of silver nanowires embedded in PolyVinylPyrrolidone (PVP) with a high filling factor. These two routes lead to reproducible core-shell new nanostructures that will be used in transparent flexible electrodes and pave the way of promising integration for transparent electronics, solar cells or chemical sensing.
Authors : B. Reiser, J. H. M. Maurer, I. Kanelidis, L. Gonzalez-Garcia, and T. Kraus
Affiliations : INM - Leibniz Institute for New Materials, Campus D2 2, 66123 Saarbrücken, Germany
Resume : Transparent conductive materials (TCM) based on metal nanostructures are an interesting alternative to the established oxide-based systems. Their properties are often dominated by ligands that stabilize the metal nanostructures, direct their geometries during synthesis, and affect their deposition as layers. Insulating ligand layers constitute tunnel barriers that lower specific conductivity.[2,3] We will discuss the application of gold nanostructures with spherical, rod or wire-like geometries for metal-based TCM. The particles are stabilized by surface ligands and processed using wet-chemical techniques. The morphology, size distribution and optical properties of the nanoparticles were determined by means of electron microscopies (SEM, TEM), dynamic light scattering (DLS) and UV-vis spectroscopy. Combinations of infrared and Raman spectroscopy provided information in terms of surface coverage and binding site of the used capping molecules. Ligands were adsorbed on the metal surfaces either during synthesis or by ligand exchange. We discuss ligand-dependent optical and electrical characteristics of the nanoparticles. Transparent conductive particle layers were deposited and their properties correlated with the ligand shell composition.  C.F. Guo, et al. Mater. Today, 18, 2015, 143  T. Geyer, et al. Phys. Rev. Lett., 109, 2012, 128302  J. B. Pelka, et al. Appl. Phys. Lett., 89, 2006, 063110
Authors : Assia Kasdi, Chi Neo, Jamie H Warner, Andrew A.R Watt
Affiliations : University of Oxford, Department of Materials, Parks Road, OX1 3PH, Oxford, United Kingdom
Resume : Thin films of nanowire (NW) networks have the potential to replace metal oxide thin films as transparent conductors for use in a range of applications, for example organic light-emitting diodes, liquid-crystal displays and solar cells. Two dimensional NW networks can be optimized to have low sheet resistance and high transparency films by controlling NW aspect ratio, size dispersity and surface roughness. In this paper we investigate transparent copper NW films in quantum dot solar cells using a printing process. The method is solution based synthesis using low cost earth abundant materials compatible with large scale manufacturing methods. We demonstrate that solar cell performance is enhanced by the addition of an intermediate layer between the NW and quantum dots to eliminate the effects of NW pointing out of plane and use a series of bias treatments to improve efficiency.
Transparent Conductive Oxides Part 3 : Delfina Muñoz
Authors : J. Proost,* F. Henry, F. Van Wonterghem, R. Tuyaerts and S. Michotte (* firstname.lastname@example.org)
Affiliations : Division of Materials and Process Engineering, Université catholique de Louvain (UCL), Louvain-la-Neuve, Belgium
Resume : One of the challenges in the search for a "Holy Grail" TCO is to arrive at sufficiently large electrical conductivities while at the same time guaranteeing sufficient optical transparency. In this work, we will report on scientific efforts aimed at unraveling the quantitative effect of strain on the electro-optical performance of Al-doped zinc oxide. AZO thin films have been deposited by reactive magnetron sputtering to thicknesses from 300 to 500 nm. During deposition, the internal stress evolution was monitored in-situ . The resulting growth-induced strain could be modulated by appropriately choosing the oxygen partial pressure and the deposition temperature. The latter also induces an additional extrinsic thermal stress component, whose sign depends on the substrate used. As such, mean biaxial internal stresses could be achieved ranging from - 600 MPa (compression) upto 800 MPa (tension). The resulting charge carrier mobilities were found to range between 5 and 25 cm2/Vs, with the maximum mobility occurring at the zero-stress condition. Together with a charge carrier concentration of about 10 1020 cm-3, this gave rise to a resistivity of only 2.5 10-4 Ohm.cm. From the stress-dependent optical transmission spectra in the range 200-1000 nm, the pressure coefficient of the optical bandgap was estimated to be 278 meV/GPa, indicative for a very high strain-sensitivity.  S. Michotte and J. Proost, Solar Energy Materials & Solar Cells 98 (2012) 253
Authors : Sujaya Kumar Vishwanath, Jihoon Kim
Affiliations : Division of Advanced Materials Engineering, Kongju National University, Cheonan, Chungchungnam-do 331-717, Korea.
Resume : One of the challenges in solution based process is to produce high quality films. In this paper, we report a novel chemical solution method, a polymer assisted solution (PAS). We use a new strategy to control the distribution of metal ions in solution with desired viscosity. The metal ions are encapsulated to prevent chemical reaction in the solution state by actively binding the metal ions with the polymer. This ensures a homogeneous metal distribution and avoids unwanted reaction of metal precursors in the solution state. The metal ions are released from the polymer during an annealing process of the coated layer, resulting in the formation of dense film. Molybdenum doped indium oxide (IMO) thin films have been prepared by PAS. The structural, optical and electrical properties have been investigated as function of Mo (0 at% to 2.5 at%) concentration. The deposited IMO films are in polycrystalline, very dense and smooth, as determined by X- ray diffraction and scanning electron microscopy, respectively. All IMO films shows, the high optical transmittance at visible to near infrared regions. The optimum concentration of Mo in IMO film was found at 1.5 at%, shows low resistivity of 3.2 10-3 Ω-cm, and high mobility of 43 cm2 V-1s-1.
Authors : Albert de Jamblinne de Meux, Geoffrey Pourtois, Jan Genoe, Paul Heremans
Affiliations : KU Leuven, ESAT, B-3001 Leuven, Belgium , imec, Kapeldreef 75, B-3001 Leuven, Belgium; imec, Kapeldreef 75, B-3001 Leuven, Belgium; imec, Kapeldreef 75, B-3001 Leuven, Belgium; KU Leuven, ESAT, B-3001 Leuven, Belgium, imec, Kapeldreef 75, B-3001 Leuven, Belgium;
Resume : Amorphous Indium-Galium-Zinc-Oxyde (a-IGZO) is a promising semiconducting material for large area electronics applications, displays and imagers. It combines both a sizable mobility, a good stability and a very low off current compared to conventional amorphous silicon (a-Si). However, little is known on its fundamental properties and how they could be potentially engineered. In this paper, the electronic properties of stoichiometric and defective a-IGZO will be investigated using first-principles simulations. An emphasis will be set on the statistical distribution of the energetic and of the electronic signatures of neutral and charged oxygen vacancies. In opposition to the results reported in literature, we find that oxygen vacancies do not always display a negative-U behavior but can rather adopt a smoother charge transition. Also, a non-negligible number of vacancies (~50 %) does not induce defective states in the band gap. We will illustrate that this difference with respect to previous works, is bound to the limitations of the dimensions of the models used. Finally, we will show that some oxygen vacancies adopt a meta-stable behavior upon charge loading due to the complexity of the energetic landscape built during the amorphization process.
Authors : Andrej Čampa1, Marko Berginc1, Katarina Vojisavljević2, Barbara Malič2, Peter Panjan2, Marko Topič1
Affiliations : 1 University of Ljubljana, Faculty of Electrical Engineering, Laboratory of Photovoltaics and Optoelectronics, Traka cesta 25, 1000 Ljubljana, Slovenia 2 Joef Stefan Institute, Jamova cesta 39, 1000 Ljubljana, Slovenia
Resume : In the optoelectronics, especially in thin-film photovoltaics, the transparent conductive oxides (TCO) play an important role to minimize the front contact optical losses. The TCOs used as a front contact needs to have low resistivity (<1 mOhmcm), high optical transparency in the broad wavelength region (>80% at 400-1000 nm) and high temperature stability. In the case of using nano-imprinted lithography for reproduction of the morphologies the good electrical and optical properties should be obtained at low deposition or post-annealed temperatures. To translate the morphology, at which the light is efficiently scattered, to the internal interfaces of the solar cells very low thickness of TCO is required (<200 nm). One of such candidates is Ga doped SnO2:In (ITO), which exhibits better optical and similar electrical properties to ITO 90/10, additionally it has lower indium content. A multicomponent Ga-In-Sn oxide target with Ga:In:Sn = 4:64:32 metal ratio was prepared, that was used in RF sputtering system for deposition of high quality GITO thin-film layers on glass. In this study, we will focus on electrical (specific resistivity, mobility and carrier concentration) and optical properties (thickness and refractive index) as a function of deposition and annealing parameters. The results of optical and electrical characterization of the two best GITOs will be presented, one globally optimized and one optimized with the respect to the low temperature deposition prerequisite.
Carbon Nanotubes and Metallic Nanowires : John Boland
Authors : S. Khasminskaya ; F. Pyatkov [1,2]; B.S. Flavel ; F. Hennrich ; W.H.P. Pernice [1,3]; R. Krupke [1,2]
Affiliations : Institute of Nanotechnology, Karlsruhe Institute of Technology, Karlsruhe, Germany; Department of Materials and Earth Sciences, Technical University of Darmstadt, Germany; Institute of Physics, University of Münster, Germany
Resume : Broadband emission source based on carbon nanotubes (CNTs) was successfully integrated in CMOS compatible waveguide architecture . The electrically induced light can be efficiently coupled into photonic structure and propagate over centimeter distances. On-Chip CNT emitters can be used for chipscale information processing and for high bandwidth on-chip communication with high scalability and reproducibility. For application where specific wavelengths are required desired emission wavelengths can be spectrally selected using one-dimensional photonic crystal cavities . Also passive structures such as Mach-Zehnder interferometer or grating structures can be used on chip to control the spectral properties of the emitter.We also demonstrated that electrically driven CNTs can be used as high speed light emitter with a Gbps response speed. Ultra-high speed light source opens a new opportunities for integrated optical communication devices.  Waveguide-Integrated Light-Emitting Carbon Nanotubes, Svetlana Khasminskaya, Feliks Pyatkov, Benjamin S. Flavel, Wolfram H. Pernice, Ralph Krupke, Advanced Materials 26 (2014) p.3465.  Cavity enhanced luminescence light emission from an electrically driven carbon nanotube, Felix Pyatkov, Valentin Fütterling, Svetlana Khasminskaya, Frank Hennrich, Ralph Krupke, and Wolfram H.P. Pernice. Submitted to Nature Photonics.
Authors : Yi-Ting Lai, Nyan-Hwa Tai
Affiliations : Department of Materials Science and Engineering, National Tsing-Hua University
Resume : This work demonstrates a one-step process to synthesize uniformly dispersed hybrid nanomaterial containing silver nanowires (AgNWs) coated with p-type reduced graphene (p-rGO). The hybrid nanomaterials were coated onto a polyethylene terephthalate (PET) substrate for preparing high performance flexible transparent conductive films (TCFs). The p-rGO plays the role of bridging discrete AgNWs, which provides more electron holes and lowers the resistance of the contacted AgNWs; as a result enhancs the electrical conductivity without sacrificing too much transparence of the TCFs. Additionally, the p-rGO also improves the adhesion between AgNWs and substrate by covering the AgNWs on substrate tightly. The study also shows that coating of the hybrid nanomaterials on the PET substrate demonstrates exceptional optoelectronic properties with a transmittance of 94.68% (at a wavelength of 550 nm) and a sheet resistance of 25.0 Ω/sq; furthermore, no significant variation in electric resistance can be detected even the film was subjected to a bend loading with a radius of curvature of 5.0 mm or the film was loaded with a reciprocal tension or compression for 1000 cycles. The study shows that the fabricated flexible TCFs have the potential to replace indium tin oxide film in the optoelectronic industry.
Authors : Çağla Çetin, Hasan Akyıldız*
Affiliations : Department of Metallurgical & Materials Engineering, Selçuk University, Konya, 42075, Turkey
Resume : Delafossite type oxides including CuCrO2 have attracted considerable attention due to their unique properties, such as p-type electrical conductivity and transparency in the optical region . This provides the opportunity to use n-and p-type TCOs together to develop all transparent p-n junctions which can be utilized in many optoelectronic applications. Delafossite oxides also showed promising thermoelectric, ozone sensing, photo-catalytic hydrogen evolution properties and enhanced cathodic photocurrents in p-type dye-sensitized solar cell applications . Among these oxides, Mg-doped CuCrO2 has a conductivity up to 220 Scm−1, which is the largest conductivity measured in the A+M3+O2 systems . Studies on the utilization of wet chemical synthesis-based techniques with flexible sample design showed that a variety of delafossite materials and sample geometries are possible with these approaches instead of using conventional solid state synthesis. Recently, it was shown that delafossite oxides could successfully be synthesized via electrospinning [4,5]. Chiun and Chen, reported on the formation of single-phase CuCrO2 wires having 434 nm diameter with vacuum annealing at 700 °C for 20 min . Considering of diverse potential applications such as optoelectronic devices, sensor and catalysis applications, production of CuCrO2 nanostructures via electrospinning is an alternative method with the added advantage of allowing an easy control of material chemistry with various morphologies. This study aims to understand the fundamentals of the formation mechanism of CuCrO2 in the form of nanofibers. By the investigation of the effect of time, temperature and annealing atmosphere on the formation of single phase material, the study expects to reveal a correlation between the phase purity, size, microstructure, and optoelectronic properties for specific applications. For this purpose appropriate amounts of copper chloride, chromium nitrate and polyvinylpyrrolidone were mixed in water to obtain a viscous solution. The solution was transferred on an aluminum foil substrate in the form of nanofibers, via electrospinning method. All samples were collected at room temperature with 0.3 mL/h feeding rate under an applied voltage of 16 kV. Collected fibers were annealed under two different conditions; namely isochronal and isothermal. Isochronal experiments involved heating from room temperature to various temperatures, i.e., 400, 500, 600, 650 and 700 °C under high purity flowing nitrogen gas in a tube furnace and holding the samples at relevant temperature for 1 h. Isothermal experiments were carried out at temperatures of up to 700 °C. This involved heating the furnace to a selected temperature and loading of the sample for certain durations, i.e. 15, 30, 45 and 60 min. According to X-ray diffraction measurements, with isochronal annealing, the formation of CuCrO2 phase starts at 500 °C and at least 700 °C is necessary to obtain single phase material. Scanning electron microscopy examinations revealed the formation and coarsening of plate-like grains with increasing annealing temperature. Due to this, the fiber structure was completely disappeared after heat treating the fibers at 700 °C for 3 h. To preserve the nanofiber structure and prevent coarsening, isothermal annealing experiments were performed at 700 °C. In summary, it was shown that CuCrO2 nanofibers could successfully be synthesized via isochronal and isothermal annealing of electrospun polymer/metal composite fibers. We have found that isothermal annealing at 700 °C for 1 h in flowing nitrogen atmosphere leads to the formation of a refined structure while preserving the nanofiber morphology. We have also carried out measurements on the structural, morphological, optical and electrical properties of the fibers. Support for this work was provided by TUBITAK MAG (Project no 214M410),and Scientific Research Foundation (BAP) of Selçuk University (Project no 15201028) which we gratefully acknowledge. 1. References  F. A. Benko, F. P. Koffyberg, J. Phys. Chem. Solids, 45, 1984, 57-59.  A.N. Banerjee, K.K. Chattopadhyay, Prog. Cryst. Growth Charact. Mater. 50, 2005, 52-105.  R. Nagarajan, A.D. Draeseke, A.W. Sleight, J. Tate, J. Appl. Phys., 89, 2001, 8022-8025.  S. Zhao, M. Li, X. Liu, G. Han, Mater. Chem. Phys., 116, 2009, 615-618.  T. Chiun, Y. Chen, Cer. Inter., 41, 2015, doi:10.1016/j.ceramint.2015.03.224.
Authors : Youngwoo Lee, Jihoon Kim*
Affiliations : Kongju National University
Resume : We successfully prepared Ag-grid flexible transparent electrodes (TEs) by Electrohydrodynamic (EHD) jet printing using Ag nano-particle inks. Ag-grid width less than 10 μm was achieved by the EHD jet printing, which was invisible to the naked eye and embedded in plastic substrate by thermal pressing. Ag-grid line-to-line distance (pitch) was modulated in order to investigate the electrical and optical properties of the EHD jet-printed Ag-grid TEs. The figure of merit of Ag-grid TEs with various Ag-grid pitches was investigated in order to determine the optimum pitch condition for both electrical and optical properties. With 300 μm Ag-grid pitch, the EHD jet-printed Ag-grid TE has the sheet resistance of ~1.2 Ω/sq and the transmittance of 82% after thermal pressing. The EHD jet-printed invisible Ag-grid transparent electrode with good electrical and optical properties implies its promising application to the printed optoelectronic devices. The optimized Ag-grid transparent electrode is employed of organic solar cells to confirm their feasibility as electrodes for device applications.
Authors : Beate Reiser, Dominik Gerstner, Lola Gonzalez-Garcia, Johannes H. M. Maurer, Sebastian Beck, Ioannis Kanelidis, Tobias Kraus
Affiliations : INM - Leibnitz Institute for New Materials
Resume : Wet processing is a promising concept for high-throughput and low-cost production of transparent conductive materials (TCMs) (J.-H. Jou et al., Organic Electronics, 2012). Nanocomposites containing anisotropic metal nanostructures such as nanowires (NWs) are among the most auspicious approaches (S. Ye et al., Adv. Mater., 2014). Ultrathin gold NWs with diameters below 2 nm and aspect ratios above 1000 have high mechanical flexibility and good colloidal stability. They can be synthesized using a facile, scalable one-pot route with oleylamine (OAm) as a capping ligand (H. Feng et al., Chem. Comm. 2009), (J. H. M. Maurer et al., Appl. Mater. Interfaces, 2015). The combination of oleylamine with certain solvents drives the wires to form bundle-like structures, other solvents keep them separated from each other. We tuned solvents and OAm excess concentration to tune the bundling of the NWs. This allowed us to align NWs in shear flow. In-situ small angle X-ray scattering (SAXS) and polarized UV-Vis-NIR spectroscopy indicated that the degree of alignment depends on the shear flow rate. Deposition of NW layers from shear flow yielded layers with preferential orientation that we studied for optical and electrical properties. The approach is compatible with the slot die coaters used for industrial large-scale coating.
Transparent Conductive Oxides Part 4 : Thomas Riedl
Authors : Junjun Jia and Yuzo Shigesato
Affiliations : Graduate School of Science and Engineering, Aoyama Gakuin University
Resume : Recently, transparent conducting oxide films that contain a reduced amount or no indium are of considerable research interest as alternative materials for Sn doped In2O3 (ITO) transparent electrode in optoelectronic applications. Here, we discussed the structure, optical and electrical properties for amorphous In2O3-ZnO (IZO) and polycrystalline Al doped ZnO (AZO) thin films as next generation transparent electrode. The structure of IZO films can be easily tailored from amorphous to polycrystalline states by changing the sputtering deposition conditions, indicating the possibility to produce the film without internal stress between the film and flexible substrate for flexible devices. Amorphous IZO films has the similar optical bandgap to ITO films, and hard x-ray photoemission spectroscopy measurements for IZO films with various carrier densities show the existence of the bandgap narrowing effect in amorphous IZO films. We also investigated the optical bandgap and work function in polycrystalline AZO films. The optical band gap and work function showed the positive and negative linear relationships with the two-thirds power of carrier density, respectively, which are explained by Burstein-Moss effect considering nonparabolic conduction band. We also discussed the carrier transport mechanism of IZO and AZO films in detailed.  J. Jia, Y. Shigesato et. al, J. Appl. Phys., 113, 163702 (2013), J. Appl. Phys., 112, 013718 (2012), Appl. Phys. Express, 7, 105802 (2014).
Authors : Mandeep Singh, Maria Magliulo, Kyriaki Manoli, Mohammad Yusuf Mulla, Maria Vittoria Santacroce, Cinzia Di Franco, Gaetano Scamarcio, Gerardo Palazzo, Luisa Torsi
Affiliations : Dipartmento di Chimica, Universita degli Studi di Bari Aldo Moro, Bari, Italy-70126 CNR-IFN and Dipartimento Interateneo di Fisica University of Bari "Aldo Moro", Bari, Italy-70126
Resume : Solution processed metal-oxides based electronic devices have attracted great deal of attention during the past few years for their potential use in next generation transparent optoelectronic devices. They have high charge-carrier mobility, high optical transparancy and excellent chemical/mechanical stability. Among the metal oxide, ZnO has a wide band gap (3.37 eV), non-toxic and environmentally stable, biocompatible, biodegradable and, at the same time, is made of zinc that is among the most abundant elements in earth's crust. Recently solution processed ZnO thin-films and nano-rods have been successfully implemented as active layers in a number of different electrolyte gated TFT configurations. We are presenting a solution processed electrolyte gated ZnO based TFT. ZnO thin films were prepared with the sol-gel spin coating method. The ZnO structure has been assessed by XRD, XPS and Raman spectroscopy. The gating of the transistor has been performed with water, Posphate Baffered saline and ionic liquids. Impedance spectroscopy has been performed to measure the capacitance of the ionic liquids. The devices gated with ionic liquid shows very high drain current with mobility as high as 4.7 cm2/Vs and Ion/Ioff ratio in the order of 103. The water gated devices was further used for biofunctionalization of ZnO active channel layer and have potential to be used for biosensing applications.
Authors : G. Bonneux (1), K. Elen (1), E.J. van den Ham (1), W. Marchal (1), J.P. Locquet (2), M. Seo (3), A. Hardy (1), M.K. Van Bael (1)
Affiliations : (1) Hasselt University, Institute for Materials Research (IMO), Inorganic and Physical Chemistry, and IMEC vzw, division IMOMEC, Martelarenlaan 42, 3500 Hasselt; (2) KU Leuven, Dept. Physics & Astronomy, Celestijnenlaan 200D, 3001 Leuven, Belgium; (3) KU Leuven, Dept. Materials Science, Kasteelpark Arenberg 44, 3001 Leuven, Belgium
Resume : The last decade has seen an increased attention towards the implementation of InGaZnO (IGZO) as a metal oxide channel material in TFT-devices. Crystalline IGZO shows a high electron mobility and low off-state leakage current, which results in an improved device performance compared to amorphous IGZO [Yamazaki et al., Jpn. J. Appl. Phys. 53 (2014)]. Thin film deposition of the IGZO superlattice structure requires a good layer homogeneity in addition to control of the stoichiometry, which can be achieved by using a solution-based process. In practice, this is usually achieved using 2-methoxyethanol (2-ME) based precursors. However, due to its harmful and teratogenic properties, alternative solvents are being explored. In this work, an aqueous precursor system is developed, in which the metal ions are stabilized by α-hydroxy carboxylic acids as ligands. By spray-coating this precursor, dense and uniform layers are deposited. Through an optimized multi-step thermal treatment, crystalline thin films of IGZO are obtained that show a preferential c-axis orientation after rapid thermal annealing at 1000°C in inert conditions. Preliminary electrical characterization of the deposited thin films already shows promising resistivities of around 8 mΩ*cm, which can apply to several areas of interest. Acknowledgements: This research is financially supported by the Research Foundation-Flanders (FWO Vlaanderen, project nr. G054312N). We thank Y.Guo, P.Homm, M.Menghini for characterization.
Authors : Andriy Lyubchyk, Antonio Vicente, Bertrand Soule, Tiago Mateus, Andreia Araujo, Manuel J. Mendes, Hugo Aguas, Elvira Fortunato and Rodrigo Martins
Affiliations : CENIMAT/I3N, Departamento de Ciencia dos Materiais, Faculdade de Ciencias e Tecnologia, Universidade Nova de Lisboa (FCT-UNL), and CEMOP-UNINOVA, 2829-516 Caparica, Portugal.
Resume : The increasing demand of transparent conducting oxides (TCO) materials for optoelectronic devices  has turned into a worldwide multi-billion economy that nowadays depends on the availability of ITO [ ]. Global ITO sputtering targets demand is 1,400 tons (2014) and it will increase up to 2,500 tons by 2016. However, In is a rare and expensive material, hence, there is a critical need to replace ITO with reliable alternative TCOs made of abundant compounds. The post-deposition modification of ZnO-based TCOs can be the key to produce thin films with optoelectronic properties similar to ITO and at a lower cost. Here, we present our findings for post-deposition annealing enhancement of AZO, AZOH, GZOH and ZnOH deposited by RF sputtering at room temperature. These studies comprise results of thermal annealing at atmospheric pressure, vacuum, forming gas, H2 and Ar atmospheres and H2 and Ar plasma, which lead to significant improvements of the optical, morphological and electrical properties. The post-deposition annealing leads to a gain in resistivity above 20% for AZO, AZOH and GZOH, reaching ρ≈2.4?10-4, while ZnOH showed a smaller gain of 7%. The averaged optical transmittance in the visible region is about 85% for the investigated TCOs. Such results match the properties of state-of-art ITO (ρ≈10-4 and transmittance in VIS range of 90%). 1 Antonio Vicente et al, J. Mater. Chem. A, 2015; DOI:10.1039/C5TA01752A 2 TCC: Technologies & Global Markets, AVM105A, 2014
Poster Session Part 2 : N.N.
Authors : Ja-Yeon Kim, Jong-Hyun Jeon, Min-Ki Kwon
Affiliations : Ja-Yeon Kim Korea Photonics Technology Institute (KOPTI), 9 Chemdan venture-ro, Buk-gu, Gwangju 500-460, Korea; Jong-Hyun Jeon, Min-Ki Kwon Department of Photonic engineering, Chosun university, 309 Pilmun-daero, Dong-gu, Gwangju 501-759, Korea
Resume : Transparent conducting electrodes are important components of highly efficient ultraviolet light emitting diodes (UV LEDs). Indium tin oxide (ITO) is commonly used to form a current spreading layer, but ITO is costly and shows low transparency in the UV range and instability in the presence of acids or bases.. We demonstrate a simple solution-based coating technique to obtain large-area, highly uniform, and conductive silver-nanowire-based electrodes that exhibit UV-range optical transparency better than that of ITO for the same sheet resistance.In this study, we demonstrate an UV LED with a single Ag NW-based TCE deposited by the simple solution based coating method. After optimization of deposition condition, the Ag NW-based TCE showed a sheet resistance of 3040 Ω/sq and an optical transmittance of over 85% at UV wavelength, which are better than the characteristics of ITO. With optimization of annealing condition, the measured I-V curves of Ag NW-based TCE exhibit fairly good Ohmic behavior while that of Ag NW-based TCE before annealing shows Schottky behavior. The electrical and optical properties of a UV LED with a Ag NW-based TCE were better than those of a UV LED with an ITO-based TCE.We anticipate the application of the Ag NW-based TCE to a wide variety of devices, including UV LEDs, with lower fabrication costs and improved performances.
Authors : J. Ram?rez-Castellanos1, G. C. V?squez2, M. A. Peche-Herrero1, D. Maestre2, A. Cremades2, J. Piqueras2 and J. M. Gonzalez-Calbet1
Affiliations : 1 Dpto. de Qu?mica Inorg?nica I, Facultad de Qu?micas, Univ. Complutense de Madrid, 28040, Madrid, Spain 2Dpto. de F?sica de Materiales, Facultad de F?sicas, Univ. Complutense de Madrid, 28040, Spain.
Resume : The efficiency of TiO2 is strongly dependent on the ability to control the morphology and crystal size, defects, doping and also its crystallographic phase, which plays a key role in the functionalization of this material. TiO2 crystallizes in three polymorphs: anatase (tetragonal), rutile (tetragonal) and brookite (orthorhombic), being anatase and rutile the most investigated and extensively used so far. The characteristic physical and chemical properties associated to rutile and anatase phases, i.e. different bandgap, surface energy, dielectric constant, refractive index or mechanical properties, among others, make them specifically suitable for different applications. The anatase to rutile transition (ART) is not totally understood so far, and several issues still require to be addressed. In this work, locally promoted ART and micropatterning based on titania polymorphs have been achieved by means of controlled laser irradiation on doped (Al, Fe) TiO2 nanoparticles synthesized by a modified Pechini method. This method allows us to obtain high homogeneity in size and composition for the doped anatase TiO2 nanoparticles, for which high dopant (Al, Fe) cationic concentration were obtained avoiding phase segregation . Control of the anatase to rutile transition was achieved by laser irradiation and the kinetic of this process has been studied as a function of the dopant and the irradiation conditions . Raman and PL results demonstrate that the ART can be either inhibited or promoted by doping with Al or Fe, respectively. The higher the concentration of Fe in the anatase TiO2 nanoparticles, the faster the phase transformation evolves. Stabilization of anatase due to the presence of Ti3 at the surface of the nanoparticles, reduction of Fe3 to Fe2 involving oxygen deficiency during laser irradiation and formation of rutile starting at the surface of the nanoparticles have been found to influence the ART process. HRTEM results point out to the relevance of the presence of twins in the formation of rutile phase by laser irradiation. An improvement in the control of the ART has been described, as compared with other methods, such as thermal annealing for which micrometric control of local ART is not achieved. The possibility of achieving an ART micrometric patterning has been demonstrated , thus facing challenging performances of this material.  G. C. V?squez, M.A. Peche-Herrero, D. Maestre, A. Cremades, J. Ram?rez-Castellanos, J.M. Gonz?lez-Calbet, J. Piqueras. J. Phys. Chem. C, 117, 1941, (2013)  OEPM Patent P201400722, (2014) and OEPM Patent P201400759, (2014)  G. C. Vasquez, A. Peche-Herrero, D. Maestre, A. Gianoncelli, J. Ram?rez-Castellanos, A. Cremades, J. M. Gonzalez-Calbet and J. Piqueras, J. Phys. Chem C (in press).
Authors : O. Ivanyuta, Yu. Pogrebnyak
Affiliations : Department Electrophysics, Faculty of Radiophysics, Taras Shevchenko National University of Kyiv
Resume : Hydroxyapatite (HA - Ca10(РО4)6 (OH)2) of the apatite group, hydroxyl analogue fluor apatite and hlor apatita. Is the main mineral component of bone (about 50 % of the total weight of the bone) and the tooth (enamel 96 %). We have conducted testing technologies and studied the process of synthesis of hydroxyapatite deposition homogeneous mode using complex calcium - sodium salt of ethylenediaminetetraacetic acid to obtain a powder with high specific surface area , apparent stoichiometry and crystallinity , analogue in properties on Botox.
Authors : SangHun Park1,2, Muhammad Arslan Shehzad1,2 Yongho Seo1*
Affiliations : 1 Faculty of Nanotechnology and Advanced Material Engineering, Sejong University, Seoul, 143-747, Korea. 2 Graphene Research Institute, Sejong University, Seoul 143-747, Republic of Korea
Resume : Chemical vapor deposition (CVD) is used to grow graphene and other 2D materials conventionally. Although single-crystalline growth of graphene is possible only under limited conditions[1-2], but in general CVD method results in poly-crystalline graphene with grain boundaries. These domains with different orientations and grain boundaries degrade the electrical efficiency of graphene in comparison with single-crystalline graphene. In this work we report a new approach to determine the grain and grain boundaries of as-grown graphene using a polarized optical microscope (POM). Our study is focused on analyzing the electrical performance of the device having at least two grains with different orientations. At first, CVD grown graphene was transferred to SiO2/Si wafer with PMMA. After the polymer was removed and liquid crystal was coated on polycrystalline graphene, which acts as a polarizer. We expect that the electrical efficiency of polycrystalline graphene grains can be controlled by using this novel approach. The strength of this method is convenient process of searching suitable grains of graphene and marking on a specific area to use that as proper coordinates for making the device. We measured the electrical properties between grains having different orientation and calculated the exact value of orientation difference. Our study suggests a new technique to fabricate devices on single crystal area, using optimized growth conditions and device geometry.
Authors : Colin O'Callaghan, Claudia Gomes da Rocha, Hugh Manning, Allen Bellew, Mauro Ferreira, John Boland.
Affiliations : School of Physics and CRANN, Trinity College Dublin; School of Physics and CRANN, Trinity College Dublin; CRANN, Trinity College Dublin; CRANN, Trinity College Dublin; School of Physics, Trinity College Dublin; CRANN, Trinity College Dublin
Resume : Nanowire networks (NWNs) comprised of randomly dispersed metallic wires have been seen as promising candidates for a wide range of technological breakthroughs including transparent conductors, thin-film solar cells, sensor devices, etc. The electrical features of NWNs depend on a multitude of physical parameters including their connectivity profile, material properties, inter-wire contact resistance, to name but a few. A way to probe the electrical response of NWNs is to submit the samples to multiple voltage sweeps at high current compliance. The latter must be carefully chosen to electrically load the network without causing its failure. In general, electrically stressed networks have their conductivity maximized with the vast majority of junction resistances optimized. Nonetheless, excessive stress can lead the network to fail. This work studies the conduction pattern of NWNs at the eminence of failure as a result of excessive electrical stressing. A digital version of real NWN samples is created from experimental micrograph images capturing hence all their geometric details. We employed Kirchoffs current laws combined with a complete node-voltage representation which accounts for junction and wire inner resistances to generate real-space current flow maps directly on the micrograph images. This allows us to identify the network spots through where most of the current is flowing. Additionally, one can pinpoint the most likely network spots for failure. Our results were subsequently compared with experiments and they reveal remarkable agreement. This work confirms hence that is possible to predict the most sensitive and robust spots of the networks.
Authors : Fabio Niosi, Claudia Gomes da Rocha, Allen T. Bellew, Mauro Ferreira and John J. Boland.
Affiliations : Centre for Research on Adaptive Nanostructures and Nanodevices (CRANN), Trinity College Dublin, Dublin 2, Ireland.
Resume : Over the past few years the growth and continued improvement of devices like smartphone, e-readers, touch screen etc. has enabled an exponential increase in the cost of the ITO (Indium Tin Oxide). As a consequence, alternative materials with equal or greater performance is needed. The materials for this application should have a high transmittance, >90 %, and low sheet resistance [1-3]. One of the best candidates to replace ITO are the metallic nanowire networks. In this work we will focus on silver nanowire network in which we study the activation process at the level of individual junctions. The Ag nanowire network were fabricated using a standard spray deposition method combined with a shadow mask technique for the electrode deposition. We demonstrate that during the activation two different processes are involved. Specifically we show that when the current compliance levels is set at a low level, the current increases slowing as the voltage is increased and then sharply increases at the turn-on voltage is reached the network attains the set current compliance. Repeating this measurement at increasingly higher set compliance levels and recording the conductance of the film as a function of the total integrated charge reveals a remarkable scaling behaviour. The scaling shows two regimes. At low levels of integrated charge the increased conductance of the network is believed to be due to the strengthening of the junctions that contribute to the conduction mechanism. This is likely due to enhanced tunnelling rates across these junctions. The break in the slope points to a new mechanism which we suggest is due to the completion of junction strengthening and the co-opting of additional junctions to densify the numbers of junctions participation in the conduction process. Based on these observations, we believe that we can improve the electrical properties of metallic nanowire networks. References Cui et al, ACS NANO, (2010) Vol. 4, No. 5  D.P.Langley et al,Solar Energy Materials & Solar Cells125(2014)318324 Erik C. Garnett et al,NATURE MATERIALS(2012) DOI: 10.1038/NMAT3238  S. Gao, Applied Physics Letters (2013) 102, 141606
Authors : A. Vlad1, R. Birjega1, A. Matei1, V. Ion1, M. Dinescu1, R. Zavoianu2
Affiliations : 1National Institute for Lasers, Plasma and Radiation Physics, 409 Atomistilor Str., 77125 Bucharest- Magurele, Romania 2University of Bucharest, Faculty of Chemistry, Department of Chemical Technology and Catalysis, 4-12 Regina Elisabeta Bd., Bucharest, Romania
Resume : The preparation of photofunctional hybrid thin films of intercalated chromophores in Layered double hydroxides (LDH) matrix by pulsed laser deposition (PLD) is investigated, and the functionality of the films will be examined through the optical properties introduced by the chromophore. An interesting class of chromophores is coumarins and coumarins derivates. Two systems will be studied: coumarin intercalated in MgAl-LDH and coumarin and dodecyl sulfate (DS) co-intercalated in MgAl-LDH. The introduction into the LDH gallery of a second anion, dodecyl sulfate anion aimed the suppression of the aggregation of chromophore anions. X-ray diffraction, infrared spectroscopy and UV-vis spectroscopy were the techniques used for the investigation of the functional hybrid targets and the as prepared films. The effect of the deposition condition, primarily of the laser wavelength on the optical properties of the photofunctional coumarine intercaleted - LDH films was examined.
Authors : E. Norton, L. Farrell, D. Mullarkey, I.V. Shvets and K. Fleischer
Affiliations : Centre for Research on Adaptive Nanostructures and Nanodevices (CRANN) and School of Physics, Trinity College Dublin, Dublin 2, Ireland
Resume : Thin films of p-type Cr2O3:Mg have been produced by Molecular Beam Epitaxy (MBE) as well as amorphous p-type CuCrO2 deposited by a low temperature solution based method (spray pyrolysis). These thin films are deposited on top of a n-type Indium Tin Oxide substrate creating transparent pn junctions. The band alignment of these two interfaces is studied using X-ray Photoelectron Spectroscopy (XPS) and Ultra Violet Photoelectron Spectroscopy (UPS). An estimate of the band discontinuities at the interfaces of ITO/ Cr2O3:Mg and ITO/a- CuCrO2 are given. An emphasis is given to the fact that the Fermi level and work function position for both Cr2O3:Mg and a-CuCrO2 show changes with surface preparation and surface termination.
Authors : M. Duta1, L.Predoana1, S.Preda1, P.Osiceanu1, M.Nicolescu1, M.Gartner1, M.Zaharescu1, S. Simeonov2, D. Spasov2, P.Terziyska2, A. Szekeres2
Affiliations : 1Institute of Physical Chemistry Ilie Murgulescu, Romanian Academy 202 Splaiul Independentei, 060021 Bucharest, Romania; 2Institute of Solid State Physics, Bulgarian Academy of Sciences, 72 Tzarigradsko Chaussee, 1784 Sofia, Bulgaria
Resume : Titanium dioxide has found a wide application in novel environment- and energy-related processes such as photocatalysis for water purification, gas sensing, etc. Adding Nb or V dopants improves its electrical conductivity without decreasing its visible transmittance what makes it promising for TCO applications. The role of generation and transformation of point defects by technological processes in the electrical conduction mechanism is important for TiO2:Nb(V) film application. We report on TiO2 multilayers deposited on glass and Si substrates by the sol-gel method, focusing on the influence of 1.2 at.% Nb(V) doping on the structure of the films and their optical and electrical properties. The TiO2:Nb(V) films crystallized in anatase phase as evidenced by XRD analyses. XPS measurements revealed that Nb(V) dopants segregated from bulk to the surface. The transmittance values were around 80 % in the 400- 900 nm visible range of light. Electrical measurements of the I-V and C-V characteristics of MIS structures with the TiO2:Nb(V) films pointed out that the doping level in the films had be equal or greater than 10^16 cm^-3. The character of I-V dependences and decrease of the specific resistivity (10^4-10^5 Ohm.cm) by increasing the electrical field evidenced for bulk character of electrical conduction in the TiO2:Nb(V) films and revealed that the current through the films is space charge limited current via deep levels with energy distribution in the energy gap of TiO2.
Authors : J. Resende1,2, N. D. Nguyen2, J. L. Deschanvres1
Affiliations : 1 Laboratoire des Mat?riaux et du G?nie Physique, Univ. Grenoble Alpes, LMGP, F-38000 Grenoble, France; CNRS, LMGP, F-38000 Grenoble, France 2 Department of Physics, Universit? de Li?ge, Belgium
Resume : Oxide electronics is an important emerging area, notably for the development of transparent thin film transistors (TFTs) and other complex electronic circuits. The successful application of n-type oxides to TFTs has motivated the interest in p-type oxide based semiconductors, also to be applied to TFTs or to complementary metal-oxide semiconductor (CMOS) technology. However, until now there is a lack of p-type oxide semiconductors with performance similar to that of n-type oxide. Among the different metallic oxides, Cu (I)-based oxides exhibit one of the lowest ionic character. These compounds are therefore one of the most promising candidates as p-type transparent semiconductors.Nevertheless, the band gap of 2,17eV is modest for transparent electronics applications, since the transmittance of Cu2O films is low on the visible part of the light spectrum. The incorporation of cations with large radii than Cu has been proposed as a way to achieve a higher band gap, by diminishing of three-dimensional Cu-Cu interactions, only possible with larger cations than Cu . Therefore, cation doped Cu2O thin films were grown by metal-organic chemical vapor deposition (MOCVD). The three doping elements studied (Sr2 , Sn2 and La3 ) were selected having in account theoretical predictions for the band structure and the deposition conditions of Cu2O. The study focus on thin films growth optimization combined with electronic transport analysis and optical transmittance measurements.
Authors : Ngoc Minh Le, Hoang Ba Cuong, Byung-Teak Lee
Affiliations : Chonnam National University
Resume : Transparent conductive oxide (TCO) materials with wide energy band gap (Eg) recently attracted attention, as research on the electro-optical devices expands to the ultraviolet (UV) range. In this work, Zn0.88Mg0.05Be0.03Ga0.04O (ZMBGO) TCO film was prepared on the quartz substrate by RF magnetron sputtering, with the energy band gap of ~3.8 eV, the optical transmittance of ~92% in the visible range, ~97% in the UV range (370-400nm), and the resistivity of ~4x10-3 Ωcm. The ZMBGO/Ag/ZMBGO and the ZMBGO/Cd1-x(Tix)O/ZMBGO multilayer structures were investigated in an effort to improve the conductivity. Results indicated that the multilayer with Ag showed much lower resistivity of ~4x10-5 Ωcm and reasonable transmission of 75% ~ 90% over the visible range. Initial results on the multilayers with (Ti)CdO indicated much improved transmission but slightly higher resistivity. Results with optimized multilayer structures with high transmission and low resistivity and the mechanisms operating will be further discussed in the presentation.
Authors : Petru Lunca Popa, Jonathan Crepeliere, Renaud Leturcq and Damien Lenoble
Affiliations : Materials Research and Technology Department (MRT), Luxembourg Institute of Science and Technology (LIST), L-4422 Belvaux, Luxemburg
Resume : CuxCryOz thin-films are grown via a DLI-MOCVD (Direct Liquid Injection - Chemical Vapour Deposition) process for the substrate temperature range of [400-650oC], different precursors concentrations and at different oxygen partial pressure. Electrical and optical properties of thin films, and the influence of depositions parameters on these properties are deeply investigated. The as-deposited films present a medium degree of crystallinity, a good transmission up to 80% in the visible range with a corresponding band gap around 3.2 eV, making such films particularly appealing for transparent electronics applications. Electrical conductivity values up to 30 S/cm were measured. Thermal activation energies are in range of hundreds of meV, strongly influenced by the oxygen partial pressure. The crystallinity of the films is improved by increasing the precursor concentration and by tailoring substrate temperatures. No influence of the oxygen partial pressure on to crystallinity was observed. The band gap can also be tuned by adjusting the precursors concentration, the oxygen partial pressure and the substrate temperature. The conduction mechanisms are also studied and significant shifts in the activation energy of the conductivity are evidenced. Various hypotheses in terms of dopants, defects, crystallinity and polarons are discussed to interpret the conduction mechanisms of holes.by change in the polaron hopping mechanism.
Authors : Mesa F, Chamorro W, Hurtado M
Affiliations : a Unidad de Estudios Universitarios, Colegio Mayor de Nuestra Senora del Rosario, Cra. 24 N◦ 63C-69, Bogotá, Colombia; CNRS, Institut Jean Lamour, Université de Lorraine, UMR7198, Nancy F-54011, France; c Departamento de Quimica, Universidad Nacional de Colombia, Cra. 30 N◦ 45-03, Bogotá, Colombia; d Departamento de Física, Universidad de los Andes, Calle 21 No. 1-20, Bogotá, Colombia
Resume : Maximum conversion efficiency achieved in thin film technology CIGS-based solar cells is 21.7% using CdS as buffer layer. However, due to the toxicity of Cd, a special interest has emerged searching for candidates to replace it. In2S3 is a promising buffer layer because it has no toxic elements and the production cost is low. Moreover, recent researches have shown a good performance with CIGS absorber layers achieving good conversion efficiencies compared to those using CdS layers. However, the In2S3 films optical properties vary depending on the synthesis conditions. Regarding the absorber layer, special attention have led to propose compounds without non-abundant elements as Ga and In in their structure as the Cu2ZnSn(S,Se)4 or the Cu3BiS3 compounds. We present the growth of In2S3 onto Cu3BiS3 layers and soda-lime glass substrates by using chemical bath deposition and physical co-evaporation. The results show In2S3 films microstructure and optical properties strongly dependent on the growth method. X-ray diffractrograms show that In2S3 films have a higher crystallinity when growing by co-evaporation than by CBD. In2S3 thin films grown by CBD with a thickness below 170 nm have an amorphous structure however when increasing the thickness the films exhibit two diffraction peaks associated to the (103) and (107) planes of the In2S3 tetragonal structure. It was also found that the In2S3 films present an Eg of about 2.75 eV, regardless of the thickness of the samples.
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Graphene : Benjamin Wiley
Authors : Young Hee Lee
Affiliations : 1Center for Integrated Nanostructure Physics, Institute for Basic Science, Sungkyunkwan University,Suwon, Kyunggi-do 440-746, South Korea 2 Department of Energy Science, Department of Physics, Sungkyunkwan University,Suwon, Kyunggi-do 440-746, South Korea
Resume : In addition to metallic graphene monolayer, nsulating hexagonal-BN monolayer and semiconducting layered transition metal dichalcoginides (LTMDs) are new classes of transparent and flexible materials, which can be used as essential components of transistors for soft electronics. While large-area graphene is available in a meter-scale, synthesis of large area monolayer h-BN and LTMDs are still a long way to realize. We introduce conventional chemical deposition approach to synthesize such materials in a centimetre-scale. Among LTMDs, semiconducting 2H phase MoS2 was converted partially to metallic 1T phase by strong chemical dopings such as lithium intercalation and electron beam irradiation, where such a phase transition was irreversible, limiting their applications. In our study, however, we found that thin MoTe2 revealed a reversible phase transition from 2H to 1T at around 650-900oC depending on the Te-rich conditions. We will demonstrate that the phase transition of MoTe2 can be provoked by several robust parameters and even the phase transition temperature can be reduced to room temperature.
Authors : S. Majee, M. Song, S.L. Zhang, Z.-B. Zhang
Affiliations : Solid State Electronics, Angstrom Laboratory, Uppsala University, Uppsala, Sweden
Resume : Electrical interconnections are one of the main challenges in the printed electronics, to connect different functional units of an electronic device. With the progressive advancement of large area and low cost printed electronic devices on polymeric and paper substrates, the requirement for reliable interconnections with lower power consumption fabricated at low temperature is necessary. The conventional copper-based interconnections suffer severe problems in terms of cost efficiency when they are processed with photolithography technique. To replace the conventional metallic interconnections we have proposed printed interconnects with graphene inks. This is mainly motivated by two reasons. First, printing is a low-cost patterning approach which is performed at ordinary ambient condition. Printing of graphene proved to be a promising since it combines the attractive features of graphene and the cost effective printing methods (ink-jet printing, nozzle printing, spray printing) which enable additive patterning, direct writing, scalability to large area manufacturing. In order to facilitate the inkjet printing process, the graphene solution needs to be highly stable, uniform and should contain smaller sheet sizes (~ 1 micro meter) because of the limitation of the nozzle size of inkjet printing machine. In this work we have proposed a cost-effective approach for large-scale production of printable stable graphene suspension by liquid-phase shear exfoliation of graphite for printed electronics application. The process is scalable and requires shorter processing time compared to the other existing exfoliation methods. Graphene sheets have been exfoliated from graphite flakes in a solvent, cyclohexanone with ethyl cellulose as stabilizer. The graphene based solution prepared after several optimizations leads to a stable ink for more than six months without any sedimentation. The initial studies confirmed the production of graphene films with average sheet thickness of 10 to 20 nm and without any agglomeration with sheet sizes less than 1 micro meter. The rheological properties, such as, viscosity, of the produced graphene ink has been carefully tuned in order for successful inkjet printing process. Highly conductive and transparent (~70 % in the visible region) interconnections have been developed after several inkjet printing steps.
Authors : Taras Radchenko, Valentyn Tatarenko, Igor Sagalianov, Yurij Prylutskyy
Affiliations : Institute for Metal Physics, N.A.S.U., 36 Acad. Vernadsky Blvd., Kyiv, Ukraine; Taras Shevchenko National University of Kyiv, 64 Volodymyrska Str., Kyiv, Ukraine
Resume : The electron-transport properties of adatom-graphene system are investigated for different spatial configurations of adsorbed atoms: when they are randomly-, correlatively-, or orderly-distributed over different types of high symmetry sites with various adsorption heights. Potassium adatoms in monolayer graphene are modeled by the scattering potential adapted from the independent self-consistent ab initio calculations. The results are obtained numerically within the framework of quantum-mechanical Kubo-Greenwood formalism. A band gap may be opened only if ordered adatoms act as substitutional atoms, while there is no band gap opening for adatoms acting as interstitial atoms. The type of adsorption sites strongly affect the conductivity for random and correlated adatoms, but practically does not change the conductivity when they form ordered superstructures with equal periods. Depending on electron density and type of adsorption sites, the conductivity for correlated and ordered adatoms is found to be enhanced in dozens of times as compared to the cases of their random positions. These the correlation and ordering effects manifest weaker or stronger depending on whether adatoms act as substitutional or interstitial atoms. The conductivity approximately linearly scales with adsorption height of random or correlated adatoms, but remains practically unchanged with adequate varying of elevation of ordered adatoms.
Authors : Massimo Spina*, Mario Lehmann*, Bálint Náfrádi*, Laurent Bernard*, Eric Bonvin*, Richard Gaál*, Arnaud Magrez', László Forró*, Endre Horváth*
Affiliations : *, Laboratory of Complex Matter Physics, EPFL, Lausanne 1015, Switzerland ', Crystal Growth Facility, EPFL, Lausanne 1015, Switzerland
Resume : Methylammonium lead iodide perovskite has revolutionized the field of third generation solid-state solar cells leading to simple solar cell structures1 and certified efficiencies up to 20.1%2, 3. Recently the peculiar light harvesting properties of organometal halide perovskites have been exploited in photodetectors where responsivities of ~3.5 A/W and 180 A/W have been respectively achieved for pure perovskite-based devices4-6 and hybrid nanostructures7. Here, we report on the first hybrid phototransistors where the performance of a network of photoactive Methylammonium Lead Iodide nanowires (hereafter MAPbI3NW) are enhanced by CVD-grown monolayer graphene. The measured device photoresponsivity was as high as 2.6x106 A/W that is 4 orders of magnitude higher the best hybrid perovskite photodetector reported by Y. Lee et al7 and comparable to the best hybrid graphene photodetectors reported so far18,13 under similar operating conditions. We attribute these very high device performances mainly to the nanowire perovskite morphology. The drastic enhancement of the responsivity at very low light intensities (pW) suggest the use of MAPbI3 nanowire/graphene devices as low-light imaging sensors and single photon detectors. Nature 2013,501(7467),395-8. Nat Photon 2014, 8(7),506-14. J Mater Chem A 2015. Adv Funct Mater 2014, 24(46), 7373-80. Adv Mater 2015, 27(1), 41-6. Nano Lett 2014, 14(12), 6761-6. Nat Nano. 2013;8(11):826-30. Nat Nano. 2012, 7(6),363-8
Transparent Conductive Oxides Part 5 : Joris Proost
Authors : Thomas Riedl
Affiliations : Institute of Electronic Devices, University of Wuppertal, Wuppertal, Germany
Resume : Today, ITO is the most frequently used transparent electrode material. The limited abundance of Indium is expected to cause severe issues. In my presentation I will discuss two possible alternatives. Firstly, a hybrid approach based on a composite of a mesh of silver nanowires and a conductive metal-oxide will be demonstrated. Here, SnOx or Al:ZnO prepared at low-temperatures (100°C) will be used to fuse the wires together and also to "glue" them to the substrate. The resulting electrodes show a low sheet resistance (5.2 Ohm/sq) and high average optical transmission of 87%. Their application as transparent top-electrodes semitransparent organic solar cells will be shown. In the second part, I will introduce the first robust transparent electrodes which are at the same time gas diffusion barriers (GDBs). Generally, GDBs are inevitable to protect sensitive organic devices against ambient gases. Transparent and electrically conductive GDBs (TCGDBs) could serve as electrode and moisture barrier simultaneously. As of yet, work on TCGDBs is very limited. TCGDBs based on ZnO suffer from the severe degradation of their electrical conductivity by orders of magnitude upon exposure to damp heat conditions after very short time. We will show that these issues can be overcome by the use of tin oxide (SnOx) grown by ALD. Robust conductivities of up to 300 S/cm and extremely low water vapor transmission rates (WVTR) on the order of 10-6 g/(m2 day) can been achieved.
Authors : S.T. Zhang, G. Giusti, S. Brochen, M. Jouvert, J.L.Deschanvres, C. Jiménez, D. Munoz-Rojas, V. Consonni, D. Bellet
Affiliations : Univ. Grenoble Alpes, LMGP, F-3800 Grenoble, France CNRS, LMGP, F-38000 Grenoble, France; Technische Universität Darmstadt, Institute of Materials Science, Surface Science Division Jovanka-Bontschits-Str. 2, 64287 Darmstadt, Germany
Resume : Over the past few decades, polycrystalline fluorine-doped SnO2 (FTO) thin films have received increasing interest due to their promising applications in a wide variety of devices such as gas sensors or solar cells. FTO thin films can exhibit remarkable electro-optical properties while showing high work function as well as good thermal and chemical stability. As such, FTO can act as an efficient front transparent electrode for solar cells. In this work, FTO thin films are grown by spray pyrolysis on glass or flexible substrates. The interplay between structural, electrical and optical properties of FTO thin layers is investigated with a special emphasis on electron scattering mechanisms. We demonstrate that FTO thin films combined with different types of nanoparticles (NPs) can form nano-composites which show varying diffuse component of transmitted light as a function of NP surface density. In the first step, ZnO NPs were used , haze factors of the resulting nano-composites are varied from 0.4% to 64% in the visible range without degrading total optical transmittance (~90%), while maintaining good electrical properties (i.e. sheet resistance 10-15 ohm/square). Studies with Sulfur doped TiO2 NPs and SnO2 NPs are then carried out to study the influence of NP conductivity and morphology on composite performance. With such high haze factors, the nano-composite FTOs are very valuable in integration in solar cells.  G. Giusti et al. ACS Appl. Mater. and Interf. 6 (2014)14096
Authors : Kiyoshi Kanie* Takafumi Sasaki, Yuki Akama, Syunsuke Takeya, Kazuyoshi Hara, Yusuke Tsujikawa, and Atsushi Muramatsu
Affiliations : Institute of Multidisciplinary Research for Advanced Materials, Tohoku University
Resume : Tin-doped indium oxide (ITO), an n-type transparent conducting oxide (TCO), have been extensively investigated due to many ITO applications as typified by a flat panel display technology and electrical paper. In general, ITO electrode is industrially prepared by sputtering or laser deposition method. On the other hand, TCO nanoink has been paid attention as an alternative to the conventional processes to produce ITO electrode. In the present study, we have investigated solvothermal synthesis of ITO, gallium-doped zinc oxide (GZO), and aluminium-doped zinc oxide (AZO) NPs with use of quaternary ammonium hydroxides. As a result, highly-crystalline ITO, GZO, and ATO NPs were successfully prepared through a one step process under solvothermal condition. Blue-coloured compacts of the TCO NPs obtained by the present method exhibited low resistivity. In particular, cubic-shaped single-crystalline ATO nanoparticles were obtained in the presence of amine derivatives. Nano-ink property of TCO NPs thus obtained has been also investigated for the development of TCO nanoinks with low sintering property. References  Y. Endo, T. Sasaki, K. Kanie, and A. Muramatsu, Chem. Lett., 2008, 37, 1278-1279.  T. Sasaki, Y. Endo, M. Nakaya, K. Kanie, A. Nagatomi, K. Tanoue, R. Nakamura, and A. Muramatsu, J. Mater. Chem., 2010, 20, 8153-8157.  K. Kanie, T. Sasaki, M. Nakaya, and A. Muramatsu, Chem. Lett., 2013, 42, 738-740. Acknowledgements: This work was financially supported by Industrial Technology Research Grant Program in 2011 (No. 11b15004d) from NEDO, Japan
Authors : James Lourembam1; Tarapada Sarkar2; T. Venkatesan2; Elbert E.M. Chia1
Affiliations : 1Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371, Singapore ; 2NUSNNI-Nanocore, National University of Singapore, Singapore 117411, Singapore,
Resume : Introduction of Ta as a dopant into TiO2 not only renders the system to conductive, but also introduces phenomena such as defect induced Kondo effect and ferromagnetism. Such exciting properties has been characterized using traditional DC transport measurements, but no work has been done to understand these phenomena using an AC measurement techniques like THz-TDS. Interestingly, we observe an isosbestic point in the THz range when the temperature-dependent optical conductivities curves are plotted.
Metallic Nanowires or Nanoparticles Part 3 : Young Hee Lee
Authors : Benjamin J. Wiley
Affiliations : Duke University
Resume : Abstract: The primary goal of research focused on solution-based processes for the manufacture of solar cells is to lower the cost of generating electricity from sunlight. Most solution-processed solar cells rely on vapor-deposited indium tin oxide (ITO) as the transparent electrode, and ITO film represents the single largest contribution to the cost of a solution-processed solar cell. Replacing ITO with a solution-deposited film of copper-based nanowires can potentially eliminate this barrier to low-cost production of photovoltaic modules. Copper nanowires can be produced with a scalable, solution-based process in which they grow at ~100 nm/s through the diffusion-limited addition of a copper(I) precursor to a copper nanoparticle. Maximizing the optical transmittance of a nanowire film while minimizing its electrical resistance requires minimizing the diameter of the nanowires, area fraction of the nanowires, the number of contacts between nanowires, and the contact resistance between nanowires. Minimization of diameter, area fraction, and number of contacts was achieved by development of a synthesis that produces copper nanowires with aspect ratios as high as 5700 in 30 min. The contact resistance between copper nanowires is initially high due to the presence of a native oxide; this oxide can be eliminated by dipping the nanowires in acetic acid. Subsequent oxidation of copper nanowires can be prevented by coating them with a thin layer of Ni, Zn, Sn, or In. Organic solar cells made with copper-based nanowires exhibit device efficiencies of 5%, comparable to values obtained for devices made with silver nanowire-based transparent electrodes.
Authors : L. González-García, J.H.M. Maurer, B. Reiser, I. Kanelidis, T. Kraus
Affiliations : INM - Leibniz Institute for New Materials, Campus D2 2, 66123 Saarbruecken, Germany
Resume : Metal nanoparticles (NPs) are currently used to fabricate functional materials for optics, SERS, catalysis, sensing, and transparent electronics. A wide variety of NPs is available through published synthetic routes and, increasingly, as commercial products. We study Transparent Conductive Materials (TCMs) based on metal NPs that combine high electrical conductivity with optical transparency and mechanical flexibility. Wet-processed films of metallic nanowires networks are considered promising candidates for a new generation of transparent electrodes with a relatively cost-effective, scalable production. In random deposition, percolation requires a high density of NPs that reduces the transparency of the final material. We develop wet deposition methods that provide control over TCMs microstructure and properties. Here, we present a new strategy to align and to deposit anisotropic metal NPs into well-defined structures using patterned PDMS masters. We deposited gold NPs from suspension to obtain homogeneous coatings over areas of cm2. We investigated the interplay between template, particle arrangement and optical properties of the final material by electron microscopy and atomic force microscopy in combination with optical spectroscopy. The choice of particle ligands affected both the deposition process and the final material properties. We will discuss the different mechanisms affected by ligand choice, resulting trade-offs, and propose new ligand concepts for TCMs.
Authors : Claudia Gomes da Rocha, Colin OCallaghan, Carlos Ritter, Hugh Manning, Allen T. Bellew, John J. Boland, Mauro S. Ferreira
Affiliations : School of Physics, Trinity College Dublin, Dublin 2, Ireland; School of Physics, Trinity College Dublin, Dublin 2, Ireland; Departamento de Química, Universidade Federal do Paraná (UFPR), CEP 81531-990, Curitiba-PR, Brazil; School of Chemistry, Trinity College Dublin, Dublin 2, Ireland; School of Chemistry, Trinity College Dublin, Dublin 2, Ireland; School of Chemistry, Trinity College Dublin, Dublin 2, Ireland; School of Physics, Trinity College Dublin, Dublin 2, Ireland
Resume : In this work, we introduce a combined experimental and computational approach to describe the conductivity of metallic nanowire networks. Due to their highly disordered nature, these materials are typically described by simplified models in which network junctions control the overall conductivity. Here, we introduce a combined experimental and simulation approach that involves a wire-by-wire junction-by-junction simulation of an actual network. Rather than dealing with computer-generated networks, we use of a computational approach that captures the precise spatial distribution of wires from an SEM analysis of a real network. In this way, we fully account for all geometric aspects of the network, i.e. for the properties of the junctions and wire segments. Our model predicts characteristic junction resistances that are smaller than those found by earlier simplified models. Moreover we show that it is possible to predict the optimum performance for any network and introduce an optimization parameter that describes the scope for improvement.
Authors : M. Lagrange1, T. Sannicolo1,2, D. P. Langley1,3, D. Muñoz-Rojas1, C. Jiménez1, M. Anikin1, O. Chaix-Pluchery1, C. Celle2, J.P. Simonato2, N. D. Nguyen3, Y. Bréchet4, D. Bellet1
Affiliations : 1 Univ. Grenoble Alpes, CNRS, LMGP, F-38000 Grenoble, France 2 CEA/LITEN/DTNM/SEN/LSIN, Univ. Grenoble Alpes, 17 Rue des Martyrs, F-38054 Grenoble, France. 3 Laboratoire de Physique des Solides, Interfaces et Nanostructures; Département de Physique, Université de Liège. Allée du 6 Août 19, B-4000 Liège, Belgique. 4 Univ. Grenoble Alpes, SIMAP, F-38000 Grenoble, France CNRS, SIMAP, F-38000 Grenoble, France.
Resume : Transparent electrodes (TE) constitute a key component of optoelectronic devices such as solar cells, efficient organic light-emitting diodes (OLEDs), touch screens. Currently the most widely used TE is indium tin oxide (ITO), which offers low resistivity and high transparency in the visible. However the scarcity of indium and the lack of flexibility of ITO has prompted the search for alternative materials. Among emerging TE, metallic nanowire (NW) networks appear to be a promising solution since these percolating networks exhibit excellent properties with sheet resistance of a few Ω/ and optical transparency of 90%, fulfilling the requirements for many applications. In addition, the fabrication of these electrodes involves low-temperature process steps and upscaling methods, thus making them very appropriate for future use as TE for flexible devices. Our research is focused on both the fabrication of TE based on silver NW and the optimization of their physical properties, using experimental and modelling approaches. The influence of several key parameters such as network density, silver NW dimensions as well as thermal annealing, on the networks physical properties is thoroughly explored. A comprehensive understanding of the relationship between design and main physical properties of these promising nanostructured networks will be presented. Their stability will also be discussed. Finally, we will also show that such TE can be very well adapted as transparent heaters.
p-type Transparent Conductive Materials Part 2 : Daniel Bellet
Authors : Loraine Duclaux, Negar Naghavi, Julien Vidal
Affiliations : Institut de Recherche et Développement sur lEnergie Photovoltaïque (IRDEP), UMR EDF-CNRS-Chimie ParisTech 7174, 6 quai Watier, 78401 Chatou Cedex, France
Resume : N-type Transparent and Conductive Materials (TCMs) have been optimized for the past decades and are nowadays widely used in optoelectronics . However, p-type TCMs conductivities are still 2 to 4 orders of magnitude lower than the best achieved values for n-type , constituting a technological key lock to build all-transparent devices. The p-type chalcopyrite CuAlS2 (3.5 eV band gap) is a promising candidate owing to its 0.9 S/cm conductivity reported for the intrinsic compound that can be enhanced up to 63.5 S/cm when Zn-doped . In this work, ab initio calculations on CuAlS2 have been carried out in order to understand the physics of intrinsic and extrinsic defects in CuAlS2. Study of point defects in CuAlS2 highlights intrinsic conductivity pathway, identifying CuAlS2 to be a compensated material whose conductivity results from the equilibrium between holes produced by copper vacancies VCu and electrons generated by aluminum-on-copper AlCu. The resulting variations of the Fermi level were studied for different thermodynamic growth conditions. P-type character of CuAlS2 was then confirmed, yielding large hole concentrations up to 1019 /cm3 under optimumum growth conditions. To achieve even higher carrier concentrations, extrinsic doping has been considered and several cations (Zn, Mg, Be, Ca, Sr, Sc, Li and Na) and anions (N, O, P) were considered and their potential as p-type dopant investigated in terms of transition levels and atomic radii.  C. G. Granqvist,, Sol. Energy Mater. Sol. Cells, 91, 17, 1529‑1598, 2007.  S. Nandy, R. Martins, , Rev. Adv. Sci. Eng., l. 2, 4, 273‑304, 2013.  M.-L. Liu,Q. Zhang,, Appl. Phys. Lett.,. 90, 7, 072109, 2007.
Authors : L. Farrell , E. Norton , B.J. ODowd , D. Caffrey, I.V. Shvets, and K. Fleischer
Affiliations : L. Farrell ; E. Norton ; B.J. ODowd ; D. Caffrey; I.V. Shvets; and K. Fleischer : School of Physics and Centre for Research on Adaptive Nanostructures and Nanodevices (CRANN), Trinity College, University of Dublin, Dublin 2, Ireland D. Caffrey; Advanced Materials Bio-Engineering Research Centre (AMBER)
Resume : p-type transparent conducting materials are sought after for optoelectronic devices. Little work has been done on low cost synthesis of these materials for large area flexible substrates. In this contribution a low temperature (≈ 345°C) growth method for CuCrO2 is demonstrated by spray pyrolysis using metal-organic precursors. Smooth films were grown on glass substrates with a highest conductivity of 10 S/cm. The most conductive samples are transparent enough to have figure of merits as high as 390 μS. Remarkably despite the low crystallinity of the films, properties comparable with crystalline CuCrO2 are observed. Mobilities of the films are estimated to be 5×10-3 cm2/Vs using the small polaron hopping model. No post-annealing of the films is required in contrast to previous reports. The ability to form material at lower temperatures greatly improves prospects for applications. As this is a solution based technique it is more attractive to industry as PVD methods are slow and costly in comparison.
Authors : Chamorro W.1, Boulet P.1, Migot S.1, Miska P.1, Shyju T.S.2-3, Kuppusami P.2-3, Pierson J.F.1
Affiliations : 1CNRS, Institut Jean Lamour, Université de Lorraine, UMR7198, Nancy F-54011, France 2 Centre for Nanoscience and Nanotechnology, Sathyabama University, Chennai-600119,India 3 Cntre of Excellence for Energy Research, Sathyabama University, Chennai-600119,India
Resume : ZnS, a II-VI semiconductor, has been studied due to its unique optical properties and could be a promising candidate for p-type semiconductor materials. When doped with Cu their luminescence properties are well known however the literature reports of ZnS:Cu films exhibiting a p-type behavior is low. In this work, ZnS:Cu thin films were synthetized by RF magnetron sputtering using ceramic ZnS and metallic Cu targets. The Cu target power was changed in order to vary the Cu content in the films while other experimental parameters remain constant. (0002)-oriented hexagonal ZnS films are obtained for all the conditions. XRD results suggest the Cu insertion in Zn atomic positions of the ZnS crystal lattice decreasing the a and c lattice parameters and therefore the ZnS volume. Films with Cu contents above 6% show changes in the microstructural, optical and electronic properties of the films. Looking at the intensity of the (0002) ZnS diffraction peak, when the Cu content is increased, a striking loss in the preferential orientation growth is found also related with a loss in the ZnS crystal quality. Regarding the optical properties, the energy bandgap found by optical absorption decreases with the Cu content, moreover, it appears an absorption in the near infrared region probably due to a plasmon resonance due to an increase in the carrier concentration. From electrical measurements it was found that above a concentration of 6%, the films are conductive and have a p-type behavior.
Authors : Emma Norton, Leo Farrell, David Caffrey, Stephen Callaghan, Cormac McGuinness, Igor Shvets, Karsten Fleischer
Affiliations : Centre for Research on Adaptive Nanostructures and Nanodevices (CRANN) and School of Physics, Trinity College Dublin, Dublin 2, Ireland
Resume : The valence band structure of novel p-type transparent oxides crystalline Cr2O3:Mg and amorphous CuCrO2 is analysed as a function of incoming photon energy. By analysing the valence band photoemission data across the Cr 3p-3d, Cu 3p-3d, and Mg 2p-3s transitions the contributions of Cu and Cr d-states and Mg s-states to the valence band structure is evaluated. The valence band of both p-type TCOs show striking similarities to measurements on crystalline CuCrO2, highlighting the importance of the Cr-O octahedra on the electronic states at the top of the valence band.
Authors : S. Agnello1*, A.Piazza1,2,3, G. Buscarino1, G. Fisichella2, A. La Magna2 , F. Roccaforte2, M. Cannas1, F.M. Gelardi1, F. Giannazzo2
Affiliations : 1Department of Physics and Chemistry, University of Palermo, Italy; 2CNR-IMM, Catania, Italy; 3Materials Science and Nanotechnologies PhD School, University of Catania and University of Palermo, Italy
Resume : Electronic applications of Graphene (Gr), the two dimensional carbon layer, pushes to clarify the potentialities of tuning the content and type of mobile species. Doping effects can be obtained on Gr grown by chemical vapor deposition (CVD) on metal (Cu, Ni, ) and transferred on specific substrates either during growth or by subsequent definite thermal treatments in controlled atmosphere. Many aspects of this latter procedure are still to be clarified as, for example, the role of Gr defective structures and planar morphology, or the Gr substrate features. The same thermal activated process is a matter of debate to try to clarify the nature of dopant-Gr physical bonding features. We report an experimental study by Raman and Atomic Force Microscopy of the thermal doping effects in the temperature range below 400°C on graphene grown by CVD on Cu and transferred on X/Si (where X = SiO2, Al2O3) substrates. The role of treatment atmosphere is shown highlighting a prominent role of oxygen in obtaining p-doping and vacuum in avoiding successive reactivity of entrapped species. By comparing different substrates the features of doping related to Gr and those connected to Gr substrate properties are clarified also by employing electrical characterization.
|18:00||Best Student Presentation Awards Ceremony and Reception (Main Hall)|
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