Nanomaterials- electronics & -photonics

Resume : All-inorganic cesium lead halide (CsPbX3, X = Cl, Br, I) perovskite nanocrystals have been regarded as emerging materials in diverse fields due to their excellent photophysical properties. Recently, our group have developed some new synthetic strategies including solvothermal, microwave-assisted, post-treatment and room-temperature injection synthesis methods to prepare colloidal CsPbX3 perovskite nanocrystals. By the manipulation of reaction parameters (surface ligands, reaction kinetics…), CsPbX3 perovskite nanocrystals with controllable morphologies such as nanocube, nanowire, nanoplate, have been synthesized. In addition, the stabilities of such nanocrystals against water, polar solvent, heat and light treatment can be improved by surface engineering. Ligands (trioctylphosphine oxide, 1-octylphosphonic acid) and oxides (SiO2 and ZrO2) have been successfully demonstrated. We believe these work will shed some light on not only CsPbX3 nanocrystals synthesis and their nanocomposite design, but the stability problem-solving.

Resume : Hybrid organic-inorganic perovskites have become one of the most promising materials in the photovoltaic field. The best performance was found in compounds with general chemical formula, ABX3, when A is either organic or inorganic cation, like methylammonium (MA+), formamidinium (FA+) or Cs+, B is a bivalent metal cation, such as Pb2+ and X is a halide, Cl−, Br−, or I−. The amazing performance of ABX3 perovskites is attributed to their direct band gap, high absorption coefficient, long carrier diffusion length, hot carrier bottleneck, an ambipolar carrier transport property and low production costs. Perovskites have also been demonstrated as suitable materials for detecting visible light, x-ray, or γ-ray. While remarkable observations were reported in recent years, there is a little knowledge about their spin properties and their on the optical and magneto-optical of perovskite materials. The present work describes a research that explored the band-edge properties of CsPbBr3 perovskites, to elucidate the electronic origin for some of the unique phenomena. This compound was selected for the study due to its relative chemical and photochemical stability. The samples were supplied by the group of Prof. Maksym Kovelenko at ETH. The study focused on the investigation of single colloidal nanocrystals (NCs) as well as on bulk structures. The band-edge properties were examined by recording the linearly and circularly polarized micro-photoluminescence spectra in the presence of an external magnetic field up to 9 Tesla. The high resolution gained in the measure of a single NC enabled resolving fine split in the exciton emission at zero magnetic field, which grew gradually with the increase of the field strength. Surprisingly, the split energy grew nonlinearly with the increase of the magnetic field, a fact that indicated a deviation from a linear and from second order corrected Zeeman effects. Theoretical simulations, carried out by a collaborative work with the group of Prof. Andrew Rappe at University of Pennsylvania, revealed the existence of a Rashba effect predominantly at field strength < 4 Tesla, explaining the non-linear behavior. Further on, the circular polarized measurement showed an asymmetry between the σ components, suggesting a partial mixing of one of them with higher electronic states. This point should be further explored in order to gain better understanding in the near future. The Rashba effect emanates in cases experiencing lack or breakage of inversion of symmetry and existence of spin-orbit coupling, both conditions presumably existing in the Perovskites materials, where the small cation A liability induces a crystal distortion and consequent inversion symmetry breaking. Current observations on bulk CsPbBr3 single crystal reflected similar observations for those viewed in analogous NCs, particularly when examined along unique crystallographic direction. In addition, the observations found in the bulk samples indicate a plausible contribution of cubic Rashba effect, which may indicate a mixing of high lying states to the band-edge properties and may support also the asymmetry in the σ emission band patterns as was found in a single NC. This open question will be further investigated in the coming months. In any event, the Rashba effect split the band edge extrema to a k0 a Brillouin point with momentum forbidden transitions, thus, extending the carriers lifetime at the excited state with a large benefit in photovoltaic devices and in x-ray, or γ-ray detectors.

Resume : Halide perovskites are inexpensive and easily processable next generation semiconductors. We here demonstrate perovskite solid-state confinement in nanoporous oxide matrices as a general strategy to control the size of the nanocrystallites (<10 nm) in the strong quantum size effect region. Photoluminescence tuning between near infrared and ultraviolet is achieved by manipulating the size of perovskite crystals through confinement in nanoporous alumina (npAAO) or silicon (npSi) scaffolds [1]. Our novel method of nanocrystalline perovskites preparation within a porous oxide matrix results in device-relevant structure that requires no colloidal stabilization. Low-voltage LEDs with narrow, blue-shifted emission fabricated with perovskite nanocrystallites confined within npAAO thin films support the general concept for next-generation photonic devices. The template-controlled size of the perovskite crystals is quantified in npSi with microfocus high-energy X-ray depth profiling in transmission geometry, verifying the growth of perovskite nanocrystals throughout the entire thickness of the nanoporous films. We study in detail exciton recombination, exciton-phonon interactions and energy trap states in confined and bulk semiconductor films using low temperature photoluminescence spectroscopy down to 3.8 Kelvin. Further areas of application include photon detectors, (polarized) electroluminescent devices, single-photon sources and metasurfaces. Future developments will include increasing the efficiency of the LEDs, exploring their applications in flexible devices and in depth study of the fundamental properties of the confined structures. [1] S. Demchyshyn, J. Roemer, H. Groiss, H. Heilbrunner, C. Ulbricht, D. Apaydin, A. Böhm, U. Ruett, F. Bertram, G. Hesser, M. Scharber, N. S. Sariciftci, B. Nickel, S. Bauer, E. D. Głowacki and M. Kaltenbrunner, “Confining Metal-Halide Perovskites in Nanoporous Thin Films”, Science Advances 3 (8), e1700738 (2017).

Resume : It is well known that interaction of two resonances results in their hybridization and splitting of crossed dispersion relations. Strong interaction exceeding damping of separated resonances gives so called Rabi splitting. Ellipsometry was used for investigations as this method registers the ratio of the ratio of reflected fields in p- and s-polarization recording in such a way all resonances of the system independently on their polarization. Investigation of layers of monodisperse spherical gold nanoparticles on gold films was made as in standard configuration with external reflection as in Kretschmann configuration with internal reflection. Obtained results allow to build dispersion curves, which demonstrate splitting in the case of interactions of localized plasmon of nanoparticles with surface plasmon of the gold substrate. Interaction of nanoparticles with the substrate lifts the degeneration of localized plasmon on a spherical nanoparticle. Parts of dispersion curves obtained at external and internal reflection join each other what demonstrates that the excitation of surface plasmon via nanoparticles is visible even at external reflection in such a system.

Resume : Phase-matching conditions are exploited to enable nonreciprocal optical propagation and enhanced magneto-optic responses in magnetoplasmonic systems [1]. Here we show that exploiting diffraction in conjunction with plasmon excitations adds further versatility and flexibility in the design of photonic systems. As a testbed we analysed transverse magneto-optic Kerr (TMOKE) responses in magnetoplasmonic gratings etched into gold/cobalt multilayers [2]. The grating coupler was chosen as the simplest system where we can combine the three distinct phenomena: magneto-optics, diffraction and plasmonics. Angular resolved measurements revealed narrow line-shape plasmon resonances, enabling large diffracted magneto-optical intensity effects. We show that exploiting diffraction in magnetoplasmonic crystals allows unexpectedly large TMOKE responses above that exceed 3% - one of order of magnitude larger than conventional TMOKE. Our results pave the way towards using magneto-optical modulation of SPPs to build non-reciprocal, active photonic components. We anticipate that our results can be used to design more complex diffractive surfaces, such as plasmonic metasurfaces, with the objective to enable creation of novel non-reciprocal photonic devices. [1] V. I. Belotelov et al., Nat.Nanotechnol. 6, 370 (2011). [2] R. Cichelero et al., submitted.

Resume : Single Electron Transistors (SETs) are an ultra-low power consumption alternative to Field Effect Transistors (FETs). Their room temperature operation is based on two conditions: (i) The Coulomb energy for charging the dot with an electron must exceed kT. This requires Si dot sizes <5 nm. (ii) The tunneling distance between dot and electrodes through SiO2 must be <1.5nm. These requirements are beyond current top-down approaches. Thus, we follow a bottom-up approach: (i) A single Si dot forms self-organized by phase separation of a tiny metastable SiOx volume into a Si precipitate and a SiO2 matrix. (ii) If the tiny SiOx volume is sandwiched between Si, then the single dot becomes self-aligned, i.e. two tunnel barriers form due to condensation of excess Si from SiOx onto the Si/SiO2 interfaces. Here, a CMOS compatible fabrication of vertical-nanowire-based SETs will be presented. Regular arrays of Si nanowires with diameters down to 20nm are fabricated by top-down processes. A SiO2 layer of 7nm thickness is sandwiched between the upper and lower Si of the pillar. This SiO2 is transformed to SiOx(x<2) by ion beam mixing. During subsequent thermal activation (RTA) the dot structure evolves as described above. Experimental and computer simulation results will be presented, and critical fundamental issues of the nanofabrication will be discussed. This work has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 688072.

Resume : Perovskite nanocrystals (NCs) are gaining increasing attention in many fields ranging from chemistry to physics and engineering owing to their extremely interesting properties such as high photoluminescence quantum yields, tunable optical bandgap, enhanced stability, large diffusion lengths and shape controllability. Shape-controlled synthesis and their self-assembly into ordered superlattices has emerged as a powerful tool for tailoring the nanoscale optical properties. Such coupled optical and electronic properties can be utilized for the development of novel optoelectronic devices. In this talk, I will present a one-pot shape-controlled synthesis of highly crystalline and monodisperse CsPbX3 (X=Cl, Br and I) perovskite NCs of various morphologies such as nanocubes, nanoplates (NPls), nanowires (NWs) and nanorods (NRs) starting from their precursor powders. [2-5] The morphology of perovskite NCs can be controlled by means of simple chemistry such as Cs/Pb precursor ratios, reaction time and ligand concentration. We discovered that the perovkite NCs spontaneously self-assemble into nanowires or supercrytals (SCs) depending on the reaction conditions. The optical bandgap of the perovskite NCs as well as SCs can be controlled over the entire visible range by varying the halide (Cl, Br, and I) composition. Our work not only provides a facile method for the shape-control of monodisperse perovskite NCs and their self-assembly, but also expands our current understanding of the morphology-dependent optical properties, and open new avenues for the fabrication of highly ordered architectures using perovskite NC building blocks for future optical and optoelectronic devices.

Resume : Nanostructure application in electrochromic electrode can effectively enhance the ion diffusion efficiency , which can greatly optimize their contrast and switching. This phenomenon has been proved both in inorganic material and organic material. In this presentation, we will focus on the organic nanoparticles engineering in electrochromics, study how the nanostructure affects the electrochormic performance. Different electrolyte will also be discussed. Both of the problems are very important steps towards the industrail appllication of organic electrochromics.

Resume : Inorganic perovskite nanocrystals have recently emerged as a highly promising material in light emission due to color tunability by chemical composition and quantum confinement, and bright emission from nanocrystal films with photoluminescence quantum yields up to unity has been demonstrated. [1,2] In this talk the photo-physical properties of perovskite nanocrystal in solution and in thin films will be discussed. [3] Plasmonic resonances of metal/dielectric multilayers can be used to enhance the emission and radiative rate of the perovskite nanocrystals spincoated on their surface. We demonstrate four-fold emission enhancement of a film of CsPbBr3 nanocubes [4] deposited on such layered metamaterial structures, and highlight how the plasmonic resonances can be tuned to the emission and absorption bands of the emitter.[5] Quantum confinement in CsPbBr3 nanoplatelets results in blue emission and films with 25 % PLQY are be obtained by spin-coating. The nanoplatelets in such films can be transformed to green emitting nanobelts by high intensity UV light exposure. [6] The transformed films manifest extremely stable emission and are robust to treatment with different solvents, which enables the fabrication of all-solution processed light emitting diodes. References [1] Nano Lett. 15, 3692 (2015). [2] Nature Commun. 6, 8056 (2015). [3] J. Phys. Chem.Lett. 8, 2725 (2017). [4] J. Am. Chem. Soc. 140, 2656 (2018). [5] ACS Photonics 5, 2287 (2018). [6] ACS Nano 11, 10206 (2017).

Resume : CdSe based QDs have been intensively studied, however, due their toxicity Cd-based materials are not acceptable for real-life applications. Indium phosphide (InP) based QDs represent the most advanced alternative without toxic heavy metals. Nevertheless, for industrial applications, the photoluminescence quantum yield (PLQY) and the emission linewidth (FWHM) of InP QDs have to be significantly improved. The analysis of InP specificities shows that in contrast to their CdSe analogues, the InP QDs suffers from a high oxophilicity. This leads a strong tendency to oxidize and results in the formation of an amorphous phosphate layer at the surface of the InP QDs either during the synthesis or the shelling (often with ZnS). The role and the influence of this oxidation on the optical properties (PLQY and FWHM) is still a matter of controversy and the definitive answer has so far been precluded because of the lack synthesis method allowing the access to comparable oxide-free samples. In this presentation, we will describe our new approach to prepare oxide-free InP core and InP/ZnS core/shell QDs. Then, we will compare the structural (using XRD, TEM, MAS NMR) and the optical properties (UV-Vis and PL) of oxidized vs. oxide-free samples. The use of the same InP QDs core for the preparation of the samples provides fully comparable data and will thus allow unraveling for the first time the influence of phosphate at the core/shell interface.

Resume : Colloidal quantum dots (QDs) have received great interest as promising active materials in optoelectronic devices, owing to their unique optical properties such as broad absorption ranges, high extinction coefficients, sharp symmetric emission peaks and tunability of the band gap. Because of the small size of QDs, their physical and chemical properties are highly affected by the surface environment. Therefore, appropriate selection of surface ligands is important for specific applications such as QD light-emitting diodes (QD-LEDs). QD-LEDs have been developed in recent years as the next-generation, low-cost, solution-processible, full-color displays. We have studied the effects on performance of QD-LEDs when the surface ligands were modified. The short length of molecule was selected as a new surface ligand and it was functionalized on QDs’ surface by exchange from long hydrocarbon chain original surface ligands. Both the short molecular length and appropriate HOMO level of ligand improve the hole transport to QDs. All three fundamental colors, red-, green-, and blue-emitting QD-LEDs functionalized with this short length molecule showed enhanced current efficiencies, power-efficiencies and low turn-on voltages compared with the QD-LEDs capped with the original surface ligands. They showed narrow emission peaks and 159% covered the NTSC color gamut. This is an easy and efficient surface-modification strategy for developing high-performance QD-LEDs in the future. -This work was supported by Institute for Information & communications Technology Promotion (IITP) grant funded by the Korean goverment (MSIT) (2017-0-00065, The core technology development of high performance materials and devices for volumetric display)

Resume : Lead halide perovskites, both in form of thin films and colloidal nanocrystals (NCs), have attracted a lot of attention as components of solar cells, light-emitting diodes, and photodetectors. Size, shape, composition and thus optical properties of perovskite NCs can be conveniently tuned by controlling reaction parameters such as precursor concentration, temperature, ratio of halide ions for mixed compositions, as well as via post-synthetic treatment.[1] The understanding of the formation mechanism of perovskite NCs is crucially important for the further optimization of their synthesis. The new and reliable synthetic route is also needed in the field. Besides what we already discover for the formation mechanism of CH3NH3PbBr3 before, we future explore the formation for CsPbBr3.[2] We developed a microwave-assisted slowed-down synthesis of CsPbBr3 perovskite NCs, which retards the reaction and allows us to gather useful insights into the formation mechanism of these nanoparticles, by examining the intermediate stages of their growth.[3] The formation mechanism based on the information we obtained, indicating first the formation of a bromoplumbate ionic scaffold, with Cs-ion infilling lagging a little behind. We also introduce new synthetic route for obtain perovskite NCs. 1. Huang, H., Polavarapu, L., Sichert, J. A., Susha, A. S., Urban, A. S., Rogach, A. L. NPG Asia Mater. 2016 8, e328 2. Huang, H., Raith, J., Kershaw, S. V., Kalytchuk, S., Tomanec, O., Jing, L., Susha, A. S., Zboril, R., Rogach, A. L. Nat. Commun. 2017 8, 996 3. Li, Y., Huang, H., Xiong, Y., Kershaw, S., Rogach, A. L. Angew. Chem. Int. Ed. 2018, DOI: 10.1002/anie.201713332

Resume : Parabolic quantum wells (PQWs) are known as a promising candidate for a compact efficient terahertz (THz) source. PQW has equidistant quantum energy levels (QELs) that can be designed to be separated by few meV to meet THz frequency range. Moreover, PQWs are little sensitive to applied electric field and thermal influence. To enhance the efficiency and power of THz emission from PQWs, the new approach is proposed by employing depopulation of the lowest QEL of PQW. The performance of the device is modeled solving the Schrödinger and rate equations taking into account different transition time constants for scattering mechanisms. The pumping of the device is realized through the photoexcitation (band-to-band transitions). The carriers are emitting THz quanta by intersubband transitions down to the lowest QEL. The fast depopulation of the lowest QEL of PQW leads to THz emission enhancement by overcoming the carrier crowding effect. Two designs are considered for 2.5 and 7 THz emission. Inclusion of additional quartic term in Al content distribution was important to compensate the influence of electron effective mass change on QELs separation. Three depopulation mechanisms - the sweep-out by reversed voltage, re-excitation with MIR laser of doped PQWs, and introduction of quantum dot in the PQW are considered. The findings suggest that these depopulation mechanisms in AlGaAs/GaAs PQWs leads to radiation enhanced efficient compact incoherent THz source - THz torch.

Resume : Unlike graphene, black phosphorus (BP) is one of the promising materials to be used in many optical and electronic field. Bandgap can tunable depending on its number of layer, which made this two dimensional material a good candidate for future application. In 1914, BP was synthesized from white phosphorus by Bridgeman. It was high pressure synthesis method. Red phosphorus (RP) is more convenient to synthesize BP, as RP is not much reactive at room temperature. In this study, we synthesized BP from RP in presence of tin and iodine. All of these materials are poured into a quartz ampoule inside a glove box and then sealed. The ampoule was heated in a box furnace at sequential temperature in argon atmosphere. The full process was done in low pressure of Ar. Ribbon like BP has formed by vapor transfer method. Synthesized BP has characterized with FE-SEM which shows the formation of multilayered BP. XRD shows the synthesized BP is well crystalline with orthorhombic structure, whereas RP was amorphous. Raman spectra of synthesized BP also done to confirm the formation of BP.

Resume : In the last decade, THz technologies and applications have attracted lots of attention because of its unique properties such as non-ionizing nature, minimal effect on human body and penetration through a wide variety of materials (paper, wood, plastic, and fabric). These valuable properties have made THz technology a great candidate in medical imaging, security imaging, biochemical spectroscopy, nondestructive test, and others. One of the most common ways of generating THz wave is utilizing photoconductive antennas (PCAs). THz PCA despite of its advantages, such as room temperature operation, and compact design broadband radiation acquires low optical to THz efficiency that limits its applications. Terahertz photoconductive antenna incorporated with ZnO nanorods, gold nanodisk array and disordered plasmonic nanostructure have been simulated and fabricated using electron beam lithography, combined with optical lithography and standard CMOS technology fabrication technology. Experimental results showed that using ZnO nanorods, gold nanodisk array and disordered plasmonic nanostructure results in 2, 5.6 and 2 times enhancement of THz peak signal compared to conventional PCA with 200 nm Si3N4 antireflection coating, respectively. In addition, THz waves with the spectral range between 0.1-2.5 THz with signal-to-noise ratio of 60-70 dB obtained using 800 nm femtosecond laser.

Resume : Shape-controlled nanoparticles can be assembled into structurally diverse superlattices. However, it remains challenging to control the organization of one nanoparticle morphology into multiple superlattices over large areas. Here, we demonstrate the concept of ‘one nanoparticle, multiple plasmonic metacrystals’ using Ag octahedra and nanocubes. We tailor the nanoscale surface wettability of the Ag octahedra and nanocubes using a family of thiol-terminated molecules. Subsequent assembly of these nanoparticles at the oil/water interface gives rise to multiple plasmonic metacrystals. Increasing the surface hydrophobicity of the nanoparticle surfaces leads to increasingly open metacrystals with packing densities as low as 24 %. At this packing density, the nanoparticles are standing on their vertices in their respective plasmonic metacrystals. Notably, we can achieve large areas of these plasmonic metacrystals despite their structural instability. A structure-to-function characterization for these metacrystals shows that the lowest packing density metacrystals generates the highest surface-enhanced Raman scattering (SERS) enhancement factors for both the metacrystals of nanocubes and octahedra. Numerical simulations indicate that this strong enhancement arises from the large-area field delocalization within the metacrystals. Our findings imply that packing the highest number of NPs within a given area will not always generate the strongest SERS enhancement.

Resume : Plasmonic metamaterials with engineered optical density of states can be particularly interesting in nanophotonics or quantum optics for controlling the emission efficiency of suitable quantum emitters (QE) coupled in near-field. Among different possible QEs, rare-earth (RE) ions (like Er3+ and Eu3+) are particularly interesting for their intense room temperature emission as a two-level system in the visible or near-infrared spectral region. In this work, we studied the coupling of RE QEs with plasmonic nanostructures to achieve quantum emission enhancement. Two classes of ordered metamaterials were investigated: (i) nanohole arrays (NHA) and (ii) hyperbolic metamaterials (HMM) in form of periodic multilayers. We coupled Er3+ ions emitting at 1.5 microns with the extraordinary optical transmission (EOT) of a Au NHA. This resulted in a reduction of the emission lifetime by a factor 2-3 (in quantitative agreement with FEM simulations), together with external quantum efficiency of about 0.9, with reduced losses and a high directionality in the emission pattern. We investigated also the coupling between Eu3+ emitting at 615 nm and a HMM made of Au-Al2O3 periodic multilayer. We found that when the metamaterial is designed to be in its hyperbolic regime, the measured lifetime strongly decreses (up to a factor 3) with a concomitant high increase of the PL intensity, whereas for the same metamaterial in the conventional elliptical regime the decrease is significantly smaller.

Resume : Plasmonic nanostructures offer great enhancement of the Raman signal due to the strong confinement of the electromagnetic field. Thus, they are considered as suitable candidates for surface-enhanced Raman spectroscopy (SERS). In this work, we present an alternative fabrication route, called the glancing angle deposition (GLAD), for tunable fabrication of plasmonic self-organised Ag nanoparticle arrays aimed at SERS. Using the GLAD technique, the inter-particle distance within the arrays can be made as small as 1 nm. Moreover, the plasmonic resonance can be precisely tuned over the whole visible range. The GLAD method can be up-scaled; and when a transparent substrate is used, it enables various measurement geometries. The enhancement factor for the employed probe molecule in this study, rhodamine 6G, is estimated to be in the order of 10E8. It is noted that the nature of the GLAD-made substrates leads to the polarisation dependence of the signal enhancement. The polarisation studies show a stronger enhancement along the nanoparticles chain.

Resume : Absorptivity is the property by which plasmonic dipoles are known rather than reflectivity. Here, we introduce and utilize the so far unknown specular reflection and the Brewster effect of ultrafine plasmonic dipoles and metaparticles as the basis of new design rules for advanced applications. A setup of ''Plasmonic metaparticles on a black body'' is exhibited and used for the design of a tailored perfect-colored absorber and for visual detection of surrounding medium dielectrics that isn't promptly done by extinction plasmonics. The Plasmonic Brewster Wavelength (PBW) effect is exploited as a new platform for the naked-eye and bulk biodetection of analytes. The method works based on slight changes in molecular polarizability which cannot be recognized with currently known Plasmon resonance techniques. As a particular feature the clinical applicability of the PBW strategy is exhibited for the detection of bulk refractive index changes in healthy and diseased human serum exosomes. Moreover, here a simple, low cost and scalable sputtering-based fabrication method utilized which avoids complications of lithography or precise alignment of light coupling for biodetection.

Resume : Nanostructured materials, including nanowires, particles and tunnels, have shown to have unique optical properties compared to their bulk counterparts, like increased band gap, indirect to direct band gap transition, and an increased charge carrier concentration. Such nanostructures can therefore be interesting for use in optoelectronic devices, such as solar cells and sensors, as well as for energy storage purposes. Utilizing the immiscibility between aluminium and silicon resulted in a self-organizing process creating Al nanowires in an amorphous silicon (aSi) matrix when thin films were prepared by magnetron co-sputtering. Removing the Al nanowires by etching created an aSi matrix with nanotunnels, similar to a honeycomb structure. In order to investigate their optical properties, reflectance and simple calculations have been carried out on the Al nanowires with various sizes. The surface plasmon nodes of the Al nanowires have then been investigated and mapped on the nanoscale using electron energy loss spectroscopy with transmission electron microscopy. In addition, the band gap of the surrounding aSi have been measured.

Resume : Achieving accurate and ultratrace detection of gas/vapor is impervious as toxins are deadliest in gaseous form due to its acute toxicity upon inhalation, high mobility and difficulty in containment. However, current gas detection techniques still face several limitations such as low sensitivities and susceptibility to give false positives. Herein, we design a plasmonic nose based on zeolitic imidazolate framework (ZIF)-encapsulated Ag nanocubes array, to directly sniff out toxic volatile organic compounds (VOCs) vapors from air and realize ultratrace recognition of these vapors down to ppm level. Our plasmonic nose consists of multifaceted and synergistic strategies – (1) optimizing preconcentration of gas volume conferred by ZIF, and (2) intensifying plasmonic hotspots by modulating the interparticle spacing of adjacent Ag nanocubes. The plasmonic nose is capable of in-situ adsorption kinetics and quantitative detection of non-adsorbing toluene vapor from 200 to 20000 ppm. This detection range is the within regulatory limits and covers the concentrations where human exposure at these levels could lead to health hazards ranging from throat/eye irritation to even death. The vibrational fingerprint obtained from SERS also permits the molecular recognition of a series of VOCs such as chloroform and 2-naphthalenethiol, effectively eliminating false positives. Our plasmonic nose also possess excellent recyclability simply via vacuum regeneration. This multifaceted approach provides a paradigm shift in the current MOF-SERS systems, and can push the detection capability beyond boundaries, shaping future toxic gas regulations.

Resume : Non-volatile memories will play a decisive role in the next generation of digital technology. Flash memories are currently the key player in the field, yet they fail to meet the commercial demands of scalability and endurance. Resistive memory devices, and in particular memories based on low-cost, solution-processable and chemically tunable organic materials, are promising alternatives explored by the industry. However, to date, they have been lacking the performance and mechanistic understanding required for commercial translation. Here we report a resistive memory device based on a spin-coated active layer of a transition metal complex, which shows high reproducibility ~350 devices), fast-switching <30 ns), excellent endurance (~10^12 cycles), stability (>10^6 s) and scalability (down to ~60nm^2). In situ Raman and ultraviolet–visible spectroscopy alongside spectroelectrochemistry and quantum chemical calculations demonstrate that the redox stateof the ligands determines the switching states of the device whereas the counterions control the hysteresis. This insight may accelerate the technological deployment of organic resistive memories. [1] Goswami, Sreetosh, et al. "Robust resistive memory devices using solution-processable metal-coordinated azo aromatics." Nature Materials 16.12 (2017), 1216. [2] Valov, Ilia, and Michael Kozicki. "Non-volatile memories: Organic memristors come of age." Nature Materials 16.12 (2017), 1170.

Resume : Light extraction from ZnO-based devices can be enhanced via metal nanoparticles (NPs). In this work, the enhanced UV emission of metal NP-coated ZnO was systematically studied using cathodoluminescence (CL) and photoluminescence (PL) spectroscopy. Two metals – 5nm Au NPs and 2nm Al – were deposited onto ZnO nanorods (NRs), and single crystals. CL and PL spectra of uncoated ZnO exhibited a sharp UV emission at 3.36 eV from excitonic recombination, and a broad visible defect-related emission. Au-coated ZnO showed a 4-fold UV enhancement, while Al increased the UV emission up to 10 times, with highest enhancement near the surface. Both metals reduced the excitonic lifetime, which indicates the creation of an additional, faster recombination path, enhancing the spontaneous emission rate. For Al, this can be via localized surface plasmons (LSPs), as its plasmon resonance energy (LSPR) is in the UV. Au’s green LSPR is spectrally too far to allow direct LSP-exciton coupling, suggesting faster recombination via interband transitions in Au. Temperature-dependent PL of Al-coated ZnO showed highest enhancement at 80K, where ZnO’s emission is dominated by free excitons (FX). This strongly suggests that the LSPs couple more efficiently to FX than to bound-excitons. The enhancement of Au-coated ZnO is temperature-independent. In conclusion, interband transitions in Au can be responsible for the enhanced UV emission, while the enhancement mechanism in Al was assigned to LSP-exciton coupling.

Resume : Semiconducting metal oxides are the most widely used photocatalysts in the field of sunlight-driven fuel generation owing to their cost effectiveness, good stability, and natural abundance. However, the lack of visible light absorption leads to severe mismatch with the solar irradiance spectrum and thus limits the photocatalytic performance of many metal oxides. As a result, the introduction of oxygen vacancies is becoming an increasingly popular strategy to extend the light absorption of these systems into the visible range.1,2 In this study, we investigate the charge carrier dynamics such highly oxygen-deficient metal oxides for the case of nanostructured WO3. The high degree of oxygen deficiency introduces defect states throughout the band gap which give rise to visible and near-infrared light absorption, resulting in an intense blue coloration of the material. We herein use transient absorption spectroscopy (TAS) to probe the kinetics and lifetimes of photogenerated charge carriers over timescales, ranging from femtoseconds to seconds after light absorption. To compare the excited state evolution of regular WO3 thin films to that of highly oxygen-deficient WO3, we distinguish between band gap excitation using UV light and the direct excitation of sub-band gap states using visible to near-infrared light. This comparison allows us to elucidate the charge recombination mechanisms as a function of both oxygen vacancy density and excitation wavelength. To shed light on the local bonding environment at different oxygen vacancy densities, we perform first-principles density functional theory (DFT) calculations. Taken together, the results presented herein illustrate opportunities and challenges of oxygen-deficient metal oxides for solar energy applications. (1) Chen, X.; Liu, L.; Yu, P. Y.; Mao, S. S. Increasing Solar Absorption for Photocatalysis with Black Hydrogenated Titanium Dioxide Nanocrystals. Science 2011, 331, 746–750. (2) Wang, G.; Ling, Y.; Wang, H.; Yang, X.; Wang, C.; Zhang, J. Z.; Li, Y. Hydrogen-Treated WO3 Nanoflakes Show Enhanced Photostability. Energy Environ. Sci. 2012, 5, 6180–6187.

Resume : Challenges associated with mechanical fracture of electrical conductors has hindered the realization of truly flexible high performance wearable electronics. Here, transparent healable electrodes have been developed and examined to alleviate these problems. The composite electrode features a layer of interconnecting AgNWs network on a polyurethane film modified with Diels–Alder adducts (PU-DA). Surface modification using hydrophilic molecules improved adhesion of the AgNWs network and resulted in mechanically robust flexible electrodes with a figure of merit sheet resistance of 13.3 Ω/sq and 77% transmittance at 550 nm. Transparent and flexible healable heaters (TFHH) with good mechanical and thermal stability were fabricated using these electrodes for potential applications in thermochromics, electrically driven displays and defrosters. The PU-DA TFHHs exhibited high Joule heating temperatures of 102 °C with a low operation voltage (6 V), fast thermal response (150 s) and enhanced robustness to endure large repeated mechanical strain for over 500 bending cycles with small variance in resistance(<10%). After deliberate damage by a knife cut, the electrodes healed and recovered back to its original conductivity via a simple heat treatment at 120 °C. Uniquely, the healing process can also be triggered by utilizing electrical power.

Resume : We propose a novel gap-plasmon excitation structure for photonic integrated circuits. The structure consists of a Au stripe and tapered gap for refractive index matching to a gap plasmonic waveguide and was fabricated at the top surface of a dielectric-stripe-type plasmonic waveguide deposited on a Au film. The width of the gap-plasmonic waveguide is designed to 50 nm by considering fabrication accuracy. Propagating surface-mode plasmons, confined into the dielectric-stripe waveguide, are localized at the corner of the Au stripe. Then, the localized lateral plasmons are converted to the orthogonal-polarized gap-plasmonic mode by increasing the effective refractive index of the gap waveguide using the tapered gap. The intensity ratio of the gap-waveguide mode to the dielectric-stripe-waveguide mode was estimated to be of 0.75 using the finite-difference time-domain method, and the high converting efficiency was confirmed. The proposed structure was fabricated by patterning a 50-nm-thick Au film on the 600-nm-wide dielectric stripe plasmonic waveguide using focused ion beam milling technique. We have experimentally observed the gap-mode plasmonic intensity distribution using scanning near-field optical microscopy and confirmed the high conversion efficiency. The proposed novel excitation structure will pave the way for higher density photonic integrated circuits.

Resume : Produced water (PW) represents the largest waste stream integrated with oil exploration, which is one of the crucial environmental and health issues. In this study, we report the synthesis of an effective and novel magnetic nanohybrid, ZnO-Tetrapods/Iron Oxide Nanorods (ZnO-T/Fe2O3-NR) using hydrothermal process. The synthesized nanohybrids was applied as a magnetic adsorbent for remediation of lead (cationic) and chromium (VI) (anionic) metal ions and separation of oil from produced water. The structural, chemical and magnetic characterizations of synthesized nanohybrids were performed using X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Brunauer–Emmett–Teller (BET) analysis, Vibrating Sample Magnetometer (VSM) and X-ray photoelectron spectroscopy (XPS). These characterizations suggested successful preparation of nanohybrids consisting of Fe2O3-NR coated on the surface of ZnO-T. The as-synthesized nanohybrids exhibited enormous surface area and high magnetic saturation value, indicating its exceptional adsorption ability and magnetic separation. The treatment capability was investigated in terms of removal of heavy metal ions, oil sorption studies, Total Dissolved Solids (TDS) and Chemical Oxygen Demand (COD). The mechanism for the adsorption was explicated by exploring different adsorption kinetics and isotherms models. Interestingly, as-prepared nanohybrids demonstrated extraordinary remediation capacity toward removal of cationic and anionic heavy metal ions, compared to ZnO-T. Overall, the findings inferred that this nanohybrid can be employed for effective water reclamation from produced water.

Resume : Mg and Ni doped ZnO and pure ZnO nanostructures have been synthesized by a simple and cost effective wet chemical / hydrothermal method for its potential application in Organic Light Emitting Diodes (OLED). Studies have been undertaken for structural as well as optical properties of ZnO after Mg or Ni doping with various concentrations. Field Emission Scanning Electron Microscopy with Energy-dispersive X-ray analysis reveals the morphology and chemical composition of nanostructures and indicated the different structure for ZnO and with doping it’s converted into the multi facet structure. X-ray diffraction reveals the pure hexagonal phase of the wurtzite structure of ZnO and finds other peaks related to Mg and Ni. UV–Visible suggested the exciton characteristic at room temperature and band gap variation while Photoluminescence spectra reveal two different regions (ultraviolet and blue). Synthesized materials have been blended with Poly [9, 9-dioctylfluorene-2, 7-diyl] (PFO) and prototype OLED has been fabricated using these materials as an emissive layer. Electroluminescence spectra show prominent blue emission at 433nm, 460 nm and 490 at 10V. Current-Voltage (I-V) curve reveal that the stability of OLED device at 20% of doping with Mg and 1% of doping with Ni as compared with pristine PFO device.

Resume : Binding energy and photo-ionization cross section of an off center single shallow dopant in core/shell have been investigated. A variational treatment is developed in the framework of the effective-mass theory, including the effects of interaction between the charge carriers and the longitudinal-optical (LO) phonons and by considering the central-cell correction. The effects of the core and shell sizes, the position of the ionized donor in the shell region and the nature of the dopant are analyzed. Quantitative results are given for quantum dots of Si, GaP and ZnSe coated by SiO2 material. This analysis contributes to understand the external control of the optoelectronic properties of core/ shell structures in order to produce new devices for new applications.

Resume : In devices such as photomixers or insulated gate bipolar transistors, the limitation of minority carrier lifetime (MCL) enables high frequency operation. This has triggered the investigation of lifetime killers (LK) such as noble metal atoms and irradiation-induced defects in silicon lattice. In these approaches, however, it is difficult to confine LK due to their diffusion or to the extension of irradiation damage in the Si matrix. In this paper, we characterize polycrystalline silicon as LK. Focusing on lowly doped p-type Si capped with 1.2 µm polycrystalline Si layer, we used several characterization techniques to relate morphology and LK properties. Quasi Steady State PhotoConductivity measurements indicate effective MCL reduction by more than 100x. TEM reveal a distinct interfacial morphology. The surface of LK layer gives photoluminescence response that relates to the combined contributions of several types of dislocations. Scanning Spreading Resistance Microscopy reveals grain boundaries and dislocations in higher density near the deep interfacial layer. X-Ray Diffraction yields dislocation density at the sample surface above 10^10 /cm² and near 10^12 /cm² at the bottom. Modelling positron annihilation response requires considering two distinct defective layers, including the deep interfacial region with enhanced positron-electron recombination on larger defects than Si divacancies.LK layer efficiency mostly owes to the interfacial defect-rich layer. The ECSEL Reference project has funded this work.

Resume : Electrochromic devices have been focused for their very unique property of changing transmittance by applied external electric field past decades. Especially in the point of energy saving view, the smart windows adopting electrochomic devices have been studied by many researchers and groups. The electrochromic devices are very capable to control the sunlight which giving thermal effect to the indoor environment as changing the color also. However in order to use the smart windows with electrochromic devices it should be shown good long term stability without deterioration their properties. In case of using liquid electrolyte, the electrochromic devices have been easily affected to lower their grade of long term use by incident sunlight. Therefore we studied the long term stability of the electrochromic devices using gel electrolyte to investigate the feasibility for smart window application. We used WO3 nanostructured film as a cathodic electrode and Prussian blue thin film as a anodic electrode by spin coating on ITO glasses of 105 mm x 105 mm. As we fabricated PVB (Polyvinyl butyral) with 1.1% lithium bis-trifluoromethanesulfonimide for gel electrolyte the full cell of electrochromic devices finalized by injection of the electrolyte. The fabricated electrochromic devices have been driven by /- 1.5 volts for bleaching and darkening process within 30 seconds for each change. The lowest transmittance was 9.1 % and the maximum was 79.7 % after 10,000 cycles.

Resume : Semiconductor nanomaterials have been explored in variety of environmental applications. In this study, an attempt was made to synthesize various nanoparticles and their nanocomposites showing photocatalyst, such as CuO, ZnO and ZnO-T (ZnO-Tetrapods), and their nanocomposites i.e. CuO/ZnO and CuO/ZnO-T(ZnO-Tetrapods) by a facile and economically viable hydrothermal route. The resulting photocatalysts were characterized to determine their properties, such as morphology, band gap, crystalline structure, etc. by Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray Spectroscopy (EDX), UV-Visible Absorption Spectroscopy, Fourier Transform Infrared Spectroscopy (FTIR) and X-Ray Diffraction (XRD). The potential efficacy of above photocatalysts was evaluated towards the photoremediation of Crystal Violet (CV) dye under solar light. The fast photocatalytic degradation of CV dye by pure ZnO-T could be further enhanced by hybridization with CuO due to the suppressed charge-carrier recombination. The results suggested that pure as well as nanocomposites of ZnO may be a promising candidate for waste water treatment.

Resume : Bandgap engineering and surface nano structuring of TiO2 thin films play a crucial role in increasing its efficiency to get utilized in fabrication of sensors and in optoelectronic devices [1-2]. Precise control over the defects is needed to modify the binding energy of O-2p and Ti-3d states which can bring the change in bandgap and enhance the photocatalytic activity of these thin films [3]. Ion irradiation modify the structural and electronic properties of Cr-doped TiO2 prepared by RF sputtering [2]. In the present work, we tailored the material properties by Cr-doped TiO2 prepared by pulsed laser deposition and modify its properties using swift heavy ion irradiations with different ions. The films were irradiated with 100 MeV Au and Si ion beams at different fluences ranging from 5X1012 ions/cm2 to 1X1013 ions/cm2. Structural characterization shows that as-deposited films were amorphous in nature and no phase change has been observed with increasing ion fluence rather successive amorphization of the films as confirmed by angle dispersive X-Ray diffraction technique. Field emission scanning electron microscopy images shows the agglomeration and reveals the localized defects caused by two swift heavy ions of different masses which appear as segregated clusters over the surface of thin film. Atomic Force Microscopy shows the segregation over the surface and increment in the roughness after ion irradiation. UV visible studies reveals the variation in band gap energy as the consequence of formation of various sub band-gap energy states due to accumulation of oxygen vacancies near the Fermi edge. Detailed electronic structure will be correlated with its optical properties will be discussed. References: 1. S.K.Zheng, et.al., Vacuum 62 (2001)361. 2. Sagar Sen et.al., Applied Surface Science 440 (2018) 403. 3. C. P. Cheney et.al., Phys. Rev. Lett. 112 (2014) 036404.

Resume : Spintronics represents a new paradigm of electronics that utilizes both the electron’s charge as well as its spin degrees of freedom. It has the potential to facilitate a new generation of devices possessing high-speed, large memory and ultra-low power consumption. The most critical step in the functioning of a spintronic device is the injection and detection of spin-polarized carriers at the ferromagnet-semiconductor interface. Despite considerable efforts, efficient injection of spins into nonmagnetic semiconductors still continues to be a major hurdle in this field. In this talk, I will present some of our very exciting research going on in this field in my group at the University of Utah. Particular focus will be on the injection and detection of spin polarized carriers in semiconductors using electrical and thermal routes. In the later part of my talk, I will discuss about new oxide-based material systems for next-generation 2D-electronics application.

Resume : The fabrication of highly efficient bio-organic nanoelectronic devices is still a challenge due to the difficulty in interfacing the biomolecular to the organic counterparts. One of the way to overcome this bottleneck is to add a self-assembled monolayer (SAM) in between the electrode and the biological material. The addition of a pyrene-nitrilotriacetic acid layer to a graphene metal electrode enhances the charge transfer within the device. Our theoretical calculations and electrochemical results show that the formation of the pyrene-nitrilotriacetic acid SAM enforces a direct electron transfer from SAM to graphene, while the addition of Ni2+ cation and imidazole reverses the charge transfer direction, allowing an atomic control of the electron flow, which is essential for a true working device. Moreover, the physisorption of SAM containing nitrilotriacetic acid as chelating agent strongly modify the flow of charges from and to graphene depending on the metal center used.

Resume : Accumulation of nitrate in groundwater has been mainly attributed to agricultural activities and application of fertilizers. Excessive presence of nitrate in potable water is associated with methemoglobinemia in infants, as nitrate is converted to nitrite which binds to oxygen molecules in red blood cells. The maximum acceptable contamination level in drinking water in the EU countries is 10 mg/L for nitrate nitrogen (N-NO3-) and is endorsed by World Health Organization. Therefore, the removal of nitrate from potable and groundwater has drawn considerable attention in the water supply industry. At present, conventional water treatment plants (WTPs) cannot sustainably deliver this limit and call for implementation of advanced treatment technologies. Membrane separation processes can produce highly pure water but also give a concentrated reject solution creating a cost for its disposal. Biological denitrification can selectively convert nitrate into N2 gas, but the low reaction rate aside, biological processes cannot be applied in drinking water treatment due to the possibility of bacterial contamination of water. Catalytic chemical reduction is a promising process using metal loaded oxide supports as catalyst and hydrogen gas as the reducing agent for direct catalysis of nitrate. However, pure hydrogen gas is essential, and other disadvantages such as ammonia formation, surface rust formation and slow kinetics provide a driving force for continuing research. Electrocatalytic reduction of NO3- has been recognized as a promising alternative as it offers advantages such as elimination of pre- and post-treatment of chemicals, small footprint and relatively low investment costs with facile system control. However, energy efficiency needs improvement to reduce the operational costs. At this point, the development of stable, selective and low-cost electrodes for denitrification which can reduce nitrate (NO3-) and nitrite (NO2-) to dinitrogen (N2) is critical for sustaining the nitrogen cycle. In the scope of an ERC StG project ELECTRON4WATER, we tackle this problem via use of low-cost graphene oxide/reduced graphene oxide (GO/rGO) as catalyst electrode materials. Nanosheets of graphene oxide on glassy carbon electrode promotes the electroreduction of nitrate ions as compared with a pristine electrode (Figure 1). This also reflects to experiments with rGO modified graphite felt electrodes which were synthesized using hydrothermal method with different parameters, i.e. temperature (100 – 170 ºC) and pressure (2 – 20 kbar) to enrich its surface functionality. The results show that, the defective structure of rGO acts as active sites to induce the reduction of nitrate, and high specific surface area of the porous electrode enhanced electrocatalytic degradation of NO3-. Besides, the flow-through design of the electrochemical stack cell improves the mass transfer to reach higher reaction rates for nitrate removal. Based on the existing literature, electrochemical denitrification using flow-through stack cells and low-cost graphene based porous electrode materials has not been explored to date. A benchmark of materials synthesis parameters and its effect on the catalytic property will be highlighted. Finally, the strategies towards an innovative, next-generation water treatment technology which has the potential to create a circular nitrogen economy will be explained.

Resume : Electronic properties and function of graphene oxide and reduced graphene oxide depend on the surface structure, origin of defects, and adsorption of molecules at surface. To understand and control these processes, molecular level knowledge on surface structure and dynamics is required. Thus, technique specific to both interface and molecular structure must be applied. In this study, a novel surface-enhanced Raman spectroscopy (SERS) technique named “shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS)” was used to probe the nature of defects and adsorption of molecules at surfaces of graphene, graphene oxide and reduced graphene oxide. Some experiments were conducted in electrochemical cell at controlled electrode potential. SHINERS approach provides possibility to overcome important SERS limitations. The dielectric shell prevents direct interaction of probed molecules with the plasmonic metal and eliminates possible electronic effects caused by deposition of metal nanoparticles on surface. Thus, unperturbed vibrational spectroscopic information with submonolayer sensitivity might be acquired. Spectroscopic evidence for presence of perturbed aromatic rings and functional groups attached to the basal graphene plain will be discussed. Special attention will be given for analysis of electrochemical potential effect on the structure of defects and adsorption properties of aromatic molecules.

Resume : Chemical vapor deposition of graphene is currently the most viable method in producing large- scale graphene for industrial purposes. However, due to the complexities of the process, we are yet to be able to produce graphene in large scale. This study focuses on a novel method of tailoring the quality of graphene synthesized via CVD. Here, we apply a specific amount of biased current on the substrates using a double-Langmuir probe. We postulate that this method will enable the restructuring of carbon atoms and defects thus resulting in high-quality, pristine graphene. The samples used in this study are polycrystalline Cu foils and the CVD steps proceed as per usual with heating, annealing, growth, and cooling step. In addition to these four steps, we also introduce an additional post-growth annealing treatment with temperature lower than the precedent growth temperature under stagnant Ar and H2 gas. The application of biased current proceeds separately at two steps ; 1) during the growth of graphene and 2) during post-growth annealing treatment. Raman spectroscopy is done to provide the primary graphene quality characterization. The sheet resistance of the deposited graphene is also done using a 4-point sheet resistance measurement. Lastly, a transmission electron microscopy (TEM) measurement is done to analyze the atomic structure of the graphene.

Resume : Versatile technological applications of fullerenes have been proposed and are in continuous development in different fields that cover lubricants, superconductors, solar cells, photocatalysis, contrast agents, and, in general, new applications for nanotechnology and nanomedicine. The insolubility of fullerene and the formation of fullerene aggregates, also in organic solvents, hampers its exploitation. The photophysical and photochemical properties of C60 depend strictly on the nature of the fullerene dispersion and a strict control of the dispersion is truly necessary for technological applications. Proteins recognize and disperse monomolecularly fullerenes. The adducts are stable in physiological and technologically-relevant environments, and easily storable. Hybridization with proteins preserves the electrochemical properties of fullerenes. Near infrared fluorimetry and EPR spin-trapping experiments show that the C60-proteins hybrids produce reactive oxygen species (ROS) following both the type I and type II mechanisms. C60 shows a significant visible light-induced generation of ROS, that can be exploited in photocatalysis or photodynamic therapy. C60-protein hybrids significantly reduced the HeLa cell viability in response to visible light irradiation. The different chemical groups offered by the protein platform allow an easy route for the functionalization of the hybrids, without altering the structure and properties of fullerene.

Resume : The application of field emission (FE) devices requires emitters having a low threshold field (Eth, applied field at 10 mA/cm2) and an excellent FE stability at a high emission current density. Herein, we report on the fabrication and field emission characteristics of a carbon nanotube (CNT) emitter formed as a CNT film grown directly onnickel–chromium(Ni80Cr20)alloy wire using microwave plasma enhanced chemical vapour deposition (PECVD). The FE performance of the emitter has a low threshold field of 0.72 V/µm, a large field enhancement factor (8311.3±53.1) and an extremely large emission current density (Jmax) of 37.55 A/cm2 at a relatively low electric field of 2.13V/µm. The great increase in Jmax is ascribed to the reinforced adhesion of CNTs to the Ni80Cr20 alloy wire substrates. We believe that the direct synthesis of CNTs on the nickel–chromium wire substrate without any catalyst layers and the wrapping of the CNTrootswith a carbon nanoflake layer deposited on the surface of the wire substrate are responsible for the enhanced adhesion. Due to the strong adhesion between the CNTs and the substrate, the CNT emitter presents an excellent field emission stability at high emission current densities (14.98A/cm2), and could potentially be applied to field emission devices.

Resume : One of the main factors which limits performances of short-channel graphene field-effect transistors (GFETs), is contact resistance. It inhibits the use of GFETs in low-voltage applications, which is required for reducing the overall power consumption of graphene integrated circuits. We performed an extensive study on the contact resistance between graphene grown by chemical vapour deposition (CVD) and different metals. We found that etching holes in graphene below the metal contacts, strongly reduced the contact resistance reaching an exceptionally low value of 23 Ω μm in case of Au contacts. Previous studies showed that the contact resistance depends on the carrier density of graphene, i.e., it is maximum at the Dirac point and decreases by increasing the carrier density. However, we obtained the lowest contact resistance where the carrier density of graphene reaches its minimum, i.e., at the Dirac point. The application of this technology in common CVD graphene FETs, allowed us to reach an average transconductance of 940 S/m for a 500 nm channel length transistor at a drain bias of only 0.8 V, which out-perform conventional GFETs.

Resume : Heterogeneous photocatalysis finds more application in environmental clean-up as the water re- sources diminish enormously and the air pollution threatens the human health seriously. TiO2 is one of the most widely used photocatalytic materials for environmental remediation applications due to its low cost, chemically inertness, non-toxicity, high photocatalytic activity and recyclability. This talk will present recent activities on understanding and improvement of photocatalytic performance of TiO2 thin films. Basically main focus will be given on three main aspects: 1-Analytic approaches for determining catalytic performance, 2-Influence of UV plasmonics on the performance of TiO2 photocatalysis and 3-Functional applications of TiO2 photocatalysis: A novel method for nanostructuring.

Resume : ZnO nanowires (NWs) are considered as building blocks for a number of sensing, optoelectronic, and electronic devices, where the control of their electrical properties is required through intrinsic and extrinsic doping. While the doping of ZnO NWs has been performed by vapour phase deposition techniques, it is still a major issue by solution deposition techniques. In the present work, ZnO NWs are doped with different metal(III) dopants by using the low-cost, low-temperature, and easily implemented chemical bath deposition technique. Metal nitrate is basically added in various concentrations to the standard precursors [1] in deionized water. This addition completely modifies the structural morphology of ZnO NWs, as shown by electron microscopy [2]. The formation mechanisms are investigated and supported by thermodynamic simulations yielding theoretical solubility plots and speciation diagrams. Their dependence on the pH of the solution through the addition of ammonia is further studied [3]. The incorporation of metal dopants is eventually investigated by energy dispersive x-ray spectroscopy using scanning transmission electron microscopy and by temperature-dependent Raman spectroscopy, showing the occurrence of characteristic additional modes. [1] R. Parize et al., The Journal of Physical Chemistry C 120, 5242 (2016). [2] C. Verrier et al., The Journal of Physical Chemistry C 121, 3573 (2017). [3] C. Verrier et al., Inorganic Chemistry 56, 3573 (2017).

Resume : INTRODUCTION Nowadays, diabetes is regarded as one of the most important health problems on a global scale. Diabetes is a life-long disease that growing with insulin deficiency or ineffectiveness. In case of necessary precautions are not taken against diabetes, it causes some different eye, heart and kidney diseases and it might be fatal. The most effective method for diabetes diagnosis is blood test that has been used for many years. However, an effortless, painless and fast diagnostic method is desirable to assure patient comfort. Many breath markers or tracer compounds are accumulated and related to different diseases, either for diagnostics or monitoring. It is known that acetone presents on a certain concentration as sub-ppm (particle per million) levels in human breath is the indicator of diabetes disease [1]. For this reason, monitoring acetone level in exhaled breath for diagnosis of diabetes disease is very important issue. Semiconductor metal-oxide (MOXs) materials such as TiO2, ZnO, SnO2 and WO3 have been emphasised for use as exhaled breath analysis sensors due to their superior properties such as easy production process and reactivity against volatile organic compounds (VOCs). Several promising research efforts have been conducted for fabrication of highly sensitive exhaled breath sensors, by combining noble metals as catalyser and unique MOXs nanostructures that possess a high surface to volume ratio [2,3]. In this study, TiO2 nanorods (NRs) were synthesized via hydrothermal process. Then, noble metals such as Ag (silver), Pd (palladium), Pt (platinum) were loaded on the TiO2 NRs via magnetron sputtering or thermal evaporation techniques for exhaled breath analysis. Finally, sensor tests were performed at low concentrations of different breath markers such as acetone, ethanol, HCN (hydrogen cyanide). MATERIALS and METHODS TiO2 NRs were synthesized via hydrothermal method on Al2O3 (alumina) substrate. A solution that is consist of titanium (IV) n-butoxide, hydrochloric acid and deionized water mixture was used for hydrothermal process [4]. Then, catalytic metals (Ag, Pd, Pt, etc.) were deposited with magnetron sputtering or thermal evaporation methods. Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction spectroscopy (XRD) methods were used to characterize the morphology and crystal phase of fabricated samples. For gas sensor measurements, Au interdigital electrodes (IDEs) were thermally evaporated on top of the sample surface. The fabricated sensor devices were exposed to acetone, ethanol and HCN for the concentrations ranging between 128 and 4 ppm at different operating temperature between 50 and 300oC. RESULTS and DISCUSSIONS SEM images show that TiO2 NRs homogenously cover entire alumina surface. NRs are tetragonal in shape and they have an average diameter of 250 nm. XRD spectra demonstrated that TiO2 NRs arrays have crystallized in a rutile phase. Sensor measurements were performed at varying temperatures and concentrations to understand loading effect on sensor properties. According to sensor measurements, functionalised TiO2 NRs with Ag catalyst shows clear response toward 4 ppm acetone. Metal catalysts on TiO2 NRs show different catalytic characteristics, thus specify sensor properties such as sensor response, sensitivity, selectivity and optimal operation temperature. ACKNOWLEDGEMENTS This study is financially supported by Scientific and Technological Council of Turkey (TUBITAK) project number 116M201. REFERENCES [1] Marco Righettoni et al., Materials Today 18 3 (2015) 163-171. [2] Erdem Şennik et al., Sensors and Actuators B, 199 (2014), 424–432. [3] Seon-Jin Choi et al., Analytical Chemistry, 85 (2013), 1792-1796. [4] Onur ALEV et al., Procedia Engineering 120 (2015) 1162-1165.

Resume : The use of perovskite oxide materials assembled into thin film heterostructures appears promising for future prospects in the field of oxitronics. However, due to technological constraints, these materials cannot compete yet with other technologies for integration and device processing. Indeed, effective heterostructures require high quality materials, stable over time, whose morphology and roughness are well-controlled. SrVO3 (SVO) is a remarkable material because it presents a metal–insulator transition (MIT). It is also a great candidate for transparent conductive oxide. In this context, Pulsed Laser Deposition (PLD) technique is a good technique to grow complex ternary oxide with an efficient cationic transfer of target. Nevertheless, some parameters as laser fluency, repetition rate, temperature and O2 partial pressure in the deposition chamber are able to strongly modify the obtained materials. Influence of the oxygen pressure has been studied previously. Layers with differences in terms of morphology and physico-chemical properties have been obtained. We were able to form Sr3V2O8 nanostructures on SVO thin films or to obtain flat surfaces. A fine physico-chemical study and an accurate chemical environment determination by XPS, Auger nano-probe of conductive oxide SVO ultra-thin layers is presented, in relation with this morphology and structure by AFM and STEM, and discussed. This will allow a better integration of SVO in a “all oxide” integrated electronics.

Resume : A comprehensive understanding of the oxidation behavior of thin Cu films is an issue of a fundamental interest and particularly relevant for applications in the fields of microelectron-ics, sensors, catalysis and solar cells. The current study reports on the oxidation kinetics and phase formation evolution (Cu2O to CuO) upon heating of magnetron sputtered Cu (111) films in a temperature range of 100 to 450 °C as a function of oxygen partial pressure. In-situ resistance measurements were performed to follow oxide growth rate of Cu films (20 to 150 nm) to Cu2O films in a temperature range of 100 - 300 °C in air. It is found that the oxidation kinetics of Cu films follows the linear rate law, which indicates that oxygen dissociation at the surface is rate-limiting process in this temperature range. As shown by XRD investiga-tions (both in the laboratory and the synchrotron), the oxide phase formation critically de-pends on the oxidation conditions. Cu2O is the major oxide phase at 300 °C at 1 bar in air, whereas CuO becomes dominant at 400 °C for oxidation of 150 nm thick Cu films. The in-situ real-time synchrotron XRD measurements, as conducted at 400 °C (for 50 nm) and 450 °C (for 150 nm) at 1-10 mbar, reveal that the formation of CuO only starts after complete ox-idation of the Cu thin films to Cu2O.

Resume : Halloysite nanotubes (HNTs) with surface-immobilized silver (Ag) nanoparticles (NPs) were explored as nano-templates for surface-enhanced Raman scattering (SERS). The structure and plasmonic properties of NHTs/Ag NPs nanocomposite during storage in water was checked by means of the transmission electron microscopy and optical absorption spectroscopy, respectively. A remarkable SERS response for tested dye molecules of R6G was observed for fresh HNTs/Ag NPs and the SERS activity decreased by several times for the samples stored in water for one week. The observed SERS-activity is explained by desired morphology of Ag NP distribution on the surface of HNTs, which was only slightly modified during storage in aqueous medium. The revealed stability of the SERS activity of NHTs/Ag NPs nanocomposites seems to be promising for their application in biosensorics. The work was supported by the Ministry of Education and Science of the Russian Federation in the framework of Increase Competitiveness Program of NUST "MISIS" (No. K2-2017-084) implemented by a governmental decree dated 16 March 2013, No. 211.

Resume : The design of advanced transition-metal chalcogenides (TMCs) photocatalysts for water splitting is highly important, in which both light absorption and interfacial engineering play vital roles in exciton generation, separation, electron transport, and ultimately speeding up water splitting. To this end, plasmonic metal nanomaterials with surface plasmon resonances are promising candidates. However, it is very difficult to enhance the light absorption and manage the interfacial engineering simultaneously, thus, resulting in suboptimal photocatalytic performance. Here, a nonmetal plasmon is proposed to optically and electrically enhance TMCs hydrogen evolution. With the tunability of plasmon resonance in a MoO3 semiconductor via hydrogen reduction, the broadband absorption and good interfacial engineering have simultaneously been demonstrated in flexible MoS2@MoO3 core-shell nanowire photocatalysts. Better energy-band alignment with MoS2 can also be realized, thereby achieving improved photoinduced exciton separation in the hybrid structure. More importantly, the defects at the interface between MoO3 and MoS2 are effectively reduced because of precise tunability of nonmetal plasmon resonance, which enhances electron transport. As a proof of concept, this optimized hybrid nanostructure exhibits outstanding H2 evolution characteristics (841.4 μmol h-1 g-1) that is 6.73 times of the pure MoS2, excellent stability, and good flexibility. The value is also one of the highest hydrogen evolution activity rate to date among the 2D layered visible light photocatalysts. This work opens a new direction to simultaneously improve the light-absorption characteristics and achieve efficient electron transport in the photocatalytic water-splitting reaction.

Resume : Conversion of solar energy to chemical fuel in a photoelectrochemical (PEC) devices requires an inexpensive and stable semiconductor photoelectrode materials with explicit control over the three main requirements in a single material system: 1) chemical stability 2) visible light absorption and 3) band edges matching to redox levels of water. This talk will summarize the results obtained for photoelectrochemical water splitting using metal oxide semiconductor such as BiVO4, TiO2 and α-Fe2O3. Our attention has been devoted to further modify these oxide semiconductors by using various strategies like band edge engineering, material disordering, nano/micro engineering, surface/interface engineering to improve the performances of metal oxide-based materials, especially favoring the photoelectrochemical activity under simulated sunlight. Recently, a new engineering strategy, i.e., band re-alignment at the heterostructure was achieved by gas–phase modification technique which strongly promotes interfacial interaction at the junction and leads to an effective interfacial charge separation and transport. The modified α-Fe2O3/TiO2 heterostructures exhibit significant enhancement of visible light absorption and improve the photoelectrochemical response.

Resume : Abstract An outstanding challenge in the realm of photocatalysis is the development of functional nanomaterials in the visible region of the electromagnetic spectrum. We have investigated the tunability of electronic and optical properties of semiconductor nanostructures by control of their shape, size and also the mechanism of growth of anisotropic nanostructures1 which have applications in water splitting, photocatalysis and photovoltaics. Coupling of wide band gap semiconductor such as ZnO, NaNbO3, SnO2 with narrow band gap semiconductors like Ag2S, In2S3, CuInS2 etc. (which acts as sensitizer) forms efficient heterostructures (core/shell) for the separation of photogenerated charge carriers and makes it a good candidate for visible-light photocatalysis. The enhancement in photocatalytic activity also elaborate is due to the efficient photoinduced interfacial charge transfer (IFCT) mechanism.2,3 The spatial electron-hole separation between the core and shell, is greatly enhanced by the type-II band alignment between core/shell heterostructures, results in the extremely long exciton lifetime.4 In the aim of society to move towards a clean environment5 and availability of sufficient energy, hydrogen is the key to both these challenges. Tremendous interest exists on hydrogen generation from electrochemical or photoelectrochemical water splitting. Hydrogen having highest energy density per unit mass is eco-friendly as it produces only water after combustion as a direct fuel or after transformation to electricity in fuel cells. Among earth abundant non-noble metals, molybdenum-based materials are important for hydrogen evolution reaction because of low cost, good conductivity and catalytic efficiency. The interfacial charge transfer at various heterojunctions such as core/shell, composite and doped nanomaterials is important for energy conversions. Current research of our group is focused on 2D materials, metal oxides, metal chalcogenides and alloy nanostructures for photoelectrochemical water splitting, photocatalytic organic pollutant (dye) degradation, photocatalytic fuel generation and water purification. References 1. Kumar, S.; Parthasarathy, R.; Singh, A. P.; Wickman, B.; Thirumal, M.; Ganguli A. K. Dominant {100} Facet Selectivity for Enhanced Photocatalytic Activity of NaNbO3 in NaNbO3/CdS core/shell heterostructures, Catal. Sci. Tech., 2017, 7, 481-495. 2. Kumar, S.; Ojha, K.; Ganguli, A. K. Interfacial Charge Transfer in Photoelectrochemical Processes, Advanced Materials Interfaces, 2017, DOI: 10.1002/admi.201600981. 3. Kumar, S.; Singh, A. P.; Bera, C.; Thirumal, M.; Mehta, B. R.; Ganguli, A. K. Visible Light Driven Photoelectrochemical and Photocatalytic Performance of NaNbO3/Ag2S Core/Shell Heterostructure, ChemSusChem, 2016, 9, 1850–1858. 4. Kumar, S.; Singh, A. P; Yadav, N.; Thirumal, M.; Mehta, B. R. Ganguli, A. K. Fabrication of TiO2/CdS/Ag2S Nano-Heterostructured Photoanode for Enhancing Photoelectrochemical and Photocatalytic Activity under Visible Light, Chemistry Select, 2016, 1, 4891–4900. 5. Sunita Khanchandani, Sandeep Kumar, and Ashok K. Ganguli: Comparative Study of TiO2/CuS Core/Shell and Composite Nanostructures for Efficient Visible Light Photocatalysis ACS Sustainable Chem. Eng.2016, 4, 1487−1499.

Resume : Recently, amorphous chalcogenides from ternary Ge-Sb-Se system have grabbed the attention in the field of nonlinear optics due to its high refractive index and wide transmission window in the mid-IR region. Fabrication and studies of amorphous thin films are of great importance for both general research of various properties and applications in the form of slab waveguides. GeSe2, GeSe4, Sb2Se3 and Ge28Sb12Se60 sputtering targets were used for extensive research of optical properties of Ge-Sb-Se thin films fabricated by co-sputtering technique. Variable angle spectroscopic ellipsometry was used for the determination of optical bandgap (Eg) and linear refractive index (n). Third-order nonlinear optical susceptibility (χ(3)) and non-linear refractive index (n2) were extracted from dispersion characteristics. Furthermore, morphological and topographical properties of fabricated films were studied by scanning electron microscopy and atomic force microscopy, respectively. Suitability of amorphous chalcogenides as a novel nonlinear materials for photonics is discussed.

Resume : Titanium (IV) oxide (TiO2) is a commonly used as a photocatalyst because of its availability, chemical/physical stability, non-toxicity and low-cost. However, the low quantum efficiency and the wide bandgap (3.0-3.2 eV) of TiO2 limit its use in photocatalytic applications. Moreover, the high rate of charge recombination of photo-generated electron/hole pairs dramatically decreases the photocatalytic efficiency of TiO2. Several studies have reported that plasmonic metal nanoparticles (NPs), such as gold (Au) and silver (Ag), and improve the photocatalytic performance of TiO2 and extend the electron/hole pairs lifetime by trapping electrons 1. In such studies mostly Ag NPs are preferred to modify TiO2 because of silver’s low-cost, excellent conductivity, chemical stability and near-field enhancement. Although various methods are available for the deposition of Ag NPs on TiO2 surfaces, controlling the size of the Ag NPs at the nano-scale and depositing a uniform distribution without any NP agglomeration are challenging 2. In this study, we deposited uniform Ag NPs on TiO2 thin films by photocatalytic deposition over different time intervals (from 1 min to 5 min). Detailed structural and compositional analyses of prepared samples were performed by SEM, TEM and XPS. Additionally, UV-Vis spectroscopy was used to measure the photocatalytic activity of prepared samples. Under UV irradiation, Ag NP-decorated TiO2 thin films exhibited enhanced photocatalytic performance compared to bare TiO2 thin films. The results indicate that photo-generated electrons are trapped due to the strong electron accepting ability of Ag NPs (deposited in <1 min), resulting in an effective separation of electron/hole pairs. However, excessive Ag NPs (deposited in >1 min) on TiO2 not only act as electron/hole recombination centers but also partially shade TiO2 surface from UV irradiation. 1. Clavero, C. Plasmon-induced hot-electron generation at nanoparticle/metal-oxide interfaces for photovoltaic and photocatalytic devices. Nat. Photonics 8, 95–103 (2014). 2. Barhoum, A., Rehan, M., Rahier, H., Bechelany, M. & Van Assche, G. Seed-Mediated Hot-Injection Synthesis of Tiny Ag Nanocrystals on Nanoscale Solid Supports and Reaction Mechanism. ACS Appl. Mater. Interfaces 8, 10551–10561 (2016).

Resume : Semiconductor based photocatalysts have been examined for their potential in solving many environmental and energy problems. Developing highly efficient visible light active photocatalyst has therefore become the focus of most researchers. A highly efficient Ag-Ag3PO4 photocatalyst was synthesized by including formaldehyde in the precipitation synthesis of Ag3PO4. The as-synthesized Ag-Ag3PO4 was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and diffuse reflectance spectroscopy (DRS). The Ag-Ag3PO4 photocatalyst shows an increase of over 300 % in rate of photocatalytic rhodamine blue dye degradation compared to Ag3PO4 under visible light illumination. Heat treatment of the as synthesized Ag-Ag3PO4 almost doubled its pseudo first order rate constant for the degradation of rhodamine blue dye. The synthesized photocatalyst was stable after cycles of photocatalytic degradation of rhodamine blue dye. The photocatalytic activity enhancement can be attributed to the good electron trapping role of Ag nanoparticles deposited on the surface of the Ag3PO4.The potential application of the Ag-Ag3PO4 in oil spill remediation will be examined through photocatalytic degradation of aromatic and aliphatic components in crude oil. The rate of degradation of the aromatic components will be compared with that of the aliphatic components. The intermediate components generated will also be reported.

Resume : The industrial fabrication of organic solar cells is often hampered by toxic solvents that require strong safety precautions. Whereas the use of chlorinated solvents or toxic hydrocarbons is feasible in the lab, their use in large scale printing processes would lead to enormous operational costs, which conflicts with the goal of cost effective production. In this work, we present efficient organic solar cells that were fabricated from non-toxic and eco-friendly organic nanoparticle dispersions. In an inverted solar cell architecture with a nanoparticulate P3HT:ICBA layer, the power conversion efficiency of 5% nearly matches the performance of reference devices that were fabricated from dichlorobenzene. We further demonstrate that this device fabrication concept is well suited for upscaling. To understand the origin of the high performance of these surfactant-free nanoparticulate organic solar cells, we performed small angle neutron scattering (SANS) and transient absorption spectroscopy (TAS) on precipitated P3HT:ICBA nanoparticles. In contrast to the well-known core-shell morphology of miniemulsion-nanoparticles, we found the nanoparticles formed by surfactant free precipitation were homogenous, that is, the donor and acceptor were evenly distributed in the nanoparticle. We find that the bulk-heterojunction is already prearranged within the nanoparticles, allowing for assembly of nanoparticulate layers with optimal morphologies, with thermal annealing leading to merging of nanoparticle interfaces to facilitate charge extraction.

Resume : Acetylcholine (ACh) is a neurotransmitter found in the autonomic ganglia and the neuromuscular junction. Synthesis of ACh takes place in nerve terminals from acetyl coenzyme A and choline. This reaction is catalysed by choline acetyltransferase (CAT). Altered levels of Ach are associated with dementia, hallucinations, memory loss and Alzheimer’s disease. In the present work, Multi-walled Carbon Nanotubes- Manganese oxide nanoparticles (MWCNT-MnO2 NPs) are utilized for the amperometric detection of ACh. Nanoparticles and their composites impart various advantageous characteristics than their bulk counterparts. MnO2 NPs are important functional metal oxide, as it is attributed with unique chemical and physical properties along with low cost and less toxicity, environmental compatibility. Due to these properties they can be utilized in applications, such as, ion exchange, catalysis, biosensor, and energy storage particularly, molecular adsorption. MWCNT is widely utilized as a supporting material due to their excellent properties such as high surface area, electrical and thermal conductivity and chemical stability. Due to larger surface area, they can be used as effective templates to deposit the MnO2-NPs on the surface with high stability. In order to further enhance the electrochemical efficiency of the system, the MWCNT-MnO2 is deposited on the surface of reduced graphene oxide (rGO).

Resume : Germanium-Tin (GeSn) alloy, a low-bandgap group-IV material, has attracted growing attention in recent years for its potential integration in microelectronic and optoelectronic devices. It is expected a high carrier mobility and an indirect to direct bandgap transition for Sn concentration as low as 8% [1]. However, the low solubility (<1%) of Sn in Ge and their large lattice mismatch (≈15%) are real challenges to be overcome for the epitaxy of high-crystalline quality GeSn alloy. Several research groups have shown the possibility to elaborate 2D GeSn thin films on Si using chemical vapor deposition (CVD) [2] or molecular beam epitaxy (MBE). These approaches offer a good control for the tin incorporation and the possibility to create heterostructures with sharp interfaces. However, the large lattice mismatch between GeSn and Si (>4.2%) [3] leads to a high density of misfit dislocations during the growth of 2D thin film, hindering the alloy crystalline quality. Direct growth of NWs via the vapor liquid solid (VLS) mechanism offers a full strain relaxation, and thus, a high crystalline quality. In this work, we have investigated the CVD-VLS direct growth of GeSn nanowires and Ge/GeSn core-shell structures. GeH4 and SnCl4 are used as germanium and tin precursors, respectively. A flow of HCl was maintained in the chamber during the process in order to limit the 2D uncatalyzed growth along the nanowires. Au colloids of calibrated diameter of 50 nm and 100 nm were used as catalysts. The nanowires morphology and growth rate were investigated as a function of the growth temperature and the partial pressure ratio of precursors by SEM. Nano-auger and STEM-EDX analysis reveal the existence of a thin Sn rich shell (> 10%) [4]. Core-shell NWs exhibit a variety of {112} and {110} facets with different tin composition. The non-homogenous distribution of Sn in these NWs will be discussed. [1] D. Stange et al, ACS Photonics, vol. 2, no. 11, pp. 1539–1545, 2015. [2] J. Aubin et al, ECS J. Solid State Sci. Technol., vol. 6, no. 1, pp. P21–P26, 2017. [3] H. S. Mączko et al, Sci. Rep., vol. 6, no. 1, p. 34082, 2016. [4] T. Haffner et al, Phys. status solidi, vol. 215, no. 1, p. 1700743, 2018.

Resume : Silicon nanoparticles (Si NPs) with sizes 10-100 nm were prepared from Si microcrystalline powder by arc-discharge plasma-assisted ablative synthesis. The structure and physical properties of Si NPs were investigated by means of the transmission electron microscopy, spectroscopy of Raman scattering and photoluminescence, as well as by electron paramagnetic resonance technique. Aqueous suspensions of Si NPs were examined as contrast agents (CA) for magnetic resonance imaging (MRI). Both the transverse relaxation time and longitudinal one for protons in water were found to decrease strongly in aqueous suspensions of Si NPs due to a high concentration of the paramagnetic centers in the latter. The corresponding transverse proton relaxivity was comparable with commercially available CAs. Aqueous suspensions of Si NPs at concentration above 0.1 g/L exhibit noticeable contrast enhancement for T2-weighted MRI. In-vivo MRI visualization of mice with grafted malignant tumor and introtumorally administrated Si-NPs indicate a significant potential of the latter NPs as potential CAs for MRI diagnosis and therapy of cancer.

Resume : Hectic lifestyle in the modern world demands a rapid, accurate and reliable early diagnosis of “Heart Attack” (acute myocardial infarction). Our primary objective is to develop a cost-effective, rapid and label-free point of care diagnostic test kit for detection of cardiac marker (troponin-I) based on paper-based multi-frequency impedimetric transducers. Paper based sensing platforms were developed by integrating carboxyl group functionalized multi-walled carbon nanotubes (MWCNT’s) with anti-cTnI biomarker. The MWCNT’s/anti-cTnI modified micro-paper based analytical device (µPAD) was characterized using Electrochemical Impedance Spectroscopy (EIS). Various concentrations of cardiac troponin I (cTnI) with anti-cTnI were studied as a function of impedance change. The suitability of the proposed µPAD immunosensor is demonstrated with spiking of cTnI in blood serum samples. The limit of detection of the proposed sensor was found out to be 0.05 ng/mL, with response time of < 1 min. The rapid response, very low detection limit, and cost effectiveness makes the proposed immunosensor a potential platform to screen the presence of cTnI in blood serum samples. The proposed immunosensor can, therefore, offers an affordable healthcare system in resource limited areas.

Resume : The lifetime risk of people with diabetes to develop a foot ulcer is 34%. More than 50% of diabetic foot ulcers (DFUs) become infected, in which case, the patient may need to undergo amputation. L-tyrosine is an amino acid, the concentration of which is found to be highly elevated in patients suffering from DFUs. Therefore out of 20 standard amino acids present in wound fluid, we have chosen L-tyrosine as the potential bio-marker (analyte to be detected). The highly expensive and time consuming conventional diagnostic protocols demand the development of micro/nano-fluidic point-of-care (POC) sensors for early and real time monitoring of DFUs. Various transducer-surfaces, based on numerous nanomaterials, have been reported for bio-sensing out of which molecular imprinted polymer (MIP) is well known for specific target-binding which yields high sensitivity and detection limit. In this work, an electrochemical sensor based on molecular imprinted poly-pyrrole (MIPPy) has been synthesized on ITO electrodes (2 cm x 1 cm) using L-Tyrosine as the template. The thin film of poly-pyrrole was electro-deposited on an electrode area of 1 cm2. The electrochemical response of imprinted polymers has been extensively studied, using cyclic voltammetry and impedance spectroscopy, by varying the concentration of tyrosine from 1 µM ? 1 fM. The MIPPy based sensor displayed detection limits in the order of femto-molar along with response time of about 5 seconds.

Resume : The metal oxide quantum dots (QDs), which are having a special place in the family of nanoscience and nanotechnology because of their very small dimension ~2-10 nm, having about 10-50 atoms in diameter. These unique material exhibit larger surface area of the crystals, highest valence and lowest conduction band and releases more energy, when the crystal returns to its resting state. Although, QDs are having various applications in electronic such as solar cells, LED, UV illuminator, screen televisions, has property to glow particular color after being illuminated by light. Very limited informations are available to use of QDs as a nanomedicine. Due to their very small size, it provides various advantages and can be possible to enter in any types of biological identities/targets such as cells and microbes etc. The studies demonstrated the use of QDs as nanomedicine and were check their efficacy against myoblast cancer cells. Various studies were performed such as MTT assay was used to know the % viability of cells in presence of different concentration of QDs, incubation period (24, 48, and 72 h), cells morphology, intrinsic effect etc. The Real Time PCR, which is the back bone to know the genetic studies, was used to check the apoptosis in cells with different genes at different incubation time. Including this, the study was also authenticated with different analytical parameters such as limit of quantitation, detection, recovery, relative standard deviation, which is highly affected and significant analysis under the different doses of QDs with cells. On the basis of acquired studies and their observations, the possible mechanism was also presented.

Resume : Detection of drinking water contaminations such as heavy metal ions and toxic chemicals is costly, time-consuming and requires an accompanying computing device to capture and analyze the data. Therefore, there is an extensive need for rapid, user-friendly, cost-effective, portable and ubiquitous detection technique. Utilizing smartphone is an effective way to measure, analyze and send the results. Here, we quantify mercury and lead in water samples with an excellent level of sensitivity. The designed device is a 3D printed structure which can be attached to any smartphone and is integrated with optical components. Gold nanoparticle and aptamer based colorimetric sensor are utilized to determine concentration of Hg2 and Pb2 . Interaction between aptamer and the analytes leads to a color change in the solution due to aggregation of gold nanoparticles. Optical sources used in the system are light-emitting diodes (LEDs) at 450, 523 and 625 nm and a dedicated App on smartphone to communicate, receive and analyze data. The proposed method offered a detection limit in ppb range for the mentioned ions. This approach provides an instrument for accurate, rapid and in situ control of water safety with no need of technical expertise. This platform on the smartphone has the benefit of improving sensing, cloud storage, sharing information and online data management.

Resume : Since Jelley and Scheibe discovered J-Aggregates (J-A) in 1937, scientists and engineers are studying how to control and exploit the properties of these supramolecular structures in photonic technologies. Their intriguing properties such as spontaneous and reversible self-assembly, dramatically strong molar absorbance, narrow absorption bands or insensitivity to the environment combined with their coherent exciton transport along molecular chains makes them an extraordinary nanophotonic building block. In this talk I will explain two different approaches to exploit these supramolecular dyes as building blocks for photonic applications. Firstly, I will explain how densely doped J-A polymer films can establish a novel molecular route for nanophotonics. These densely packed J-A thin films exhibit inherent metal-like properties making them able to confine the field at nanoscale similar to plasmonic metals. As metals were the motor of plasmonics, molecular materials can guide us to establish the parameters for a fully plastic excitonic nanophotonics. Secondly I will go further in the application of J-As in photonics combining them with plasmonic nanoparticles (NPs). Hybrid plexcitonic NPs were prepared by the combination of Au NPS with J-A. Their optical properties evidence the achievement of strong coupling regime between plasmonic NPs and molecules. We will analyze the advantages of these plexcitonic NPS and their potential use as robust SERS tags in the strong coupling regime.

Resume : The efficiency of Si solar cells can be raised by converting two low energy photons into one photon with energy above the Si band gap, which then adds to the current production in the Si cell. This is not efficient at natural sunlight intensities, and the light therefore needs to be focused to enhance the non-linear upconversion process. Metal nanostrips and nanoparticles on top of an erbium-doped TiO2 upconverting thin film can be used to focus the part of the incoming light that matches the absorption band of erbium into the thin film. The focusing efficiency depend on the geometry of the metal nanoparticles and gradient-based topology optimization is used to efficiently calculate optimized designs. Topology optimization allows for almost unlimited freedom in the design and several techniques are used to make the design production-friendly with respect to electron beam lithography. Physically, the optimization process can exploit scattering, plasmonic, and waveguiding as well as diffraction effects for periodic arrays. Designs utilizing the latter tend to show very good performance but are also extremely sensitive with respect to changes, e.g. in wavelength and angle of incidence. Topology optimization can find non-trivial designs which are efficient and, at the same time, not so sensitive to variations in wavelength, angle of incidence, and particle geometry.

Resume : In the present study, we set out to show that α-alumina hollow nanoshell structure can exhibit an ultrahigh fracture strength even though it contains a significant number of nanopores. By systematically performing insitu mechanical testing and finite element simulations, the high fracture strength of an α-alumina hollow nanoshell structure can be explained in terms of conventional fracture mechanics even at the nanoscales. More importantly, by deriving a fundamental understanding, we would be able to lay down predictions and guidelines for the design of reliable ceramic nanostructures for advanced GaN LEDs. To that end, we demonstrated how our ultra-strong α-alumina hollow nanoshell structures could be successfully incorporated into GaN LEDs, thereby greatly improving the luminous efficiency and output power of the LEDs.

Resume : Halide perovskite nanocrystals are prepared via several synthetic routes to obtain dimension-controlled nanocubes, nanoplatelets or nanowires. We investigate the effect of size and dimensionality on the optical and electronic properties of the nanocrystals, focusing on quantum-confinement and carrier dynamics. With binding energies of up to 300 meV, 2D nanoplatelets exhibit many properties reminiscent of epitaxially grown quantum wells but at room temperature. However, due to their unique geometry and organic ligand surrounding, they exhibit vastly different carrier relaxation dynamics, with a strong dependence on the thickness of the samples. These nanoplatelets are shown to be excellent emitters in the blue spectral region, where perovskite nanocrystals typically perform poorly. Inorganic Cs-based nanocubes, which have previously displayed extremely high quantum yields, are used as precursors to create larger structures. We explore the energetic and electronic coupling between the NCs and explore the resulting optical properties, especially for lasing applications.

Resume : Liquid marbles are quasi-spherical or puddle-like structures which efficiently isolate microdroplets in a non-stick shell formed spontaneously via coating of solid particles onto the liquid surface.1 Using functional particles as the encapsulating layers, the application of liquid marble has been further broadened. Here, we demonstrate liquid marble as microreactor, microsensing, and even micromanipulation platform for triggering, radiating, and even monitoring reactions in enclosed environment. We firstly fabricate plasmonic liquid marble to form 3D multilayer SERS-active shell, allowing rapid and molecular-level sensing of enclosed contents of liquids.2 We unravel reaction mechanism and kinetics using the experimental time-dependent SERS spectra and DFT simulation. Such microreactor system can be further utilized as unit to develop microchemical factory for automatically mixing reactants, monitoring reaction, and sensing product.3 We also utilize magnetic nanoparticles to fabricate liquid marble, exhibiting superior spinning behaviour when floating on water surface.4 Such dynamic and highly controlled spinning behaviour is benefit for microcentrifudge and microsensing platform for liquid surface viscosity. Moreover, taking advantage of the centrifugal force created during liquid marble rotation, we investigate the centrifugal force driven chemical reaction kinetics control.5 Overall, the ensemble benefits offered by functional liquid marbles create enormous opportunities in the development of multifunctional microreactor for versatile applications.

Resume : Handling of big data necessitates the need for disruptive innovations in computing devices. The new generation of devices should be able to process high data density at the cost of low energy. At the moment, devices meeting both these criteria are rare and demand a quantum leap from the state-of-the-art systems. Here we report resistive memory devices based on a spin-coated active layer of a transition metal complex, which shows high reproducibility (~350 devices), fast switching (<30 ns), excellent endurance (~10^12 cycles), stability (>10^6 s) and scalability (down to < 60nm^2). In devices with an active area of ~ 60nm^2, we are able to demonstrate switching energy on the order of 100aJ (4 orders better than the next best report), where the local-field enhancement on the nano-sized electrodes facilitate the switching. In-situ Raman and ultraviolet-visible spectroscopy alongside spectroelectrochemistry and quantum chemical calculations demonstrate that the redox state of the ligands determines the switching states of the device whereas the counterions control the hysteresis [1,2]. Based on this insight, we are able to further engineer our molecules to realize a ternary memory device where two of the conductance plateaus are formed due to different molecular redox states, while the third one arises from charge disproportionation (CD) and formation of supramolecular dipoles, characterized by an enhanced dielectric constant. The realization of a voltage-controlled, disorder driven CD state at room temperature is mechanistically unprecedented and suggests a new route to tailor a wide range of reconfigurable optical as well as electronic multi-state devices. Having realized these functionalities with a metal-organic complex, we resolve the long-standing problems of organic electronics including poor reproducibility, fragility, low speed, and poor scalability making them a potential candidate for wearable and flexible electronics which are becoming integral parts of emerging technologies like the internet of things (IoT) and artificial intelligence (AI). [1] Goswami, Sreetosh, et al. "Robust resistive memory devices using solution-processable metal-coordinated azo aromatics." Nature Materials 16.12 (2017), 1216. [2] Valov, Ilia, and Michael Kozicki. "Non-volatile memories: Organic memristors come of age." Nature Materials 16.12 (2017), 1170.

Resume : The hallmark of many nanomaterials is that the interlayer or interparticle distances are often close to the size of the particle itself. At these length scales, noncovalent (van der Waals) forces are paramount. They drive several phenomena with far reaching real world implications in electronics, sensors, batteries, fuel cells, carbon capture and many more. Originating from correlated electron fluctuations, they require an electronic structure solution. I will discuss efforts predicting atomic and magnetic structure of layered 2D materials and illuminating the importance of van der Waals interaction. Emphasis will be on accurate first-principles solutions for describing nanoscale materials properties derived from van der Waals interactions. I will show how it helped in understanding the spin-lattice coupling in magnetic layered materials as well. I will demonstrate how the inclusion of these forces is essential to their fundamental understanding; thus, being crucial to the computational design of functional nanomaterials.

Resume : Chalcogenides are very promising materials for using in optoelectronics as high-speed optical elements, for applications such as data processing devices, electronic switches and optical elements. Phase-change chalcogenides being already employed in the optical data storages are among the most promising functional materials for new generations of multilevel data storage and data visualization applications. These applications employ the property contrast between amorphous and the crystalline states. In the present study, we report our results on the Urbach-Martienssen tails in the IR spectra of amorphous AsxSy and (GeTe)x(Sb2Te3)1-x chalcogenides. This study is aimed to reveal the compositional dependences of optical properties of studied alloys. We have also tried to deduce whether the absorption edge fluctuations associated with structural disordering have influence on the absorption process through the compositional dependences of the bandgap energy Eg and the Urbach energy Eu.

Resume : Microbial Fuel Cell (MFC) is a sustainable energy transducer, that directly coverts organic matter into electrical energy. The present work demonstrates the MFC to be promising for wastewater treatment and bio-energy production. A bio film of photosynthetic green alga Chlamydomonas sp. TRC-1 deposited on fluorine doped tin oxide (FTO) electrodes was investigated for its ability to generate power. Cyclic voltammetry (CV) scans recorded, sharp anodic and cathodic peak with a potential difference ∆V= 0.239 V. A peak power output of 10.02 mW/m2 was observed with a current density of 27A/m2. The algal biofilm applied in MFC improved the physicochemical parameters of the wastewater, significantly reducing the chemical oxygen demand (COD: 77.1%), total dissolved solids (TDS: 82.1%) and total suspended solids (TSS: 87.4%). The study not only offers an economically and eco-friendly solution to successful power generation but also contributes towards waste water treatment and biofuel production.

Resume : Conventional electronics, which is based on rigid substrates, cannot respond to the requirements of new generation of applications such as wearable electronics or bio-implanted systems. In today?s information oriented world, there are many applications such as medicine, aeronautic, entertainment and RFID that the antenna needs to be bended, rolled and potentially folded. Having the merits of light weight, low profile, low manufacturing cost, decreased fabrication complexity in addition to easy access to inexpensive substrates are the main causes for the increasing demand of flexible and wearable electronics. In this paper, a monopole antenna operating over dual band of 900 MHz and 2.4 GHz for conformal wireless application is proposed and simulated. We used silver nanoparticle ink and Epson inkjet printer to print the designed antenna on a 150 µm transparent and flexible polyethyleneterephthalate (PET) substrate. To measure the antenna, we used Agilent vector network analyzer (VNA). We achieved return loss of -14 dB at 900 MHz and -22 dB at 2.4 GHz that were matched with the simulation results. In simulation results, we reached the gain of 1.96 dBi and 2.77 dBi for 900 MHz and 2.4 GHz, respectively and 10.9? and 20.78? bandwidth for 900 MHz and 2.4 GHz, respectively. We also tested antenna in bending situations to characterize its performance in realistic setups. The results showed that the proposed antenna works properly in curved situations.