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2017 Fall Meeting



Scanning probe microscopy for energy applications

Nanoscale phenomena at surfaces and interfaces play the essential role for energy conversion and energy storage. Therefore the plethora of modes of scanning probe microscopy is inevitable to characterize and understand the behavior of modern energy conversion and energy storage materials in operando.


Intensive research is performed to fulfil the future requirements for low-cost energy conversion and storage. Relevant fields which will be addressed in our symposium will be photovoltaics, batteries, fuel cells, super-capacitors and emerging energy harvesting devices based on piezoelectric and thermoelectric effects.  The operation of energy materials includes electrochemical reactions and (opto-)electronic transport phenomena at interfaces at the nanometer scale. Furthermore, these phenomena are strongly coupled with materials properties such as roughness, grain size and mechanical properties which vary on a nanometer scale. In order to characterize and understand this complex interaction at the nanoscale, adapted characterization methods are mandatory. In this context Scanning Probe Microscopy (SPM) with its plethora of operation modes plays currently a major role. Hereby SPM methods can be often applied in- situ and under in-operando conditions. The latter means for example that charging and discharging of batteries can be characterized in electrolyte solution or that the charge generation and transport phenomena at specific interfaces of hybrid or organic solar cell can be probed.   Our aim is to bring together the scientists who are working on Scanning Probe Microscopy (Kelvin Probe Force Microscopy, Scanning Conductive Microscopy, Piezo Force Microscopy, Scanning Microwave Microscopy, etc.) related to energy conversion and storage materials. The symposium should lead to an exchange of knowledge in surface properties of energy related materials. In particular, we want to stimulate the development and spreading of new SPM methods which would advance the understanding of energy related materials (such as newly developed time-resolved electrostatic modes of the SPM, or advanced modes combining nano-mechanical and potentiometric imaging capabilities). A deeper understanding of advanced SPM methods and its theory for energy applications is highly desirable. Finally, this symposium should be a platform to enable cooperation and future projects.  In general, material scientists will benefit from the results of this symposium enabling them to tailor material properties for energy applications.

Hot topics to be covered by the symposium:

  • Local performance of solar cells (organic, inorganic and hybrid materials)
  • Time resolved EFM/KPFM imaging of the charge carrier dynamics of energy devices
  • (Photo)degradation of energy materials and devices (solar cells, lithiation/delithiation processes, etc.)
  • Novel materials for Li-ion batteries (electrodes, …)
  • Advanced Scanning Probe Microscopy Methods
  • Novel methods for electrochemical characterization of surfaces (for instance in batteries)
  • PiezoForce Microscopy on piezoelectric materials for mechanical energy harvesting flexible devices

Tentative list of invited speakers:

  • David Ginger (University of Washington, Seattle, USA)
  • Marina S. Leite (University of Maryland)
  • Peter Grütter (McGill University): Measurement of Surface Photovoltage by Atomic Force Microscopy under Pulsed Illumination
  • Jaime Colchero (Departamento de Fisica, Universidad de Murcia)
  • Steven Jesse (ORNL, USA)
  • Sascha Sadewasser (International Iberian Nanotechnology Laboratory)

Tentitive list of scientific committee members:

  • Stefan Weber (Max Planck Institute for Polymer Research)
  • Thilo Glatzel (Univ. of Basel, Switzerland)
  • Hendrik Hölscher (Karlsruher Institut für Technologie)
  • Brian Rodriguez (UCD Dublin)
  • Panos Keivanidis (Cyprus University of Technology)
  • Frider Muggele (Twente)
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SPM on Solar Cells I : Ruediger Berger
Authors : Rüdiger Berger, Phil Leclere, Benjamin Grevin and Yi Zhang
Affiliations : -

Resume : We will introduce ourselves and welcome everybody to the Session Scanning Probe Microscopy for Energy Materials. Original research papers of this symposium can be submitted to a special edition of the Beilstein Journal of Nanotechnology on Scanning Probe Microscopy for Energy Applications.

Authors : Nicoleta Nicoara, Sascha Sadewasser
Affiliations : International Iberian Nanotechnology Laboratory (INL), Av. Mestre José Veiga s/n, 4715-330 Braga, Portugal

Resume : The post-deposition treatment (PDT) of Cu(In,Ga)Se2 (CIGSe) absorbers with alkali-fluorides has led to a significant increase in solar cell efficiencies over recent years. The effect of the alkali elements and the mechanisms leading to the efficiency improvements are currently heavily investigated. We have studied the influence of the alkali-treatments on the CIGSe surface and on the absorber/buffer interface on the nanoscale using Kelvin probe force microscopy (KPFM). We investigated different alkali-elements and different buffer layers. For increasing deposition times of the typical CdS buffer layer (by chemical bath deposition) on RbF-treated CIGSe, we observe an initial increase in work function, followed by the expected decrease only after 3 min CdS deposition. At the same time, an increase in the surface photovoltage to >150 mV indicates the formation of a charge-separating pn-junction. However, inhomogeneities in the surface potential on the scale of 5-10 micrometers are still observed after 3 min CdS deposition. Thus, the frequently reported possibility of reduced chemical bath deposition times of the CdS buffer layer has to be carefully considered to avoid incomplete or inhomogeneous coverage potentially leading to efficiency losses [1]. The interface formation of CIGSe with CdS is also compared to that with Zn(O,S) buffer layers [2]. We also studied the effect of alkali-fluoride PDT on the electronic properties of grain boundaries (GBs). For the case of the wide-spread KF-treated CIGSe surface, we observe that the band bending at the GBs is increased by ~70% with respect to the untreated absorber. Moreover, the variation of the magnitude of the band bending is reduced, indicating more homogeneous GB electronic properties. These results reveal that the KF-PDT also has a beneficial effect on the GBs, which presumably contributes to the improved efficiency values observed for alkali-treated CIGSe thin-film solar cells [3]. [1] N. Nicoara et al., in submission. [2] N. Nicoara et al., in preparation. [3] N. Nicoara et al., Scientific Reports 7, 41361 (2017).

Authors : BOSSARD-GIANNESINI Léo 1, CRUGUEL Hervé 1, SNEGIR Sergii 2, PLUCHERY Olivier 1
Affiliations : 1 Institut des Nanosciences de Paris, UPMC-CNRS UMR 7588, 4 place Jussieu, 75005 Paris, France. 2 Chuiko Institute of Surface Chemistry of National academy of sciences of Ukraine, Gen. Naumov str.17, Kyiv, 03164, Ukraine.

Resume : Work-function is defined as the energy needed to extract an electron from the Fermi level to the vacuum. It is an essential property of materials that must be known in complex nano-electronic devices. But when this property is scaled down from bulk to nano-objects, many electrostatic effects can play a role: nanometer size, substrate effect or molecular environment. Zhang et al. have evidenced with Kelvin Probe Force Microscope (KPFM) measurements the size dependence of the change in work-function for spherical gold nanoparticles (AuNPs) grafted on silicon and they have explained it by charge transfers from the substrate [1]. Starting from this point we investigate now how the work-function of spherical AuNPs can be tuned by a molecular functionalization and what is the effect of the particle size. First, in order to minimize charge transfer from the surface, AuNPs are grafted on a gold substrate by a self-assembled monolayer (SAM) of di-thiol. Although the formation of SAMs on gold is well-known some experimental conditions remain controversial. We have evidenced that in liquid phase deposition, kinetics is critical. Rather quickly, free thiols endgroups tend to form disulfide (S-S) bonds which cannot attach AuNPs [2]. Therefore we found the right deposition parameters for an efficient AuNPs grafting. The AuNPs functionalization is then achieved with molecules having a thiol (HS-) head group molecules and two possible tails, -COOH or -NH2. Our first KPFM measurements results show an evolution of work-function as a function of the AuNPs diameter and two different behaviors for the two tails. Density Functional Theory (DFT) calculations are being implemented in order to calculate the work-function of these systems and support our KPFM measurements.

Authors : M. Kratzer(1), O.P.Dimitriev(2), D.O.Grynko(2), A.M.Fedoryak(2), T.P.Doroshenko(2), C. Teichert(1), P. Balaz(3), M.Balaz(3), M.Tesinsky(3), M.Hegedus(4)
Affiliations : (1) Institute of Physics, Montanuniversitaet Leoben, Franz-Josef-Straße 18, Leoben 8700, Austria; (2) V.Lashkaryov Institute of Semiconductor Physics, NAS of Ukraine, pr.Nauki 41, Kiev 03028, Ukraine; (3) Institute of Geotechnics, Slovak Academy of Sciences, Watsonova 45, Kosice 04001, Slovakia; (5) Faculty of Science, P. J. Safarik Unviersity, Moyzesova 11, 040 01 Kosice, Slovakia

Resume : Solar cells based on Kesterite have attracted considerable attention in recent years. It is a promising material with potential to replace Cu(In,Ga)Se2 (CIGS) and related alloys. Compared to CIGS, it exhibits a reduced toxicity and greater abundance of the constituent elements. In solar cells the p-type Kesterites can act as efficient absorbers due to their direct band gap between 1 - 1.5 eV, and a high absorption coefficient of ~104 cm-1 [1]. Here, we test the applicability of mechanochemically prepared selenium free Kesterite Cu2ZnSnS4 (CZTS) nano-powders for bulk-heterojunction solar cells. The CZTS powder is mixed with powders of the n-type semiconductors CdS, ZnO and TiO2. The individual mixtures are mechanically pressed into small pellet forms of ~ 1 mm in diameter forming a bulk-heterojunction. The surfaces of these pellets have been investigated by Kelvin probe force microscopy (KPFM) and conductive atomic force microscopy (C-AFM) in dark and under illumination. First results indicate that the strongest photoresponse is obtained for the CdS/CZTS mixture, where changes in the contact potential difference between dark and illuminated surface of up to 250 mV occurred. However, the photogeneration of charge carriers mainly occurs in the CdS whereas the specifically prepared CZTS nanopowder is essentially non-responsive to light. In order to further improve the performance, sensitization of the developed kesterite powder is under way now. [1] Mitzi DB, et al. Solar Energy Materials and Solar Cells 95, 1421-1436 (2011)

Authors : Yann ALMADORI, Benjamin GREVIN
Affiliations : INAC-SYMMES - UMR 5819 CEA-CNRS-UGA, F-38000 Grenoble, France

Resume : Monolayer transition metal dichalcogenides (TMDCs) display outstanding optoelectronic properties such as direct bandgap in the visible range, and exceptionally strong light-matter interaction regarding their thickness, opening up the way to extremely thin and highly performant photovoltaic (PV) devices [1]. Several pairs of TMDCs (e.g. WS2/MoS2) are theoretically predicted to form type-II PV interfaces [2], and have already shown efficient photo-induced electron-hole pairs separation [3]. Kelvin probe force microscopy (KPFM) coupled with non-contact atomic force microscopy (nc-AFM) has demonstrated a great potential to study photovoltaic systems [3]. However, so far KPFM study of surface photo-voltage (SPV) on TMDCs vHJ and its dynamics remains confidential. In this context, we report a comprehensive nc-AFM/KPFM study performed on a 2D WSe2/MoS2 vHJ lying on a dielectric buffer. SPV imaging reveals the impact of structural/chemical defects on the optoelectronic properties. Differential SPV imaging is successfully achieved both in the temporal regime for various optical powers and under frequency modulated illumination [4]. This unique approach allows investigating the interlayer photo-carrier recombination dynamics and the trapping processes at the vHJ/dielectric interface. [1] Britnell et al. Science 2013, 340, 1311 [2] Kang et al. Appl. Phys. Lett. 2013, 102, 012111 [3] Zhang et al. ACS Nano 2016, 10, 3852 [4] P. Fernández et al. ACS Appl. Mater. Interfaces 2016, 8, 31460

SPM on Solar Cells II : Sascha Sadewasser
Authors : Peter Grutter
Affiliations : Department of Physics, McGill University

Resume : AFM has made amazing progress in the past 30 years in terms of high ?speed structural characterization of surfaces. Imaging rates of 30 frames per second have been achieved, allowing dynamics of surface structures as well as molecular confirmation changes to be observed down to the atomic scale. Measuring properties such as surface potentials at these length scales has also become possible. Renewable energy generation and storage is one of the key issues facing our generation. A challenging AFM frontier that can help addressed relevant materials issues is to achieve ultrafast time resolution in the localized measurement of electronic properties. In this presentation, I will give an overview of our recent successes at characterizing surface potentials using EFM on time scales below fs. Ultrafast EFM techniques will have a major impact is in our understanding of what determines the mobility of charge carriers in photovoltaic systems. We have combined a UHV AFM system with a fs laser excitation system tunable in the optical spectrum. By developing a new pump-probe method we can measure ultrafast decay times using EFM as a spatial detector [1]. We have applied this technique to GaAs, LiNb, Si as well as perovskites to measure ultrafast charge carrier decay times as well as mobility. By combining these results with regular AFM structure characterization, mesoscopic 4-point probe transport measurements, nm scale conductivity measurements using THz spectroscopy as well as fs absorption spectroscopy one can start to achieve a complete understanding of the fundamental as well as material limitations in these materials. [1] Schumacher et al., Appl. Phys. Lett. 110, 053111 (2017)

Authors : P. Fernandez Garrillo*, ?. Borowik*, F. Caffy**, R. Demadrille**, B. Grévin**
Affiliations : *Univ. Grenoble Alpes, F-38000 Grenoble, France CEA, LETI, MINATEC Campus, F-38054 Grenoble, France **Univ. Grenoble Alpes, F-38000 Grenoble, France UMR5819 CEA-CNRS-UGA SYMMES, INAC, F-38054 Grenoble, France

Resume : The photo-carrier lifetime plays a major role in the overall efficiency of a solar cell because it limits the proportion of photo-generated charges collected at the electrodes. This parameter is rather difficult to measure in nanostructured materials. Most of the experimental approaches developed so far consist in studying recombination by techniques such as transient photovoltage or charge extraction. These techniques average sample properties over macroscopic scales, making them unsuitable for directly assessing the impact of local heterogeneity on the recombination process. Recently, we showed that it is possible to measure the photo carrier lifetime with nanometric spatial resolution by photo-modulated techniques based on Kelvin probe force microscopy (KPFM). Additionally, we demonstrate how this setup can be used to simultaneously image surface photo-potential dynamics at different timescales. [1] We will present the principle of this original method based on the nanometrically resolved measurement of the surface potential by KPFM under a modulated illumination. Instrumental aspects as well as data treatment will be reviewed, especially, the correct interpretation of KPFM signal under modulated illumination will be highlighted. We will show how the changes in the capacitance gradient [2] under illumination can be taken into account by analyzing the second harmonic signals. Measurements obtained on third generation solar cells such as organic donor-acceptor blend (PDBS-TQx and PC71BM), and inorganic silicon type junctions will be presented to illustrate the technique?s potential. 1. P. Fernandez et al. ACS Appl. Mater. Inter, 8, 31460?31468 (2016). 2. Z. Schumacher et al. Phys. Rev. Appl. 5, 044018 (2016).

Authors : R. Jöhr, A. Hinaut, R. Pawlak, L. Zajac, P. Olszowski, J.S. Prauzner-Bechcicki, B. Such, M. Muntwiler, S.-X. Liu, J.J. Bergkamp, S. Decurtins, M. Szymonski, E. Meyer, Th. Glatzel
Affiliations : Department of Physics, University of Basel, Basel, Switzerland Department of Physics, Jagiellonian University, Krakow, Poland Department of Chemistry & Biochemistry, University of Bern, Bern, Switzerland Photoemission and Atomic Resolution Laboratory, Paul Scherrer Institute, Villigen, Switzerland

Resume : Functionalization of surfaces by organic molecules has become of high interest for a wealth of energy related applications such as sensors, hybrid photovoltaics, catalysis, and molecular electronics. Molecule-surface interactions, electrical and structural, are therefore of fundamental importance for the understanding of these hybrid interface properties. The anchoring of the molecules is not only important for the stabilization of the molecular film but also for its density and the resulting surface dipole moment. In this presentation, we summarize our achievements in characterizing porphyrin based molecules equipped with carboxylic acid anchoring groups on TiO2 using scanning probe microscopy. The molecules have been thermally evaporation on TiO2 surfaces in ultrahigh vacuum conditions allowing to control the deposition conditions (temperature, deposition rate, and density). Upon adsorption the porphyrins are not covalently bound to the surface and are interacting only weakly with step edges, defects and in between each other. Upon annealing, the carboxylic acid anchors undergo deprotonation and bind to surface titanium atoms. The formation of covalent bonds is evident from the changed stability of the molecule on the surface as well as the adsorption configuration. Annealed porphyrins are in dependence of the type and amount of anchoring groups rotated by 45° and adopt another adsorption site. The influence of binding on electronic coupling with the surface is investigated using current or voltage spectroscopy as well as photoelectron spectroscopy. The determined energy levels, surface potential values, and shifts of the Zn2p and N1s levels to higher binding energies indicate charging of the porphyrin core. The strength of this charging process is influenced by the defect density below the molecules.

Authors : F. Rigoni (1), P. Ghamgosar (1), I. Dobryden (2), A. L. Pellegrino (3), R. Borgani (4), I. Concina (1), G. Malandrino (3), P. M. Claesson (2), N. Almqvist (1), A. Vomiero (1)
Affiliations : (1) Division of Materials Science, Department of Engineering Science and Mathematics, Luleå University of Technology, SE-971 87 Luleå, Sweden (2) KTH Royal Institute of Technology, School of Chemical Sciences and Engineering, Department of Chemistry, Surface and Corrosion Science, Drottning Kristinas väg 51, SE-10044 Stockholm, Sweden (3) Dipartimento di Scienze Chimiche, Università degli Studi di Catania, INSTM UdR-Catania, Viale A. Doria 6, Catania, 95125, Italy (4) KTH Royal Institute of Technology, Nanostructure Physics, Roslagstullsbacken 21, SE-106 91 Stockholm, Sweden

Resume : Nanowires (NWs) are considered appealing and promising candidates in solar cell (SC) applications. It was shown that the theoretical limit, i.e. the maximum obtainable photoconversion efficiency (PCE) under one sun irradiation (33.7%), could be exceeded using vertical GaAs single-NW SC [1], which however requires complicate and highly expensive routes of synthesis, hardly compatible with the scale-up production of solar cells. For this reason, intense research activities have been developed to investigate alternative materials (in particular metal oxides), which would be low cost, large-area scalable and environmentally friendly, while keeping the required high performances of the NW-based SC. In this work, we apply the conductive atomic force microscopy (c-AFM) with scanning spreading resistance microscopy (SSRM) and single pass intermodulation electrostatic force microscopy (ImEFM) to study the electrical properties and surface morphology on a nanometer scale of ZnO NW-based all-oxide solar cells. The n-type ZnO NWs were coated with a p-type semiconducting material, such as Cu2O and Co3O4, to create p-n junctions. The unique capabilities of SSRM, among which the high spatial resolution (1-3 nm), provide local potential and resistance mapping, essential in this research to understand the relation between energy conversion and local morphological/structural and electrical properties, towards a further development of stable, high-efficiency and large-scalable p-n heterojunction SC. The contact potential difference (Vcpd), under dark and light illumination conditions, possessing high Vcpd resolution of about 1mV was as well measured with ImEFM. [1] Krogstrup et al., Nature Photonics. 7, 306-310 (2013)

Authors : Daniel Scieszka, Jeongsik Yun, Aliaksandr S. Bandarenka
Affiliations : Physics of Energy Conversion and Storage (ECS), Physik-Department, Technical University of Munich, James-Franck-Str. 1, 85748 Garching, Germany. Nanosystems Initiative Munich (NIM), Schellingstraße 4, 80799 Munich, Germany.; Physics of Energy Conversion and Storage (ECS), Physik-Department, Technical University of Munich, James-Franck-Str. 1, 85748 Garching, Germany. Nanosystems Initiative Munich (NIM), Schellingstraße 4, 80799 Munich, Germany.; Physics of Energy Conversion and Storage (ECS), Physik-Department, Technical University of Munich, James-Franck-Str. 1, 85748 Garching, Germany. Nanosystems Initiative Munich (NIM), Schellingstraße 4, 80799 Munich, Germany.

Resume : The great urgency of finding new energy sources resulted in an upsurge in the electrocatalysis and battery research. However, optimization and improvement of various energy conversion and storage systems require a better understanding of the electrochemical processes limiting their performance. Thus, further development of new in-situ characterization methodologies is of great importance. One of the methods providing a deeper insight into the electrode/electrolyte interface processes is the laser induced current transient (LICT) technique. This technique can be easily combined with other commonly used methods (i.e. cyclic voltammetry, electrochemical impedance spectroscopy and electrochemical nano-gravimetry), providing a powerful tool for detailed characterization of various systems. The rapid illumination of the electrode surface results in an increase in its temperature directly influencing the inner Helmholtz plane of the electric double layer. As a consequence, one observes current transients whose sign, in the simplest case, corresponds to the sign of the excess electrode surface charge. The LICT is also a relatively simple technique of evaluating the potential of maximum entropy (PME) and, closely related to it, the potential of zero charge (PZC)- the fundamental properties of the electric double layer. We present for the first time the results of the in-situ LICT technique implementation for battery systems investigating Na2Ni[Fe(CN)6] thin films as model electrodes. Surprisingly, the electrode surface charge stays positive within the whole potential range of intercalation/de-intercalation of sodium and potassium cations from aqueous media. This indicates that the complexity of intercalation mechanisms of alkali metal cations into the films might be oversimplified. Further, we demonstrate the influence of the electrolyte pH on the net charge of the pure Pt(poly) electrode surface. Apparently, the behavior of the system is not only governed by the concentration of H+ cations but also by the metal cations present in the electrolyte. All the obtained data emphasize the role of the electrolyte composition for the kinetics and mechanisms of the interfacial processes.

Authors : Jonathan Op de Beeck, Umberto Celano, Valentina Spampinato, Alexis Franquet, Thierry Conard, Nouha Labyedh, Alfonso S. Marquez, Philippe Vereecken, Wilfried Vandervorst
Affiliations : Jonathan Op de Beeck, Umberto Celano, Valentina Spampinato, Alexis Franquet, Thierry Conard, Nouha Labyeda,b, Alfonso S. Marquez, Philippe Vereecken, Wilfried Vandervorst a) IMEC, Kapeldreef 75, 3001 Leuven, Belgium, b) KU Leuven, Department of Physics and Astronomy, Celestijnenlaan 200D, B-3001 Leuven, Belgium, c) KU Leuven, Department of Microbial and Molecular Systems , Celestijnenlaan 200D, B-3001 Leuven, Belgium

Resume : Secondary ion mass spectroscopy (SIMS) is a characterization technique with ultra high chemical sensitivity and high depth resolution, widely established for materials analysis in the field of semiconductors. Recent advances, including the reduction of the lateral resolution to ca. 50 nm and the combination of SIMS with atomic force microscopy (AFM)-techniques are enabling the application of this method to energy materials such as Li-ions battery. In this work, we review some applications of the combined AFM-SIMS methodology to high capacity Li-ion battery electrodes. LiMn2O4, 296 mAh/g is used as test vehicle, while two different deposition techniques are studied. We investigate the impact of different analysis conditions which unravel the impact of the analysis conditions (Bi analysis beam, sputtering with large Oxygen clusters) on various artifacts induced by the ion-beam such as sputtering process, topographic ion yield variations, charging effects and bias-induced electro-migration of mobile cations. Fundamental insight related to the battery anodes is obtained by combining electrical atomic force microscopy (AFM) and SIMS in a single apparatus whereby C-AFM samples the local conductivity and SIMS the local Li-concentration. This allows us to establish the correlation between the electrical and the chemical inhomogeneities in the materials and identify the role of nanoscopic non uniformities. In addition we demonstrate that it is possible to monitor with SIMS the Li-migration when we mimic battery charging through local biasing with the C-AFM.

Authors : Shokoufeh Rastgar, Gunther Wittstock
Affiliations : Carl von Ossietzky University of Oldenburg, Institute of Chemistry, D-26111, Oldenburg, Germany, Carl von Ossietzky University of Oldenburg, Institute of Chemistry, D-26111, Oldenburg, Germany, Gunther.

Resume : Interfaces between two immiscible electrolyte solutions (ITIES) are a promising model mimicking some functional biomembranes in nature (charge carrier separation by two interacting photocenters-z-scheme) and offer novel opportunities for catalyst regeneration or exchange at the interfaces of liquids [1]. Polarizable interface represents molecularly sharp platform suitable for assembling of nanostructured semiconductor photocatalysts which have been proposed as a novel approach, generating charge careers (electron-holes pair) reactants in either side of interface, involving in photo-induced charge transfer reactions at liquid-solid-liquid boundaries [2]. We studied O2 evolution by hyperbranched nanocrystaline BiVO4 at chemically polarized ITIES by [Co(bpy)3](PF6)3 as an electron-acceptor compound in organic phase [3], which dramatically inhibits fast unfavorable electron-hole recombination, similar to z-schemes in natural photosynthesis [4]. The high surface area of nanosized BiVO4 crystals with a specific hyperbranched structure [5] along with the defect free liquid/liquid (L/L) interface could overcome the inherent poor electron transport properties of BiVO4 materials and minimize the interfacial recombination of photo-excited electrons-hole pairs by rapidly transferring them to reactants in the adjacent liquid phases. Then, it clearly influences the efficiency of the parallel reaction of photo-generated hole-driven water oxidation by increasing the O2 evolution rate. This systems also allows to interrogate the photoelectrochemical reaction by oxidation of [Co(bpy)3]2 as a photo-induced electron transfer product in an organic phase of interface by utilizing detector microelectrode (ME in the organic phase) in a scanning electrochemical microscope (SECM). Furthermore, interfacial polarization effects on the photogenerated charge transfer reactions were investigated by recording regeneration of the reduced form of [Co(bpy)3](PF6)3 in organic side of the BiVO4 layer in SECM feedback approach curves and detection of O2 as main product of water photo-oxidation in aqueous side in the generation collection mode. The study of such systems is particularly efficient with a co-linearly arranged micropipette mecha¬nically stabilizing the L/L interface and a microelectrode for detection. Firstly, the micropipette can be prepared with orifices much smaller than the Au ME so that very high collection efficiencies for [Co(bpy)3]2 is attained. Secondly, the capillary can also be used as a wave guide for an approximately homogeneous illumination of the L/L interfaces. Thirdly, such a micro L/L interface can be used as substrate for the surface interrogation mode of SECM (SI-SECM) enhanced by new experimental routines to allow pulses of different signals (potentials, light source, switches). This mode allows quantitative assessment of adsorbed hydroxyl radicals (OH?) at the surface of nanocrystaline BiVO4 substrate as previously demonstrated on solid-liquid interfaces [6]. In the interrogation step, the ME-generated titrant (Co2 ) reacts with adsorbed hydroxyl radicals. Reference: [1] D. R. Weinberg, C. J. Gagliardi, J. F. Hull, C. F. Murphy, C. A. Kent, B. C. Westlake, A. Paul, D. H. Ess, D. G. McCafferty, T. J. Meyer, Chem. Rev., 2012, 112, 4016-4093. [2] E. Smirnov, P. Peljo, H.H. Girault, Chem. Commun., 2017, 53, 4108-4111. [3] S. Rastgar, M. Pilarski, G. Wittstock, Chem. Commun. 2016, 52, 11382-11385. [4] M. K. Dymond, C. V. Hague, A. D. Postle, G. S. Attard, J. R. Soc. Interface 2013, 10, 1-13. [5] Y. Zhao, Y. Xie, X. Zhu, S. Yan, S. Wang, Chem. Eur. J. 2008, 14, 1601-1606. [6] H. S. Park, K. C. Leonard, A. J. Bard, J. Phys. Chem. C 2013, 117, 12093-12102.

Poster Session for Scanning Probe Microscopy for Energy Materials II : Rüdiger Berger
Authors : Yue Shen, Ying Wang, Jun Hu, and Yi Zhang
Affiliations : Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, China

Resume : Charging and discharging of nanometer-sized and tunable-shaped objects are very important to fundamental research as well as to potential applications. For instance, isolated external charges can be used as an electrostatic gating for material transport in the nano-channels. On the other hand charging and discharging of objects provide a powerful tool to studying the electrostatic properties on the nanometer scale. Here, we report on the charging of individual graphene oxide (GO) sheets with varied degrees of reduction by using electrically biased atomic force microscope (AFM) tips. AFM measurements indicate that the apparent height of reduced GO (rGO) sheets increases sharply after charging, while the charging ability is enhanced when the GO sheets are deeply reduced. Charging on isolated areas with tunable shape and size on single-layered GO has been achieved. In addition, charge transfer between rGO sheets separated in hundreds of nanometers on insulating substrates was investigated. It was found that the rGO sheet collects charges from the adjacent charged rGO sheet through the dielectric surfaces. The efficiency of charge transfer between the separated rGO sheets is dependent on their separation distance, gap length, and the substrate type. The findings suggest that the charge interflow should not be neglected in a graphene circuit.

Authors : Ying Wang, Yi Zhang
Affiliations : Key Laboratory of Interfacial Physics and Technology and Division of Interfacial Water, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, China

Resume : Local dielectric property detecting is of great importance in many scientific research and application. In the last two decades, many scanned probe microscopy (SPM) techniques have been developed to fast detection of surface dielectric properties of nanoscale materials. Here, we report a novel method for characterization of local dielectric property based on surface adhesion mapping by atomic force microscopy (AFM). We use two dimensional (2D) materials—graphene oxide (GO) and partially reduced graphene oxide (rGO) sheets, which have similar height but large difference in dielectric property, as the model systems. Through direct imaging the samples with an alternative voltage biased tip in PeakForce Quantitative Nano-Mechanics (PF-QNM) mode, we can unambiguously differentiate GO and rGO by monitoring the change of the sample’s surface adhesion force. By comparing with scanning polarization force microscopy (SPFM), our approach is found to have higher sensitivity and lateral resolution. It is expected to provide a better and faster characterizing of local dielectric property of nanoscale materials, and will further facilitate applications in future nanomaterial based device.

Authors : Ilka M. Hermes (1), Yi Hou (2), Victor W. Bergmann (1), Rüdiger Berger (1), Christoph Brabec (2), Stefan A.L. Weber (1,3)
Affiliations : (1) Max Planck Institute for polymer research, Mainz, Germany; (2) Friedrich Alexander University Erlangen-Nürnberg, Department of Materials Science and Engineering, Erlangen, Germany; (3) Jonhannes Gutenberg University, Department of Physics, Mainz, Germany

Resume : Efficient charge extraction within solar cells explicitly depends on the optimization of the internal interfaces. Potential barriers, unbalanced charge extraction or interfacial trap states can prevent cells from reaching high power conversion efficiencies. In the case of perovskite solar cells, slow processes happening on timescales of seconds cause hysteresis in the current-voltage characteristics. Although hysteresis can nowadays be mostly avoided by selection of suitable selective electrode materials[1], its origin is not yet fully understood. Here, we report on local and time-dependent potential measurements with Kelvin probe force microscopy (KPFM) on cross sections[2] of planar methylammonium lead iodide (MAPI) perovskite solar cells. Our experiments revealed distinct differences in the charging dynamics at interfaces of the MAPI to adjacent layers[3]. Measurements while switching on and off the illumination attest that more than one process is involved in hysteresis. Furthermore, we used KPFM to investigate perovskite solar cells with different electron transport materials (ETM), which exhibited a different hysteretic behavior. Depending on the ETM we observed oppositely oriented electric fields within the perovskite layer, which either aid or counteract the charge carrier extraction from the active layer. Our findings suggest that the introduction of electric fields in the perovskite layer and thus the occurrence of J-V hysteresis could be controlled by the choice of ETM. 1. Hou, Y., et al., Advanced Energy Materials, 2015. 5(20) 2. Bergmann, V.W., et al., Nat. Commun., 2014. 5. 3. Bergmann, V.W., et al., ACS Applied Materials & Interfaces, 2016.

Authors : Núria Garro1, Ana Cros1, Eleonora Secco1, Jaime Colchero2, Jorge Ávila3, Michele Sessolo3, Pablo P. Boix3, Henk J. Bolink3
Affiliations : 1 Materials Science Institute, ICMUV, University of Valencia, P. O. Box 22085, E46071, Valencia, Spain. 2 Departamento de Física, Universidad de Murcia, 30100 Murcia, Spain 3 Instituto de Ciencia Molecular, ICMOL, Universidad de Valencia, C/ Catedrático J. Beltrán 2, 46980 Paterna, Spain.

Resume : Kelvin probe force microscopy (KPFM) is long known as a powerful tool for mapping surface potential and topography with nanoscale resolution. The capability to correlate optoelectronic properties with local structure has been crucial to elucidate some fundamental properties responsible for the high performance of perovskite solar cells. This work aims to go beyond previous KPFM studies through the precise quantitative analysis of tip-sample interaction in multi-dimensional spectroscopy. These measurements, combined with advanced data analysis, allow to obtain separately the contact potential difference, the capacitance, and the van der Waals interaction of the tip-sample system as a function of their relative distance. The samples investigated were 500 nm thick methylammonium lead iodide films deposited on a 50 nm organic hole/electron transport layer on ITO. The whole preparation was based on vacuum deposition and resulted in a densely packed mesh of nanocrystals with an average grain size of 100 nm. The first set of measurements, performed in the dark, revealed that the contact potential is determined mostly by the work function of the charge selective contact and remains constant with the tip-sample distance, indicating that there is no net charge at the perovskite surface. When the same experiments were repeated under illumination, the contact potential difference varied according to the strength of the photovoltaic effect. Much more acute changes were observed in the second derivative of the capacitance which can be interpreted as photoinduced variation of the dielectric constant of the perovskite.

Authors : Daniela Täuber1, Anne-Dorothea Müller2, Katarzyna Wiesenhütter3, Marcel Neubert3, Lars Rebohle3, Ilona Skorupa3, Mahdi Kiani4,5, Nan Du4,5, Danilo Bürger4,5, Frank Falkenberg6, Heidemarie Schmidt4,5
Affiliations : 1. Lund University, Chemical Physics, Naturvetarvägen 16, Lund S-22362, Sweden 2. Anfatec Instruments AG, Melanchthonstr. 28, 08606 Oelsnitz, Germany 3. Institute of Ion Beam Physics and Materials Research, Helmholtz-Zentrum Dresden-Rossendorf, Dresden 01314, Germany 4. Material Systems for Nanoelectronics, Technische Universität Chemnitz, Chemnitz 09126, Germany 5. Fraunhofer Institute for Electronic Nano Systems, Technologie-Campus 3, 09126 Chemnitz, Germany 6. CIRES GmbH, BioMedizinZentrum Bochum, Universitätsstrasse 136, D-44799 Bochum, Germany

Resume : A procedure for the functionalization of BioChips for adherent biomaterials is the modification of the surface by coating or by roughening. PolCarr®-BioChip are volume-functionalized BioChips, which consist of silicon with an implanted charge pattern and allow the attachment of electrically polarizable biomaterials by means of electrostatic forces (SNEF) near the surface. SNEF are caused by an asymmetric electric dipole in the semiconductor surface region and detected using Kelvin probe force microscopy measurements [1]. BioChips with a stripe-like pattern have been fabricated. The electrical properties of the implanted silicon wafers have been characterized by Hall and electrical impedance measurements. SNEF allow for a patterned adhesion of electrically polarizable biomaterials [2,3], e.g. cells of a murine renal carcinoma cell line in a nutrition solution. SNEF above PolCarr®-BioChips are independent of the environment and stable during sterilization, shock freezing, and incubation. As an outlook it is discussed how the properties of adherent biomaterial, e.g. attachment/detachment, cell division/cell death, extension / retraction of pseudopodia, enlargement / reduction of the attachment area, can be detected using impedance spectroscopy. Finally, it is discussed how the electrical polarizability of biomaterials on the nanometer and micrometer length scale can be investigated by means of photo-induced force measurements with an AFM platform and tunable lasers. References: [1] C. Baumgart, M. Helm, and H. Schmidt, Phys. Rev. B, 2009, 80, 085305 [2] C. Baumgart, A.-D. Müller, F. Müller, H. Schmidt, Phys. Stat. Sol. (a), 2011, 208, 777–789 [3] H. Schmidt, S. Habicht, S. Feste, A.D. Müller, O.G. Schmidt, Appl. Surf. Sci. 2013, 281, 24-29 (invited)

Authors : Bora Kim, Daehee Seol and Yunseok Kim*
Affiliations : School of Advanced Materials Science and Engineering, Sungkyunkwan University (SKKU), Suwon, 16419, Republic of Korea

Resume : In polymer electrolyte membrane fuel cell (PEMFC), polymer electrolyte membrane is one of the key components for high efficiency performance because proton conductivity is basically dependent on the properties of the membrane, e.g. Nafion, during operation. Typically, Nafion membranes have been widely used in PEMFC due to its high proton conductivity and chemical stability. Until now, most of studies have investigated macroscopic electrochemical properties of the Nafion membrane for improving their performance. Although there are numerous macroscopic studies that enable to undserstand and evaluate performance of PEMFC, there is still lack of information on fundamentals and insight of local proton conductivity at the nanoscale. In this presentation, we investigated the tip-induced reversible and irreversible electrochemical phenomena on the Nafion membrane using atomic force microscopy. We measured local surface displacement induced by proton transport and corresponding electrochemical reactivity through current-voltage measurement and electrochemical strain microscopy. The observed results show locally different electrochemical reactivity on the Nafion membrane that may be related to the proton conducting channel. Our observation can provide insight into not only nanoscale electrochemical reactivity but also fundamental information for improving the performance of the Nafion membrane in PEMFC.

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Novel SPM Methods for Energy Materials I : Steven Jesse
Authors : J. Sánchez Lacasa, M. Fernandez Orihuela, E. Escasain, E. Palacios-Lidon, A. M. Somoza, M. Ortuño and J. Colchero
Affiliations : Centro de Investigacion en Optica y Nanofisica (CIOyN) Departamento de Fisica, Campus Espinardo Universidad de Murcia E-30100 Murcia

Resume : Quantitative Scanning Force Microscopy in ambient conditions Understanding tip-sample interaction in a Scanning Force Microscopy (SFM) setup is fundamental for optimum data acquisition as well as data interpretation. To minimize noise and simplify the interpretation of experiments, data should be acquired in the (true) non-contact regime at low oscillation amplitude. Two methods will be described to characterize nanoscale systems: data I(U,z) can be acquired either as a function of tip-sample voltage U and tip-sample distance z allowing to separate the Van der Waals force from the electrostatic force. Alternately, normal images U(x,y) can be acquired by minimizing the electrostatic tip-sample interaction (Kelvin Force Microscopy [1]) in order to determine the local Contact Potential. Experiments will be presented to demonstrate the capability of nanoscale characterization of samples in air. We will show, on the one hand, how the spatial and time evolution of the surface potential can be studied. We find strong (time) fluctuations of the surface potential and a static lateral corrugation of this potential. On the other hand, we will discuss how multidimensional SFM spectroscopy (?interaction images?, [2]) allows separation of Van der Waals and electrostatic forces. From these forces, the Hamaker Constant and the Contact Potential can be determined, allowing for precise characterization of material properties on the nanoscale. 1. S. Sadewasser, Sascha, Th. Glatzel, Kelvin Probe Force Microscopy. Springer Series in Surface Sciences. 2012. 2. E. Palacios-Lidón and J. Colchero, Nanotechnology 2006, 17 (21), 5491-5500.

Authors : Yonatan Calahorra, Michael Smith, Anuja Datta, Hadas Benisty, Sohini Kar-Narayan
Affiliations : 1 Department of Materials Science and Metallurgy, University of Cambridge, Cambridge, UK: Yonatan Calahorra; Michael Smith; Anuja Datta; Sohini Kar-Narayan 2 Department of Electrical Engineering, Technion-IIT, Haifa, Israel: Hadas Benisty

Resume : Since its emergence, piezo-response force microscopy (PFM) is the prevailing method to examine fundamental ferro/piezoelectric materials. However, a fundamental limitation lies in its contact mode operation, leading research to focus on flat and durable samples. Recently, a great deal of attention has been dedicated to ferro/piezoelectric nanomaterials, and to soft piezoelectric biological or bio-compatible materials. Considering the limitations of contact PFM, a significant barrier for quantitative analysis of these materials arises. We present an intermittent contact PFM mode (IC-PFM), overcoming some of the barriers for the study of ferro/piezoelectric nanomaterials. The IC-PFM mode stems from a scanning nanoindentation mode (peakforce by Bruker), where the tip is oscillated into intermittent contact with the sample, and resulting force-curves are analysed to yield mechanical information about the sample. We superimpose an electrical signal atop this mode, and extract the piezo-response related deflection signal for each indentation point of a scanning line; notably, only data obtained when the tip contacts the sample is analyzed. We present measurements performed on poly-L-lactic-acid nanowires (NWs), III-V semiconductor NWs, and on a ceramic NW network, where all samples proved nearly impossible to examine in contact mode. We expect this operation mode would become invaluable for ferro/piezoelectric nanomaterials research and induce further advances in this filed.

Authors : Thomas R. Albrecht, Derek Nowak, Anne-D. Müller, William A. Morrison, Sung Park
Affiliations : Molecular Vista, Inc., 6840 Via Del Oro, Suite 110, San Jose, CA 95119; Molecular Vista, Inc., 6840 Via Del Oro, Suite 110, San Jose, CA 95119; Anfatec Instruments AG, Melanchthonstr. 28, 08606 Oelsnitz, Germany; Molecular Vista, Inc., 6840 Via Del Oro, Suite 110, San Jose, CA 95119; Molecular Vista, Inc., 6840 Via Del Oro, Suite 110, San Jose, CA 95119;

Resume : The combination of optical spectroscopy and atomic force microscopy (AFM) is very promising, because it enables the chemical mapping far below the diffraction limit of light. Amongst the available techniques are the scanning scattering near-field microscopy (sSNOM), photothermal induced resonance (PTIR), and Photo-induced Force Microscopy (PiFM): three techniques that are based on physically distinct sensing mechanisms. While sSNOM relies on collection of scattered light, PTIR and PiFM detect the light-induced changes in the sample mechanically. Both illuminate the tip-sample interface with a pulsed tunable laser source and utilize the resonance enhancement of AFM cantilevers. PTIR, which operates in contact mode, relies on the detection of the thermal expansion of the sample and requires a metal, often gold, substrate for best sensitivity. PiFM, presented here, senses the induced polarization of the sample via an attractive image force acting on a metalized tip and is thus applicable in a much wider wavelength range. In PiFM, the tip-sample interaction is highly localized and provides spectrographic mapping with < 10 nm lateral resolution and a penetration depth in the same order of magnitude. Operated with a tunable IR light source, PiFM routinely achieves low noise IR absorption spectra from samples as thin as a few nm. Due to the fact that PiFM relies on the detection of polarizability, it easily operates on insulating substrates such as mica or glass, on very thin layers and on samples with low thermal expansion, such as graphene. This presentation will focus on the application of PiFM at various examples. Results on a wide variety of organic and inorganic samples, including self-assembled block copolymers, polymer blends, perovskites, pharmaceutical compounds, biological materials, microelectronic devices, boron nitride nanotubes, and many others will be presented. Finally, its combination with Kelvin-Probe Force Microscopy (KPFM) and the resulting benefits will be discussed.

Authors : Dmitry Kazantsev 1,2*, Vyacheslav Polyakov 2, Sergey Lemeshko 2, Elena Kazantseva 3
Affiliations : 1) Institute for Theoretical and Experimental Physics, Moscow, Russia 2) NT-MDT Spectrum Instruments, Limerick, Ireland 3) Moscow Technological University, Moscow, Russia *) E-mail

Resume : We present physical principles of Apertureless Scanning Near-field Optical Microscopy (ASNOM) [1,2,3] and report on its application to a mapping of the nanoscale objects optical properties with nm-resolution. Normally, the dipole oscillations in a point-like object (like a single molecule or nano-particle) can hardly be emitted into an environmental space as a running electromagnetic wave. Its dipole momentum determined by a few oscillating electrons (typically single one) and angstrom-range oscillation span of charge density yields in vanishingly low efficiency in a light emission. The situation changes dramatically if a rod-like antenna of some micrometer length is attacted ?electrically? to that object (see Figure.1). A huge amount of free electrons in a metal of a tip being involved in the charge density oscillations under an influence of the object being investigated, as well as tip large dimensions lead to 104-105 increase of radiation efficiency [4]. An external electromagnetic field can, vice versa, be applied to a surface with a help of an ASNOM tip. The dimensions of area where the field is applied are determined just by mechanical dimensions of a tip (5-20 nm) [5,6,7], regardless to the wavelength of a light being used (up to THz range). The amplitude and phase of the wave re-emitted by a tip antenna depend on its ?grounding conditions?, and therefore an ASNOM signal being collected contains information on the sample local dielectric function as a complex value [8]. We present ASNOM images of semiconductor and polymer (e.g. Figure 2) structures of nanometer scale to demonstrate an ability of an ASNOM to map a clear material contrast, with a lateral resolution of 10-30 nm. Figure 1. Polystyrene embedded in a PVAC matrix. (a) AFM-like topography map of the sample. ASNOM signal (?=10.6 ?m) with (b) an optical phase corresponding to Au (known to perfectly reflect 10.6 ?m radiation) and (c) collected with an optical phase 90° with respect to (b). We also present the maps of running surface polariton waves collected with an ASNOM on different samples. A nanometer lateral resolution of ASNOM allows for mapping the surface waves with a lateral resolution much better than a wavelength and, therefore, to investigate the polariton optics phenomena in such kind of structures with a rather good precision. References. [1] H.K. Wickramasinghe, C.C. Williams, Apertureless near field optical microscope. //US Pat. 4,947,034, (1990) [2] F. Zenhausern; Y. Martin & H.K. Wickramasinghe, Scanning Interferometric Apertureless Microscopy: Optical Imaging at 10 Angstrom Resolution. //Science, 269, 1083-1085 (1995). [3] Y. Inouye & S. Kawata, Near-field scanning optical microscope with a metallic probetip. //Opt. Lett., OSA, 19, 159-161 (1994). [4] L. Novotny; R. X. Bian & X. S. Xie, Theory of Nanometric Optical Tweezers. //Phys. Rev. Lett., American Physical Society, 79, 645-648 (1997). [5] Y. Martin; F. Zenhausern & H. K. Wickramasinghe, Scattering spectroscopy of molecules at nanometer resolution. //Applied Physics Letters, AIP, 68, 2475-2477 (1996). [6] A. Bek; R. Vogelgesang & K. Kern, Apertureless scanning near field optical microscope with sub-10 nm resolution. //Review of Scientific Instruments, AIP, 77, 043703 (2006). [7] A. Huber; D. Kazantsev; F. Keilmann; J. Wittborn & R. Hillenbrand, Simultaneous IR Material Recognition and Conductivity Mapping by Nanoscale Near-Field Microscopy. //Advanced Materials, WILEY-VCH Verlag, 19, 2209-2212 (2007). [8] F. Keilmann & R. Hillenbrand, Near-Field Microscopy by Elastic Light Scattering from a Tip. //Philosophical Transactions: Mathematical, Physical and Engineering Sciences, The Royal Society, 2004, 362, 787-805.

SPM on Perovskite Solar Cells I : Peter Grütter
Authors : Marina S Leite
Affiliations : Department of Materials Science and Engineering; Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, MD, USA

Resume : The electrical behavior of materials for photovoltaics (PV) at the mesoscale strongly determines device performance. Thus, spatially resolving the electrical and optical response of emerging materials, such as perovskites and polycrystalline owns, is crucial to advance our understanding of charge carrier generation, recombination and collection at the nanoscale. We use scanning probe microscopy methods to realize a novel platform to image the functionality of materials for PV. Through time-dependent Kelvin-probe force microscopy (KPFM) we quantify the transient behavior of perovskite solar cells. Upon and post illumination we measure ion accumulation and migration, respectively, resulting from the occupation of trap states and in a residual Voc even when the material is under dark conditions. In the realm of polycrystalline materials, we implement KPFM to quantify the local Voc of CdTe and CIGS, where we find spatial variations >20%, most likely caused by the material?s structural properties. We anticipate our functional imaging approach to impact the rational design of the next generation of high-efficiency and low-cost PV devices, by establishing a correlation between the materials electrical, chemical and structural properties. Further, the time-dependent KPFM could be extended to probe the stability of lead-free perovskites.

Authors : Daehee Seol1, Ahreum Jeong1, Man Hyung Han1, Seongrok Seo2, Tae Sup Yoo3, Woo Seok Choi3, Hyun Suk Jung1, Hyunjung Shin2, and Yunseok Kim1
Affiliations : 1School of Advanced Materials Science and Engineering, Sungkyunkwan University (SKKU), Suwon 16419, Republic of Korea 2Department of Energy Science, Sungkyunkwan University (SKKU), Suwon 16419, Republic of Korea 3Department of Physics, Sungkyunkwan University (SKKU), Suwon 16419, Republic of Korea

Resume : Organic?inorganic hybrid perovskite solar cells, e.g. CH3NH3PbI3, with perovskite structure have been received extensive attention for photovoltaic applications owing to their superior properties. However, anomalous current?voltage (I?V) hysteresis has hindered the attainment of an even higher efficiency performance. Although recent experiemtnal studies based on piezoresponse force microscopy (PFM) have shown that the perovskite solar cells have ferroelectricity that causes hysteresis, there still remain an ambiguity because PFM response can originate from the surface volume change by ion migration as well as piezoresponse. In this presentation, we examine the origin of the I-V hysteresis in CH3NH3PbI3 thin films. We first demonstrate the existence of ferroelectricity by observing collapse of the PFM hysteresis loop above the Curie temperature of CH3NH3PbI3 thin films through temperature dependent PFM. Furthermore, by measuring the voltage scan-rate-dependent nano/macroscopic I?V curves, we find that grain boundaries assisted ion migration can be a dominant origin of I?V hysteresis at the macroscopic scale, while ferroelectricity contributes to the I-V hysteresis at the grains. Our findings suggest that, although there is ferroelectricity in the CH3NH3PbI3 thin films, ion migration mainly contributes to the macroscopic I?V hysteresis. The presented results could provide basic guidance to the resolution of I-V hysteresis issues in perovskite materials.

Authors : Min-Chuan Shih,1,2 Shao-Sian Li,3 Cheng-Hua Hsieh,2 Ying-Chiao Wang,3 Hung-Duen Yang,2 Chia-Seng Chang,4 Ya-Ping Chiu,1,2,4,* and Chun-Wei Chen3,*
Affiliations : 1Department of Physics, National Taiwan University, Taipei, Taiwan 2Department of Physics, National Sun Yat-sen University, Kaohsiung, Taiwan 3Department of Materials Science and Engineering, National Taiwan University, Taipei, Taiwan 4Institute of Physics, Academia Sinica, Nankang, Taipei, Taiwan

Resume : The charge carrier transport behavior and solar cells efficiency of perovskite solar cells were shown to be dramatically influenced by the existence of PbI2 phase in perovskite films. In present work, the original combination of light-modulated scanning tunneling microscopy (LT-STM) and spectroscopy (STS) reveals the interfacial electronic configuration at the PbI2/perovskite hetero-interface of polycrystalline CH3NH3PbI3 perovskite grain under light illumination. The unique advantage of the LM-STM/STS technique enable directly visualizing the spatially-resolved mapping images of electron and hole carriers photogeneration and photoinduced interfacial band bending of both the valence bands and conduction bands at the PbI2/perovskite interface of perovskite crystals. According to the investigation at the interfacial electronic configuration of individual perovskite grains under illumination, the enhanced photogenerated carrier separation and reduced back recombination were observed as an optimal interfacial PbI2 passivation layers with a thickness less than 20 nm at perovskite crystal grains was applied.

SPM on Perovskite Solar Cells II : Benjamin Grevin
Authors : David S. Ginger
Affiliations : University of Washington

Resume : A range of emerging materials, from perovskite solar cells, to polymer batteries, and even bioelectronic transistors, show strong variations in performance associated with the nanoscale structure of the active material. In this talk, I will discuss our work using a combination of multimodal in situ probes to unravel the often complex interplay of electronic, ionic, and even ferroelectric, behaviors that connect processing, structure, and function in these materials. For instance, by classifying local current-voltage curves according to the corresponding local photoluminescence, we show that local variations in electronic coupling between the semiconductor and electrode are present across a wide range of common hybrid perovskite semiconductor photovoltaic device architectures, pointing a clear path forward in attempts to improve Voc in these materials. In addition, we disentangle the competing effects of electronic carrier injection with voltage bias stress, providing a clearer picture of the role of ion migration vs. trap filling in device aging. Finally, we discuss nanoscale measurements of ion transport in a range of soft polymer systems, using both electrochemical strain microscopy (ESM) as well as time-resolved electrostatic force microscopy (trEFM), showing how local polymer crystallinity influences ion uptake and motion in organic semiconductors that serve as a model for materials being studied for battery binders as well as bioelectronic transducers.

Authors : Ilka M. Hermes (1), Victor W. Bergmann (1), Wolfgang Tress (2), Michael Grätzel (2), Rüdiger Berger (1), Stefan A.L. Weber (1,3)
Affiliations : (1) Max Planck Institute for polymer research, Mainz, Germany (2) École polytechnique fédérale de Lausanne, Department of Chemistry and Chemical Engineering, Lausanne, Switzerland (3) Johannes Gutenberg University, Department of Physics, Mainz, Germany

Resume : Although hybrid lead halide perovskites have shown great promise as a new cheap and flexible alternative to silicon, these so-called perovskite solar cells exhibit unusual behaviour such as current-voltage hysteresis. This effect is also manifested in an unstable power output over the course of milliseconds to minutes and hours following the exposure to light. A stable and reliable power output, however, is a prerequisite for the commercialization of new photovoltaic materials. Depending on the choice of materials for the selective electrodes, hysteresis could recently be mostly suppressed, indicating that internal interfaces play a decisive role. Nevertheless, the exact mechanism behind the hysteresis could not yet be clarified. Space charge layers formed due to migrating ionic species and non-radiative recombination at the interfaces are thought to play a dominating role. Here, Kelvin probe force microscopy (KPFM) offers the unique opportunity to map charge accumulation at the interfaces of operating devices [1]. However, the conventional scanning approach of KPFM limits the time resolution to ~1 s due to the scan rate of the SFM tip. Here, we present a pointwise KPFM spectroscopy approach that allows recording complete potential maps of a device cross section with a time resolution of up to 500 µs. Thereby, the formation and dissipation of the internal electric field caused by the migrating ions in the perovskite layer can be measured and visualized. [1] Bergmann et al., Nat. Comm., 5, 5001 (2014); ACS AM&I, 8, 19402 (2016).

Authors : Andrés Lombana, Philippe Lang, Nicolas Battaglini
Affiliations : Université Paris Diderot, Sorbonne Paris Cité, ITODYS, UMR 7086 CNRS, 15 rue J-A de Baïf, 75205 Paris Cedex 13, France

Resume : Light-Assisted Scanning Tunneling Microscopy (LA-STM) experiments have been performed on very thin molecular assemblies on Au(111), which have been elaborated by a solution-based process. D/A assemblies have been achieved by adsorbing a submomolayer of fullerene (PC71BM) on a monolayer of PTB7/Au(111), the pair (PTB7/PC71BM) being known to exhibit a high power conversion efficiency in organic photovoltaic cells.[1] Photo-induced current images are expected to provide a signature of exciton formation-dissociation. Nevertheless, the tip and sample thermal expansion caused by the power modulation of the laser source introduces an important « thermic » component.[2] By working simultaneously at two opposite potentials and by studying the signals obtained on non-photoactive systems, such as self-assembled monolayers of alkanethiols, we succeed to isolate the real molecular photocurrent and to image it. A model of the photochemical process with location of the expected electronic levels is proposed and discussed. References [1] Y. Liang, Z. Xu, J. Xia, S.-T. Tsai, Y. Wu, G. Li, C. Ray, L. Yu, Adv. Mater. 2010, 22, E135. [2] S. Grafström, J Appl. Phys. 2002, 91, 1717.

Authors : Amelie Axt(1), Victor W. Bergmann(1), Ilka M. Hermes(1), Niklas Tausendpfund(1), Rüdiger Berger(1), Stefan A.L.Weber(1)(2)
Affiliations : (1) Max-Planck-Institute for Polymer Research, Mainz, Germany (2) Institute of Physics, Johannes Gutenberg University Mainz, Germany

Resume : Quantitative surface potential measurements are crucial to understand electronic processes on functional nanostructures in solar cells. Here, Kelvin probe force microscopy (KPFM) on device cross sections has become a popular method to map the potential distribution across the functional layers of solar cell devices. Cross sectional KPFM can both visualize and quantify effects such as an unbalanced charge transport [1] or slow migration of ions and charge trapping [2]. To provide quantitative and local information, the KPFM methods have to be free of cross talk from topography and electrostatic interactions with adjacent layers. In particular in thin film solar cells with active layers thinner than one micrometer, the proper choice of KPFM method is crucial. Here we study the influence of the KPFM method on the measured potential distribution as well as on crosstalk on a model electrode geometry. We directly compare the lateral resolution and the measured contact potential difference for different Amplitude Modulation (AM) and Frequency Modulation (FM) KPFM methods in air. We then suggest a ?best practice? for quantitative measurements on nanoscale device cross sections to understand the limiting factors of the solar cell performance. [1] Bergmann et al., Nat. Comm. 2014, 5 : 5001. [2] Bergmann et al., ACS Appl. Mater. Interfaces, 2016, 8 (30):19402?19409.

SPM on Energy Materials : Marina Leite
Authors : Suman Nandy, Sumita Goswami, Tomas R Calmeiro, Rodrigo Martins, Elvira Fortunato
Affiliations : i3N/CENIMAT, Department of Materials Science, Faculty of Science and Technology, Universidade NOVA de Lisboa and CEMOP/UNINOVA, Campus de Caparica, 2829-516 Caparica, Portugal

Resume : Conjugate polymers are of great interest because of their ability to control the energy gap and electronegativity through molecular design that has made possible synthesis of conducting polymers with a range of ionization potentials and electron affinities. The excellent properties of ?-electron delocalization at the backbone of conjugate polymer can be initiator of charge transfer mechanism with the incorporated nanoparticles, resulting tunibility of electronics dynamics within the composites, can have exciting opportunities to nano-electronics. Aim of our work is to develop novel strategies for synthesis of PANI and its composite via simple cost effective techniques towards the smart applications of ?electro-nanoimprinting? memory devices based on controlled and localized charge trapping phenomenon. As the size of electronic device is scaled down towards the nanometres dimensions architecture, AFM can be used as a technique of choice to study the influence of controlled charge injection phenomenon into the materials at the time of scanning. Our experimental findings open up a way for ?writing-reading? of memory bits on polymer data sheet using mechanic/electrical bias by AFM probe. For pristine PANI, core idea of ?charge pattern? was by transmuting mechanical stress in to electrical outputs by contact electrification mechanism, to the concept of non-destructive self-powered data sheet. Secondly, carbon nanoparticles (CNPs) have been deployed into PANI as a charge trapping sites, where data has been recorded on the device layer by electrical pulse (±1V to ± 7V) through AFM by localized charge injection method. Time evolution of ?read-out? image indicates well retention effect of stored charge for a significant time up to 6 hrs. kkkk

Authors : Ana Pérez-Rodríguez, Inés Temiño, Marta Mas-Torrent, Carmen Ocal, Esther Barrena
Affiliations : Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), 08193-Bellaterra (Spain)

Resume : Blending small conjugated molecules as organic semiconductor with an amorphous insulating polymer has been probed to improve the device processability, reproducibility and stability1-2. The key to understand the superior performance of organic field effect transistors (OFETs) fabricated with blended films seems to be the vertical phase separation of the two material components. Thus, deciphering the microstructural details of the vertical stratification of the two organic materials in the blend and its influence on the macroscopic electrical performance is an issue of fundamental importance. This important question is addressed here for blends of 2,7-Dioctyl[1]benzothieno[3,2?b][1]benzothio-phene (BTBT-C8), promising organic semiconductor with some of the highest mobilities reported to date, and polystyrene (PS) processed by a solution-shearing technique [1,2]. We show that Friction Force Microscopy (FFM) can be used to distinguish between regions of pure BTBT-C8 and PS thanks to their different frictional behavior, allowing us to obtain a complete nanoscale characterization of their lateral and vertical distribution. In addition, a Kelvin Probe Force Microscopy (KPFM) study was performed to understand the influence of the morphology on the macroscopic device performance and elucidate charge trapping and contacts-related effects. (1) Temiño, I.; Del Pozo, F. G.; Ajayakumar, M. R.; Galindo, S.; Puigdollers, J.; Mas-Torrent, M. A Rapid, Low-Cost, and Scalable Technique for Printing State-of-the-Art Organic Field-Effect Transistors. Adv. Mater. Technol. 2016, 1600090. (2) Del Pozo, F. G.; Fabiano, S.; Pfattner, R.; Georgakopoulos, S.; Galindo, S.; Liu, X.; Braun, S.; Fahlman, M.; Veciana, J.; Rovira, C.; et al. Single Crystal-like Performance in Solution-Coated Thin-Film Organic Field-Effect Transistors. Adv. Funct. Mater. 2016, 26, 2379?2386.

Authors : Silviu-Sorin Tuca (1), Georg Gramse (1), Manuel Kasper (2), and Ferry Kienberger (2)
Affiliations : 1 - Institute of Biophysics, Johannes Kepler University, Gruberstrasse 40, 4020 Linz, Austria 2 - Keysight Technologies Austria GmbH, Keysight Labs, Gruberstrasse 40, 4020 Linz, Austria

Resume : Scanning Microwave Microscopy (SMM) is a recently developed nanoscale imaging technique that combines the lateral resolution of Atomic Force Microscopy (AFM) with the high measurement precision of microwave analysis at GHz frequencies, provided by Vector Network Analyzers (VNA). SMM enables measuring complex materials properties for nano-electronics, materials science, and life science applications. SMM operates at broadband frequencies between 1 MHz and 20 GHz. We developed novel calibration workflows for complex impedance imaging [1-2] and dielectric quantification [3]. Various nanodevices are studied including dopant profiling layers [4], high voltage transistors [5], buried oxide structures, and 2D materials like graphene and MoS2. Owing to the high frequency of the measurements, the laborious fabrication of back electrode contacts is not required, making it an easily applicable tool for electrical characterization of nanodevices. The capability of the electromagnetic waves to penetrate the surface of the sample under study allows the technique to be used to selectively sense sub-surface features [6,7]. The sub-surface and quantitative resistivity measurement capabilities are demonstrated for silicon back-wafer imaging and semiconductor failure analysis. The SMM was also applied to study magnetic materials including YIG films and permalloy samples [8]. In summary, we present an extended SMM for advanced voltage and impedance spectroscopy, along with novel RF calibration workflows that can be applied to nanoscale semiconductor devices and advanced materials at high frequency. References: [1] G. Gramse et al, ?Calibrated complex impedance and permittivity measurements with scanning microwave microscopy?, Nanotechnology, 25, 145703 (2014) [2] M. Kasper et al, ?An advanced impedance calibration method for nanoscale microwave imaging at broad frequency range,? IEEE Transactions on MTT, (2017), in press [3] M.C. Biagi et al, ?Nanoscale Electric Permittivity of Single Bacterial Cells at Gigahertz Frequencies by Scanning Microwave Microscopy,? ACS Nano, 10, 280 (2016) [4] E. Brinciotti et al., ?Probing resistivity and doping concentration of semiconductors at the nanoscale using SMM,? Nanoscale 7, 14715 (2015) [5] E. Brinciotti et al, ?Calibrated nanoscale dopant profiling and capacitance of a high-voltage lateral MOS transistor at 20 GHz using Scanning Microwave Microscopy,? IEEE Transactions on Nanotechnology, vol.16, no.2, pp.245-252 (2017) [6] G. Gramse and E. Brinciotti et al, ?Quantitative sub-surface and non-contact imaging by scanning microwave microscopy,? Nanotechnology 26, 135701 (2015) [7] E. Brinciotti et al, ?Frequency Analysis of Dopant Profiling and Capacitance Spectroscopy Using Scanning Microwave Microscopy,? IEEE Transactions on Nanotechnology, vol.16, no.1, pp.75-82 (2017) [8] C. Joseph et al., ?SMM for nanoscale characterization of magnetic materials,? J. Magnetism and Magnetic Materials 420, 62 (2016)

Authors : Hai Li,* Lin Wang, Yang Liu
Affiliations : Key Laboratory of Flexible Electronics (KLOFE) & Institute of Advanced Materials (IAM), Jiangsu National Synergetic Innovation Center for Advanced Materials (SICAM), Nanjing Tech University (NanjingTech), 30 South Puzhu Road, Nanjing 211816, P.R. China

Resume : Graphene nanoscroll (GNS),1-3 a wrapped graphene sheet with tubular structure, has been receiving increasing interest due to its potential applications in the fields of hydrogen storage, supercapacitors, batteries, and nanodevices. Several methods have been reported to fabricate the GNS, such as scrolling of the mechanically exfoliated graphene sheets with the aid of isopropyl alcohol in water, sonication of graphite intercalation compounds, microwave-assisted scrolling in ethanol or liquid nitrogen, and Langmuir-Blodgett compression of functionalized graphene oxide single sheets. In this work, well-aligned functionalized graphene oxide (GO) scrolls are prepared through the controlled folding/scrolling of single-layer GO and functionalized GO sheets by using molecular combing on hydrophobic substrates,4-5 such as aged gold substrate, polydimethylsiloxane film, and octadecyltrimethoxysilane-modified silicon dioxide. As a proof of concept, as-prepared functionalized GO scrolls have been used to detect NO2 gas and humidity.6 This simple method shows the potential ability to control the shape, orientation, position and functionalization of GO sheets over large area. References (1) S. F. Braga, V. R. Coluci, S. B. Legoas, R. Giro, D. S. Galvao, R. H. Baughman, ?Structure and dynamics of carbon nanoscrolls? Nano Lett. 2004, 4, 881-884 (2) L. M. Viculis, J. J. Mack, R. B. Kaner, ?A chemical route to carbon nanoscrolls? Science 2003, 299, 1361 (3) X. Xie, L. Ju, X. F. Feng, Y. H. Sun, R. F. Zhou, K. Liu, S. S. Fan, Q. L. Li, K. L. Jiang, ?Controlled Fabrication of High-Quality Carbon Nanoscrolls from Monolayer Graphene? Nano Lett. 2009, 9, 2565-2570 (4) H. Li, J. Wu, X. Qi, Q. He, C. Liusman, G. Lu, X. Zhou, H. Zhang. ?Graphene Oxide Scrolls on Hydrophobic Substrates Fabricated by Molecular Combing and Their Application in Gas Sensing?, Small 2013, 9, 382-386 (5) J. Wu, H. Li, X. Qi, Q. He, B. Xu, and H. Zhang, ?Graphene Oxide Architectures Prepared by Molecular Combing on Hydrophilic-Hydrophobic Micropatterns?, Small 2014, 10, 2239-2244 (6) L. Wang, P. Yang, Y. Liu, X. Fang, X. Shi, S. Wu, L. Huang, H. Li,* X. Huang, W. Huang, ?Scrolling up graphene oxide nanosheets assisted by selfassembled monolayers of alkanethiol?, Nanoscale, under revision.

Poster Session for Scanning Probe Microscopy for Energy Materials II : Rüdiger Berger
Authors : Yu Jin Kim
Affiliations : POSTECH Organic Electronics Laboratory, Department of Chemical Engineering, Pohang University of Science and Technology, Pohang 790-784, Republic of Korea Current address: Center for Nanoscale Materials, Argonne National Laboratory, 9700 S. Cass Ave. Lemont, IL 60439, USA.

Resume : The physical nature of solvent vapor annealing (SVA) treatment is quite straightforward, and its application is ideal in small molecule-based bulk heterojunction solar cells. It has been suggested to rapidly achieve high-performance small molecule photovoltaics by alternating the blends to ideally connect the crystallite morphology. However, most previous reports on SVA have shown only influences of the degree of donor/acceptor phase separation within part of active textures. Here, we investigated solution-processed small molecule solar cells consisting of the previously developed DR3TSBDT and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) after SVA in terms of the vertical gradient crystalline phase in three-dimensional (3D) active layers. These systematic studies of the vertically phase-separated morphology for 3D heterojunction structures clarified in more detail the fundamental mechanisms and dynamics underlying SVA and showed a clear structure-property relationship in related device performance. This not only provided a clear understanding of precise effect of SVA treatments on varied 3D morphological structures, but also a path towards the rational optimization of device performance.

Authors : Ilka M. Hermes (1), Sarah Vorpahl (2), Christopher Gort (1, 3), Rüdiger Berger (1), David Ginger (2), Stefan A.L. Weber (1, 3)
Affiliations : (1) Max Planck Institute for polymer research, Mainz, Germany (2) University of Washington, Department of Chemistry, Seattle, United States (3) Johannes Gutenberg University, Department of Physics, Mainz, Germany

Resume : The organic-inorganic hybrid material methylammonium lead iodide (MAPI) is successfully used as active layer in a new class of photovoltaics called perovskite solar cells. Crystallizing in a perovskite structure it has long been discussed if MAPI is ferroic, a common property in many perovskite minerals. In a recent piezoresponse force microscopy (PFM) study, we imaged a previously unobserved pattern of nanoscale domains in solvent annealed MAPI thin films[1]. We concluded that the domain pattern is connected to ferroelastic domains in MAPI that form due to sample stress during the cubic-tetragonal phase transition after the solvent annealing. This hypothesis was recently supported by others [2, 3]. Here, we used combined variable temperature PFM and local photoluminescence measurements as well as time-resolved Kelvin probe force microscopy to investigate the influence of the ferroelastic domain walls on the charge carrier dynamics within µm-sized MAPI crystals. 1. Hermes, I.M., et al., The Journal of Physical Chemistry C, 2016. 120(10). 2. Strelcov, E., et al., Science Advances, 2017. 3(4). 3. Rothmann, M.U., et al., Nature Communications, 2017. 8.

Authors : F. Bouhjar , B. Marí and B. Bessaïs
Affiliations : a. Institut de Disseny i Fabricació, Universitat Politècnica de València. Camí de Vera s/n 46022 València (Spain) b. Laboratoire Photovoltaïques, Centre de Recherches et des Technologies de l’Energie Technopole H.lif 2050 (Tunisia) c. University of Tunis

Resume : Polycrystalline Cr-doped hematite thin films have been successfully deposited on fluorine-doped tin oxide coated (FTO) glass substrates using the facile hydrothermal method. The hydrothermal bath consists of an aqueous solution containing a mixture of FeCl3.6H2O and NaNO3 adjusted to a pH = 1.5. The samples were introduced in an autoclave and heated for a fixed duration and temperature. Afterward, the hematite coated samples were annealed for a 4 h at 550°C. The Cr doping fractions were varied from 2 to 20 %. All samples were submitted to structural and morphological studies using X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM) and High-resolution transmission electron microscopy (HRTEM). Cr doping induces a slight shift of the main diffraction peaks (012) and (104) towards lower angles. On the other hand, chronoamperometry technique showed that Cr-doped films exhibited higher photoelectrochemical activity relatively to un-doped α-Fe2O3 thin films. Maximum photocurrent densities as well as incident photon conversion efficiencies (IPCE) have been obtained for 16% Cr-doped films in a normal alcaline solution and under standard illumination conditions. We attributed this high photoactivity to the high active surface area of the nanostructured hematite and to the increasing donor density caused by Cr doping.

Authors : Georges BREMOND, Lin WANG, Jean-Michel CHAUVEAU, Corine SARTEL , Vincent SALLET
Affiliations : -Université de Lyon, Institut des Nanotechnologies de Lyon (INL), UMR-5270, CNRS, INSA Lyon, 7 avenue Jean Capelle 69621 Villeurbanne, France - Centre de Recherche sur l'Hétéro-Epitaxie et ses Applications (CRHEA),CNRS UPR10, rue Bernard Grégory, 06560 Valbonne Sophia Antipolis, France - Université de Versailles St Quentin en Yvelines, Groupe d'étude de la matière condensée (GEMaC), CNRS - Université Paris-Saclay, 45 avenue des Etats-Unis, 78035 Versailles, France

Resume : Measurement methods to quantitatively determine the doping in semiconductor nanowires (NW) are strongly requested for understanding the doping incorporation in such one-dimensional structures and so for developing technology which would use them. In the last two decades, scanning capacitance microscopy (SCM) and scanning spreading resistance microscopy (SSRM) based on atomic force microscopy, has emerged as promising tools for two-dimensional high resolution carrier/dopant profiling. These two techniques need of an accurate calibration method for a quantitative doping analysis. A calibration method allowing the quantitative measurement of n-type ZnO doping by SCM and SSRM has been established, based on cross-sectional scanning of multilayers samples with different Ga doping concentration. Then, in order to study ZnO NWs, we have developed a sample preparation method using dip-coating filling of vertical NWs field. The non-intentionally n-type doping (nid) of the ZnO nanowires have been measured using SCM and SSRM, estimated at 2.E18cm-3, explaining the difficulty to turn these NWs into p-type during p-type doping experiments, a crucial problematic in ZnO. Then we have successfully determined the decrease of carrier concentration with respect to the nid core ZnO in antimony (Sb) doping in nid ZnO core/ Sb ZnO shell NW structures. This carrier concentration lowering can be ascribed to the formation of Sb-related acceptors compensating the native donors in ZnO NW. The understanding of this electric compensation mechanism is a clear signature of p-type Sb doping in ZnO NW. This important result opens the way to a possible development of p-type doping in ZnO.

Authors : Yasushige Mori, Asako Osaki, Katsumi Tsuchiya
Affiliations : Doshisha University, Department of Chemical Engineering and Materials Science

Resume : The solar cells using the electrode consisted of titania nanoparticles (NPs), such as dye-sensitized solar cells or perovskite solar cells, sometimes have very low power conversion efficiencies due to the lack of homogeneity of the layers comparing with that prepared by chemical or physical vaper deposition methods. It is important for improving power conversion efficiencies of solar cells to develop the method to prepare more homogenous titania NPs layer, and also to propose the technique to analyze the homogeneity of the layer, for example, Kelvin probe force microscopy (KPFM). In this study, we used KPFM with the frequency modulation system and measured the local working function of the thin layer of titania NPs prepared by the electrophoretic deposition method. When UV-light was irradiated on the titania NPs layer, the local surface potential of the layer increased immediately. After turn off the light, the local surface potential generally decreased and settled on the original potential at dark state. We found the local surface potential of this layer was more homogeneous than that prepared by the ordinal squeegee method.

Authors : Nicolas F. Martinez and Louis Pacheco
Affiliations : Concept Scientific Instruments, 2 Rue de la Terre de Feu, 91940 Les Ulis, France

Resume : Over the past 30 years, Atomic Force Microscopy has evolved from a microscope to measure just the surface topography to a wide variety of measurement modes that provides a way to characterize other atomic interactions or physical properties like magnetic field, electric field, nanoscale dissipation processes, thermal conductivity, electrical conductivity, resistance, surface potential, piezoresponse, Young modulus,… Electrical nanocharacterization with AFM has emerged as a powerful tool to map electrical properties at the nanoscale, like surface potential (work function) and conductivity. However, traditional setups in AFM make difficult to obtain accurate and repeteable results over several types of samples. In this contribution we will show the capabilities new developed AFM modes: High Definition Kelvin Force Microscopy (HD-KFM), ResiScope, Soft-Resiscope and Scaning Microwave that overcome the intrinsic difficulties of electrical nanocharacterization with AFM. This two techniques have been applied on a wide variety of substrates: bidimensional materials, like graphene or molibdene disulfide, organic and peruvskite solar cells or nanoparticles providing high stability, sensitivity and lateral resolution.

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Novel SPM Methods for Energy Materials II : David Ginger
Authors : Stephen Jesse
Affiliations : Center for Nanophase Materials Sciences and the Institute for Functional Imaging of Materials, Oak Ridge National Laboratory

Resume : Over the last 30 years, scanning probe microscopy has emerged as a powerful tool for imaging structure and functionality of matter on nano- and atomic scales. In the most general terms, SPM images represent the convolution of dynamic interactions at the tip-surface junction as interrogated through chosen measurement protocol. Correspondingly, much of the attention of SPM practitioners was aimed at the development of progressively more complex protocols for excitation and detection, starting from original static modes in contact AFM, to lock-in and phase-locked loops in single frequency SPMs, to multifrequency methods of the last decade. The increase in sensitivity these developments have afforded have enabled access to capture new material functionalities. Along with this added capability is the requirement that the myriad of possible nanoscale phenomena be differentiated. Part of this talk will discuss the development of contact mode kelvin force probe microscopy (cKPFM) used to measure the induced charge on surfaces by a biased tip and differentiate this from piezo electric effects and ferroelectric switching thereby enabling more reliable measurements of nanoscale material behavior especially those related to charge migration. However, even such complex measurements invariably rely on a predefined model for processing the information flow, as limited by data analysis electronics. In this this presentation, I will also discuss existing approaches for information processing in SPM and introduce an approach for full information capture in SPM based on recording and more complete analysis of the data stream from photodetector. This general-mode (G-Mode) SPM is illustrated for classical SPM modes such as intermittent contact mode SPM and Kelvin probe microscopy. The analysis of the information allows deducing in which cases classical signal processing allows unbiased representation of the tip-surface interactions and which it incurs significant information loss. These approaches for full mapping of the frequency response provides a complete view of tip-surface interactions and also enables far higher temporal resolution than existing methods. Finally, perspective and critical needs for the full information analysis imaging in SPM are presented, and some possible solutions based on crowd sourcing data analytic platforms are discussed. This research is supported by and performed at the Center for Nanophase Materials Sciences, which is sponsored at Oak Ridge National Laboratory by the Scientific User Facilities Division, BES DOE.

Authors : Tricard S.
Affiliations : LPCNO, INSA, CNRS, Université de Toulouse, 31077 Toulouse, France.

Resume : The elaboration of hybrid molecule/nanoparticle self-assemblies is a first step towards nanoelectronic systems, where the charging energy of the nanoparticles is tuned by the nature of the molecules. We recently developed simple chemical tools to tune Coulomb blockade in dense three-dimension self-assemblies of metallic nanoparticles. Several techniques give the possibility to measure charge transport in such systems (interdigitated combs, evaporated electrodes, dielectric spectroscopy, etc.) and to follow the response of a given sample to variation of external parameters (temperature, light, magnetic field). However, the experimental variability of such techniques is often too high to reliably compare different samples, and even more samples of different nature. To circumvent this drawback, we developed an original approach combining conductive AFM measurements and statistical analysis. Thanks to it, we were able to relate information between charge transport at the nanoscale and the structural geometry of the molecules, in the Coulomb blockade regime. This presentation will describe the advantage of this approach using a scanning probe technique, and its complementarity to other charge transport measurements at larger scales. Towards energy applications, the electrical behavior of self-assembled systems responsive to light will be described under irradiation.

Authors : Alexander Tselev
Affiliations : CICECO-Aveiro Institute of Materials and Department of Physics, University of Aveiro, 3810-193 Aveiro, Portugal

Resume : Near-field microwave microscopy is an emerging tool exploiting reflection of GHz-frequency microwaves from a sharp scanning probe in contact with or in the vicinity of an object. Dependence of the microwave reflection from material properties allows non-destructive mapping and quantitative characterization of dielectric permittivity and conductivity with a spatial resolution as high as ~50 nm. The technique is versatile and can be straightforwardly applied to investigations of solids as well as liquids. In this talk, we illustrate the power of this technique in applications to ferroelectric thin films and in-situ imaging of processes in electrolytes. Ferroelectric as well as multiferroic materials and structures are currently considered for electrocaloric and photovoltaic applications. Using the technique, we were able to show that spontaneous and recorded domain walls in thin films of Pb(Zr0.2Ti0.8)O3 and BiFeO3 exhibit large conductance at GHz frequencies being insulating at dc, which points to the existence of free-carrier clouds at the walls. Simultaneous detection of piezo- and microwave responses separates relaxations of polarization and injected charges. We also demonstrate in situ imaging of dendrite formation near electrodes in a liquid electrolyte. This work was sponsored in part by DMSE, BES, US DOE. SPM was conducted at ORNL?s CNMS, sponsored by SUFD, BES, US DOE. 1. A. Tselev, et al., ACS Nano 10, 3562 (2016) 2. A. Tselev, et al., Nat. Comm. 7, 11630 (2016)

Authors : R. Heiderhoff, T. Haeger, K. Dawada, and T. Riedl
Affiliations : University of Wuppertal, Institute of Electronic Devices, Rainer-Gruenter-Str. 21, 42119 Wuppertal, Germany

Resume : Understanding thermal transport in thin-films on the nanometer scale is essential for solar cells, thermoelectric generators, batteries, etc.. Consequently, advanced Scanning Probe Microscopy methods and novel approaches are mandatory. Within this contribution, the transition from diffusive in-plane heat flux to a ballistic Stefan?Boltzmann like out-of-plane heat transport will be studied in thin, amorphous TiO2 films prepared by atomic layer deposition. We employ Scanning Near-field Thermal Microscopy (SThM), which as we will demonstrate is perfectly suited to assess thermal transport in ultra-thin layers as the width of the heater/thermometer is very small. With the support of equivalent thermal circuit modelling we show, that coating of a substrate with thin films of higher thermal conductivity than that of the substrate does not immediately lead to an increase of the heat flux from a nanoscale heat source. On the contrary, the heat transport can be significantly reduced at certain layer thicknesses. Besides, already at film thicknesses, which are much larger than the phonon mean-free path, the description of thermal transport in this assembly has to take phonon scattering as well as ballistic thermal phonon transport phenomena into account. Our results are expected to significantly influence the thermal management and reliability investigation using thin film technologies in energy applications.

Authors : R. Borgani, and D. B. Haviland
Affiliations : Nanostructure Physics KTH Royal Institute of Technology

Resume : Intermodulation Electrostatic Force Microscopy (ImEFM) has been used for imaging the contact potential difference Vcpd on organic photovoltaic materials, as well as nanocomposite insulators and 2D electron gases. We now propose a time resolved variant of ImEFM that is able to image the rise and fall time of Vcpd, in response to an external illumination coherent with the tip oscillation. The technique uses the intermodulation of the cantilever mechanical oscillation frequency with the modulation frequency of a luminous excitation of the sample to extract the dynamics of the charge carriers. The method relies on a calibrated measurement of force and the intermodulation products are measured near the mechanical resonance, where the force sensitivity is close to the thermal limit. We describe the theory of the technique, its validation with simulations, and we show the first experimental results.

SPM on fuel cells : Phil Leclere
Authors : J.P. Cosas Fernandes, V.H. Mareau and L. Gonon
Affiliations : Univ. Grenoble Alpes, CEA, CNRS, INAC, SYMMES, F-38000 Grenoble

Resume : Proton-Exchange Membrane Fuel Cells (PEMFC) has emerged as a promising emission-free energy conversion device. We work on a new generation of hybrid membrane for fuel cell based on commercial sPEEK membrane modified with a Sol-Gel (SG) phase (mechanical and chemical stabilization). To study the process-structure-properties relationship of our alternative membranes we had to develop an innovative approach of characterization that couples Atomic Force Microscopy (AFM) and Raman microspectroscopy with an unusual sample preparation technique for polymer membranes: cryo-ultramicrotomy without epoxy embedding. Here we demonstrate the powerfulness of colocalized AFM-Raman analysis, revealing the inner structure of hybrid polymer membranes by probing the cross-section (accessing both bulk and surfaces). We obtained quantitative data on the diffusion of SG precursors through the host sPEEK membrane, and complementary AFM and Electron Microscopy (EM) measurements on the morphology of the SG phase. Co-localized analyses revealed the formation of a depleted skin layer (lower SG concentration) about one micrometer thick on both sides of the membrane (SG being homogeneously distributed otherwise). The diffusion of water-soluble species from the SG phase up to the cross-section surface, and the resulting crystallization of these species (morphologically, mechanically and chemically characterized by co-localized AFM-Raman), only observed for the membrane at the first step of fabrication, gave us an insight on the SG condensation process through the fabrication steps. Finally, the nano-mechanical data collected by AFM revealed a densification of the SG phase through the fabrication process.

Authors : Michael Handl, Tobias Morawietz, Claudio Oldani, K. Andreas Friedrich, Renate Hiesgen
Affiliations : University of Applied Sciences Esslingen,Kanalstraße 33, 73728 Esslingen, Germany; University of Applied Sciences Esslingen,Kanalstraße 33, 73728 Esslingen, Germany; , Solvay Speciality Polymers, R&D Center, Viale Lombardia 20, 20021 Bollate, Milan, Italy; German Aerospace Center, Institute of Engeneering Thermodynamics, Pfaffenwaldrig 38-40, 70569 Stuttgart, Germany; University of Applied Sciences Esslingen,Kanalstraße 33, 73728 Esslingen, Germany;

Resume : The performance of polymer electrolyte fuel cells and electrolysers, depends on the nanostructure of its components. In particular, the nanostructured electrodes have an important impact on cell performance and degradation. In working fuel cell electrodes, the ionomer layers are in the range of 4-20 nm and fall within the range of ultrathin films. In this contribution, the analysis of cross-sections of fuel cell electrodes investigated by material-sensitive AFM will be presented. The high contrast between the ionomer- and the Pt/C phase in adhesion force mapping allowed studying the distribution and thickness of the ionomer layers that cover the Pt/C agglomerates. After operation, significant thinning of the ionomer layers, depending on the location within the MEA and the preparation, was found. Differences of the swelling behavior prior and after operation were assigned to ionomer degradation. The average ionomer layer thickness was found to correlate with the macroscopic degradation of fuel cells. As the thickness of the ionomer layer that covers the catalyst agglomerates is crucial for fuel cells performance, ultra-thin model layers of different commonly used ionomers (i.e. Nafion®, Aquivion® PFSA) and alternative materials were examined on their morphology and phase-separation on various substrates of different surface energies. Conductive AFM allowed investigations of through- and in-plane conductivity in dependence of the film thickness of these ultrathin films.

Authors : Yue Shen1, Ying Wang2, Chunxi Hai1, Yuan Zhou1, Jun Hu2, Yi Zhang2
Affiliations : 1 Key Laboratory of Salt Lake Resources Chemistry of Qinghai Province, Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, Xining, Qinghai 810008, China; 2 Key Laboratory of Interfacial Physics and Technology of Chinese Academy of Sciences, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, China

Resume : The reduced form of graphene oxide (GO) is an attractive alternative to graphene for producing large-scale flexible conductors and for creating devices that require an electronic gap. By controlling the reduction degree of GO, varied electronic properties of graphene which can be applied in the construction of electronics can be obtained. Herein, scanning polarization force microscopy (SPFM) is used to distinguish the one-atom-thick GO and reduced GO (rGO) sheets and monitor the thermal reduction process in-situ. The reduction degree related electrostatic properties such as the charge storage character of nanostructured and partially reduced GO sheets are further studied by using the scanning probe microscopy (SPM) based charging and discharging technique and the sample-charged mode SPFM (SC-SPFM). Furthermore, charged nanostructures with controllable geometry and charge density are achieved with the thermal nanolithography method. And such charged nanostructures could be used to construct charge gated graphene nanoelectronics. In the last part, we will briefly report the effects of injected charges to adjacent rGO sheets, such as the inhomogeneous charges distribution in rGO sheet induced by adjacent charged ones and the charges transfer behavior between physically separated rGO sheets on insulating substrates. These effects are of great value for rational design of graphene nanoelectronics with desired functionality.


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Symposium organizers

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Philippe LECLEREUniversity of Mons (UMONS)

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Rüdiger BERGERMax Planck Institute for Polymer Research

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Yi ZHANGShanghai Institute of Applied Physics

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