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FUNDAMENTALS

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X-ray based techniques for sustainable energy related materials

The Symposium is devoted to the presentation of original contributions on fundamental research of the surface, interface and bulk properties of the energy related materials using the X-ray based state of the art techniques.

Scope

The sustainable energy related materials research is now the top priority among the material research community. The X-ray based techniques (photon in - photon out and/or photon in - electron out) are instrumental to study the physiochemical properties of materials. In particular, the characterization techniques such like XPS, XAS, PEEM, LEEM, LEED, XRD, XES, etc. can be used to study the spectro-microscopic and crystallographic properties of sample surface and bulk.  

The X-ray based characterization techniques can inform about the electronic and/or chemical properties of the materials and their effect on the performance of the devices. Moreover, the dependence of physiochemical properties on the morphology and size of the material can also be analyzed. 

The techniques used in equilibrium can only inform about the static physiochemical properties while in operando conditions the mechanism of various process deciding the activity of the materials can be explained.

The symposium aims to cover four main divisions of sustainable energy materials research such as photoelectrochemical water splitting devices, solar cells, Li ion batteries, and fuel cells. Papers related to all aspects of the fundamental properties of the energy related materials used in the above mentioned devices and investigated by laboratory and synchrotron based X-ray methods are invited.

Hot topics to be covered by the symposium:

  • Effect of surface and interface properties on photoelectrochemical water splitting
  • X-ray based characterization of contemporary photovoltaic (perovskite solar cell, CIGS, III-V  solar cells)
  • Solid electrolyte interphase, material development, stability, electrolyte for Li ion battery
  • Development of materials for fuel cells and their X-ray based characterization methods
  • Ex-situ, in-situ and in-operando studies of photocatalysts, Li ion batteries and solar cells 
  • Development of new materials for sustainable energy technology
  • Investigation of surface and interface of energy materials using various X-ray based techniques
  • Fundamental electronic properties of materials

List of invited speakers (confirmed):

  • Frank DE GROOT
    X-ray spectroscopy of energy-related materials
  • Marko HUTTULA
    Unveiling physical mechanisms of catalytic functionalities via in house XAS and synchrotron PEEM
  • Chris BLACKMAN
    Correlation of Optical Properties, Electronic Structure and Photocatalytic Activity in Nanostructured Tungsten Oxide
  • Regan G. WILKS
    Metal Halide Perovskites Illuminated by X-ray Spectroscopies - Results and Challenges
  • Björn WICKMAN
    X-ray characterization of Pt3Y alloy catalyst for low temperature fuel cells
  • Gianluca CIATTO
    Synchrotron radiation investigation of III-V semiconductor and oxide components for photovoltaics
  • David J. PAYNE
    In-situ spectroscopic techniques for understanding surfaces
  • Wolfram JAEGERMANN
    Performance of Li-ion batteries as studied by X-ray spectroscopies: contribution of electronic and ionic factors
  • Moniek TROMP
    Operando X-ray Absorption Spectroscopy probing Dynamic Processes in Batteries
  • Jakub DRNEC
    X-Ray Insight Into Fuel Cell Catalysis: Operando Studies of Model Surfaces and Working Devices
  • D. D. SARMA
    Space-resolved photoelectron spectroscopy of energy materials with tunable x-rays
  • Yaroslava LYKHACH
    Model approach to fuel cell catalysis
  • Malgorzata WIERZBOWSKA:
    XANES in perovskites and GaN under pressure, theory compared to experiment

Scientific Committee Members:

  • Silma Alberton  (Brazil)
  • Susana Darma (Germany)
  • Jan Ingo Flege (Germany)
  • Karsten Henkel (Germany)
  • Niroj Kumar Sahu (India)
  • Petr Novak (Switzerland)
  • Sandeep Yadav (Germany)

Publication:

Journal: Applied Surface Science (Impact Factor: 5.155)
Special Issue Title: X-ray based techniques for sustainable energy related materials
Guest Editors: Dr. Malgorzata Kot, Dr. Chittaranjan Das, Dr. Mykhailo Vorokhta
Managing Guest Editor: Dr. Malgorzata Kot
Manuscript submission opening: 20-Sept-2019
Manuscript submission deadline: 30-Nov-2019
Acceptance deadline: 28-Feb-2020
When submitting the papers, authors must select “VSI: X-rays in energy res” as the article type.

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13:45 OPENING REMARKS    
 
Session I : Małgorzata Kot
14:00
Authors : Frank de Groot, Ahmed Ismail, Yohei Uemura
Affiliations : Inorganic Chemistry and Catalysis, Utrecht University, Universiteitsweg 99, 3584 CG Utrecht, Netherlands.

Resume : X-ray spectroscopy is an important probe to study photocatalytic materials. We use x-ray absorption spectroscopy (XAS) and resonant inelastic x-ray scattering (RIXS) to probe the electronic structure of the transition metal ions in the NiFeOOH, Fe2O3 and CuWO4-based photocatalytic systems. With operando hard x-ray XAS at the SLS synchrotron we study with the metal K edges the nature of the Ni and Fe sites under operando (photo)electrochemical conditions. Femtosecond time-resolved XAS and RIXS is used at the SACLA and Pohang XFEL x-ray FEL sources in combination with high-harmonic laser experiments. The fs-XAS and fs-RIXS experiments show the changes of the electronic structure of the Fe2O3 and CuWO4 photo-excited states. We observe a very fast electronic change at the copper site in CuWO4 upon laser excitation from the valence to conduction band.

U.1.1
14:30
Authors : Juhan Matthias Kahk, Johannes Lischner
Affiliations : Imperial College London

Resume : Core-electron X-ray photoemission spectroscopy is a powerful experimental technique to gain information about chemical reactions on catalytic surfaces. Interpreting experimental spectra, however, is often challenging and theoretical modelling of core-electron binding energies is required to meaningfully assign peaks to adsorbate species. In this talk, I will present a novel first-principles modelling strategy to calculate core-electron binding energies of molecules on metallic surfaces. Specifically, we combine plane-wave/pseudoptential DFT calculations of surface slab models for geometry optimizations with all-electron Delta-SCF calculations on cluster models for determining accurate core-electron binding energies. This approach is computationally efficient and yields good agreement with experimental measurements for a wide range of adsorbates on copper(111) surfaces.

U.1.2
14:45
Authors : Yannick Hermans, Andreas Klein, Henrik Junge, Thierry Toupance, Wolfram Jaegermann
Affiliations : Y. Hermans; Prof. Dr. A. Klein; Prof. Dr. W. Jaegermann: Surface Science TU Darmstadt Otto-Berndt-Str. 3, 64287 Darmstadt (Germany); Thierry Toupance: Molecular Chemistry and Materials, ISM UBordeaux ISM, UMR 5255 CNRS, 351 Cours de la Libération F-33405 Talence Cedex (France); Henrik Junge: Leibniz-Institut für Katalyse e.V. Universität Rostock Albert-Einstein-Str. 29a, 18059 Rostock (Germany)

Resume : CuFeO2 has been recognized as a potential photocathode for photo(electro)chemical (PEC) water splitting, because of its reduced band gap of 1.5 eV, its suitable conduction band minimum, its good electronic properties and because it is made from earth-abundant materials. However, only limited photocurrents have been achieved so far with CuFeO2 based photocathodes. The limited hydrogen evolution performance may be due to surface state induced Fermi level pinning according to a recent study in which the photoelectrochemical properties of CuFeO2 were probed through a varied set of redox systems. We have studied whether the creation of anisotropic CuFeO2 heterostructured powders with suitable contact materials would induce an enhanced unbiased water photoreduction efficiency. However, none of the heterostructured powders gave rise to any gas evolution after visible light exposure. Through these results we believed that there was an intrinsic problem with CuFeO2, which we analyzed through so-called interface experiments, i.e. a combination of stepwise thin film sputtering and photoelectron spectroscopy. Particularly, we analyzed the Fermi level tunability in CuFeO2 as well as the induction of chemical changes. In addition, the interaction between the CuFeO2 surface and water was studied. The results indicate the occurrence of Fermi level pinning, as well as the reduction of Fe3+ to Fe2+, which may be the origin of the Fermi level pinning and which was also recently observed for hematite based interface experiments. Hence, the photo(electro)chemical water splitting performance of CuFeO2 may be limited due to an intrinsic bulk problem.

U.1.3
15:00
Authors : Kim-Chi Le, Madeleine Han, Clément Larquet, Sophie Carenco, Victor Pinty, Benedikt Lassalle-Kaiser
Affiliations : Madeleine Han; Victor Pinty; Benedikt Lassalle-Kaiser: Synchrotron SOLEIL, l’Orme des Merisiers, 91192, Gif sur Yvette, France. Kim-Chi Le; Madeleine Han; Clément Larquet; Sophie Carenco: Sorbonne Université, CNRS, Collège de France, Laboratoire Chimie de la Matière Condensée de Paris, 4 Place de Jussieu, 75005 Paris, France.

Resume : The development of catalysts that can perform electrical-to-fuel reactions requires a deep understanding of their structures, catalytic behaviour and failure modes. Reactions such as the Oxygen Evolving Reaction (OER), Hydrogen Evolving Reaction (HER) or CO2 Reducing Reaction (CRR) all require metal-based catalysts, which undergo electronic and structural changes during along these reactions. Observing these changes under catalytic conditions is of critical importance to understand how the catalysts are activated and what species are active. While X-ray absorption spectroscopy is becoming more and more common to probe transition metals in the hard X-ray range, little work has been done at lower energies under working conditions. In this talk, we will present a spectroelectrochemical cell that allows recording XAS data in the tender and soft X-ray energy ranges. This fluorescence mode cell fits the primary vacuum chamber of the LUCIA beamline and allows collecting data while flowing a liquid solution and/or applying a constant electrochemical potential. After describing the technical design of the cell, we will present a few examples of scientific cases that were studied using this cell. XAS spectra at the sulphur K-edge were recorded on sulphides and oxysulfides of transition metals that are active for the HER and/or ORR were studied under basic/acidic conditions and under applied potential. These examples will highlight the possibilities offered by tender X-ray spectroscopic techniques for the study of electrochemical reactions under in situ or operando conditions.

U.1.4
15:15
Authors : I.A. Kowalik, (1) M. A. Niño, (2) Juwon Lee, (3) N.G. Subramaniam, (3) T.W. Kang (3), D. Arvanitis (4)
Affiliations : (1) Institute of Physics, Polish Academy of Sciences, Warsaw, Poland (2) IMDEA Nanociencia, Campus de Cantoblanco E-28049 Madrid, Spain (3) Quantum Functional Semiconductor Research Center and Nano Information Technology Academy(NITA), Dongguk Univ., 26 Phildong 3ga Chung gu, Seoul, 100-715, Rep. of Korea (4) Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden

Resume : We present X-ray Absorption Spectroscopy (XAS) results on materials suitable for magnetic applications. We focus on FenN (n=1-4) nanocrystals on GaN [1] and Bi doped ZnO thin films [2]. These materials have been found to exhibit a stable magnetic response at room temperature making them suitable for spintronic devices. [1,2] Measurements were performed both at the MAX-IV [3] and Soleil laboratories. Our XAS results are analyzed using the FEFF9 package, an ab initio self-consistent, multiple scattering code for the simultaneous calculations of excitation spectra and electronic structure. [4] For FenN we have calculated the theoretical FEFF XAS spectra for the various FenN phases, n=1-4 at the N K-edge. The theoretical spectra do exhibit fine structure features, which allow for the identification of specific FenN phases in the experimental spectra. In the case of Bi doped ZnO the theoretical spectra do allow to identify structural variations in the near surface region of the ZnO:Bi films versus the bulk. [2] For this system, the x-ray magnetic circular dichroism measured at the O K-edge can also be reproduced by the theoretical spectra. The FenN and ZnO:Bi work is supported by the Polish NCN (DEC-2011/03/D/ST3/02654) and the Swedish C. Tryggers Foundation (CTS 16:32). The Spanish MICCINN/MINECO (MAT2013-49893-EXP and MAT2014-59315-R) did also support the FenN work. The Korean NRF (NRF-2016R1C1B1014103) did also support the ZnO:Bi work. [1] I. A. Kowalik, A. Persson, M. Á. Niño et al. Physical Review B 85, 184411 (2012) [2] J. Lee, N.G. Subramaniam, I. A. Kowalik et al. Scientific Reports 5, 17053 (2015) [3] I. A. Kowalik Acta Phys. Pol. A 127, 831 (2015) [4] J. J. Rehr and R. C. Albers, Rev. Mod. Phys., 72, 621 (2000).

U.1.5
15:30 Coffee break    
 
Session II : Chittaranjan Das
16:00
Authors : Marko Huttula
Affiliations : University of Oulu, Faculty of Science, Finland

Resume : Novel energy materials are in the heart of research aiming to future sustainability. The pursuit of ultimate performance requires physical mechanism explorations to deepen understanding of material functionality, to optimize materials utilities and to guide synthesis. Here, we present a brief review of using in-house x-ray absorption (XAS) and synchrotron-based photoemission electron microscopy (PEEM) techniques to unveil physical origins enabling the advanced electro- and photo- catalytic abilities within our latest developed materials. Recorded on a table equipment, the XAS at K-edge of 3d transition metals were compared with surface sensitive XPS results for electrocatalysts of MnCo2O4 spinel, LaMnO3+δ perovskite, and Co‐Fe‐Al hydroxide. Results show that the overall stability and catalytic activity rely on the intrinsic properties of the host, while the surface states and additional 3d vacancies will serve distinct functionalities during electrocatalysis. A simultaneous microscopic and spectroscopic determination through PEEM provides electronic signature of metallic heterojunction contact between the Ni particle to the semiconductive MoS2 layered crystals bridged by the gold nanoglue. Enhanced photocatalytic ability of the heterojunction arises from the band alignment at the Ni/MoS2 interface which enable charge migration from the MoS2 to the Ni side and prohibits electron-hole recombination. An outlook of using in situ spectroscopic and microscopic x-ray combination for energy material characterizations is presented.

U.2.1
16:30
Authors : Chris Blackman
Affiliations : Department of Chemistry, University College London, WC1H 0AJ c.blackman@ucl.ac.uk

Resume : We have found that the electronic structure, defect chemistry, optical bandgap and photocatalytic activity of nanostructured tungsten oxide (WO3-x), deposited using a chemical vapour deposition method, varies progressively with the length of the deposited nanorods. Nanorods less than 1 µm in length showed a widening of the optical bandgap (up to 3.1 eV), more disorder states within the bandgap, an absence of reduced tungsten cation states, and increased photocatalytic activity for destruction of a test organic pollutant (stearic acid) compared to nanorods of 2 µm length or greater which possessed bandgaps close to the bulk value for tungsten oxide (2.6 – 2.8 eV), the presence of reduced tungsten states (W4+), and lower photocatalytic activity. The results indicate that for maximum photocatalytic performance in organic pollutant degradation, tungsten oxide should be engineered such that the bandgap is widened relative to bulk WO3 to a value above 3 eV; although less photons are expected be absorbed, increases in the over-potential for oxidation reactions appear to more than offset this loss. It is also desirable to ensure the material remains defect free, or the defect concentration minimised, to minimise carrier recombination.

U.2.2
17:00
Authors : Rik Mom, Lorenz Frevel, Juan Velasco-Velez, Axel Knop-Gericke, Robert Schlögl
Affiliations : Fritz Haber Institute of the Max Planck Society, Faradayweg 4-6, 14195 Berlin, Germany

Resume : Knowledge of the oxidation state and structure of electrocatalyst surfaces under operating conditions is essential for proper understanding of their function. X-ray photoelectron spectroscopy (XPS) is ideally suited for providing such surface specific information, yet cannot probe through the electrolyte. Here, we present a new approach to overcome this challenge, and its application to platinum electrocatalysts [1]. To interface our near-ambient pressure XPS end station with an electrochemical cell, we sandwiched the Pt particles between a proton exchange membrane and graphene. Electrolyte permeates from the back of the membrane to the confined layer around the catalyst, while the graphene minimizes evaporation into the XPS chamber. This results in the formation of a thin liquid electrolyte layer around the catalyst. Due to the minimal thickness of the electrolyte layer and the electron transparency of the graphene, the Pt catalyst can be probed by XPS. Using Pt 4f and O K-edge spectra, we characterize the potential-dependent surface state of Pt nanoparticles and ultrathin films. We show that Pt4+ is part of all oxides formed on the Pt surface, even at the onset of oxide formation. Time-resolved studies show that the oxidation and reduction kinetics are faster for nanoparticles than for ultrathin films or planar electrodes: even bulk oxide growth occurs on the sub-minute timescale. [1] Mom et al., J. Am. Chem. Soc., 2019, 141 (16), pp 6537–6544

U.2.3
17:15
Authors : Janis Timoshenko, Hyo Sang Jeon, Beatriz Roldan Cuenya
Affiliations : Department of Interface Science, Fritz-Haber-Institute of the Max Planck Society, 14195 Berlin, Germany

Resume : Extended X-ray absorption fine structure (EXAFS) spectroscopy is a premier method for studies of catalysts (and other functional materials) due to its element-specificity and unique sensitivity to the local environment around the absorbing atoms. Moreover, EXAFS analysis is well suited for in-situ and operando investigations, providing possibility to track the changes in working catalyst structure. Unfortunately, the intrinsic heterogeneity and enhanced disorder, characteristic for catalytic materials under harsh reaction conditions, as well as low signal-to-noise ratio that is common for EXAFS spectra, acquired in-situ, hinder the application of conventional data analysis approaches. Here we address this problem, by complementing experimental data interpretation with theoretical simulations of catalyst structure and machine learning methods. We demonstrate that an artificial neural network (NN), trained on theoretical EXAFS data obtained in molecular dynamics simulations, can be successfully used to establish the relationship between EXAFS features and structural motifs in metals as well as oxide materials. The trained NN can then be employed to decipher experimental in-situ EXAFS spectra. Here we apply this approach to reveal from time-dependent EXAFS data the details of structural evolution and brass alloy formation during the electrochemical reduction of copper-zinc nanoparticles, a promising catalyst for CO2 conversion to higher-value chemicals and fuels.

U.2.4
17:30
Authors : Ivan Khalakhan, Marco Bogar, Heinz Amenitsch
Affiliations : Charles University, Faculty of Mathematics and Physics, Department of Surface and Plasma Science, V Holešovičkách 2, 18000 Prague, Czech Republic; Graz University of Technology, Institute for Inorganic Chemistry, Stremayrgasse 9, 8010 Graz, Austria; CERIC-ERIC c/o Elettra Synchrotron, S.S. 14 Km 163.5, 34149 Basovizza, Trieste, Italy

Resume : Platinum-nickel bimetallic alloy catalyst has attracted enormous attention in the field of proton exchange membrane fuel cells (PEMFCs). It is suggested to replace seemingly indispensable platinum cathode catalyst. Along with reducing the cost, the addition of Ni to Pt induces catalyst electronic structure so that it improves sluggish kinetics of the oxygen reduction reaction (ORR). On the other hand, bimetallic catalyst is a very complex system, which often does not maintain its surface structure and chemical integrity under specific reaction conditions. Since the cathode catalyst in PEMFCs needs to withstand corrosive conditions under high potentials, the degradation of catalyst under specified operating conditions has become one of the most critical issues in fuel cell research. Herein, we applied in situ grazing incidence small angle X-ray scattering (GISAXS) technique to investigate morphology evolution of PtNi model thin film catalyst during potentiodynamic cycling in an aqueous acidic electrolyte which simulates the working conditions of a real fuel cell device. GISAXS provides the catalyst’s in-depth mean structure variation by probing a large sample area in a relatively short time ensuring very good statistical accuracy. Along with electrochemical atomic force microscopy (EC-AFM) which, in turn, gives local surface information about morphology changes on the nanometer scale a comprehensive study of the PtNi catalyst degradation process has been performed.

U.2.5
 
Poster session : Mykhailo Vorokhta
18:00
Authors : E. Guziewicz*, B. A. Orlowski, A. Reszka, M.A. Pietrzyk, B.J. Kowalski
Affiliations : Institute of Physics Polish Academy of Sciences, Al. Lotnikow 32/46, PL-02 668 Warsaw, Poland

Resume : The PbTe is a IV-VI narrow-gap semiconductor, which is considered as a suitable material for infrared detectors, lasers and thermoelectric devices. Introducing Sm atoms into Pb1xGexTe lattice we make a system belonging to the family of diluted magnetic semiconductors, in which Sm magnetic ions interact ferromagnetically via the RKKY mechanism. In this study we doped a surface region of Pb0.97Ge0.03Te by deposition of Sm atoms under UHV conditions and annealing in order to facilitate Sm diffusion into the crystal. The experiment was carried out in the HASYLAB synchrotron radiation laboratory in Hamburg, Germany. The Fano resonance photoemission study of the Sm/Pb0.97Ge0.03Te was performed in order to determine the contribution of both Sm2+ and Sm3+ to the valence band of the system. Additionally, the Pb5d10 electron states were analyzed in order to monitor the process of introduction of Sm into the substrate crystal host lattice. The results show that the thermal treatment of Pb0.97Ge0.03Te at 250degC leads to conversion of Sm2+ to Sm3+. [1] [2] Guziewicz, E., Orlowski, B.A., Kowalski, B.J. et al., Appl. Surf. Sci. 282, 326-334 (2013). [2] B.A. Orlowski, E. Guziewicz, B.J. Kowalski, et al., Rad. Phys. Chem. (2019), in print. Acknowledgements. The work was supported by the Polish National Centre for Research and Development (NCBiR) through the project PBS2/A5/34/2013.

U.P.1
18:00
Authors : Agar L. 1, 3, D. Bradai1,2 ; M. Abdesslam1,3, , Y. Bourezg1, A.C Chami1, C. Mocuta2, D. Thiaudiere2, C. Speisser3, C. Bouillet4, F. Le Normand F.3
Affiliations : 1 Faculty of Physics, University of Sciences and Technology Houari Boumediene, Algiers, Algeria 2 Synchrotron SOLEIL, L’Orme des Merisiers, Saint-Aubin, 91192 Gif-sur-Yvette Cedex, France. 3 ICube, UMR 7357 CNRS-Université de Strasbourg, 67037 Strasbourg, France 4 IPCMS, UMR 7504 CNRS-Université de Strasbourg, Strasbourg, France.

Resume : The formation of GaN nanocrystals in SiO2/Si and SiNx/Si wafers implanted with Ga and N ions was analyzed through high resolution transmission (HRTEM) and scanning (SEM) electron microscopies, X-ray photoelectron (XPS), synchrotron radiation- X-ray absorption spectroscopy (EXAFS) and synchrotron radiation- X-ray diffraction (XRD). GaN nanocrystals were formed into SiO2/Si by implantation of Ga and N and subsequent annealing under N2 flux at 950°C for at least 60 minutes. EXAFS allowed the detection of Ga-N bonds. High resolution transmission electron microscopy and high energy X-ray diffraction revealed the presence of GaN clusters besides some Ga nanoparticles and Ga2O3 nanostructures present at the surface of the sample.

U.P.2
18:00
Authors : Ahmad Ghamlouche (1), Chittaranjan Das (1), Julia Maibach (1)
Affiliations : 1 Institute for Applied Materials - Energy Storage Systems

Resume : Photoelectron spectroscopy has become a widely used tool for characterizing and understanding interfacial phenomena in lithium ion batteries such as the solid electrolyte interphase (SEI) formation. The SEI composition depends largely on the electrolyte used in the battery and is also influenced by the binder and active material of the electrode itself. In this work, we study the effects that certain electrolyte-binder interactions can have on Silicon in Silicon/Graphite (Si/C) composite electrodes for lithium ion batteries. Using hard and soft X-ray photoelectron spectroscopy on commercial Si/C composite electrodes, we found that the silicon surface shows an intense Si-component (“SiFx”) at high binding energies that is rarely discussed in literature. The XPS data further indicates that this peak correlates with an intense Na1s-signal, stemming from the cellulose-based binder. The observed correlation of “SiFx” species and Na1s intensity could be explained by a reaction between Si/SiOx, Na-containing binder and HF, which is a likely contamination in fluoride-based electrolytes. Therefore, we systematically analysed the effect of the binders Poly(acrylic acid), Li-Poly(acrylic acid) and Na-Poly(acrylic acid) in combination with 1 M LiPF6 in EC:DMC electrolyte on the surface chemistry of cycled silicon composite electrodes.

U.P.3
18:00
Authors : Liao Yen-Fa (1) ; Chiu Jian-Ming (2) ; Hu Chih-Wei (3)
Affiliations : (1) National Synchrotron Radiation Research Center (2) National Taiwan University of Science and Technology (3) Natianal Chung-Shan Institute of Science and Technology

Resume : The operando synchrotron techniques were performed to dynamic investigate the structure evolutions and the mechanisms of enhancing the electrochemical performance of the LiFePO4 (LFP) positive electrodes in lithium-ion batteries (LIBs). The X-ray absorption near edge structure (XANES) has been demonstrated to be a powerful technique in unraveling the local chemical and electronic structure of battery materials. Operando XANES studies and utilizes a lithium-iron composite electrode optimized for both efficient transports of charge carriers and structure changed from LFPO to FPO. Our XANES show clear valence changed on Fe K edge from LFPO to FPO phase transition after charging-discharging process. Operando X-ray powder diffraction (XRD) also can provide precise phase changed under charging-discharging of LFPO to FPO anode material on LIB. Our operando XRD also consist with the XANES result. However, XRD is long range (total crystal structure) order and XANES show indirect the lithium ion moved out and in process. The X-ray ramen scattering is unique and advantage technique on measure data under special environment especially on lithium K-edge absorption in battery cell. The hybridization state was observed with lithium K and iron M edge on the LFPO material by X-ray ramen scattering. That maybe cause a new state by easy through lithium ion in and out on LFPO material. The XANES, XRD and X-ray ramen scattering were carried out to comparison after charging-discharging process of LFPO battery.

U.P.4
18:00
Authors : Chittaranjan Das, Ahmad Ghamlouche and Julia Maibach
Affiliations : Institute for Applied Materials - Energy Storage Systems Karlsruhe Institute of Technology Eggenstein-Leopoldshafen

Resume : The solid electrolyte interphase (SEI) is an organic-inorganic layer formed from the decomposition of electrolyte on the anode during cycling in a Li ion battery. The chemistry and morphology of the SEI play influence the performance of the Li ion battery. Even though Li ion batteries are the commercial state-of-the-art for electrochemical energy storage, the exact formation mechanism and the chemical nature of the entire SEI layer are still not fully understood. X-ray Photoelectron Spectroscopy (XPS) depth profiling can be used to study both the surface and the bulk chemical and electronic properties of SEI. The commonly used monoatomic Ar sputtering for depth profile alters the original chemical nature of the SEI [1]. However, an Ar ion cluster source can be used to minimize the sputtering damage and retain the chemical nature of the surface intact. In the present work, we evaluate different Ar cluster sizes and energies to find the optimum sputtering conditions to achieve depth profiling without any alteration of the SEI chemistry on graphite electrodes. We found that at a sputtering energy of 6 keV and an Ar ion cluster size of 1000, the SEI overlayer is removed with a minimal change to its surface chemistry. Also, we observed a shift in the binding energy for the SEI components with decreasing thickness, i.e. with increasing material removal. The effectiveness of the sputtering process and its impact on binding energy and chemical composition of the SEI are the open questions that will be discussed in the presentation when using Ar ion cluster sputter depth profiles to study the SEI in Li ion batteries. References [1] S. Oswald, M. Hoffmann and M. Zier, Applied Surface Science 2017, 401, 408–413.

U.P.5
18:00
Authors : Malgorzata Kot, Klaus Müller, Karsten Henkel, and Dieter Schmeißer
Affiliations : Malgorzata Kot: Applied Physics and Semiconductor Spectroscopy, Brandenburg University of Technology Cottbus-Senftenberg, Konrad-Zuse-Straße 1, 03046 Cottbus, Germany; Klaus Müller: Applied Physics and Semiconductor Spectroscopy, Brandenburg University of Technology Cottbus-Senftenberg, Konrad-Zuse-Straße 1, 03046 Cottbus, Germany; Karsten Henkel:Applied Physics and Semiconductor Spectroscopy, Brandenburg University of Technology Cottbus-Senftenberg, Konrad-Zuse-Straße 1, 03046 Cottbus, Germany Dieter Schmeißer: Applied Physics and Sensor Technology, Brandenburg University of Technology Cottbus-Senftenberg, Konrad-Wachsmann-Allee 17, 03046 Cottbus, Germany

Resume : CH3NH3PbI3 (MAPI) based photovoltaic devices showed recently increased long-term stability upon the growth of Al2O3 films prepared by atomic layer deposition at room temperature. Synchrotron radiation based photoelectron spectroscopy is applied to study the initial interaction of these Al2O3 layers on MAPI. We focus on the electronic properties of MAPI and its interface and identify a delicate charge balance between polaronic and excitonic states in MAPI and Al2O3. The polaronic states up-take a charge from the MAPI substrate which is transferred to and stabilized in the excitonic state of Al2O3. The initial Al2O3 film at the MAPI interface shows a high abundance of excitonic states which are assigned to predominately tetrahedral coordinated Al sites. The aforementioned charge transfer further stabilizes a covalent bonding at the interface which is confirmed by Cooper minima found for both, the Pb5d and the O2p states. The presence of Iodine and MA vacancies at the interface is deduced from changes in the core level intensities. Vacancies provide charges to ensure the covalent bonding described above. In addition, they lead to the formation of grain boundaries and a roughening of the interface. Such initial grain boundaries are sealed again by the growth of 2D clusters of Al2O3 and the vacancy concentration is stabilized against interdiffusion (long term instabilities). Further Al2O3 growth causes a self-healing of the structural defects and causes a long-term passivation.

U.P.6
18:00
Authors : Rahim Munir1, Aboma Merdasa1, Katrin Hirselandt1, Oleksandra Shargaieva1, Janardan Dagar1, Florian Mathies1, Roland Mainz1, Eva Unger1,2
Affiliations : 1Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Berlin 12489, Germany 2Chemical Physics and NanoLund, Lund University, P.O. Box 124, Lund 22100, Sweden

Resume : Despite being solution processed, hybrid lead halide perovskite demonstrates excellent optoelectronic properties that have opened the doors to various applications such as photovoltaics, light emission, and photodetection. However, the stability of these materials is one of the critical bottlenecks for its commercialization. Recent reports show the use of larger size cations, such as butylammonium iodide (BAI) and phenyethylammonium iodide (PEAI), cannot be incorporated in the perovskite structure, thereby forms reduced dimensional perovskites (RDP)[1]. These materials exhibit high stability against moisture, heat, and light exposure. There are several methods reported in the literature to fabricate RDPs. The solution to thin film transformation and crystallization of the RDP layer varies with the processing technique, which affects the performance and stability of the device[2]. Here, we employ three different methods of incorporating large cations to fabricate RDPs: (i) in the perovskite precursor ink, (ii) via the anti-solvent, and (iii) as post-treatment. We study the formation of RDPs through in-situ photoluminescence measurements performed during spin coating and reveal significant differences in kinetics caused by each processing method. Furthermore, we investigated the orientation of the perovskite thin film through grazing incidence wide-angle x-ray scattering (GIWAXS). It is reported that the oriented growth of perovskite is more efficient than the randomly oriented perovskite layer. Our results suggest that the orientation of the perovskite thin film is altered when RDPs are formed using the anti-solvent method. The initial solar cell performance of the RDPs formed through each process is comparable, but the main difference is in performance stability. We conducted in-situ degradation GIWAXS experiments at high temperature and humidity to determine the most stable perovskite thin film produced through one of these methods. References [1] R. Quintero-Bermudez, A. Gold-Parker, A. H. Proppe, R. Munir, Z. Yang, S. O. Kelley, A. Amassian, M. F. Toney, E. H. Sargent, Nat. Mater. 2018, DOI 10.1038/s41563-018-0154-x. [2] X. Zhang, R. Munir, Z. Xu, Y. Liu, H. Tsai, W. Nie, J. Li, T. Niu, D. Smilgies, M. G. Kanatzidis, A. D. Mohite, K. Zhao, A. Amassian, S. F. Liu, Adv. Mater. 2018, 30, DOI 10.1002/adma.201707166.

U.P.7
18:00
Authors : Ashutosh Mohanty, Sharada Govinda, Diptikanta Swain, Tayur N. Guru Row and D. D. Sarma
Affiliations : Solid State and Structural Chemistry Unit, Indian Institute of Science, Bengaluru - 560012, India

Resume : The perovskite materials with ABX3 structure, where A = organic cation, B = inorganic cation and X = halides, are commonly known as Organic-Inorganic Hybrid Perovskite. In this regard, FAPbI3 and MAPbI3 (FA = NH2CHNH2 cation and MA = CH3NH3 cation) with perovskite structures are excellent solar absorber materials and potential candidates for the future photovoltaic applications. However, at ambient temperature the stability is a matter of concern for these materials as FAPbI3 transforms to a non-perovskite phase which is a bad solar absorbent and MAPbI3 decomposes with time. In this connection, it is found that the solid solutions of FAPbI3 and MAPbI3 are more stable in comparison to their individual phases. Thus, we have carried out a thorough investigation of the crystal phases of the solid solution i.e. MA(1-x)_FA(x)_PbI3 system for various x values at different temperatures covering 300 K down to 15 K by using variable temperature powder X-ray diffraction (XRD) measurement. The obtained space groups at different crystal phases are confirmed by temperature dependent single crystal XRD. In total, four crystallographic phases exist for this solid solution series namely, cubic, tetragonal, large-cell cubic and orthorhombic. By performing variable temperature dielectric measurement, we have also seen that the dielectric constant correlates strongly with the structure. Therefore, properties of such doped systems, known to be essential for high efficiency together with stability, will have to be understood in terms of their crystallographic phases, which we are discussing in detail in the present work.

U.P.8
18:00
Authors : Yong-Duck Chung1,2*, Dae-Hyung Cho1, Woo-Jung Lee1, Kihwan Kim3, Jae Ho Yun3
Affiliations : 1Electronics and Telecommunications Research Institute (ETRI), Daejeon 34129, Republic of Korea; 2Korea University of Science and Technology (UST), Daejeon 34113, Republic of Korea; 3Korea Institute of Energy Research (KIER), Daejeon 34129, Republic of Korea

Resume : The Cu(In,Ga)Se2 (CIGS)-based thin-film solar cell is considered to have a high potential for practical devices because of its beneficial properties such as flexibility, thermal stability, and hardness against space environment. Conventional CIGS solar cells have a CdS buffer layer containing a very toxic and harmful material of Cd. As an alternative to the environmentally undesirable CdS buffer layer, Zn(O,S) materials have attracted interest for use in the CIGS solar cell. The Zn(O,S) buffer layer can be grown by using various deposition methods, including physical vapor deposition and chemical bath deposition (CBD). The performance of CIGS thin-film solar cells with a Zn(O,S) buffer layer widely varies with the properties of Zn(O,S)/CIGS interfaces determined by deposition method of Zn(O,S). This implies that cell performance can be predominantly determined by the interfacial quality and the band alignment of the p−n junction between CIGS and Zn(O,S) layer. In this study, two types of CIGS absorber layers with different Ga content were employed to investigate the Zn(O,S)/CIGS interfaces. The Zn(O,S) thin films were prepared by conventional CBD and reactive sputtering process with a single ZnS target. For the reactive sputtering process, O2/Ar mixture gas ratio was controlled to vary the sulfur-to-oxygen composition ratio. The best solar cell efficiencies in two types of CIGS absorber were achieved in Zn(O,S) buffer layer at a different sulfur-to-oxygen ratio. The results suggest that the high efficiency could be obtained with appropriate CIGS∕Zn(O,S) interfaces by controlling the sulfur-to-oxygen concentration and the chemical composition in the near surface of the CIGS layer. Since the energy levels of conduction and valence band are strongly dependent on the sulfur concentration in Zn(O,S), the composition variation causes a change of band alignment. We determine the valence band energy and the band gap energy at the Zn(O,S)/CIGS interfaces by using X-ray photoelectron spectroscopy combined and electron energy loss spectroscopy, respectively. The effects on the photovoltaic performance of the thin-film solar cell employing different CIGS and Zn(O,S) layers are compared and discussed.

U.P.9
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Session IV : Gianluca Ciatto
09:00
Authors : Regan G. Wilks
Affiliations : Department Interface Design, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Hahn-Meitner Platz 1, Berlin 14109, Germany

Resume : The sudden relevance of metal-halide perovskite (HaP) materials in photovoltaics (PV) and the strong influence of composition, process parameters, and environmental effects on the resulting device behavior make it both a highly promising technology and one that is difficult to optimize in a systematic, empirical fashion. To investigate the relationships between structure ? chemical and electronic ? and function of HaPs in thin-film PV, our research group employs a large toolchest of x-ray spectroscopic techniques. Hard x-ray photoemission spectroscopy (HAXPES) at synchrotron sources can provide a depth-resolved picture or electronic structure, and in the case of materials with organic components the rate of photon-induced decomposition can be reduced. In situ treatment of HaP-related films during HAXPES measurements reveals changes in electronic structure occurring during formation ? and thermal decomposition ? of a HaP. Near-ambient pressure HAXPES was employed as part of an overall drive to understand, and ultimately to mitigate, the environmental degradation of HaP materials. Resonant Inelastic soft X-ray Scattering of the organic component of a metal-organic HaP can be used to examine projected partial density of states and molecular dynamic effects on the electron structure. By employing these advanced characterization techniques to specimens of relevant, real-world photovoltaic, we can understand performance limiting factors at a fundamental level.

U.4.1
09:30
Authors : Björn Wickman, Rosemary Brown, Mykhalio Vorokhta, TomáS Skála, Ivan Khalakhan, Niklas Lindahl, Björn Eriksson, Carina Lagergren, Iva Matolínová, Vladamír Matolín
Affiliations : Björn Wickman; Rosemary Brown; Niklas Lindahl; Department of Physics, Chalmers University of Technology Gothenburg, Sweden Mykhalio Vorokhta; Tomá? Skála; Ivan Khalakhan; Iva Matolínová; Vladamír Matolín, Charles University, Prague, Czech Republic Björn Eriksson; Carina Lagergren, Department of Chemical Engineering, KTH Royal Institute of Technology, Stockholm, Stockholm, Sweden.

Resume : In the polymer electrolyte membrane (PEM) fuel cells, the family of Pt-rare earth (RE) and lanthanide alloys, such as Pt3Y, Pt5Gd, Pt5Tb, etc. have shown great potential to catalyze the oxygen reduction reaction (ORR) with an activity up to an order of magnitude higher than Pt. Bulk samples of these alloys have shown to have up one order of magnitude higher ORR activity compared to pure Pt. In our recent work on these alloys we have successfully fabricated nanometer thin films of Pt-RE alloys and evaluated then in a real fuel cell setup. The fuel cell measurements confirm the increased ORR activity seen in previously in half-cells and also highlights the importance of catalyst structure to optimize performance. Detailed materials characterization using synchrotron X-ray photoelectron spectroscopy (XPS) of the catalyst surface show the formation of a Pt overlayer, a few monolayers thick. For a sputtered Pt3Y thin film, the majority of Y at the surface is oxidized and is removed by acid pretreatment. X-ray diffraction (XRD) measurements indicate very small grain sizes and large microstrain as well as a change in the effective lattice parameter of Pt, reflecting the loss of Y from the alloy. Understanding more about the de-alloying process and the structure of the formed overlayer will aid in the development of these catalysts for long term application in fuel cells.

U.4.2
10:00
Authors : Isheta Majumdar, Vladimir Parvan, Rutger Schlatmann and Iver Lauermann
Affiliations : Freie Universität Berlin, Competence Centre Thin Film and Nanotechnology for Photovoltaics Berlin (PVcomB)/Helmholtz Zentrum Berlin (HZB)

Resume : The importance of sodium in Cu(In,Ga)Se2 absorbers used for thin film solar cells is well known, however, its role is not fully understood. We examined Na from different sources using x-ray photoelectron spectroscopy. The origin of the chemical shifts in the various experimental XPS peak components observed in the case of Na from SLG substrate (Na-SLG) and Na as post-deposition (Na-PDT) on CIGSe surfaces has been interpreted in terms of initial and final state contributions to the binding energy shifts w.r.t. the metallic states. It has been shown how Auger parameter analysis of the XPS data can be utilized to determine chemical states of elements, in this case, for Na from the two sources. Na as post-deposition brought about a Se-enrichment and InyOz formation at the CIGSe surface. Charge sharing between Se and Ga indicated towards formation of a Na-containing complex of the form (Na,Ga)(Se,OH)(InyOz). Another component of Na may have formed a secondary phase NaxCu(1-x)(In,Ga)Se2 due to reduced [Cu]/[In] ratio at the Na-PDT CIGSe surface and charge sharing with Cu, In, Ga and Se. Elemental Na from Na-PDT also reacted with O to form NaOH. On the other hand, no interaction of Na in Na-SLG with any of the CIGSe-related components has been found. In this case, oxides of Na like NaxO and Na2CO3 and uncompensated Na+ ions have been identified at the CIGSe surface. Band-alignment studies of the Na-SLG CIGSe and Na-PDT CIGSe surfaces with a Zn(O,S) buffer layer showed a higher VBM and interface-induced band-bending leading to a type-inversion (to n-type) at the Na-SLG CIGSe/Zn(O,S) interface causing a reduced Voc and an increased FF. On the other hand, a reduced VBM at the Na-PDT CIGSe surface resulted in an increased effective p-type doping at the absorber surface and a corresponding enhanced Voc. In this case, a decreased FF was obtained due to a reduced work function at the CIGSe surface as a result of Na deposition.

U.4.3
10:15
Authors : Gabriel J. Man(1); Konstantin A. Simonov(1); Pabitra K. Nayak(2); Fredrik O. Johansson(1); Sebastian Svanström(1); Yasmine Sassa(3); Ruslan Ovsyannikov(4); Erika Giangrisostomi(4); Henry J. Snaith(2); Sergei M. Butorin(1); Michael Odelius(5); Håkan Rensmo(1)
Affiliations : 1. Division of Molecular and Condensed Matter Physics, Department of Physics, Uppsala University, Box 516, Uppsala, 75121, Sweden 2. Clarendon Laboratory, Department of Physics, University of Oxford, Oxford, OX1 3PU, UK 3. Department of Physics, Chalmers University of Technology, Göteborg, 41296, Sweden 4. Institute Methods and Instrumentation for Synchrotron Radiation Research, Helmholtz-Zentrum Berlin GmbH, Albert-Einstein-Strafze 15, Berlin, 12489, Germany 5. Department of Physics, Stockholm University, AlbaNova University Center, Stockholm, 10691, Sweden

Resume : Hybrid organic-inorganic lead halide perovskite (HaP) materials have attracted substantial research interest over the last decade, primarily due to their outstanding opto-electronic properties which are beneficial for solar cells and LED’s. HaP-based solar cells and LED’s are currently undergoing technology commercialization world-wide. In spite of the substantial research efforts invested by the global community, we currently have an incomplete understanding of the intrinsic carrier scattering mechanisms which dictate carrier mobility. One type of scattering mechanism could be due to electronic hybridization between the organic and inorganic sub-lattices, and one technique of choice for investigating this open question is X-ray absorption spectroscopy (XAS). Utilizing synchrotron-based X-ray absorption near edge structure (XANES), performed on in-vacuum cleaved single crystals at a beam-line which is designed to provide low photon fluxes for measuring radiation-sensitive materials, we find evidence that the nitrogen-derived unoccupied electronic levels, originating from the methylammonium organic cation, hybridize differently to the inorganic lead-iodide/lead-bromide sub-lattices. These findings may yield insights on the differences in electron scattering mechanisms, and possibly ambient stability, between methylammonium lead tri-iodide (MAPbI3) and methylammonium lead tri-bromide (MAPbBr3), two prototypical members of this class of materials.

U.4.4
10:30 Coffee break    
 
Session V : tba
11:00
Authors : Gianluca Ciatto
Affiliations : Synchrotron SOLEIL, L'Orme des Merisiers, Saint-Aubin, BP 48 F-91192 Gif sur Yvette CEDEX (France)

Resume : Synchrotron radiation techniques, in particular x-ray diffraction and absorption, are nowadays well-established tools to study the structure of both crystalline and disordered semiconductor materials, including low dimensional systems such as nanostructures as well as the local environment of dopants and dilute isoelectronic impurities in a semiconductor matrix. More recently, the exploitation of these techniques in situ, made possible by the high brilliance of the modern synchrotrons and the availability of dedicated reactors, has opened the way to the investigation of the growth process itself. Here, we review some recent results of the synchrotron radiation characterization of III-Vs semiconductors with potential for solar energy harvesting. This includes nitride semiconductors (InxGa1-xN) with direct bang gap spanning the entire solar spectrum from near-infrared to near-ultraviolet, dilute nitrides alloys (GaAs1-yNy, InxGa1-xAs1-yNy) which constitute a model study case for the analysis of the detailed structure of defects, and other systems in which heavier anions were incorporated to tailor the optical band gap (GaAs1-ySby, GaAs1-yBiy, etc.). The phenomena of atom clustering, hydrogen incorporation, and their effects on the optical properties of these materials for post-growth band-gap engineering have been addressed by several synchrotron radiation techniques coupled with advanced theoretical calculations. Finally, we show the advantages of the use of the same techniques in situ in the analysis of the atomic layer deposition growth and the structure-property relationship of an archetype oxide (ZnO) employed as transparent conductive electrode in both inorganic and dye-sensitized hybrid solar cells.

U.5.1
11:30
Authors : David J. Payne
Affiliations : Department of Materials, Imperial College London, Exhibition Road, London, SW7 2AZ, UK

Resume : Photoelectron spectroscopy (PES) is perhaps the most direct probe of electronic structure available to the physical scientist, as well as an invaluable tool for elucidating bulk and surface chemical composition. It is commonplace to use PES for the characterization of samples held in high or ultra-high vacuum (HV, UHV), yet what is gained in understanding the fundamental surface physics of a material, is lost when this knowledge needs to be transferred to the material operating in real-world conditions. This so-called “pressure-gap” has been the focus of intense technological development over the last 40 years. In-situ spectroscopies such as high pressure X-ray photoelectron spectroscopy (HPXPS) and high pressure X-ray absorption spectroscopy (HPXAS) provide an opportunity to capture the surface chemistry occurring in fuel cell materials, and have been developed over the last 40 years, although only in the last decade has there been a significant increase in their use. Whilst the technological concept of in-situ spectroscopy is relatively straightforward, in reality there are significant challenges to overcome in instrumentation design, experimental design and the analysis of the results. These will be addressed in this talk, focusing on some of the technological developments in lab-based HPXPS, such as increasing the transmission of the electron analyser [1], as well as important experimental considerations that need to be accounted for in order to have reliable and reproducible results [2,3] as well as recent results of CO2 on copper [4]. Finally, the future links between high pressure spectroscopy and theoretical methodologies will be discussed. [1] M.O.M. Edwards, D.J. Payne et al. Nuclear Instruments and Methods in Physics Research Section A 785, 191 (2015). [2] G. Kerherve, D.J. Payne et al. Review of Scientific Instruments, 88, 033102 (2017). [3] J.M. Kahk, D.J. Payne et al. Journal of Electron Spectroscopy and Related Phenomena 205, 57 (2015). [4] A. Regoutz, D.J. Payne et al. Surface Science, 667 121 (2018).

U.5.2
12:00
Authors : Mykhailo Vorokhta1, Ivan Khalakhan1, Tomas Skála1, Jan Vlček2, Premysl Fitl2, Martin Vrňata2, Jan Lančok3, Anton Kozma4, Iva Matolínová1, Vladimir Matolín1
Affiliations : 1 Department of Surface and Plasma Science, Charles University, Prague, Czech Republic; 2 Department of Physics and Measurements, Institute of Chemical Technology, Prague, Czech Republic; 3 Institute of Physics, Academy of Sciences of the Czech Republic, Prague, Czech Republic ; 4 Department of Physical and Colloid Chemistry, Uzhhorod National University, Uzhhorod, Ukraine;

Resume : In this study we would like to present an application of laboratory-based near ambient pressure x-ray photoelectron spectroscopy (NAP-XPS) for in-situ and operando characterizations of heterogeneous metal-oxides based catalysts and gas sensors. We show that this tool can be successfully used for study of both the model thin films in-situ prepared in high vacuum and the real nanostructured layers. First, the lab-based NAP-XPS was used for narrowing the gap between the basic knowledge of structural and physico-chemical properties of Au/CeO2 catalysts in the vacuum and in the realistic gaseous environments (under operating conditions). A basic understanding of the mechanisms of simple catalytic C1 reactions, such as water gas shift reaction and CO oxidation, at the molecular level was achieved. Together with NAP-XPS technique other powerful characterization techniques such as low energy electron diffraction (LEED), scanning tunneling microscopy (STM) and synchrotron radiation photoelectron spectroscopy (SRPES) were used in this work. Another example of application of the lab-based NAP-XPS is the study of sensing mechanisms of nanostructured tin oxide and copper oxide chemiresistors. The nanostructured layers exhibit large surface-to-volume ratio with high concentration of active surface sites for chemisorption. The SnO2 nanostructured layers were prepared by pulsed laser deposition while CuOx nanowires were obtain by the thermal oxidation method. Scanning and transmission electron microscopies (SEM, TEM) and atomic force microscope (AFM) were used to characterize the morphology of the as-prepared oxides. A simple gas sensors were realized by depositing of SnO2 and CuOx on a special fused silica substrates and were investigated in-operando under exposure to the reactive atmosphere at elevated temperatures by means of NAP-XPS. Small modification of the equipment allowed us to follow the resistivity of the nanostructured films simultaneously with NAP-XPS measurements during the gases exposure. The unique combination of thin film resistivity measurement and photoelectron study under higher pressure of investigated gases brings a new insight into sensoric properties and catalytic processes on the surface of studied sensors.

U.5.3
12:15
Authors : Xueqiang Zhang,1,2 Tadashi Ogitsu, 3 Brandon C. Wood, 3 Tuan Anh Pham, 3 Sylwia Ptasinska 1,4
Affiliations : 1 Radiation Laboratory, University of Notre Dame, Notre Dame, IN 46556, USA 2 Department of Chemistry and Biochemistry, University of Notre Dame, IN 46556, USA 3 Quantum Simulations Group, Lawrence Livermore National Laboratory, Livermore, CA 94550, USA 4 Department of Physics, University of Notre Dame, Notre Dame, IN 46556, USA

Resume : A detailed mechanism of oxidation processes on the InP surface, which can reveal a clear correlation between electronic properties, oxide morphology and local chemical oxygen environment is necessary for tuning optoelectronic properties of InP-based photoelectrodes via surface oxidation. Our approach is to take advantage of recent advances in surface-sensitive techniques, i.e., ambient pressure X-ray photoelectron spectroscopy (AP-XPS) to track the dynamic electronic, morphological and chemical structures of the O2/InP interface that allows one to access surface reaction processes under ambient conditions. We also integrate our XPS study with DFT calculations and direct spectroscopic simulations [1] which allow to obtain explicit mechanistic understandings of the O2/InP(001) interface and the evolution of InP(001) oxidation under different O2 pressures and temperatures. Our very preliminary results showed that introduction of O2 onto InP(001) surface at a low temperature regime leads to the exclusive formation of a mixture of In and crosslinked PO4 via bridging oxygen that aggregates on the surface of InP(001) with monolayer thickness. At higher temperatures, these InPOx sub-units begin to be linked amorphously across the surface forming 2-dimentional structure via bridging oxygen atoms. We also observed that different oxidation processes are activated at different O2 pressures and temperatures, thus they give rise to different types of oxides and we are continuing to investigate them. Therefore, the surface oxide composition may effectively be controlled by leveraging thermodynamics against kinetic considerations. [1] Pham, T. A.; Zhang, X.; Wood, B. C.; Prendergast, D.; Ptasinska, S.; Ogitsu, T. Integrating Ab Initio Simulations and X-ray Photoelectron Spectroscopy: Toward a Realistic Description of Oxidized Solid/Liquid Interfaces. J. Phys. Chem. Lett. 2018, 9, 194-203

U.5.4
12:30 Lunch break    
 
Session VI : tba
14:00
Authors : Wolfram Jaegermann
Affiliations : Surface Science Division, Materials Science, TU Darmstadt Otto Berndt-Str. 3, D-64287 Darmstadt, Germany

Resume : Different combinations of cathode and anode materials have been investigated for improving the energy content of Li-ion battery materials. One of the dominant factors of performance is related to the achieved battery voltage depending on the charging state of the battery. The voltage difference of the electrochemical cell is given by the change in the Gibbs energy for the exchange of Li which will again will depend on the exchange of electrons and ions between the two phases. A systematic experimental study on the relative influence of both contributions on the measurable battery voltage have not been performed yet. Therefore we will present in this contributions surface science studies of well-defined thin film electrodes which allows to compare changes in electronic structure and related electronic surface potentials with voltage measurements. In addition, we will present first experiments on the direct measurements of the ionic work function and of complete battery set-ups. A number of different thin film cathode materials with different composition of the layered oxides and olivine structural family have been prepared in recent years mostly by sputter deposition inside an integrated UHV system. Subsequently, the electronic structure and surface potentials as e. g. the electronic work function and the changes induced with charging have been determined by applying photoelectron spectroscopy. The experiments allow to relate energetic changes in the Fermi level positions to the measured battery voltage and thus deduce the relative contribution of the different electronic chemical potential to the battery voltage. Based on our data we conclude that the major contribution to the battery voltage is related to electronic work function variations of the different electrode materials. In addition, we have performed first experiments by experimentally determining the electronic and ionic work function of electrode materials. Such experiments allow to directly determine the chemical potential of the Li atom as given by the electronic and ionic contribution in relation to the vacuum level. With a Born-Haber cycle we can show that the experimentally determined values are in reasonable correspondence to the battery voltage. Finally we will present in situ quasi operando electron spectra (SXPS and XAS) on complete solid thin film battery structures using NaCoO2 as cathode, which allow to investigate the changes in surface composition and surface potentials directly after performing the polarization of the cathode. These experiments indicate that the higher stability regime of NaCoO2 with Na loss in contrast to LiCoO2 is related to a favourable involvement of O2p states to the valence band maximum involved in hole transfer. Summarizing our results we conclude that the performance of Li-ion batteries depend on the relative changes of bonding contributions for electrons and ions within the used electrodes with electrons providing the larger part to the battery voltage. Measured variations in performance must be related to deviations of the rigid band behavior of the electrode materials and to surface effects occurring in the given battery set-up.

U.6.1
14:30
Authors : Moniek Tromp
Affiliations : University of Groningen, Faculty of Science and Engineering, Zernike Institute for Advanced Materials, Materials Chemistry, Nijenborgh 4, 9747 AG Groningen, Moniek.Tromp@rug.nl

Resume : An important element in the reduction of CO2 is the change of vehicles with internal combustion engines to electric battery powered vehicles. The as such produced renewable energy can be used for individual mobility as well as for a temporary intermediate storage of excess energy. A viable electric mobility concept requires however stable cycle batteries with high specific energy (minimising weight, maximising driving range). Li ion batteries are widely used in applications such as mobile phones and laptops, and will likely be key to future electromobility. An alternative promising battery is the lithium sulfur battery with a potential twofold energy density increase. The requirements for such batteries present major challenges; e.g. energy capacity, deactivation/stability and safety. A detailed understanding of the charge, discharge and deactivation mechanisms are thus required, preferably quantitative and spatially resolved. X-ray absorption spectroscopy (XAS) is a characterisation technique which provides detailed electronic and structural information on the material under investigation, in a time- and spatially resolved manner. Here, I will explain the strengths and limitations of XAS for battery research. A novel operando XAS cell design will be described [1], including the challenges to perform reliable experiments (electrochemically and spectroscopically). The cell allows time and spatial resolved XAS, providing insights in the type, location and reversibility of the intermediates formed in electrodes and electrolyte separately. Obtained insights in cycling and deactiviation mechanisms for the different battery types will be discussed [1-6] and future research directions described. [1] Y. Gorlin, A. Siebel, M. Piana, T. Huthwelker, H. Jha, G. Monsch, F. Kraus, H.A. Gasteiger, M. Tromp, J. Electrochem. Soc. 162(7): A1146-A1155, 2015. [2] Y. Gorlin, M. U. M. Patel, A. Freiberg, Q. He, M. Piana, M. Tromp, H. A. Gasteiger, J. Electrochem. Soc. 2016, 163(6), A930-A939. [3] J. Wandt, A. Freiberg, R. Thomas, Y. Gorlin, A. Siebel, R. Jung, H. A. Gasteiger, M. Tromp, J. Mater. Chem. A 2016, 4, 18300-18305. [4] A. T. S. Freiberg, A. Siebel, A. Berger, S. M. Webb, Y. Gorlin, H. A. Gasteiger, M. Tromp, J. Phys. Chem. C 2018, 122, 10, 5303-5316. [5] A. Berger, A. T. S. Freiberg, R. J. Thomas, M. U. M. Patel, M. Tromp, H. Gasteiger, Y. Gorlin, J. Electrochem. Soc. 2018, 165(7), A1288-A1296. [6] R. Jung, F. Linsenmann, R. J. Thomas, J. Wandt, S. Solchenbach, F. Maglia, C. Stinner, H. A. Gasteiger, M. Tromp, J. Electrochem. Soc. 2019, 166(2): A378-A389.

U.6.2
15:00
Authors : Dibya Phuyal, Soham Mukherjee, Shyamashis Das, Sergei M. Butorin, D.D. Sarma, Olof Karis, Håkan Rensmo
Affiliations : Department of Physics and Astronomy, Molecular and Condensed Matter Physics, Uppsala University
Box 516, SE-75120 Uppsala, Sweden Department of Solid State and Structural Chemistry Unit, Indian Institute of Science - Bengaluru 560012, India

Resume : The use of built-in electric fields present in p-n junctions is inherently limited by the Shockley-Queisser limit. An alternative method to efficiently separate charge carriers are in ferroelectric materials due to their switchable photoelectric response and a bulk-photovoltaic effect that can generate photovoltages larger than its bandgap. To improve their performance and potential for application in solar cells, we focus on narrowing the bandgap of the model BaTiO3 by doping with transition metals to better match the solar spectrum. Using a combination of soft and hard x-ray spectroscopies and density functional theory (DFT) calculations, we reveal this compound’s electronic structure and the modifications induced by doping. Additionally, we fabricate solar cell devices and reverse the polarization in-situ to monitor the changes to the electronic band alignment at the metal/ferroelectric interface and derive the conduction and valence band offsets. Lastly, ferroelectric photovoltaics are also studied under monochromatic illumination to simultaneously understand the mechanism for photovoltaic voltage generation and interface profile during in-operando measurements. The x-ray methodologies used for ferroelectric photovoltaics can reveal mechanisms to their operation in devices and guide in design of epitaxial ferroelectrics.

U.6.3
15:15
Authors : Ameer Al-Temimy1,2, Michael Naguib3, Ronny Golnak1, Mailis Lounasvuori1, Kaitlyn Prenger3, Tristan Petit1
Affiliations : 1 Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Albert-Einstein-Str. 15, 12489 Berlin, Germany 2 Department of Physics, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany 3 Department of Physics and Engineering Physics, Tulane University, New Orleans, LA 70118, USA

Resume : MXenes are a new class of 2D materials consisting of transition metals carbides and nitrides that demonstrate extraordinary properties for electrochemical energy storage applications. In particular, Ti3C2Tx MXenes have shown very large capacitance in sulfuric acid due to the surface redox (pseudocapacitive) charging mechanism1. Intercalation of Ti3C2Tx by cations induces a larger spacing between the material sheets2 and might alter the oxidation state which would eventually result in a different surface redox mechanism. Tracking the changes associated with the average oxidation of Ti atoms of Ti3C2Tx in situ/operando in various environments could provide more insights into their energy storage mechanism. X-ray Absorption Spectroscopy (XAS) using soft X-rays is an element-sensitive technique that is very sensitive to surface chemistry and transition metal oxidation states. Herein, we present an XAS study of pristine, Li-, Na-, K-, and Mg-intercalated Ti3C2Tx in different environments. Electrochemical reaction coupled with in operando XAS at the Ti L-edge was conducted to probe the changes in the oxidation state of Ti in Na-, K-, and Mg-Ti3C2Tx MXenes in sulfuric acid. This study provides a basis for electrochemical performance of MXenes by applying the Ti L-edge sensitivity to probe the differences in the oxidation state of Ti atoms. References: 1. M. R. Lukatskaya et al., Adv. Energy Mater 2015, 5, 1500589 2. Muckley, E. S. et al., ACS Nano 2017, 11, 11118–11126

U.6.4
15:30 Coffee break    
 
Session VII : tba
16:00
Authors : J. Drnec, T. Fuchs, T. Wiegmann, I. Martens, A. Vamvakeros, R. Chattot, D. Harrington, O.M. Magnussen
Affiliations : ESRF; Kiel University; Kiel University; University of British Columbia; Finden Ltd.; Grenoble University; University of Victoria; Kiel University

Resume : Complete physico-chemical operando characterization of electrochemical devices in whole, or it?s constituent materials separately, is necessary to guide the development and to improve the performance. High brilliance synchrotron X-ray sources play a crucial role in this respect as they act as a probe with relatively high penetration power and low damage potential. In this contribution the new possibilities of using using high energy, high intensity X-rays to probe model fuel cell catalysts and energy conversion devices will be presented. HESXRD (High Energy Surface X-ray Diffraction) [1] and TDS (Transmission Surface Diffraction) [2] provide ideal tools to study structural changes during reaction conditions on single crystal model electrodes. The main advantage of both techniques is the possibility to follow the structural changes precisely with atomic resolution. While HESXRD is ideally used to determine exact atomic position, the TSD is easier to use and allows studies with high spatial resolution. For example, HESXRD can be used to follow the atomic movement of Pt atoms during electrochemical oxidation and dissolution with very high precision, explaining the different catalyst degradation behaviors and suggesting possible routes to improve its durability [3-5]. The TSD is an excellent tool to study advanced 2D catalysts. To study fuel cells or batteries as a whole, elastic scattering techniques, such as WAXS and SAXS, can be employed as they can provide important complementary information to more standard X-ray imaging and tomography. The advantage is that the chemical contrast and sensitivity at atomic and nm scales is superior. Coupling these technique with the tomographic reconstruction (XRD-CT and SAXS-CT) is much less common as it requires bright synchrotron sources, fast 2D detectors and advanced instrumentation, but allows 3D imaging of operational devices with unprecedented chemical sensitivity [6]. This can be demonstrated, as an example, on imaging of standard 5cm2 fuel cells during operation. The change in morphology and atomic arrangement of the catalysts, PEM hydration and water distribution can be followed in one experiment as a function of operating conditions. Furthermore, the fundamental processes leading to the catalyst aging can be assessed with high temporal and spatial resolution. These advanced scattering techniques open a door to holistic investigations of operational devices, which are needed to successfully incorporate new materials at the device level. [1] J. Gustafson et al., Science 343, 758 (2014) [2] F. Reikowski et al., J. Phys. Chem. Lett., 5, 1067-1071 (2017) [3] J. Drnec et al, Electrochim. Acta, 224 (2017), [4] M. Ruge et al, J. Am. Chem. Soc., 139 (2017) [5] Chattot et al., Nature Materials, 17(2018) [6] A. Vamvakeros et al., Nat. Commun., 9, 4751 (2018)

U.7.1
16:30
Authors : S. M. Polyakov,1 J. W. Wells,1 M. Nematollahi,1 U. J. Gibson1 & S. P. Cooil2,1
Affiliations : 1. Department of Physics, Norwegian University of Science and Technology (NTNU), Trondheim, Norway, NO 4791. 2. Department of Physics, Aberystwyth University, Aberystwyth, Wales, SY23 3B

Resume : Since its initial conception as a possible photovoltaic (PV) candidate around the turn of the 1930s1, 2 cuprous oxide (Cu2O) has been known to the photovoltaic community. However, the material has an intrinsic p-type conductivity due to the presence of Cu vacancies acting as acceptors,3 rendering the creation of p-n homojunctions as challenging to produce. The search for inexpensive and non toxic materials for greener energy production has now renewed interest in Cu2O for PV applications. Here we have prepared Fe-doped ZnS films with various Fe concentration by room temperature molecular beam epitaxy (MBE). The optical bandgaps of these films were determined from optical transmission spectroscopy data. A Cu2O overlayer was then produced in-situ within a custom photoemission system. Using photoelectron spectroscopy techniques (XPS/UPS) the positions of the core levels and valence band maxima (VBM) in the bulk materials were obtained. By observing the core level binding energies at the ZnS:Fe/Cu2O heterojunction interface, relative to the bulk positions of the constituent materials, the offsets between the conduction bands and valance bands (EC and EV respectively) can be calculated. For a at6% Fe dopedZnS/Cu2O the offsets were calculated to be EC = 0.22eV andEV = 0.93eV, showing an improvement over undoped ZnS/Cu2O heterojunctions, whilst bringing the conduction band offset within the desired range of 0.4 > EC > 0 eV for high efficiency photovoltaic heterojuctions4 1. Grondahl, L. O. Geiger, P. H. Journal of the A.I.E.E. 1927, 46, 215-222. 2. Grondahl, L. O. Reviews of Modern Physics 1933, 5, 141-168. 3. Raebiger, H. Lany, S. Zunger, A. Physical Review B 2007, 76, 045209 4. T. Minemoto, T. Matsui, H. Takakura, Y. Hamakawa, T. Negami, Y. Hashimoto, T. Uenoyama, and M. Kitagawa, Energy Materials and Solar Cells 67, 83 (2001)

U.7.2
16:45
Authors : Justus Just, Klara Suchan, Pascal Becker, Eva Unger and Thomas Unold
Affiliations : MAX IV Laboratory, Fotongatan 2, 22484 Lund, Sweden; Lund University, Paradisgatan 2, 22350 Lund, Sweden; Helmholtz-Zentrum Berlin, Hahn-Meitner-Platz 1, 14109 Berlin, Germany; Helmholtz-Zentrum Berlin, Hahn-Meitner-Platz 1, 14109 Berlin, Germany; Helmholtz-Zentrum Berlin, Hahn-Meitner-Platz 1, 14109 Berlin, Germany;

Resume : We present a detailed investigation of the phase formation dynamics of the chlorine derived one-step synthesis of MAPbI3 perovskite. In a specially designed atmosphere controlled in-situ reactor, synchrotron based in-situ quick scanning X-ray absorption spectroscopy (QEXAFS), X-ray diffraction (XRD) as well as X-ray fluorescence (XRF) are applied in combination with in-situ optical reflection and photoluminescence spectroscopy. This enables us to correlate the evolution of the chemical reaction from XAS, the formation of crystalline phases from XRD and the chemical composition from XRF with the evolution of the optoelectronic properties of the film on one single timeline. We observe a delayed formation of crystalline MAPbI3 and attribute it to a concentration threshold in the decreasing chlorine content of the sample. Our results give detailed insight into the formation process and can help to provide a mechanistic understanding of the reactions and intermediates involved. This knowledge can be utilized to optimize synthesis strategies and to tune the optoelectronic properties of organic-metal-halide perovskite semiconductors. As an outlook we will discuss new developments for the upcomeing in-situ multi-parameter experimental platform at the Balder beamline at MAX IV.

U.7.3
17:00
Authors : SangRim Shin, Hae Sung Cho, Suji Gim, Yongmin Jung, Hyung Jun Kim, and Jeung Ku Kang
Affiliations : Department of Materials Science & Engineering and Graduate School of Energy, Environment, Water, and Sustainability (EEWS), Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yeseong-gu, Daejeon 305-701, Republic of Korea; Inorganic Chemistry and Catalysis group, Debye Institute for Nanomaterials Science, Faculty of Science, Utrecht University, 3584 CG Utrecht, Netherland

Resume : Porous materials have been widely utilized as a key component for future molecular storage and separation. Physical and chemical environments of pores consisting of porous materials are critical to controlling characteristics for target applications, but revealing the details of adsorbate behaviors in its local pores is still limited. Herein we report the in-situ X-ray diffraction snapshots revealing the details of adsorbates within individual local pores of metal-organic frameworks, especially in MIL-101s with vanadium (V), chromium (Cr), or iron (Fe). Through this method, the adsorbate distribution map in the large and the small pores, as well as pore apertures of Cr-, Fe-, and V-MIL-101s, are revealed, and they show that the highest uptake of CO2 adsorbates is achieved in Cr-MIL-101 whose isotherm is concave during a multilayer adsorption process. Meanwhile, that of Fe-MIL-101 is linear and that of V-MIL-101 is convex during that process. Furthermore, the spinning resonance (EPR) spectroscopy, the heat of adsorption, DFT calculation show that the concave, linear, and convex isotherms originate from the adsorption energy intensity. Consequently, this work provides a new clue for previously inaccessible details and also for revealing positions within different types of multiple pores in 3-D frameworks for future applications.

U.7.4
17:15
Authors : C.Lawley, M. Nachtegaal, D. Pergolesi, T. Lippert
Affiliations : Paul Scherrer Institut, ETH Zurich.

Resume : Oxynitrides are among some of the most promising materials for hydrogen generation by visible light driven water splitting. The effect of nitrogen substitution into the oxygen sites of the pristine oxide leads to the reduction of the band gap, shifting the absorption edge towards the visible light energy range, enabling a more efficient utilisation of the solar spectrum. The oxynitrides are well known photoelectrodes and have been studied extensively in the form of powders. However, specific material properties cannot be probed with powder samples. The polycrystalline oxynitride powders do not provide any well-defined surface to allow the detailed studies of the solid-liquid interface where photoelectrochemical reactions take place. For that reason we investigate oxynitride thin films as ideal model systems to allow the investigation of the surface and interface. Using grazing incidence X-ray absorption spectroscopy (GIXAS) we are able to distinguish the surface from the bulk and, track the changes in the electronic and local structure of the cations situated at the surface of the oxynitride film as a consequence of the water splitting process. These changes are limited to the first 3nm of a 100nm film and can help to achieve a fundamental understanding of the physiochemical processes occurring at the solid-liquid interface, where the electrochemical reaction takes place. Leading to the development of new materials with better performance. In the future, operando measurements will be performed using a commissioned cell designed specifically for GIXAS at solid-liquid interfaces.

U.7.5
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09:00 Plenary Session (Main Hall)    
12:25 Lunch break    
 
Session VIII : tba
14:00
Authors : D. D. Sarma
Affiliations : Solid State and Structural Chemistry Unit Indian Institute of Science Bengaluru 560012 INDIA

Resume : X-ray photoelectron spectroscopy has played an enormous role in developing our understanding of a range of interesting materials, including energy materials, over the last five decades, primarily arising from its ability to energy-resolve electrons ejected from any sample due to its interaction with sufficiently high energy photons, thereby defining one of the most powerful spectroscopic techniques. However, when combined with space-resolution to achieve a microscopy based on this spectroscopy, it can provide us with unique information, not available otherwise. In my presentation, I shall describe two qualitatively different ways1,2 to achieve such a space-resolution to provide complementary insights into diverse systems. In the first part of the presentation, I shall focus on an elusive metastable phase, existing only as small patches in chemically exfoliated few-layer, thermodynamically stable 2H phase of MoS2 that is believed to influence critically properties of MoS2 based devices. Its electronic structure is little understood in absence of any direct experimental data and conflicting claims from theoretical investigations. I shall present data3,4 to conclusively resolve this issue based on probing the electronic structure of chemically exfoliated few layer systems using spatially resolved photoemission spectroscopy and show that the dominant belief in the community is qualitatively incorrect, requiring reinterpretations of almost all existing literature claims. In the second approach, I shall explore the rapidly expanding field that deal with emergent properties at a variety of interfaces formed in heterostructured materials, including optically active nanomaterials. It is in general difficult to probe directly the nature of such interface states since these are typically buried under a depth and represent a very small volume fraction of the entire sample. We have shown2,5-10 in recent times that x-ray photoelectron spectroscopy with a widely tunable photon energy can be used very effectively to obtain spatially resolved electronic structure information, thereby making it the ideal probe to investigate interface properties in diverse heterostructured systems. I illustrate this by discussing electronic properties of a few interesting systems, covering, based on the availability of time, LaAlO3-SrTiO3, magnetic properties at tunnel junctions with CoFeB and MgO, and optical properties of highly luminescent semiconductor nanoparticles with integrated internal interfaces. References: 1. D. D. Sarma et al., Phys. Rev. Lett. 93, 097202 (2004). 2. D. D. Sarma et al., Chem. Mater. 25, 1222 (2013). 3. Banabir Pal et al., Phys. Rev. B 96, 195426 (2017). 4. Debasmita Pariari et al., Unpublished results. 5. S. Sapra et al., J. Phys. Chem. B 110, 15244 (2006). 6. Pralay K. Santra et al., J. Am. Chem. Soc. 131, 470 (2009). 7. D. D. Sarma et al., J. Phys. Chem. Lett. 1, 2149 (2010). 8. Banabir Pal et al., J. Electron Spectrosc. Relat. Phenom. 200, 332 (2015). 9. Sumanta Mukherjee et al., Phys. Rev. B 91, 085311 (2015). 10. Sumanta Mukherjee, et al., EPL (Europhys. Lett.) 123, 47003 (2018).

U.8.1
14:30
Authors : S. Wong, B. Haberl, B. C. Johnson, A. Mujica, M. Guthrie, J. C. McCallum, J. S. Williams, J. E. Bradby
Affiliations : (1) Department of Electronic Materials Engineering, Research School of Physics and Engineering, The Australian National University, Canberra, Australian Capital Territory 0200, Australia. S. Wong; J. S. Williams; J. E. Bradby (2) Neutron Sciences Directorate, Oak Ridge National Laboratory, Neutron Scattering Division, Oak Ridge, Tennessee 37781, USA B. Haberl (3) School of Physics, The University of Melbourne, Melbourne, Victoria 3010, Australia B. C. Johnson; . C. McCallum (4) Departamento de Fisica, MALTA Consolider Team, Universidad de La Laguna, La Laguna 38206, Tenerife, Spain A. Mujica (5) European Spallation Source, Lund, SE-221 00, Sweden M. Guthrie (6) School of Physics, University of Edinburgh, Edinburgh, EH9 3FD, United Kingdom M. Guthrie (7) Department of Physics, School of Science, RMIT University, Victoria 3001, Australia S. Wong

Resume : Silicon (Si) is ubiquitous in photovoltaic (PV) solar devices due to its abundance, low cost, and non-toxicity. Despite these advantages, the optical absorption of Si leaves much to be desired. This has generated increased interest in exotic phases of Si that retain the advantages of Si while having increased optical properties. One such phase is the rhombohedral (r8-Si) phase. Modelling studies suggest r8-Si has a significantly increased optical absorption, particularly across the solar spectrum, when compared to the types of Si currently used for PV applications. This phase is formed via pressure application and is known to be stable between 2 – 9 GPa under conventional diamond anvil cell (DAC) compression. Unfortunately, r8-Si is not stable at ambient conditions and no significant amounts of r8-Si have been observed after DAC decompression. However, under point-loading a mixed structure comprised of r8-Si alongside a secondary phase (bc8-Si) can be recovered. In our work, we use a novel sample preparation method to investigate this bc8/r8 mixed structure using x-ray diffraction (XRD). The relative volume of these phases was determined, with r8-Si being the dominant phase comprising around 70% of the mixed structure. Further, a distortion within the unit cell was observed along the direction of point-loading. Theoretical calculations together with these observations suggest the recovered material contains an intrinsic compression of around 4 GPa that stabilizes the r8-Si.

U.8.2
14:45
Authors : Benedikt Schrode, Stefan Pachmajer, Christian Röthel, Sebastian Hofer, Jari Domke, Torsten Fritz, Roland Resel, Oliver Werzer
Affiliations : Institute of Solid State Physics, Graz University of Technology, Petersgasse 16, 8010 Graz, Austria; Institute of Solid State Physics, Graz University of Technology, Petersgasse 16, 8010 Graz, Austria; Institute of Pharmaceutical Sciences, Department of Pharmaceutical Technology, University Graz, 8010 Graz, Austria; Institute of Solid State Physics, Graz University of Technology, Petersgasse 16, 8010 Graz, Austria; Institute of Solid State Physics, Friedrich Schiller University Jena, Helmholtzweg 5, 07743 Jena, Germany; Institute of Solid State Physics, Friedrich Schiller University Jena, Helmholtzweg 5, 07743 Jena, Germany; Institute of Solid State Physics, Graz University of Technology, Petersgasse 16, 8010 Graz, Austria; Institute of Pharmaceutical Sciences, Department of Pharmaceutical Technology, University Graz, 8010 Graz, Austria

Resume : Grazing incidence X-ray diffraction (GIXD) is a powerful method frequently applied to characterize thin films and surfaces. Depending on the sample's crystallite alignment, special care is required during the measurement. While a static measurement at one azimuth is sufficient for 2D powders, epitaxially grown samples with defined in-plane alignment of the crystallites require data collection at all sample azimuths, i.e. 0°–360°. The rotation is necessary to obtain all information for polymorphic phase, texture and epitaxy analysis. Our state of the art measurements collect 180 or 360 images which then require a thorough processing. GIDVis [1], a software package developed in our group, allows analysis of GIXD data in general, but more importantly, calculation of pole figures, i.e. spatial distributions of all net planes accessible in the reciprocal space volume of an experiment. The power of our approach is demonstrated by two examples: In the first case, pentacenequinone (P2O) on Ag(111) is studied and its crystal structure is determined. GIXD pole figures are used to evaluate the epitaxial relationship of the two materials. In the second example, we apply our technique to a metal organic framework (MOF) deposited on a Cu(OH)2 nanobelt surface, which provides information on the alignment of the nanobelts, and to what extent the alignment of the surface is transferred to the MOF. [1] B. Schrode et al., Journal of Applied Crystallography 2019, 52, DOI 10.1107/S1600576719004485

U.8.3
15:00
Authors : Lucyna Grządziel1,*, Maciej Krzywiecki1,2, Adnan Sarfraz2 , Andreas Erbe2,3
Affiliations : 1 Institute of Physics – Center for Science and Education, Silesian University of Technology, S. Konarskiego Str. 22B, 44-100 Gliwice, Poland 2 Max-Planck-Institut für Eisenforschung GmbH, Max-Planck-Str. 1, 40237 Düsseldorf, Germany 3 Department of Materials Science and Engineering, NTNU, Norwegian University of Science and Technology, 7491 Trondheim, Norway * email: Lucyna.Grzadziel@polsl.pl

Resume : In the era of searching for efficient renewable energy sources, toxic and greenhouse gases monitoring or building specialized low-power consumption (opto-) electronics, the discovery of new and evolution of known materials becomes crucial. ZnO as a wide band gap semiconductor with high optical transparency, sensing properties and electrical conductivity, could be the answer for nowadays needs. In this work, we present fundamental physical and chemical properties of ZnO thin layers prepared by sol-gel synthesis followed by spin-coat deposition and subsequently by thermal processing. Various chemical composition of sols and post-deposition drying or annealing processes impacted the layers’ surface topography and bulk crystalline structure as monitored by atomic force microscopy and X-ray diffraction. The effect of morphological structure reorganisation induced by layer processing were also revealed by vibrational investigations using Raman spectroscopy. Detailed chemical composition obtained by X-ray photoemission spectroscopy (XPS) analysis manifested modification of O 1s, Zn 2p and adventitious C 1s species due to presence of defects depending on sol type and thermal processing. Simultaneous XPS and ultraviolet photoemission spectroscopy (UPS) studies of the ZnO valence band region revealed tendency for reaching stable intrinsic character of oxide electronic structure. The XPS and UPS results corroborated with observed oxide’s propensity for structural neutralization of defects and building of ordered, crystalline structure after thermal post-processing.

U.8.4
15:15
Authors : Claudiu Mortan1, Tim Hellmann1, Moritz Buchhorn1, Marco d'Eril Melzi1, Thomas Mayer1 and Wolfram Jaegermann1
Affiliations : 1 Technische Universität Darmstadt, Darmstadt, 64287, Germany cmortan@surface.tu-darmstadt.de

Resume : An up-scalable chemical vapor deposition process (CVD, Figure 1) for methylammonium lead iodide (MAPI, CH3NH3PbI3) and formamidinium lead iodide (FAPI, CH5N2PbI3) used in thin film perovskite solar cells has been built-up and optimized. The procedure uses exclusively gaseous precursors to transform the inorganic salt, i.e. lead iodide (PbI2) to the respective perovskite films. The mechanism of perovskite formation has been confirmed using XPS and XRD. Further characterization techniques include SEM, UV-/Vis spectroscopy, photoluminescence and solar simulator measurements. For MAPI, efficiencies of up to 12.9% have been measured, with the process still being under optimization.

U.8.5
15:30 Coffee break    
 
Session IX : tba
16:00
Authors : Yaroslava Lykhach1, Olaf Brummel1, Tomás Skála2, Nataliya Tsud2, Mykhailo Vorokhta2, Bretislav Smíd2, Vladimír Matolín2, Kevin C. Prince3, Jörg Libuda1
Affiliations : 1 Interface Research and Catalysis, Erlangen Catalysis Resource Center, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, 91058, Germany; 2 Department of Surface and Plasma Science, Charles University, Prague, 18000, Czech Republic; 3 Elettra-Sincrotrone Trieste SCpA, Basovizza-Trieste, 34149, Italy ;

Resume : Many emerging technologies, including fuels cells, water splitting, and energy storage devices, are based on principles of electrocatalysis. Yet, our fundamental understanding of electrocatalysis lags behind classical heterogeneous catalysis which has been dominating chemical technology for a long time. In order to get insight into complex electrocatalytic processes at solid/liquid interfaces, we use well-defined model Pt/Co3O4(111) electrocatalysts prepared by surface science methods in ultrahigh vacuum and transfer these into an electrochemical environment without exposure to air. The corresponding approach allows investigating the Pt/Co3O4(111) electrocatalyst under electrochemical conditions by numerous techniques including synchrotron radiation photoelectron spectroscopy (SRPES), resonant photoemission spectroscopy (SRPES) and X-ray photoelectron spectroscopy (XPS). In particular, we employ a dedicated experimental setup that combines an electrochemical cell and spectroscopic analysis to investigate the redox processes as a function of the electrode potential. Thus, the stability of Pt/Co3O4(111) electrocatalyst was characterized with respect to the oxidation state of the Pt particles and the degree of the reduction of the Co3O4(111) support. Various processes such as charge transfer, oxygen spillover, water dissociation, and reversible oxidation of Pt nanoparticles were identified under electrochemical conditions.

U.9.1
16:30
Authors : Malgorzata Wierzbowska, Bogdan Sadovyi, Svitlana Stelmakh, Izabella Grzegory
Affiliations : Institute of High Pressure Physics Polish Academy of Sciences

Resume : XANES is sensitive to the atomic structure of materials. Therefore, it is a good technique for a detection of defects and determination of crystal phases. The organic lead-halide perovskite and III-V semiconductor solar cells are in our focus. While nowadays a quality of the wurzite GaN wafers is very high, various defects in perovskites are unavoidable. The most unwanted are these defects which lead to the crystal degradation, and one such example is a deprotonation of the organic cation. Other most frequent defects in perovskites are vacancies of the organic cations and inorganic cations and anions. On the other hand, despite a wide application of the wurzite GaN crystals, the high pressure and high temperature growth leads to the mixed phases which are not yet well investigated. The most popular components, in addition to the wurzite phase, are B1 (6-fold coordinated rocksalt) and B2 (8-fold coordinated) cubic phases. However, a comparison of the calculated spectra with the recent synchrotron measurements suggests a more rich phase diagram.

U.9.2
17:00
Authors : Marco Giorgetti, Angelo Mullaliu, Giuliana Aquilanti, Jasper Plaisier
Affiliations : Marco Giorgetti (Dept. of Industrial Chemistry, University of Bologna, Italy); Angelo Mullaliu (KIT - HIU Ulm, Germany); Giuliana Aquilanti (Elettra - Sincrotrone Trieste, Italy); Jasper Plaisier(Elettra - Sincrotrone Trieste, Italy)

Resume : Dynamic processes occurring in batteries are generally studied by ex situ modality. However, those processes that rule electrochemical energy storage in batteries should be studied under operating conditions. Operando experiments provide a realistic representation of the reaction behavior occurring at electrodes. The typical drawbacks of ex situ experiments due to sample transfer, such as the alteration of air or moisture-sensitive species, are avoided, and so are the relaxation reactions that may occur when the electric circuit is opened. Operando data collection allows to check the structural and electronic reversibility of a battery system, while at least one full cycle is performed. For all these reasons, ex situ studies of electrode materials are now complemented by operando measurements using complementary tools such as X-ray diffraction (XRD) and/or spectroscopic techniques such as X-ray absorption spectroscopy (XAS). X-ray absorption spectroscopy is a synchrotron radiation based technique that is able to provide information on local structure and electronic properties in a chemically selective manner. Operando synchrotron radiation powder diffraction experiments allow monitoring the extended structure of a material during the intercalation/release process. The potentiality of the joint XAS-PXRD approach in the newly proposed Prussian Blue-like cathodes materials [1] for Li and Na batteries is here underlined. This makes designing cathode materials with improved properties. [1] A. Mullaliu, M. Giorgetti et al. J. Phys. Chem. C 123(2019)8588; A. Mulllaiu, M. Giorgetti et al. Condensed Matter 3(2018)36; A. Mullaliu, M. Giorgetti at al. J. Phys. Chem. C 122(2018)15868.

U.9.3
17:15
Authors : Pralay K. Santra
Affiliations : Centre for Nano and Soft Matter Sciences, Bengaluru 560013

Resume : All inorganic cesium lead halide (CsPbX3, X = Cl, Br, and I) perovskite nanocubes (NCs) exhibit fascinating optical and optoelectronic properties [1, 2]. Post-synthesis anion exchange by mixing NCs with reactive anion species have emerged as a unique capability of CsPbX3 perovskite NCs to fine control their composition and bandgap. Understanding such anion exchange reactions is essential for both fundamental understanding and optimized applications. However, the internal structure of the anion exchanged NCs are not probed. It is largely believed that the anion exchanged NCs possess a homogeneous composition. In this talk, we will first discuss about the surface of CsPbBr3 NCs and the internal heterostructure that exists inside the anion exchanged CsPbX3 (X = Br/I, and I) NCs probed by variable energy hard X-ray photoelectron spectroscopy. Our results show that for pure CsPbBr3 NCs, there is an excess of bromide ion on the surface of the NCs. We further probed how the ligands replace the Cs ions from the surface of the NCs to stabilize the system. Whereas the anion exchange process makes the CsPbX3 NCs as a gradient alloy with higher concentration of the exchanged anion at the surface of the NCs. A significant amount of native anions are present at the core of the NCs even optical studies suggest a complete anion conversion. The insights from this study provide important directions in future understanding about the electronic properties of the anion exchanged CsPbX3 NCs. Reference: [1] A. Swarnakar, et al, Angew. Chem., Int. Ed. 54, 15424 (2015) [2] V. K. Ravi et al, J. Phys. Chem. Lett. 8, 4988 (2017) [3] A. Haque, et al. J. Phys. Chem. C 122, 13399 (2018)

U.9.4
17:30 CLOSING REMARKS    

No abstract for this day


Symposium organizers
Chittaranjan DASKarlsruhe Institute of Technology

Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany

chittaiit@yahoo.com
Malgorzata KOT (SOWINSKA)BTU Cottbus-Senftenberg

Konrad-Zuse-Strasse 1, 03046 Cottbus, Germany

sowinska.gosia@gmail.com
Mykhailo VOROKHTACharles University

Ke Karlovu 3, 121 16 Praha 2, Czech Republic

vorokhtm@mbox.troja.mff.cuni.cz