A comprehensive study of structure and properties of nanocrystalline zinc peroxide

Abstract Nanocrystalline zinc peroxide (nano-ZnO2) was synthesized through a hydrothermal process and comprehensively studied using several experimental techniques. Its crystal structure was characterized by X-ray diffraction, and the average crystallite size of 22 nm was estimated by Rietveld refinement. The temperature-dependent local environment around zinc atoms was reconstructed using reverse Monte Carlo (RMC) analysis from the Zn K-edge X-ray absorption spectra. The indirect band gap of about 4.6 eV was found using optical absorption spectroscopy. Lattice dynamics of nano-ZnO2 was studied by infrared and Raman spectroscopy. In situ Raman measurements indicate the stability of nano-ZnO…

Extended x-ray absorption fine structure spectroscopy and first-principles study of SnWO4

The local atomic structure in α- and β-SnWO 4 was studied bysynchrotron radiation W L 3 -edge X-ray absorption spectroscopy at 10 and 300 K.Strongly distorted WO 6 octahedra were found in α-SnWO 4 , whereas nearly regularWO 4 tetrahedra were observed in β-SnWO 4 , confirming previous results. Thestructural results obtained were supported by the first-principles calculations,suggesting that the second-order Jahn-Teller effect is responsible for octahedraldistortion.

X-Ray studies on optical and structural properties of ZnO nanostructured thin films

Abstract X-ray absorption near-edge fine structure (XANES) studies have been carried out on nanostructured ZnO thin films prepared by atmospheric pressure chemical vapour deposition (APCVD). Films have been characterized by X-ray diffraction (XRD) and optical luminescence spectroscopy exciting with laser light (PL) or X-ray (XEOL). According to XRD measurements, all the APCVD samples reveal a highly (002) oriented crystalline structure. The samples have different thickness (less than 1 μm) and show significant shifts of the PL and XEOL bands in the visible region. Zn K-edge XANES spectra were recorded using synchrotron radiation at BM08 of ESRF (France), by detecting photoluminescence yield…

<title>Iridium L<formula><inf><roman>3</roman></inf></formula>-edge and oxygen K-edge x-ray absorption spectroscopy of nanocrystalline iridium oxide thin films</title>

Structural investigations of the short range order around iridium and oxygen ions in nanocrystalline iridium oxide thin films, prepared by dc magnetron sputtering technique, were performed by x-ray absorption spectroscopy. The Ir L3-edge extended x-ray absorption fine structure and the O K-edge x-ray absorption near edge structure signals were measured at room temperature and analyzed within ab initio multiple-scattering and full-multiple-scattering approaches, respectively. The x-ray absorption spectroscopy results indicate the presence in the films of orderd regions - nanocrystals, having a size of about 10 angstrom and a structure rather close to that in crystalline iridium oxide IrO2. S…

Some aspects of the solid state physics of yellow arsenic

Local structure and vibrational dynamics in NiWO4

Abstract Systematic studies of nickel tungstate thin film, amorphous and polycrystalline powders were performed by X-ray absorption spectroscopy at the Ni K and W L1,3 edges, X-ray diffraction and Raman spectroscopy. We found that in spite of the similarity of the local environment around nickel and tungsten ions in all three materials, there is strong difference in the Ni-O and W-O interactions for thin film/amorphous powder and polycrystalline powder. The nickel-oxygen bonding becomes stronger by going from thin film or amorphous powder to polycrystalline tungstate at the expense of the tungsten-oxygen bonding strength. Besides, in thin film and amorphous NiWO4, nickel and tungsten ions h…

<title>Local structure of Ta-Re mixed oxide thin films studied by x-ray absorption spectroscopy</title>

Mixed Ta-Re oxide thin films were synthesized for the first time by dc magnetron co-sputtering. Local environment around tantalum and rhenium atoms was studied by the Ta and Re L3-edges x-ray absorption spectroscopy in pure Ta2O5 and mixed Ta-Re oxide thin films (Ta:Re = 50:50, 38:62, 20:80 as determined from the ratio of the Ta-to-Re absorption edges). It was found that rhenium atoms are four-fold coordinated by oxygen atoms with R(Re-O) = 1.74 ± 0.01 Å and the mean square relative displacement (MSRD) σ2 = 0.0012 ± 0.0005 Å2. In pure Ta2O5 thin film, tantalum ions are coordinated by six oxygen atoms at R(Ta-O) = 2.02 ± 0.01 Å with the MSRD σ2 = 0.010 ± 0.001 Å2. The addition of rhenium ion…

Structural, electrical and optical characteristics of Al-doped zinc oxide thin films deposited by reactive magnetron sputtering

ZnO:Al (AZO) thin films on glass were deposited by DC reactive magnetron sputtering at approximately 300°C substrate temperature. Structural, electrical and optical properties were investigated as a function of oxygen flow. XRD data shows that AZO thin films are polycrystalline with pronounced c-axis orientation and the grain size increasing with the oxygen flow. The lowest achieved resistivity within the deposited set of samples was 7.6·10 -4 Ωcm. The transmittance of AZO films was above 80 % at 550 nm with the optical band gap between 3.4 and 3.8 eV.

Structural characterization of mixed Ta–Re oxide films

Thin films of mixed Ta and Re oxides have been produced by reactive dc magnetron co-sputtering of pure Ta and Re metal targets in Ar–O2 atmosphere. The structural evolution of these films has been studied as a function of the composition, starting from a pure tantalum oxide film up to about 82% rhenium content. The composition and the structure of the films have been investigated by using X-ray diffraction and micro-Raman spectroscopy. For low Re content (20%), islands of a well crystallized phase, based on ReO4 groups, appear in the films still composed by pure amorphous tantalum oxide, while a mixed disordered solid phase is found for the highest Re concentration (82%). © 2006 Elsevier B.…

Local structure relaxation in nanocrystalline Ni1−xO thin films

Abstract Non-stoichiometric nickel oxide (Ni 1 − x O) thin films were prepared by DC magnetron sputtering technique in mixed Ar/O 2 atmosphere and studied by synchrotron radiation Ni K-edge x-ray absorption spectroscopy, x-ray diffraction and scanning electron microscopy. The use of advanced modelling technique, combining classical molecular dynamics with ab initio multiple-scattering extended x-ray absorption fine structure calculations, allowed us to describe the structure relaxation and dynamics in nanocrystallites and to estimate their size and the concentration of nickel vacancies.

ChemInform Abstract: Some Aspects of the Solid State Physics of Yellow Arsenic

EXAFS study of mixed nickel molybdenum oxide thin films at the Ni and Mo K-edges

Mixed nickel molybdenum oxide thin films were produced by DC magnetron co-sputtering technique with the nickel content about 8, 16 and 25 at%. X-ray absorption spectroscopy at the Ni and Mo K-edges was used to study the local atomic structure in the films. The best-fit analysis of the EXAFS signals suggests that (i) the films are amorphous, except for the highest nickel content (25 at%), at which a segregation of NiO phase was observed; (ii) nickel and molybdenum atoms are octahedrally coordinated by oxygen atoms. Opposite to the NiO6 octahedra, the MoO6 octahedra are strongly distorted, that results in an existence of two groups of oxygen atoms—four nearest at B1.76 ( A and two distant at …

Proton presence and motion in rhenium-oxide films and their application to liquid-crystalline cells

Disordered solid phases, containing appreciable amounts of hydrogen ions, are grown at the surface of rhenium oxide crystals, because of the high reactivity of this compound with ambient moisture. To investigate such phenomena, a comparative study is performed on ground powder and thermally evaporated or sputtered films using x-ray diffraction and micro-Raman spectroscopy. Two types of solid phases were found in the films: HxReO3 distorted perovskite structures, based on corner-sharing ReO6 octahedra as in the bulk crystals, and ordered HReO4 crystalline structures, based on tetrahedral perrhenate ions. The complex impedance measurements on ReO3 films support the hypothesis of mobile hydrog…

A comparative study of heterostructured CuO/CuWO4 nanowires and thin films

Authors are grateful to Reinis Ignatans for XRD measurements.

Structural, electrical and optical properties of zinc‐iridium oxide thin films deposited by DC reactive magnetron sputtering

ZnO-IrO2 thin films were deposited on glass by DC reactive magnetron sputtering at room tem-perature. Structural, electrical and optical properties were investigated as a function of iridium atomic concentra-tion in the films. XRD data shows that ZnO-IrO2 thin films are X-ray amorphous and Raman spectrum resembles the spectrum of IrO2, without any distinct features of wurtzite ZnO structure. The lowest film resistivity and the highest transmittance achieved in the present study were 1.4 × 10-3 Ωcm and 33% at 550 nm, respectively. However, resistivity and transmittance are inversely related to the iridium concentration in the films.

Characterization of rhenium oxide films and their application to liquid crystal cells

Rhenium trioxide exhibits high electronic conductivity, while its open cubic crystal structure allows an appreciable hydrogen intercalation, generating disordered solid phases, with protonic conductivity. Rhenium oxide thin films have been obtained by thermal evaporation of ReO3 powders on different substrates, maintained at different temperatures, and also by reactive magnetron sputtering of a Re metallic target. A comparative investigation has been carried out on these films, by using micro-Raman spectroscopy and x-ray diffraction. Two basic types of solid phases appear to grow in the films: a red metallic HxReO3 compound, with distorted perovskite structures, like in the bulk material, a…

Pressure-induced insulator-to-metal transition in α-SnWO4

In-situ high-pressure W L1 and L3 edges x-ray absorption and mid-infrared spectroscopies complemented by first-principles calculations suggest the existence of pressure- induced insulator-to-metal transition in α-SnWO4 in the range of 5-7 GPa. Its origin is explained by a symmetrization of metal-oxygen octahedra due to a strong interaction of Sn 5s, W 5d and O 2p states along the b-axis direction, leading to a collapse of the band gap.

Sputtering deposition and characterization of Ru-doped WO3 thin films for electrochromic applications

Mixed tungsten-ruthenium oxide thin films were prepared for the first time by dc magnetron co-sputtering technique and were studied by cyclic voltammetry, optical transmission measurements, Raman spectroscopy and the W L3 and Ru K edges X-ray absorption spectroscopy (XAS) in comparison with pure WO3 films. The Ru concentration was varied in the range from 0 to 28 at.%. XAS results suggest that the average local structure around both tungsten and ruthenium ions remains unchanged within experimental accuracy in all samples, moreover, for tungsten ions, it resembles that of pure WO3 films. However, the presence of the ruthenium ions affects the electrochemical and optical properties of the fil…

Cluster simulations of structural transformations in yellow arsenic

Abstract Yellow arsenic (y-As) consists of tetrahedral As4 molecules that may be packed in some amorphous and crystalline structures. Like many other arsenic structures, y-As is metastable and undergoes irreversible transitions (polymerization) under irradiation. The process of y-As polymerization, which is observed experimentally, usually leads to the formation of amorphous arsenic (a-As) possessing a continuous random network structure. Our previous quantum chemical simulation for an eight-atom cluster model performed using semi-empirical CNDO/BW approach, combined with optimization technique of cyclic coordinate descent, have shown a formation of molecular dimers due to breaking of one b…

<title>Scanning probe microscopy of nanocrystalline iridium oxide thin films</title>

Structural investigations of nanocrystalline iridium oxide thin films, prepared by dc magnetron sputtering technique were performed by scanning probe microscopy (SPM). SPM studies, using both atomic force microscopy (AFM) and scanning tunnelling microscopy (STM), indicate that the thin films are composed of grains with a size of about 20-50 nm. Fine crystallinity and small RMS microroughness of the films, being well below 2 nm, make iridium oxide thin films promising candidates for nanolithographic applications. The possibility to perform nanolithograhpic processes at a scale of less than 150 nm was successfully examined in AFM and STM modes.© (2003) COPYRIGHT SPIE--The International Societ…

High-pressure x-ray absorption spectroscopy study of tin tungstates

Room-temperature pressure-dependent (0-25 GPa) x-ray absorption spectroscopy at the W -edges of α-SnWO4 and β-SnWO4 was performed using a dispersive setup and a high-pressure nanodiamond anvil cell. The detailed analysis of experimental x-ray absorption near-edge structure and extended x-ray absorption fine structure data suggests that upon increasing pressure, a displacement of tungsten atoms by about 0.2 A toward the center of the WO6 octahedra occurs in α-SnWO4, whereas the coordination of tungsten atoms changes from tetrahedral to distorted octahedral in β-SnWO4.

Raman, electron microscopy and electrical transport studies of x-ray amorphous Zn-Ir-O thin films deposited by reactive DC magnetron sputtering

Zn-Ir-O thin films on glass and Ti substrates were deposited by reactive DC magnetron sputtering at room temperature. Structural and electrical properties were investigated as a function of iridium concentration in the films. Raman spectrum of Zn-Ir-O (61.5 at.% Ir) resembles the spectrum of rutile IrO2, without any distinct features of wurtzite ZnO structure. SEM images indicated that morphology of the films surface improves with the iridium content. EDX spectroscopy and cross-section SEM images revealed that the films growing process is homogeneous. Crystallites with approximately 2-5 nm size were discovered in the TEM images. Thermally activated conductivity related to the variable range…

Study of Copper Nitride Thin Film Structure

Abstract X-ray diffraction and x-ray absorption spectroscopy at the Cu K-edge were used to study the atomic structure in copper nitride (Cu3N) thin films. Textured nanocrystalline films are obtained upon dc magnetron sputtering on substrates heated at about 190 °C, whereas amorphous films having strongly disordered structure already in the second coordination shell of copper are deposited in the absence of heating.

Nanoscale x-ray absorption spectroscopy using XEOL-SNOM detection mode

The first results obtained with the prototype system at the synchrotron beamline ID03 at ESRF are presented and illustrate the possibility to detect an element-specific contrast and to perform nanoscale x-ray absorption spectroscopy experiments at the Zn K and W L 3 absorption edges in mixed zinc oxide-zinc tungstate thin films.

<title>Influence of treatment on stability of electrochromic WO<formula><inf><roman>3</roman></inf></formula> film in acidic electrolyte</title>

The influence of exposure in vacuum of 10-2 - 10-3 Pa and temperature treatment at 720 - 730 K in water vapor atmosphere on stability of tungsten oxide films in 0.1 N H2SO4 electrolyte were studied. The processes that take place during the film exposure in vacuum, determine the reduction of charge injection at the constant voltage change condition. In the case of temperature treatment the opposite changes of charge injection were observed. This indicates to opposite processes in films during both expositions. According to exposures characters, they could be a reduction of tungsten oxide initiated by oxygen evacuation from film in vacuum and film oxidation in water vapor media at high temper…

In Situ Regeneration of Copper-Coated Gas Diffusion Electrodes for Electroreduction of CO2 to Ethylene

This research was funded by the European Union’s Horizon 2020 research and innovation program under grant agreement No 768789 as well as by the Polish National Centre of Science under grant no 2017/26/D/ST8/00508. The Institute of Solid State Physics, University of Latvia, as a center of excellence, has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement no. 739508, project CAMART2.

Spectroscopic studies of molecular arsenic

EXAFS Study of PressureInduced Phase Transition in SrWO4

Pressure-induced scheelite-to-wolframite structural phase transition in SrWO4 was studied using two complementary techniques—x-ray absorption spectroscopy and x-ray diffraction (XRD). In situ XRD and W L3-edge EXAFS measurements were performed using the synchrotron radiation. The experiments were done at room temperature in the pressure range from 0 to 30 GPa using the diamond anvil cell. The XRD results unambiguously show that SrWO4 transforms from the tetragonal scheelite phase to the monoclinic wolframite-type phase at about 11.7 GPa. Locally this transition appears as a change of the tungsten ions coordination from regular tetrahedral to distorted octahedral. The analysis of the EXAFS d…

Ab initio calculations of the Ni K ‐edge XANES in Ni c Mg 1‐c O solid solutions

An interpretation of the Ni K-edge X-ray absorption near edge structure (XANES) in pure NiO and NicMg1-cO solid solutions is given based on three types of ab initio theoretical calculations: the full-multiple-scattering (FMS) approach, the finite difference method (FDM) and the full potential linear muffin-tin orbital (FP-LMTO) method within the LSDA+U approach. The first two methods differ in the cluster potential approximation: the spherically symmetric muffin-tin potential is used in the FMS approach, whereas a non-muffin-tin numerical potential makes the core of the FDM. We found that the FMS and FDM techniques allow rather accurate description of the experimental XANES signal especiall…

Changes in structure and conduction type upon addition of Ir to ZnO thin films

Zn-Ir-O (Zn/Ir ≈ 1/1) thin films have been reported to be a potential p-type TCO material. It is, however, unknown whether it is possible to achieve p-type conductivity at low Ir content, and how the type and the magnitude of conductivity are affected by the film structure. To investigate the changes in properties taking place at low and moderate Ir content, this study focuses on the structure, electrical and optical properties of ZnO:Ir films with iridium concentration varying between 0.0 and 16.4 at.%. ZnO:Ir thin films were deposited on glass, Si, and Ti substrates by DC reactive magnetron co-sputtering at room temperature. Low Ir content (up to 5.1 at.%) films contain both a nano-crysta…

Preparation and Characterization of Tin Tungstate Thin Films

Tin tungstate thin films were prepared by dc magnetron sputtering method and studied by x-ray diffraction, confocal microscopy and Raman spectroscopy. It is shown that the films are composed mainly of nanocrystalline α-SnWO4 phase. The possibility to use these films as write-once optical recording media is demonstrated.

Confocal spectromicroscopy of amorphous and nanocrystalline tungsten oxide films

A Raman confocal spectromicroscopic system was used to study in situ phase composition and surface morphology in amorphous and nanocrystalline tungsten oxide and tungstate thin films, prepared on silicon and glass substrates by dc magnetron co-sputtering technique. The possible use of these films for the phase-change optical recording was demonstrated using 442 nm He–Cd laser with a variable power of up to 50 mW. The formation of nanocrystalline tungsten trioxide or tungstate phases was observed under the laser irradiation. These nanocrystalline phases show relatively strong Raman activity, which can be used for information reading purposes. A multilayer structure composed of several tungst…

Formation of As8 dimers in molecular solid-state arsenic

Abstract Molecular yellow arsenic (y-As) consists of tetrahedral As 4 molecules that may be packed in various ways. All y-As modifications, both disordered and crystalline, are metastable and undergo irreversible transitions (polymerization) under action of heat and light, which cause a change in the nature of bonding in the molecules. Polymerization of y-As leads to the formation of amorphous arsenic (a-As) possessing a continuous random network structure. DTA studies show that polymerization is an activated exothermic process. The value of its enthalpy agrees satisfactorily with an estimate of the excess energy of strained ‘banana-shaped’ bonds in an As 4 molecule. Quantum chemical calcul…

Amorphous ultra-wide bandgap ZnOx thin films deposited at cryogenic temperatures

Crystalline wurtzite zinc oxide (w-ZnO) can be used as a wide band gap semiconductor for light emitting devices and for transparent or high temperature electronics. The use of amorphous zinc oxide (a-ZnO) can be an advantage in these applications. In this paper we report on X-ray amorphous a-ZnOx thin films (~500 nm) deposited at cryogenic temperatures by reactive magnetron sputtering. The substrates were cooled by a nitrogen flow through the copper substrate holder during the deposition. The films were characterized by X-ray diffraction (XRD), Raman, infrared, UV-Vis-NIR spectroscopies, and ellipsometry. The a-ZnOx films on glass and Ti substrates were obtained at the substrate holder temp…

External pressure and composition effects on the atomic and electronic structure of SnWO4

The atomic and electronic structure of tin tungstates, α-SnWO4, α-Sn1.03W0.99O4 and β-SnWO4 ,w as studied by the W L3-edge X-ray absorption spectroscopy and first-principles linear combination of atomic orbital (LCAO) calculations based on the hybrid exchange-correlation density functional (DFT)/ Hartree–Fock (HF) scheme. It was found that the crystal structure of both α-phases is built up of strongly distorted WO6 octahedra, whereas that of β-SnWO4 is composed of nearly regular WO4 tetrahedra. In addition, there are distorted SnO6 octahedra in both α- and β-phases. The metal–oxygen octahedra distortion is explained by the second-order Jahn–Teller effect. The influence of pressure on the st…

X-ray absorption spectroscopy of Cu-doped $WO_{3}$ films for use inelectrochemical metallization cell memory

Abstract We have performed the first synchrotron radiation X-ray absorption spectroscopy (EXAFS/XANES) study of the local atomic and electronic structure around Cu and W ions in WO 3 /Cu/WO 3 /Si and WO 3 /Cu/Si multilayered structures, aimed for the application in the electrochemical metallization cell memory. The influence of low-temperature annealing at 135 °C has been investigated in details, and a structural model of Cu-doped WO 3 films is proposed.

XAS, XRD, AFM and Raman studies of nickel tungstate electrochromic thin films

Abstract Systematic studies of nanocrystalline nickel tungstate, NiWO 4 , thin films were performed by several experimental techniques such as Ni K- and W L 1,3 -edges X-ray absorption spectroscopy, X-ray diffraction, Raman spectroscopy, atomic force microscopy and cyclic voltammetry measurements. We found that the NiWO 4 thin films exhibit electrochromic properties similar to that of amorphous tungsten trioxide films, but show better structural stability upon multiple colouring/bleaching cycling. It was observed that a nanocrystallinity of the thin films results in strong modifications of the NiO and WO interactions, which affect both local atomic and vibrational structures.

Optical properties of zinc-iridium oxide thin films

We present the results of an investigation of ultraviolet, visible, near-infrared (UV-Vis-NIR) and X-ray absorption spectroscopy absorption spectra for zinc-iridium oxide (Zn-Ir- O) thin films with various iridium concentrations deposited by reactive DC magnetron sputtering. It is found that the absorption spectra of zinc-iridium oxide thin films contain a broad band with maxima at 446 nm and 710 nm in the visible region, bands with maxima at about 1100 nm and 3300 nm, and a low-intensity absorption band at 1570 nm in the near-infrared region. The obtained absorption bands are associated with iridium ions at valences of Ir3+, Ir4+ and Ir5+. Changes in the oxidation state of iridium ions fro…

A new tool for nanoscale X-ray absorption spectroscopy and element-specific SNOM microscopy.

Abstract Investigations of complex nanostructured materials used in modern technologies require special experimental techniques able to provide information on the structure and electronic properties of materials with a spatial resolution down to the nanometer scale. We tried to address these needs through the combination of X-ray absorption spectroscopy (XAS) using synchrotron radiation microbeams with scanning near-field optical microscopy (SNOM) detection of the X-ray excited optical luminescence (XEOL) signal. The first results obtained with the prototype instrumentation installed at the European Synchrotron Radiation Facility (Grenoble, France) are presented. They illustrate the possibi…

Atomic structure relaxation in nanocrystalline NiO studied by EXAFS spectroscopy: Role of nickel vacancies

Nanocrystalline NiO samples have been studied using the Ni K-edge extended x-ray absorption fine structure (EXAFS) spectroscopy and recently developed modeling technique, combining classical molecular dynamics with ab initio multiple-scattering EXAFS calculations (MD-EXAFS). Conventional analysis of the EXAFS signals from the first two coordination shells of nickel revealed that (i) the second shell average distance R(Ni–Ni2) expands in nanocrystalline NiO compared to microcrystalline NiO, in agreement with overall unit cell volume expansion observed by x-ray diffraction; (ii) on the contrary, the first shell average distance R(Ni–O1) in nanocrystalline NiO shrinks compared to microcrystall…