Thin La2Zr2O7 films made from a water-based solution

Thin films of La₂Zr₂O₇ (LZO) are highly regarded as possible buffer layers in the coated conductor configuration. This report describes a new synthesis for thin crystalline LZO films, based on a largely water-based solution, mainly containing metal acetates, acetic acid and an organic amine-base: triethanolamine. Initially, a thin layer of amorphous material is deposited on the textured Ni-5 at%W substrate by means of dip-coating. Only by careful control of the thermal treatment can the layer be transformed into a crystalline layer. Important parameters in this respect are the heating rate and the dwell time. The amorphous gel is analysed by HR-TGA/DTA and HR-TEM. The textured layers are analysed by XRD, pole figures, RHEED, AFM and SEM.     

Thick lanthanum zirconate buffer layers from water-based precursor solutions on Ni-5%W substrates

In this work, water-based precursor solutions suitable for dip-coating of thick La₂Zr₂O₇ (LZO) buffer layers for coated conductors on Ni-5%W substrates were developed. The solutions were prepared based on chelate chemistry using water as the main solvent. The effect of polymer addition on the maximum crack-free thickness of the deposited films was investigated. This novel solution preparation method revealed the possibility to grow single, crack-free layers with thicknesses ranging 100–280 nm with good crystallinity and an in-plane grain misalignment with average FWHM of 6.55°. TEM studies illustrated the presence of nanovoids, typical for CSD–LZO films annealed under Ar-5%H₂ gas flow. The appropriate buffer layer action of the film in preventing the Ni diffusion was studied using XPS. It was found that the Ni diffusion was restricted to the first 30 nm of a 140 nm thick film. The surface texture of the film was improved using a seed layer.     

Deposition of La2Zr2O7 film by chemical solution deposition

La₂Zr₂O₇ (LZO) formation of bulk powders and of films by chemical solution deposition (CSD) process have been studied using propionates. The treatment involved a one step cycle in the reducing forming gas (Ar-5%H₂) to be compatible with Ni-5at%W RABITS. Large amount of residual carbon was found in LZO powders formed in these conditions (10 wt%). The volume fraction of the cube texture in LZO films on Ni-5at%W RABITS was found to be a function of the speed of the gas flown above sample. This phenomenon is discussed in considering the C deposited from the carbon-containing gases emitted during the pyrolysis of the precursor. Using proper conditions (950 °C and the speed of gas of 6.8 × 10^?2 m/s), LZO films with good surface crystallinity could be obtained on Ni-5at%W RABITS as demonstrated by X-ray diffraction, electron backscattered diffraction and RHEED. The existence of residual carbon in oxide films is a common question to films deposited by CSD processes under reducing condition.     

XPS chemical state analysis of sputter depth profiling measurements for annealed TiAl-SiO2 and TiAl-W layer stacks

For the application of surface acoustic wave sensors at high temperatures, both a high-temperature stable piezoelectric substrate and a suitable metallization for the electrodes are needed. Our current attempt is to use TiAl thin films as metallization because this material is also known to be high temperature stable. In this study, Ti/Al multilayers and Ti-Al alloy layers were prepared in combination with an SiO₂ cover layer or a W barrier layer at the interface to the substrate (thermally oxidized Si or Ca₃TaGa₃Si₂O₁₄) as an oxidation protection. To form the high-temperature stable γ-TiAl phase and to test the thermal stability of the layer systems, thermal treatments were done in vacuum at several temperatures. We used X-ray photoelectron spectroscopy (XPS) sputter depth-profiling to investigate the film composition and oxidation behavior. In this paper, we demonstrate how the semiautomatic peak fitting can help to extract beside the elemental information also the chemical information from the measured depth profiles.     

Ce(iv)-centered charge-neutral perovskite layers topochemically derived from anionic [CeTa2O7]− layers

Layered perovskites have been extensively investigated in many research fields, such as electronics, catalysis, optics, energy, and magnetics, because of the fascinating chemical properties that are generated by the specific structural features of perovskite frameworks. Furthermore, the interlayers of these structures can be chemically modified through ion exchange to form nanosheets. To further expand the modification of layered perovskites, we have demonstrated an advance in the new structural concept of layered perovskite “charge-neutral perovskite layers” by manipulating the perovskite layer itself. A charge-neutral perovskite layer in [Ce^IVTa₂O₇] was synthesized through a soft chemical oxidative reaction based on anionic [Ce^IIITa₂O₇]⁻ layers. The Ce oxidation state for the charge-neutral [Ce^IVTa₂O₇] layers was found to be tetravalent by X-ray absorption fine structure (XAFS) analysis. The atomic arrangements were determined through scattering transmission electron microscopy and extended XAFS (EXAFS) analysis. The framework structure was simulated through density functional theory (DFT) calculations, the results of which were in good agreement with those of the EXAFS spectra quantitative analysis. The anionic [Ce^IIITa₂O₇]⁻ layers exhibited optical absorption in the near infrared (NIR) region at approximately 1000 nm, whereas the level of NIR absorption decreased in the [Ce^IVTa₂O₇] charge-neutral layer due to the disappearance of the Ce 4f electrons. In addition, the chemical reactivity of the charge-neutral [Ce^IVTa₂O₇] layers was investigated by chemical reduction with ascorbic acid, resulting in the reduction of the [Ce^IVTa₂O₇] layers to form anionic [Ce^IIITa₂O₇]⁻ layers. Furthermore, the anionic [Ce^IIITa₂O₇]⁻ layers exhibited redox activity which the Ce in the perovskite unit can be electrochemically oxidized and reduced. The synthesis of the “charge-neutral” perovskite layer indicated that diverse features were generated by systematically tuning the electronic structure through the redox control of Ce; such diverse features have not been found in conventional layered perovskites. This study could demonstrate the potential for developing innovative, unique functional materials with perovskite structures.

This study proposed a new layer modification technique, “layer charge control”, for layered perovskites, and the structures of the obtained charge neutral [CeTa₂O₇] perovskite sheet were characterized theoretically and experimentally.     

Ein neuer Zugang zu Alkalivanadaten(IV,V) Die Kristallstruktur von Rb2V3O8

A New Access to Alkali Vanadates(IV,V) Crystal Structure of Rb₂V₃O₈ By heating vanadium(V) oxide with rubidium iodide to 500°C, the vanadium experiences partial reduction and Rb₂V₃O₈ is obtained. It has the fresnoite structure. Crystal data: a = 892.29(7), c = 554.49(9) pm at 20°C, tetragonal, space group P4bm, Z = 2. X-ray crystal structure determination with 620 observed reflexions, R = 0.027. V₂O₇ units share vertices with VO₅ square pyramids, forming layers; a layer can be regarded as association product of VO²⁺ and V₂O₇^4? ions. The Rb⁺ ions between the layers have pentagonal-antiprismatic coordination.     

AES investigation of thermally sprayed Al2O3 coatings on steel

Summary The investigation of plasma sprayed steel/Al₂O₃ composites by means of Auger Electron Spectroscopy (AES) combined with depth profile analysis is described. Incomplete sprayed Al₂O₃ layers permit analysis of single sprayed particles and of surrounding uncovered steel substrate regions. More complete coatings are separated from the substrates, so that contact surfaces of substrates and Al₂O₃ layers can be analyzed. In order to determine the influence of preheating the substrates on the interface widths between steel substrate and Al₂O₃ coating and therefore on the adherence mechanism, both procedures are carried out for two preheating temperatures. It is shown that preheating hardly effects the interface widths beneath single sprayed particles but it causes laterally constant widths for complete layer fragments. Additionally, a comprehensive view about oxide layer thicknesses on the steel substrates before and after plasma spraying is offered.     

XPS Depth Profile Analysis of a Thin Non-Conducting Titanate Superlattice

 New BaTiO₃-SrTiO₃ (BTO-STO)-superlattices which may be interesting for future electronic applications have been investigated by X-ray photoelectron spectroscopy (XPS) depth profiling. At first XPS measuring conditions were optimized for that non-conducting and thin layer systems (21 nm double layer thickness) considering the practical instrumental limitations. Second a simulation of the sputtering process for the concrete experimental conditions were done by a dynamic T-DYN code. By comparison of experimental and simulated depth profiles the maximum sample roughness could be estimated to be in the range of 2 nm.     

Energy resolved XPS depth profile of (IrO2, RuO2, Sb2O5, SnO2) electrocatalyst powder to reveal core‐shell nanoparticle structure

Synchrotron‐based energy resolved XPS was used to characterize the structure of IrO₂? RuO₂‐coated Sb₂O₅? SnO₂ nanoparticles. Samples were heat treated at 300, 350, 400, 450 and 500 °C after chloride Ir and Ru precursors were added to Sb₂O₅? SnO₂. Photoelectron kinetic energies of 100, 350 and 1400 eV were employed to obtain an indication of the depth of elemental distributions and chemical shifts. It was shown that the electrocatalyst consists of a core of Sb₂O₅? SnO₂ enriched with Sb₂O₅ towards the surface, with a shell of IrO₂? RuO₂ deposited on this core, and an outer layer of Sb₂O₅? SnO₂ over this shell. No significant chemical interaction occurs between IrO₂? RuO₂ and Sb₂O₅? SnO₂. The energy resolved XPS depth profile technique is effective for studying core‐shell materials. Copyright © 2010 John Wiley & Sons, Ltd.     

Core level photoemission spectroscopy and chemical bonding in Sr2Ta2O7

Electronic parameters of constituent element core levels of strontium pyrotantalate (Sr₂Ta₂O₇) were measured with X-ray photoelectron spectroscopy (XPS). The Sr₂Ta₂O₇ powder sample was synthesized using standard solid state method. The valence electron transfer on the formation of the Sr–O and Ta–O bonds was characterized by the binding energy differences between the O 1s and cation core levels, Δ(O–Sr) = BE(O 1s) − BE(Sr 3d_5/2) and Δ(O–Ta) = BE(O 1s) − BE(Ta 4f_7/2). The chemical bonding effects were considered on the basis of our XPS results for Sr₂Ta₂O₇ and earlier published structural and XPS data for other Sr- and Ta-containing oxide compounds. The new data point for Sr₂Ta₂O₇ is consistent with the previously derived relationship for a set of Sr-bearing oxides. The binding energy difference Δ(O–Sr) was found to decrease with increasing bond distance L(Sr–O).     

Structure of trihydrated rare-earth acid diphosphates LnHP2O7·3H2O (Ln=La, Er)

In trihydrated lanthanum acid-diphosphates LnHP₂O₇·3H₂O, prepared from acid LnCl₃ and Na₄P₂O₇ solutions (pH=1), two crystal forms were obtained. Layered structures of two representative members of this family have been determined by single-crystal X-ray diffraction (XRD) technique. In the case of orthorhombic LaHP₂O₇·3H₂O (type I), lanthanum cations are ninefold coordinated and diphosphate groups adopt a staggered (alternated) configuration. In the case of triclinic ErHP₂O₇·3H₂O (type II), erbium cations are eightfold coordinated and diphosphate groups adopt an eclipsed configuration. In agreement with Infrared (IR) spectroscopic data, a bended configuration for diphosphate groups has been deduced. In both structures, one-dimensional chains of edge-sharing rare-earth polyhedra are linked together by diphosphate groups to form the phosphate layers. In both diphosphates, PO₄ and HPO₄ environments have been identified by ³¹P MAS-NMR technique. In the two compounds, OH groups of HPO₄ tetrahedra point out of diphosphate planes interacting with adjacent layers. In La-diphosphate, the interaction between HPO₄ groups and water molecules of adjacent layers is favored; however, in Er-diphosphate, the interaction between phosphate acid groups of contiguous layers is produced. Based on structural information deduced, differences detected in IR and NMR spectra of two disphosphates are discussed.     

The Application of a Y-Modified Lanthanum Zirconate Flexible Thin Film for a High-Performance Flexible Supercapacitor

With the rapid development of wearable electronics devices, there is increasing demand for the development of new flexible energy storage devices with high security, and this has become a hot research topic. Although flexible supercapacitors are considered to be high-performance energy-storage equipment because of their fast charging/discharging ability, long cycle life, good reliability, wide operating temperature range, and so on, there are still many drawbacks that need to be overcome. Herein, the La₂Zr₂O₇ (LZO) thin film is synthesized as a new energy-storage material by using a facile electrospinning method and calcination at low temperature. In addition, the mechanism of producing the flexibility of this film is determined by TG, IR, and XRD analyses. As previous studies have suggested that the charge storage of the LZO film can be attributed to the mechanism of oxygen intercalation, the Y element is doped into the LZO film to increase the concentration of oxygen vacancies. The changes in structural and electrochemical properties of La₂Y_xZr_2−xO₃ (0≤x≤0.5) nanofibers (LNF-x) with increasing Y content are studied carefully to obtain the best doping sample. The LNF-0.1 sample shows the highest areal capacitance of 605.3 mF cm⁻² at 2 mA cm⁻², so a symmetrical flexible device is fabricated with LNF-0.1 electrodes. This device has a high energy density (76.7 μW h cm⁻² at 2 mW cm⁻²), good cycling stability, and excellent mechanical flexibility. This study thus provides a new research trend for portable and wearable electronics.     

Sol-Gel Preparation and Characterization of Ag-TiO2 Nanocomposite Thin Films

Ag-TiO₂ thin films were prepared with a sol-gel route, using titanium isopropoxide and silver nitrate as precursors, at 0.03 and 0.06 Ag/Ti nominal atomic ratios. After drying at 80°C, the films were fired at 300°C and 500°C for 30 min. The films were analysed by X-ray diffraction (XRD) with glancing angle, and X-ray photoelectron spectroscopy (XPS), with depth profiling of the concentration. XPS analysis showed the presence of C and N as impurities in the nanocomposite films. Their concentration decreased with increasing the firing temperature. Chemical state analysis showed that Ag was present in metallic state, except for the very outer layer where it was present as Ag⁺. For the films prepared with a Ag/Ti concentration of 0.06, depth profiling measurements of the film fired at 300°C showed a strong Ag enrichment at the outer surface, while composition remained almost constant within the rest of the film, at 0.019. For the films heated to 500°C, two layers were found, where the Ag/Ti ratios were 0.015 near the surface and 0.026 near the substrate.     

XPS for non-destructive depth profiling and 3D imaging of surface nanostructures

Depth profiling of nanostructures is of high importance both technologically and fundamentally. Therefore, many different methods have been developed for determination of the depth distribution of atoms, for example ion beam (e.g. O₂⁺, Ar⁺) sputtering, low-damage C₆₀ cluster ion sputtering for depth profiling of organic materials, water droplet cluster ion beam depth profiling, ion-probing techniques (Rutherford backscattering spectroscopy (RBS), secondary-ion mass spectroscopy (SIMS) and glow-discharge optical emission spectroscopy (GDOES)), X-ray microanalysis using the electron probe variation technique combined with Monte Carlo calculations, angle-resolved XPS (ARXPS), and X-ray photoelectron spectroscopy (XPS) peak-shape analysis. Each of the depth profiling techniques has its own advantages and disadvantages. However, in many cases, non-destructive techniques are preferred; these include ARXPS and XPS peak-shape analysis. The former together with parallel factor analysis is suitable for giving an overall understanding of chemistry and morphology with depth. It works very well for flat surfaces but it fails for rough or nanostructured surfaces because of the shadowing effect. In the latter method shadowing effects can be avoided because only a single spectrum is used in the analysis and this may be taken at near normal emission angle. It is a rather robust means of determining atom depth distributions on the nanoscale both for large-area XPS analysis and for imaging. We critically discuss some of the techniques mentioned above and show that both ARXPS imaging and, particularly, XPS peak-shape analysis for 3D imaging of nanostructures are very promising techniques and open a gateway for visualizing nanostructures.     

Crystal structure of the pyrovanadate K4V2O7

The crystal structure of anhydrous K₄V₂O₇ (I) is determined by powder X-ray diffraction. The compound crystallizes in the monoclinic system (a = 10.222(1) Å, b = 6.2309(8) Å, c = 7.282(1) Å, β = 101.31(1)°, space group C2/m, Z = 2). The structure contains layers of isolated V₂O₇ pyrovanadate groups separated by layers of potassium cations. The hydration and dehydration of I are studied by thermal analysis and high-temperature X-ray diffraction. The dehydration is accompanied by decomposition of the starting crystal hydrate to give intermediate compounds. Anhydrous compound I undergoes a reversible phase transition at 740°C. The high-temperature phase is assumed to have a hexagonal unit cell (a = 6.169(4) Å, c = 15.72(1) Å, Z = 2).     

Preparation and characterization of single RE2O3–Mo secondary emission materials

La₂O₃–Mo, Y₂O₃–Mo, Gd₂O₃–Mo and Ce₂O₃–Mo were prepared by liquid–liquid doping combined with spark plasma sintering. The microstructure and surface behaviour of rare earth oxide of the cathode have been studied by microscope, Auger Electron Spectroscopy (AES) and X-ray Photoelectron Spectroscopy (XPS) methods. Among these four kinds of cathode, Y₂O₃–Mo cathode exhibits the best secondary emission property, i.e., the maximum secondary emission yield could reach 5.24. The penetration depth of primary electrons and escape depth of secondary electrons have been calculated and the energy distribution of primary electrons in the cathode has been simulated by Monte Carlo method. Y₂O₃–Mo cathode has the largest penetration depth and escape depth, which could be attributed to the highest secondary electron emission yield of the cathode.     

Electron Probe Microanalysis of HfO2 Thin Films on Conductive and Insulating Substrates

Quantitative electron probe microanalysis of highly insulating materials is a complicated problem, partially solved by coating samples with grounded thin conductive layers or using novel scanning electron microscopy (SEM) techniques, such as low-voltage and/or variable pressure SEM. In this work, some problems of quantitative X-ray microanalysis of thin HfO₂ films, in particular the possibility to determine mass thickness correlated to the density of the layer material, are discussed. For comparison, Al₂O₃, Ta₂O₅ and TiO₂ films grown onto both semiconductive Si and insulating quartz substrates were also analysed. All the films studied were synthesized by atomic layer deposition method.     

Electronic parameters of Sr2Nb2O7 and chemical bonding

X-ray photoelectron spectroscopy (XPS) measurements were carried out on a strontium pyroniobate (Sr₂Nb₂O₇) powder sample, which was synthesized using standard solid-state method. The binding energy (BE) differences between the O 1s and cation core levels, Δ(O-Nb)=BE(O 1s)-BE(Nb 3d_5/2) and Δ(O-Sr)=BE(O 1s)-BE(Sr 3d_5/2), were used to characterize the valence electron transfer on the formation of the Nb-O and Sr-O bonds. The chemical bonding effects were considered on the basis of our XPS results for Sr₂Nb₂O₇ and earlier published structural and XPS data for other Sr- or Nb-containing oxide compounds. The new data point for Sr₂Nb₂O₇ is consistent with the previously derived relationship for a set of Nb⁵⁺-niobates that Δ(O-Nb) increases with increasing mean Nb-O bond distance, L(Nb-O). A new empirical relationship between Δ(O-Sr) and L(Sr-O) was also obtained. Interestingly, the correlation between Δ(O-Sr) and L(Sr-O) was found to differ from that between Δ(O-Nb) and L(Nb-O). Possible cause for the difference is discussed.     

X-ray photoelectron spectroscopic and electrochemical impedance spectroscopic analysis of RuO2-Ta2O5 thick film pH sensors

The paper reports on investigation of the pH sensing mechanism of thick film RuO₂-Ta₂O₅ sensors by using X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). Interdigitated conductimetric pH sensors were screen printed on alumina substrates. The microstructure and elemental composition of the films were examined by scanning electron microscopy and energy dispersive spectroscopy. The XPS studies revealed the presence of Ru ions at different oxidation states and the surface hydroxylation of the sensing layer increasing with increasing pH. The EIS analysis carried out in the frequency range 10 Hz–2 MHz showed that the electrical parameters of the sensitive electrodes in the low frequency range were distinctly dependent on pH. The charge transfer and ionic exchange occurring at metal oxide-solution interface were indicated as processes responsible for the sensing mechanism of thick film RuO₂-Ta₂O₅ pH sensors.     

Characterization and Transport Properties of Surfactant-Templated Silica Layers for Membrane Applications

An intermediate surfactant-templated silica (STS) layer is applied between the supporting mesoporous γ-Al₂O₃ and the amorphous microporous silica overlayer resulting in dual-layered microporous silica membranes for gas separation applications that show improved values for both hydrogen flux and selectivity. Determination of thickness and porosity of as-deposited membrane layers by spectroscopic ellipsometry reveals that the STS layer is present as a distinctive layer of ～20 nm thickness, with penetration up to a depth of ～70 nm into the underlying γ-Al₂O₃support layer, whose thickness and porosity are determined to be 1.3 μm and 50%, respectively.