Photoelectron Spectroscopy Depth Profile Analysis Research Articles

External Voltage-Induced Restructuring of the Solid-State Electrode/Electrolyte Interface Revealed by X-ray Photoelectron Spectroscopy Depth Profiling Analysis.

Solid/solid interfaces between electrodes and electrolytes play an important role in all-solid-state energy devices, while microscopic investigations of the buried interfaces remain challenging. Here, we construct metal|yttria-stabilized zirconia (YSZ)|Au model cells consisting of a metal film cathode (metal (M) = Au, Ni, and Ag), a single crystalline YSZ electrolyte, and a Au film anode, and use quasi in situ X-ray photoelectron spectroscopy depth profiling analysis to investigate the restructuring of buried interfaces between metal cathodes and YSZ. After applying 2.9 V at 500 °C, interfacial Zr4+ ions in the electrolyte are reduced and then interdiffuse with metal cathode overlayers, forming a miscible ZrM alloy interlayer. The interface restructuring degree follows the sequence of Au|YSZ|Au > Ni|YSZ|Au > Ag|YSZ|Au. Meanwhile, surface segregation of Zr on the cathode surface is also observed, whose degree follows the sequence of Ag|YSZ|Au > Ni|YSZ|Au > Au|YSZ|Au. Notably, the strong ZrM alloy formation enhances the interface restructuring but suppresses the Zr surface segregation. This work provides a fundamental understanding of the interfacial reaction at the buried electrode/electrolyte interface.

Enhancement in CO Selectivity by Modification of ZnO with CuxO for Electrochemical Reduction of CO2

The electrochemical reduction reaction of carbon dioxide (CO2RR) has garnered significant attention due to its potential for the formation of carbon monoxide, which has industrial relevance. Herein, an oxide‐derived Cu–Zn electrocatalyst with an optimized Cu x O layer that shows high selectivity toward CO with a faradic efficiency of 75% at a low overpotential (−0.8 V vs reversible hydrogen electrode) is reported. Various structural characterizations and activity tests are conducted to understand the origin of this improvement depending on the Cu x O amount. Electrochemical surface area and electrochemical impedance spectroscopy measurements suggest that the addition of Cu x O increases double‐layer capacitance and decreases charge transfer resistance. Scanning electron microscopy images indicate that the electrodes undergo a severe reconstruction process, which is further confirmed by X‐ray diffraction that shows the formation of CuZn4 alloy during the reduction reaction. Furthermore, X‐ray photoelectron spectroscopy depth profile analysis shows that after CO2RR at −0.8 V, the Cu/Zn ratio is higher than that after −1.2 V, which suggests that applied potential plays a significant role in the reconstruction process and hence the difference in selectivity. The presence of copper in the surface layer has a significant impact on the improvement of selectivity toward CO.

Chemical Composition, Structure, and Physical Properties of AlN Films Produced via Pulsed DC Reactive Magnetron Sputtering

The chemical composition, structure, and physical properties of aluminum nitride (AlN) films obtained using pulsed DC reactive magnetron sputtering in asymmetric bipolar mode have been studied. X-ray diffraction and electron diffraction confirmed the composition of c–axis textured hexagonal AlN films required for piezoelectric applications. The surface of the films obtained is quite smooth; the arithmetic average roughness does not exceed 2 nm. Transmission electron microscopy has shown the presence of a transition layer at the film–substrate interface. Transmission electron microscopy and X-ray photoelectron spectroscopy depth profile analysis have shown that the films have an oxidized surface layer which has an influence on the optical model of the films derived from ellipsometric data. However, it does not significantly influence the films’ piezoresponse. Piezoelectric force microscopy indicated a piezoelectric effect in the films that is uniform over their surface.

A method of controlling the imprint effect in hafnia ferroelectric device

Recently, hafnia-based ferroelectrics are currently being investigated as next-generation memory devices due to their excellent CMOS process compatibility and functionality. However, some of the ferroelectric devices commonly exhibit an imprint effect due to charged defects around the interfacial layer, which has negative impacts on the ferroelectric memory devices. However, it can be applied to various applications as long as the imprint field is carefully adjusted. In this work, we introduced a strategy to control the imprint field in bilayer capacitors by utilizing tantalum oxide (TaO) interfacial layers and various Zr contents in Hf0.83Zr0.17O2 (HZO) films. The TaO layer (1 nm) was inserted into the bilayer capacitors to alter the imprint field's (positive or negative) direction. Whereas to control the imprint fields, we adjusted the Zr doping content (17%–83%) in the ferroelectric HZO films (8 nm). As the Zr content increased, reduced imprint fields were observed in those bilayer capacitors. In addition, it was found that a high imprint field (+2.43 MV/cm) was observed in Hf-rich films (Hf0.83Zr0.17O2) due to the higher amount of oxygen vacancies. In addition, we examined those oxygen vacancies through x-ray photoelectron spectroscopy depth profile analysis by considering sub-oxide fractions in the tantalum, which further confirms the root cause of the imprint field variations in the bilayer capacitors. Our study will contribute to a deeper understanding of imprinted hafnia-based ferroelectrics and will provide an insight into devices that utilize the imprint effect.

Understanding SEI evolution during the cycling test of anode-free lithium-metal batteries with LiDFOB salt.

Anode-free lithium-metal batteries (AFLMBs) have the potential to double the energy density of Li-ion batteries, but face the challenges of mossy dendritic lithium plating and an unstable solid electrolyte interphase (SEI). Previous studies have shown that the AFLMBs with an electrolyte containing lithium difluoro(oxalato)borate (LiDFOB) salt outperform those with lithium hexafluorophosphate (LiPF6), but the mechanism behind this improvement is not fully understood. In this study, X-ray photoelectron spectroscopy (XPS) depth profile analysis and electrochemical impedance spectroscopy (EIS) were conducted to investigate the SEI on plated Li from the two conducting salts and their evolution in Cu‖NMC full cells during cycling. XPS results revealed that an inorganic-rich SEI layer is formed in the cell with LiDFOB-based electrolyte, with a low carbon/oxygen ratio of 0.56 compared to 1.42 in the LiPF6-based cell. With the inorganic-rich SEI, a dense electroplated Li with a shining surface on the Cu substrate can be retained after ten cycles. The inorganic-rich SEI enhances the reversibility of Li plating and stripping, with a high average CE of ∼98% and a stable charge/discharge voltage profile. The changes in SEI resistance and cathode electrolyte interphase resistance are more prominent compared to the changes in solution and charge transfer resistances, which further validate the role of the passivation films on Li deposits and NMC cathode surfaces in stabilizing AFLMB cycling performance.

Oxygen Vacancy Control as a Strategy to Enhance Imprinting Effect in Hafnia Ferroelectric Devices

Hafnia-based ferroelectric materials are recently drawing a significant attention for future electronic devices; however, there is a need to further enhance their functionality for practical applications. Especially, an imprinting effect has been regarded as a defect to be reduced in ferroelectrics; yet, it can be positively applied to various electronic devices with the functionality of self-rectifying behavior and threshold voltage adjustment. For the first time, we report a high imprinting effect in bilayer stack capacitors [TiN/Hf0.5Zr0.5O2 (HZO)/tantalum oxide (TaO)/TiN] by employing an optimal TaO insertion layer. Furthermore, the imprinting effect was enhanced by adopting high-pressure annealing (HPA) process. X-ray photoelectron spectroscopy (XPS) depth profile analysis reveals that the origin of the imprint field is the tantalum suboxides (Ta2O5-x) with doubly positively charged oxygen vacancies ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{V}_{\text {o}}^{++}$ </tex-math></inline-formula> ). The imprint field increases with increasing HPA temperatures and achieved a high imprint field of 1.65 MV/cm at 600 °C. Moreover, endurance was observed up to 108 cycles without a breakdown while maintaining the original coercive fields up to 105 cycles. We also investigated how the TaO insertion layer with an imprint field influences the switching, interfacial, and ferroelectric properties. These findings on the imprinting effect provide a new strategy to improve the functionality of hafnia-based ferroelectric devices in the near future.

Planting Anion Channels in a Negatively Charged Polyamide Layer for Highly Selective Nanofiltration Separation.

A nanofiltration (NF) membrane with high salt permeation and high retention of small organics is appealing for the treatment of high-salinity organic wastewater. However, the conventional negatively charged NF membranes commonly show high retention of divalent anions (e.g., SO42-), and the reported positively charged NF membranes normally suffer super low selectivity for small organics/Na2SO4 and high fouling potential. In this work, we propose a novel "etching-swelling-planting" strategy assisted by interfacial polymerization and mussel-inspired catecholamine chemistry to prepare a mix-charged NF membrane. By X-ray photoelectron spectroscopy depth profiling and pore size distribution analysis, it was found that such a strategy could not only deepen the positive charge distribution but also narrow the pore size. Molecular dynamics confirm that the planted polyethyleneimine chains play an important role to relay SO42- ions to facilitate their transport across the membrane, thus reversing the retention of Na2SO4 and glucose (43 vs 71%). Meanwhile, due to the high surface hydrophilicity and smoothness as well as the preservation of abundant negatively charged groups (-OH and -COOH) inside the separation layer, the obtained membrane exhibited excellent antifouling performance, even for the coking wastewater. This study advances the importance of vertical charge distribution of NF membranes in separation selectivity and antifouling performance.

Impact of interfacial engineering on MgO-based resistive switching devices for low-power applications

In this work, the resistive switching characteristics of MgO/Al2O3-based resistive random-access memory (ReRAM) devices have been reported. Analysis shows the change in dominant conduction mechanism from space-charge-limited conduction to Schottky emission owing to the incorporation of an Al2O3 insertion layer. The MgO/Al2O3 bilayer ReRAM devices exhibit lower power operation (50.6% reduction) and better switching uniformity as compared to single-layer devices, depending on the stack configuration. This can be attributed to the lower oxygen vacancy accumulation and filament confinement at the MgO/Al2O3 interface, resulting in a more controllable switching operation. Further X-ray photoelectron spectroscopy (XPS) depth profile analysis of the bilayer device reveals that the switching dynamics are correlated directly with the oxygen vacancy concentrations. These findings indicate the importance of interfacial layer engineering in improving the resistive switching properties of MgO-based memory devices, thus allowing for low-power applications.

Cu-Mg-O thin films by RF magnetron co-sputtering: Their band offsets with CdS in heterojunction solar cells

We report on Cu-Mg.O thin films of 100 - 300 nm in thickness produced by radio frequency (RF) reactive sputtering fromCu and Mg-metal targets in an argon-oxygen ambient. The amount of Mg in the thin films was varied through changingthe RF power applied at the Mg target. When the Mg content in the Cu-Mg-O film changed from 0 to 0.3, the opticalbandgap increased from 1.73 eV to 2.13 eV, and the electrical conductivity decreased from 9 x 10-3 Ω-1 cm-1(CuxO) to 6.7x 10-5 Ω-1 cm-1(Cuo7/Mg0.30). Solar cells of these films, FTO/ CdS/Cu0.85Mg0.15O/C-Ag, showed a short circuit current density of 2.86 mA/cm2 an open circuit voltage of 378 mV, and power conversion efficiency of 0.25%. X-ray photo-electron spectroscopy depth profile analyses of the interfaces suggest a negative conduction band offset in CdS/Cu0.85Mg0.15O( — 0.74 eV) as well as in CdS/CuxO (0.9 eV) solar cells.

Plasma-enhanced atomic layer deposition of amorphous Ga2O3 gate dielectrics

Amorphous gallium oxide (Ga2O3) thin films were investigated as gate dielectrics for electronic device applications using plasma-enhanced atomic layer deposition. The structural and morphological properties as well as the electrical and dielectric behaviors of Ga2O3 thin films were explored. The surface morphology of the amorphous Ga2O3 thin film was highly smooth with root mean square of 0.55 nm and low defect density, which were visible to atomic force microscopy. The grazing incidence X-ray diffraction pattern showed no discernible peak, indicating that the film was amorphous. The X-ray photoelectron spectroscopy depth-profiling analysis showed that the Ga/O ratio was 0.76, slightly more than the optimum 2/3 ratio (0.67). The temperature-dependent current–voltage characteristics of the Au/Ni/Ga2O3/p-Si structure revealed that ideality factor and barrier height values decreased and increased with increasing temperature, respectively, demonstrating their high temperature dependency. Regardless of the applied frequency, Ga2O3 thin films exhibited a good dielectric constant of about ∼9 at zero bias voltage. The comprehensive capacitance–voltage analysis showed low trap densities of about 1012 eV−1 cm−2 at the Ga2O3–p-Si interface.

Effects of mineral surface silanization and bitumen coating on its filtration from an aqueous slurry

The effects of residual bitumen on oil sands tailings filtration have rarely been examined. In the present work, the filtration of bitumen-coated minerals, including quartz, rutile, kaolinite, and montmorillonite, was studied. Bitumen-coated quartz was compared with silanized quartz to decouple the effects of surface hydrophobicity and adsorbed bitumen layer on filtration. The minerals were treated in bitumen-toluene solutions with different bitumen concentrations. The treated minerals were subjected to vaccum filtration and their wettability was measured by sessile drop contact angle method. It was found that the filtration rate of silanized quartz was linearly correlated with contact angle. It was also observed that at low bitumen concentration, the contact angle and filtration rate of all tested minerals were increased. However, at high bitumen concentration, the filtration rates were reduced drastically despite the high contact angle. CHNS elemental analyses, and X-ray photoelectron spectroscopy surface composition and depth profile analyses showed that the minerals had higher C, N, S contents and thicker bitumen layer when they were treated at higher bitumen concentration. It was hypothesized that under the pressure gradient during filtration, the thick and patchy bitumen coating layers could inter-penetrate when the mineral particles were pushed together, to form a inter-locked film to close off the pores in the filter cake. Indeed, mineral-bitumen aggregates were observed by X-ray microscope/nanoCT imaging of the filter cake. It was concluded that a thin layer of bitumen coating helped filtration due to the induced hydrophobicity, but a thick (and patchy) bitumen coating impeded filtration.

Grain boundary strengthening of carbon-doped TiZrN coatings by laser carburization

ABSTRACT The improved mechanical properties of carbon-doped TiZrN coatings were investigated in terms of the microstructure and bonding state. The carbon incorporation and structural change were confirmed as a shift to lower degree of the diffraction pattern and the decreased grain size from 24.64 to 22.19 nm. The clear grain boundaries (GBs) were observed in the carbon-doped coating, and its fast Fourier transform (FFT) exhibited a diffused ring pattern. Edge dislocations were also observed in the inverse FFT image, indicating the formation of an amorphous phase due to laser carburization. From the X-ray photoelectron spectroscopy depth profile analysis, the carbon concentration decreased to 37.26 at.% after carburization, which is non-stoichiometric behavior that suggests the formation of the amorphous carbon (a-C) rather than carbides. Both sp2- and sp3-hybridized bonds were detected in the C 1s spectrum of the carbon-doped coating, indicating that the diffused carbon atoms were trapped in the GBs as a-C. The change in the GB structure increased the compressive residual stress from 3.97 to 4.63 GPa. In addition, the hardness, elastic strain to failure (H/E), and plastic deformation resistance (H3/E2) of the carbon-doped TiZrN increased by 19.22%, 12.64%, and 49.59%, respectively, demonstrating the effect of GB strengthening.

Alloy-Electrode-Assisted High-Performance Enhancement-Type Neodymium-Doped Indium-Zinc-Oxide Thin-Film Transistors on Polyimide Flexible Substrate.

Flexible thin-film transistors with high current-driven capability are of great significance for the next-generation new display technology. The effect of a Cu-Cr-Zr (CCZ) copper alloy source/drain (S/D) electrode on flexible amorphous neodymium-doped indium-zinc-oxide thin-film transistors (NdIZO-TFTs) was investigated. Compared with pure copper (Cu) and aluminum (Al) S/D electrodes, the CCZ S/D electrode changes the TFT working mode from depletion mode to enhancement mode, which is ascribed to the alloy-assisted interface layer besides work function matching. X-ray photoelectron spectroscopy (XPS) depth profile analysis was conducted to examine the chemical states of the contact interface, and the result suggested that chromium (Cr) oxide and zirconium (Zr) oxide aggregate at the interface between the S/D electrode and the active layer, acting as a potential barrier against residual free electron carriers. The optimal NdIZO-TFT exhibited a desired performance with a saturation mobility (μsat) of 40.3 cm2·V−1·s−1, an Ion/Ioff ratio of 1.24 × 108, a subthreshold swing (SS) value of 0.12 V·decade−1, and a threshold voltage (Vth) of 0.83 V. This work is anticipated to provide a novel approach to the realization of high-performance flexible NdIZO-TFTs working in enhancement mode.

Depth profile study on Ti/Al bilayer Ohmic contacts to AlGaN/GaN

The electrical performance of double layered Ohmic contacts not only depends on layer thicknesses, annealing temperatures and annealing time etc. but also Ohmic contact metals and reactions with substrates and each other. Furthermore, oxidation tendency of Ohmic contact metals is highly important for contact quality and stability. In this study, we have investigated Ti/Al Ohmic contact formation on undoped AlGaN substrates by X-ray photoelectron spectroscopy (XPS) depth profile analysis. We aimed to reveal the oxide compounds and reaction products of metals and dependencies to the contact depth. In survey mode and depth profile mode five atoms core level (Ga 3d, Al 2p, N 1 s, Ti 2p and O 1 s) was observed and the XPS core level peaks were convoluted with Gaussian profiles to identify the origin of the peaks. Our results show that Ohmic contact metals strongly incorporated with oxygen, leading to high specific contact resistivity (ρs) confirmed by the TLM measurement. Also it is found that thermal treatments cause a TiAl3 metallic alloy in the Ti/Al interface and the presence of excess Ga and TiN indicates that out diffusion of N atoms at the metal semiconductor (MS) interface.

Origin of PL emission at 0.797 eV in near stoichiometric spray deposited CZTS thin films

Photoluminescence (PL) spectroscopy has been employed for analyzing defect levels in near stoichiometric Cu2ZnSnS4 (CZTS) thin films deposited using chemical spray pyrolysis (CSP) technique. An emission at 0.797 eV could be recorded at 15 K from the near stoichiometric CZTS thin films. This emission was persistent up to room temperature and could be identified as “donor to acceptor pair (DAP)” transition and also bears close connection with concentration of copper. Using temperature as well as excitation power dependent PL measurements and X-ray photoelectron spectroscopy (XPS) depth profile analysis, the emission at 0.797 eV could be identified as arising from transition between donor level (due to OSn defect) and acceptor level (created by Cuzn defect).

Overcoming consistency constrains of ITO/ZnO/P3HT:PCBM/Ag solar cell by open air annealing and its systematic stability study under inborn conditions

Focusing on simplicity and industrial viability, polymer solar cells with configuration indium tin oxide (ITO)/ZnO/P3HT:PCBM/Ag were fabricated and characterized. Differing from the usual trend of using glove box for polymer device fabrication, here electron transport and active layer of the devices were deposited and stored in open air atmosphere without any encapsulation. Effect of active layer thickness on device performance was analyzed. Choosing the optimum thickness of 220 ± 20 nm, a number of devices were fabricated with same configuration and the effect of annealing on the photovoltaic parameters was investigated. Unlike annealing studies reported in literature, particular emphasis was given here to study the influence of annealing in ambient atmosphere, at temperature of 50 °C, for 30 s. This short period, low temperature annealing enhanced the device parameters mainly short circuit current density and hence efficiency. Lifetime measurements were done by monitoring the device and measuring its J–V parameters periodically for 1 year. X-ray photoelectron spectroscopy depth profile analysis was employed to demonstrate that surface modified ZnO effectively hinders the diffusion of indium from ITO to active layer.

Atomic-Layer-Deposited MoN x Thin Films on Three-Dimensional Ni Foam as Efficient Catalysts for the Electrochemical Hydrogen Evolution Reaction.

Future realization of a hydrogen-based economy requires a high-surface-area, low-cost, and robust electrocatalyst for the hydrogen evolution reaction (HER). In this study, the MoN x thin layer is synthesized on to a high-surface-area three-dimensional (3D) nickel foam (NF) substrate using atomic layer deposition (ALD) for HER catalysis. MoN x is grown on NF by the sequential exposure of Mo(CO)6 and NH3 at 225 °C. The thickness of the thin film is controlled by varying the number of ALD cycles to maximize the HER performance of the MoN x/NF composite catalyst. The scanning electron microscopy and transmission electron microscopy (TEM) images of MoN x/NF highlight that ALD facilitates uniform and conformal coating. TEM analysis highlights that the MoN x film is predominantly amorphous with the nanocrystalline MoN grains (4 nm) dispersed throughout it. Moreover, the high-resolution (HR)-TEM analysis shows a rough surface of the MoN x film with an overall composition of Mo0.59N0.41. X-ray photoelectron spectroscopy depth-profile analysis reveals that oxygen contamination is concentrated at the surface because of surface oxidation of the MoN x film under ambient conditions. The HER activity of MoN x is evaluated under acidic (0.5 M H2SO4) and alkaline (0.1 M KOH) conditions. In an acidic electrolyte, the sample prepared with 700 ALD cycles exhibits significant HER activity and a low overpotential (η) of 148 mV at 10 mA cm-2. Under an alkaline condition, it achieves 10 mA cm-2 with η of 125 mV for MoN x/NF (700 cycles). In both electrolytes, the MoN x thin film exhibits enhanced activity and stability because of the uniform and conformal coating on NF. Thus, this study facilitates the development of a large-area 3D freestanding catalyst for efficient electrochemical water-splitting, which may have commercial applicability.

Fabrication of solar cells based on Cu2ZnSnS4 films grown with optimized chemical composition homogeneity

Se fabricaron celdas solares con estructura Mo/CZTS/ZnS/ZnO usando como capa absorbente películas de Cu2ZnSnS4 (CZTS) crecidas por evaporación simultánea de sus precursores desde una fuente de evaporación coaxial construida con un diseño avanzado que permitió mejorar significativamente la homogeneidad en la composición química en todo el volumen. Mediante mediciones con difracción de rayos X (XRD) se verificó que bajo condiciones de crecimiento optimizado era posible obtener películas en la sola fase Cu2ZnSnS4; los análisis de perfiles de profundidad con espectroscopía de fotoelectrones de rayos X (XPS) permitieron confirmar que las muestras preparadas desde una fuente coaxial crecieron solamente en la fase CZTS y que su composición química presentaba una mejor homogeneidad en todo el volumen que aquellas depositadas desde tres fuentes de evaporación separadas. Asimismo, se encontró que las celdas solares fabricadas con una capa absorbente CZTS crecidas desde una fuente de evaporación coaxial presentaban eficiencias de conversión significativamente mayores que las celdas fabricadas con capas CZTS preparadas desde fuentes de evaporación separadas. Se obtuvieron eficiencias de conversión de 5,6%, una corriente de cortocircuito de 18,3 mA/cm2 y un voltaje de circuito abierto de 0,52 V. © 2019. Acad. Colomb. Cienc. Ex. Fis. Nat.

Enhanced Visible Light Sensitization of N-Doped TiO2 Nanotubes Containing Ti-Oxynitride Species Fabricated via Electrochemical Anodization of Titanium Nitride

The concentration and chemical state of nitrogen represent critical factors to control the band-gap narrowing and the enhancement of visible light harvesting in nitrogen-doped titanium dioxide. In this study, photocatalytic TiO2–N nanoporous structures were fabricated by the electrochemical anodization of titanium nitride sputtered films. Doping was straightforwardly obtained by oxidizing as-sputtered titanium nitride films containing N-metal bonds varying from 7.3 to 18.5% in the Ti matrix. Severe morphological variations into the as-anodized substrates were registered at different nitrogen concentrations and studied by small-angle X-ray scattering. Titanium nitride films with minimum N content of 6.2 atom % N led to a quasi-nanotubular geometry, whereas an increase in N concentration up to 23.8 atom % determined an inhomogeneous, polydispersed distribution of nanotube apertures. The chemical state of nitrogen in the TiO2 matrix was investigated by X-ray photoelectron spectroscopy depth profile analysis ...

Effect of Surface Tungstate W5+ Species on the Metathesis Activity of W-Doped Spherical Silica Catalysts

The high surface area W-doped spherical silica (SSP) catalysts were prepared with different sequences of W and Si addition (W–Si(Alt), Si1–W2, and W1–Si2) by the sol–gel method with CTAB as a structure directing agent and compared with the impregnated one (W/SSP). All the catalysts exhibited high specific surface area (∼ 1100 m2 g−1) with a closely perfect spherical shape. The presence of surface/sub-surface tungstate W5+ species, crystalline bulk WO3, and tetrahedral tungsten oxide species on the prepared catalysts was investigated by means of X-ray photoelectron spectroscopy depth profile analysis, X-ray diffraction, and Raman spectroscopy. Without in situ reduction by the reactants/products, tungstate W5+ species was found on the top surface of the as-prepared W–Si(Alt) whereas for the Si1–W2, W/SSP, and W1–Si2, the W5+ appeared only on the sub-surface of the catalysts after 5 and 15 s Ar+ etching. The abundance of surface W5+ species is suggested to facilitate the establishment of the active tungsten carbenes and was correlated well to the catalytic activity in propene metathesis. The surface W5+-activity relationship of the WO3-based metathesis catalysts is useful especially when the catalyst activity did not depend solely on the amount of active tetrahedral coordinated tungsten oxides.