X-ray Auger Electron Spectroscopy Research Articles

Phase transformation sequence of amorphous nickel-molybdenum electrodeposit

In this paper, the amorphous Ni-Mo alloy with cauliflower-like morphology is successfully prepared by electrodeposition, and the effects of heat treatment on its morphology, element content and structure are studied. The results of scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and Auger electron spectroscopy (AES) show that, when the temperature is higher than 600 ℃, the fine grains gradually appear and then cover the entire surface of Ni-Mo alloy. The Ni-Mo alloy occurs simultaneously the segregation phenomenon and the Mo content increases on the surface. Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) analysis illustrate that the Ni-Mo alloy gradually transfers from amorphous into crystalline structure, and the first phase MoNi4 and the second phase MoNi precipitate near 633℃ and 707℃ respectively. The apparent activation energy is 234.1 kJ/mol (ΔEa1) for the first phase crystallization and 819.9 kJ/mol (ΔEa2) for the second phase crystallization. The HER catalytic activity of Ni-Mo alloy increases first and then decreases with the increase of heat treatment temperature.

Exploring Stable and Selective Anode Materials for the Electrochemical Oxidative Coupling of Methane (EOCM): A Case Study of Doped Titanates

The development of next-generation solid oxide fuel cells (SOFCs) relies on integrating materials such as La0.6Sr0.4Co0.2Fe0.8O3- δ (LSCF), which has been lauded for its fast oxygen ion and electron conduction, along with its high oxygen reduction activity.[1] However, the use of LSCF has been plagued by 1) stability issues caused by surface Sr precipitation and 2) subsequent poisoning by Cr- or S- containing species.We have previously shown that the introduction of more oxidizable cations at the electrode surface can effectively improve both the stability and the oxygen exchange kinetics of the electrodes. However, the influence of these cations, as with many dopant infiltration studies, is currently not fully understood across all possible modes of electrode surface stabilization/activity enhancement. For example, we have recently discovered that at 800°C and under air atmospheres (i.e. at typical SOFC operational conditions), these Hf/Zr surface cation dopants are mobile and diffuse into the lattice of a porous LSCF electrode as evidenced by their vanishing x-ray photoelectron signals. This is accompanied nevertheless by a noticeable electrode stabilization, suggesting a sub-surface effect of the introduced dopants.Inspired by this, in this work our aim is to uncover the mechanism responsible for the stabilization of the surface oxygen exchange kinetics. Our approach involves dense thin film LSCF as model system to investigate the temperature-dependent physicochemical properties of these surface and sub-surface dopant cations. We fabricate LSCF thin films via pulsed laser deposition onto single crystalline substrates and then introduce our targeted cations at the surface via an aqueous solution infiltration. We characterize the electrochemical performance of the thin films by performing chronoamperometric and impedance spectroscopic measurements to discern the extent of the temporal electrode performance degradation using metrics such as area-specific resistance. In parallel, we aim to rationalize the observed electrochemical performance stabilization using complementary surface science techniques. We propose investigating the cation dissolution phenomenon through a combination of x-ray photoelectron and Auger electron spectroscopies, along with atomic force microscopy, scanning/transmission electron microscopy, scanning tunnelling microscopy and grazing incidence thin film x-ray diffraction. This study aims to reveal the influence of sub-surface more oxidizable cations on the extent of Sr segregation and highlights how two major factors contribute to the observed trends: Electrode fabrication conditions, for example the dopant concentration dependence (insufficient or excessive surface dopant concentrations has previously been shown to suppress the stabilization effect).[3]Electrode operation conditions, for example the temperature profile experienced by the cell (higher temperatures lead to dopant dissolution). [1] SP Jiang, Int. J. Hydrogen Energy 44 (14), 7448 (2019).[2] N Tsvetkov et al., Nature Mat. 15 (9), 1010 (2016).[3] N Tsvetkov et al., Faraday Disc. 182 (0), 257 (2015).

Water-Soluble Copper(I) Hydroxide Catalyst and Its Formation in Ligand-Free Suzuki–Miyaura Cross-Coupling Reactions

Copper has emerged as an alternative metal for metal-catalyzed cross-coupling reactions due to its low cost, readily availability, and low toxicity. This article reports a water-soluble active molecular catalyst and its formation in the ligand-free Suzuki–Miyaura (SM) cross-coupling reactions with copper iodide as the precatalyst in aqueous solutions. The SM coupling is homogeneous in nature, and the molecular catalyst is Cu(OH) in its singlet electronic state as identified by experimental and computational UV–vis absorption spectroscopy. The Cu(OH) catalyst is generated through the leaching of oval-shaped Cu2O nanoparticles, which are characterized with X-ray Auger electron spectroscopy, X-ray absorption spectroscopy, and transmission electron microscopy. The soluble Cu(OH) species is stable for at least 4 weeks under ambient conditions.

Model experiments with Auger electron and X-ray photoelectron spectroscopy at lithiated graphite material: Surface changes related to ion- and electron-beam effects

Li-based batteries as a key element for green energy economy should be permanently improved in their performance. Therefore, the complex electrochemical processes in such batteries have to be understood in detail. For their characterization beside (electro-)chemical methods also electron spectroscopic methods such as X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) are used to get more insight into the chemical processes at the surfaces. One crucial point is stability of the solid electrolyte interface (SEI) upon measurements, especially at the (graphite-)anodes. In this paper, we use highly oriented pyrolytic graphite (HOPG) as a model anode material, which was lithiated in a molten metal intercalation process. Strong beam damage effects at the lithiated HOPG under electron and ion beam radiation are observed and described. These effects are important for using of local electron beam investigations and sputter depth profiling, often applied also for SEI characterization.

Influence of Metal Cations on Corrosion Behavior of Aluminum Alloy 2024-T3 in Model Freshwater

The influence of metal cations on corrosion behavior of aluminum alloy (AA2024-T3) in model freshwater was examined by immersion experiments, surface analysis, and electrochemical measurements. After long-time immersion, the corrosion rate of AA2024-T3 decreased as the corrosion indicator Y increased, and the corrosion rate of the alloy was reduced by Zn2+. The specimen immersed in Zn2+ containing solution showed less corrosion products which were observed by scanning electron microscopy (SEM). The results of X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) showed that Zn2+ attaches to aluminum alloys and forms protective layers. Electrochemical impedance spectroscopy (EIS) results suggested that Zn2+ reduced the area of defects in the passive film.

Unified quantum theory of electrochemical kinetics by coupled ion-electron transfer.

A general theory of coupled ion-electron transfer (CIET) is presented, which unifies Marcus kinetics of electron transfer (ET) with Butler-Volmer kinetics of ion transfer (IT). In the limit of large reorganization energy, the theory predicts normal Marcus kinetics of "electron-coupled ion transfer" (ECIT). In the limit of large ion transfer energies, the theory predicts Butler-Volmer kinetics of "ion-coupled electron transfer" (ICET), where the charge transfer coefficient and exchange current are connected to microscopic properties of the electrode/electrolyte interface. In the ICET regime, the reductive and oxidative branches of Tafel's law are predicted to hold over a wide range of overpotentials, bounded by the ion-transfer energies for oxidation and reduction, respectively. The probability distribution of transferring electron energies in CIET smoothly interpolates between a shifted Gaussian distribution for ECIT (as in the Gerischer-Marcus theory of ET) to an asymmetric, fat-tailed Meixner distribution centered at the Fermi level for ICET. The latter may help interpret asymmetric line shapes in x-ray photo-electron spectroscopy (XPS) and Auger electron spectroscopy (AES) for metal surfaces in terms of shake-up relaxation of the ionized atom and its image polaron by ICET. In the limit of large overpotentials, the theory predicts a transition to inverted Marcus ECIT, leading to a universal reaction-limited current for metal electrodes, dominated by barrierless quantum transitions. Uniformly valid, closed-form asymptotic approximations are derived that smoothly transition between the limiting rate expressions for ICET and ECIT for metal electrodes, using simple but accurate mathematical functions. The theory is applied to lithium intercalation in lithium iron phosphate (LFP) and found to provide a consistent description of the observed current dependence on overpotential, temperature and concentration. CIET theory thus provides a critical bridge between quantum electrochemistry and electrochemical engineering, which may find many other applications and extensions.

Electrocatalytic reduction of nitrate at the stabilizedelectron-deficient Cu<sup><italic>δ</italic>+</sup> active sites

<p indent="0mm">With the extensive use of nitrogen fertilizers, sewage discharges and industrial processes that consume nitric acid, the exposure level of nitrate (NO₃⁻-N) in environmental water bodies has significantly increased in the past decades. The NO₃⁻ anion has a stable chemical structure, and is hardly removed by natrual self-cleaning. It has adverse effect, and is primarily responsible for the eutrophication in lakes as well as some physiological diseases in neighboring mammal inhabitants, such as the methemoglobinemia. Strict regulations on the maximum contaminant level of <sc>10 mg/L</sc> for NO₃⁻-N in the drinking water has then been set by the World Health Organization, the United States Environmental Protection Agency and the China Environmental Protection Administration. To minimize the adverse effects of NO₃⁻-N, various technologies, including ion exchange, electrolysis, biological denitrification, and catalytic reduction by H₂ or Fe⁰, have then been developed to eliminate the NO₃⁻-N from water. Among them, electrocatalytic reduction of nitrate (ENRR), driven by the renewable electric energy, is receiving increasing research interests, due to its substantial nitrate removal capacity, mild reaction conditions and minimal daily maintenances. Copper-based materials are favored as the ENRR catalysts by researchers because of their high activity, chemical stability and low cost. The electron-deficient Cu^{<italic>δ</italic>+} is the main active site at the catalyst surface, but it is readily to be reduced to Cu⁰ at the very negative ENRR potentials, leading to the performance deterioration during the long-term reaction process. In this paper, we reported a facile approach to construct the Cu^{<italic>δ</italic>+}-1,4-naphthalene dicarboxylic acid (1,4-NDC) catalytic active sites through the surface decoration of the Cu(OH)₂ particles with the 1,4-NDC molecule at room temperature, followed by an <italic>in-situ</italic> electrochemical activation process under a negative potential of <sc>−0.40 V</sc> vs. RHE (reversible hydrogen electrode, the same below) (the product is denoted as <sc>Cu(OH)₂/1,4-NDC-AT).</sc> In this structure, the Cu^{<italic>δ</italic>+} is confirmed by the X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) to survive under the negative working potential during the long-term ENRR, possibly due to the high electronegativity and chemical stability of the oxygen atoms in carboxyl group (the carboxyl group is chelated with the Cu^{<italic>δ</italic>+} site). The batch ENRR activity test results show that the Cu(OH)₂/1,4-NDC-AT delivers a NH₃ selectivity of &gt;90% in product, a specific activity of <sc>1034.7 mg N/(h m²)</sc> and a mass activity of <sc>89.1 mg N/(h</sc> g_Cu) in treating <sc>22.5 mg/L</sc> NO₃⁻-N solution at <sc>−0.40 V.</sc> The specific and mass activities are nearly 2.3 and 5.1 times those achieved by the ligand-free Cu(OH)-AT, respectively, and also higher than that of most reported catalysts. Optimizing the 1,4-NDC dosage and working potential can further improve the ENRR performance, and the mass activity increases to 147.1 and <sc>104.6 mg N/(h</sc> g_Cu) at the <inline-formula id="INLINE13"><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub other="0"><mml:mi other="0">n</mml:mi><mml:mrow other="1"><mml:mtext other="1">1</mml:mtext><mml:mo other="1">,</mml:mo><mml:mtext other="1">4-NDC</mml:mtext></mml:mrow></mml:msub><mml:mo>/</mml:mo><mml:msub other="0"><mml:mi other="0">n</mml:mi><mml:mrow other="1"><mml:mtext other="1">Cu</mml:mtext><mml:msub other="1"><mml:mrow other="1"><mml:mrow other="1"><mml:mo other="1">(</mml:mo><mml:mrow other="1"><mml:mtext other="1">OH</mml:mtext></mml:mrow><mml:mo other="1">)</mml:mo></mml:mrow></mml:mrow><mml:mtext other="2">2</mml:mtext></mml:msub></mml:mrow></mml:msub></mml:mrow></mml:math></inline-formula> of 2.16 and the potential of <sc>−0.50 V,</sc> respectively. Finally, this paper proposed the appratus for the treatment of nitrate wastewater in different concentrations. Specifically, an integrated “ENRR+NH₃-N adsorption” technology is proposed to deal with the dilute nitrate wastewater, which enables the elimination of the nitrogen-containing species in water. For the concentrated nitrate wastewater, an integrated “ENRR+NH₃-N recovery” technology is proposed, which can recover 98.0% of the produced NH₃-N via absorption by H₂SO₄ aqueous solution. This work provides new strategies and robust materials specific for NO₃⁻-N removal, which should advance the development of ENRR technology in water pollution remediation.

In Situ Monitoring of H2-Induced Nonstoichiometry in Cu2O.

Using ambient-pressure X-ray photoelectron spectroscopy and Auger electron spectroscopy to monitor the reduction of Cu2O in H2, we identify the formation of an intermediate, oxygen-deficient Cu2O phase and its progressive inward growth into the deeper region of the oxide. Complemented by atomistic modeling, we show that the oxygen-deficient Cu2O formation occurs via molecular H2 adsorption at the Cu2O surface, which results in the loss of lattice oxygen from the formation of H2O molecules that desorb spontaneously from the oxide surface. The resulting oxygen-deficient Cu2O is a stable intermediate that persists before the Cu2O is fully reduced to metallic Cu. The oxygen vacancy-induced charge of the coordinating Cu atoms results in a satellite feature in Cu LMM, which can be used as a fingerprint to identify nonstoichiometry in oxides and local charge transfer induced by the nonstoichiometry.

Investigation of Water-Washing Effect on Electrochemical Properties of Ni-Rich NCA Cathode Material for Lithium-Ion Batteries

This study was conducted to understand the effect of well-known water-washing process on Ni-rich LiNi0.885Co0.100Al0.015O2 (NCA) cathode material, which reduces the amount of residual lithium compounds in NCA to improve lithium-ion batteries (LIBs) characteristics. X-ray absorption fine structure (XAFS) analysis revealed that the oxidation state of the surface nickel in washed NCA particles was reduced. The fact was consistent with the increase in charge transfer resistance (Rct) measured by the electrochemical impedance spectroscopy (EIS) method. From X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) analyses, it was found that the residual lithium compounds were washed away not only from the surface of NCA particles but also from grain boundaries or voids in between primary particles of NCA, by water-washing process. Differential scanning calorimetry (DSC) measurements suggested that an increase in specific surface area of NCA particles by water-washing was attributed a rapid heat release from the charged cathode material during heating to. On the other hand, cross-sectional scanning electron microscope (SEM) images showed that the crack formation inside washed NCA particles were suppressed after charge/discharge cycling. As a result, the capacity retention of washed NCA electrode at 60 °C cycling was improved.

High-efficient production of fatty alcohol via hydrogenation of fatty acid over Cu-NbOx/SBA-15 catalyst

Cu/SBA-15 and Cu-NbOx/SBA-15 catalysts were prepared and evaluated in the hydrogenation of palmitic acid to palmitic alcohol. A high palmitic alcohol yield of 90.8% was obtained using palmitic acid as feedstock. NbOx has been considered to be crucial for the excellent performance and the synergy between Cu and NbOx was well investigated. The interaction between Cu species and NbOx-containing support was studied by various characterizations, such as powder X-ray diffraction (XRD), transmission electron microscopy (TEM), H2-temperature programmed reduction (H2-TPR) and X-ray photoelectron spectra (XPS) and Auger electron spectroscopy (AES). The kinetic data for rate determining step were also collected. The synergistic effect of Cu and NbOx to catalytic activity was discussed and the following insights were obtained: i) the NbOx doping led to form abundant Cu species with more electron-deficient, which is beneficial for the production of alcohol; ii) the oxygen affinity of NbOx promotes the adsorption of oxygen-containing group. Finally, the natural product of palm oil was taken as feedstock and an ideal yield 84.2% of palmitic alcohol was harvested.

Partial densities of states from x-ray absorption and Auger electron spectroscopy: Use of core-hole memory.

Ag L 3 edge x-ray absorption and L 3 - M 4,5 M 4,5 Auger electron spectra have been measured and simulated for a variety of x-ray electric-field polarization and Auger electron emission directions. The theory relies on density-functional theory, use of the Bethe-Salpeter equation, atomic multiplet theory, and a simplified model for the Auger line shape and its dependence on photon energy. We also demonstrate that partial densities of states for d T 2g , d Eg , and s Ag symmetry partial-wave channels at the Ag site in the solid can be deduced from the experimental measurements with only atomic theoretical input, i.e., with no solid-state theory other than assuming a Fermi edge.

Light-assisted defects migration in cuprous iodide (CuI)

We report light-assisted iodine ion migration in CuI – a popular wide bandgap p-type semiconductor, which was synthesized via iodinating Cu film in iodine solution. In-depth crystallographic analysis was performed with the combination methods of X-ray diffraction (XRD), selected area electron diffraction (SAED), high-resolution transmission electron microscopy (HRTEM), crystal modeling and diffraction simulation. The samples show strong diffraction peaks of γ-CuI, yet still exists β phase diffraction. Loop current-voltage (IV) test shows characteristics of resistive random access memory (RRAM), suggesting the existence of large amount of movable native defects, which forms the conductive filaments. UV irradiation was found to be effective to convert the RRAM device from low resistance state (LRS) to high resistance state (HRS), indicating potential application of novel memory device with electric read-in and optical erasure function. To study the properties of native defects, time-lapsed PL were employed, in which the near band edge defects luminescence, related to VCu, increased, whereas mid-band broad luminescence, related to VI, decreased, with the increase of irradiation time. UV irradiation induced defects evolution was also observed in X-ray photoelectron spectroscopy (XPS) and auger electron spectroscopy (AES). Finally, we propose the microscopic physical mechanism of defect migration in CuI with the assistance of UV irradiation. This work reveals the nature of point defects evolution in CuI under light irradiation and is expected to arise more discussions on defects formation, migration and light-defects interaction of CuI material.

The influence of relative humidity upon Cu(In,Ga)Se2 thin-film surface chemistry: An X-ray photoelectron spectroscopy study

We performed a comprehensive study of Cu(In,Ga)Se2 (CIGS) surface reactivity in air, focusing on the evolution of the surface chemistry via X-ray photoemission spectroscopy (XPS). By using the different transitions (photopeaks and X-ray Auger electron spectroscopy transitions) available on XPS spectra, in order to probe different surface thicknesses, complementary chemical information is provided to investigate the surface reactivity mechanism of CIGS surface and especially highlight the importance of the relative humidity rate of the atmosphere. Indeed, by maintaining a relative humidity of 20%, we demonstrate that this degradation can be limited, even almost stopped, showing that the degradation mechanism is not only related to O2 interaction but more importantly, to the thin water layer, inherent to relative humidity, formed upon surfaces.

Formation of wear-resistant graphite/diamond-like carbon nanocomposite coatings on Ti using accelerated C60-ions

The nanostructural and tribological characteristics of carbon nanocomposite coatings (CNCs), deposited by accelerated C 60 ions at high temperatures, were studied. The CNCs were successfully fabricated on Ti-alloy using a flux that contained C 60 ions with 5 and 10 keV energies. Unlike the previous studies, ion mass-separator was not implemented to the deposition process. This enabled deposition of sp 2 -rich CNCs with a lower coefficient of friction (COF) at a higher deposition rate. Laser confocal microscopy , atomic force microscopy transmission electron microscopy , Raman spectroscopy , X-ray photoelectron spectroscopy, and X-ray Auger Electron Spectroscopy were used to investigate the structure of the coatings and friction test results. A carbon nanocomposite film consisting of graphite nanocrystals enclosed in an amorphous diamond-like matrix was formed at a deposition temperature of 300–400 °C. Upon deposition of the CNC, a COF of ~0.06 was achieved, which was almost one order of magnitude lower than that of bare Ti-alloy substrate. The surface wear was reduced by 360 times. The wear mechanism was changed from abrasive wear (on bare Ti-alloy) to a burnishing smoothening of the surface roughness (on CNCs). The transfer of graphite nanocrystals from the coating to the counter surface was identified and observed to act as a solid lubricant . • Carbon nanocomposite coatings were deposited on Ti using accelerated C 60 -ions. • Graphite nanocrystals embedded in amorphous diamond-like carbon matrix were formed. • The coatings were deposited without the implementation of ion mass-separator. • Deposition temperature significantly affected the size of graphite nanocrystals. • The coatings reduced the COF and wear rate of Ti by 8 and 360 folds, respectively.

Superlow Friction of a-C:H Coatings in Vacuum: Passivation Regimes and Structural Characterization of the Sliding Interfaces

A combination of atomistic simulations and vacuum tribometry allows atomic-scale insights into the chemical structure of superlubricious hydrogenated diamond-like carbon (a-C:H) interfaces in vacuum. Quantum molecular dynamics shearing simulations provide a structure-property map of the friction regimes that characterize the dry sliding of a-C:H. Shear stresses and structural properties at the sliding interfaces are crucially determined by the hydrogen content CH in the shear zone of the a-C:H coating. Extremely small CH (below 3 at.%) cause cold welding, mechanical mixing and high friction. At intermediate CH (ranging approximately from 3 to 20 at.%), cold welding in combination with mechanical mixing remains the dominant sliding mode, but some a-C:H samples undergo aromatization, resulting in a superlubricious sliding interface. A further increase in CH (above 20 at.%) prevents cold welding completely and changes the superlubricity mechanism from aromatic to hydrogen passivation. The hydrogen-passivated surfaces are composed of short hydrocarbon chains hinting at a tribo-induced oligomerization reaction. In the absence of cold welding, friction strongly correlates with nanoscale roughness, measured by the overlap of colliding protrusions at the sliding interface. Finally, the atomistic friction map is related to reciprocating friction experiments in ultrahigh vacuum. Accompanying X-ray photoelectron and Auger electron spectroscopy (XPS, XAES) analyses elucidate structural changes during vacuum sliding of a hydrogen-rich a-C:H with 36 at.% hydrogen. Initially, the a-C:H is covered by a nanometer-thick hydrogen-depleted surface layer. After a short running-in phase that results in hydrogen accumulation, superlubricity is established. XPS and XAES indicate a non-aromatic 1–2-nm-thick surface layer with polyethylene-like composition in agreement with our simulations.

Structure, Surface Morphology, Chemical Composition, and Sensing Properties of SnO2 Thin Films in an Oxidizing Atmosphere.

We conducted experiments on SnO2 thin layers to determine the dependencies between the stoichiometry, electrochemical properties, and structure. This study focused on features such as the film structure, working temperature, layer chemistry, and atmosphere composition, which play a crucial role in the oxygen sensor operation. We tested two kinds of resistive SnO2 layers, which had different grain dimensions, thicknesses, and morphologies. Gas-sensing layers fabricated by two methods, a rheotaxial growth and thermal oxidation (RGTO) process and DC reactive magnetron sputtering, were examined in this work. The crystalline structure of SnO2 films synthesized by both methods was characterized using XRD, and the crystallite size was determined from XRD and AFM measurements. Chemical characterization was carried out using X-ray photoelectron (XPS) and Auger electron (AES) spectroscopy for the surface and the near-surface film region (in-depth profiles). We investigated the layer resistance for different oxygen concentrations within a range of 1–4%, in a nitrogen atmosphere. Additionally, resistance measurements within a temperature range of 423–623 K were analyzed. We assumed a flat grain geometry in theoretical modeling for comparing the results of measurements with the calculated results.

Advancement of ozone zero phenomenon by surface deterioration of stainless—steel electrode

It is well known that a fine powder is deposited on the surface of coaxial cylinder electrodes made from stainless steel and borosilicate glass in ozone generators. We inspected the fine powder and the stainless steel by x-ray diffraction and Auger electron spectroscopy to clarify the relationship between the gradual decrease in ozone concentration, i.e., ozone zero phenomena (OZP) produced in the ozone generator, and the deterioration of stainless steel. The results of x-ray diffraction for both specimens suggest that several oxides with iron, chromium and nickel are formed from the stainless steel exposed to an ozone–oxygen mixture and the discharge. In particular, FeO detected by x-ray diffraction analysis means that the temperature of the surface of stainless steel and the powder reaches at least 843 K owing to the generation of heat by discharge and oxidation of the fine powder and electrode surface despite the inside of electrodes being refrigerated with circulating water. This temperature is much higher than the 453 K estimated in our previous work as a threshold temperature of the thermal decomposition of ozone by model experiments using a simulated ozone generator during the OZP. On the other hand, Auger electron spectroscopy is carried out in combination with the repeated tracing of the OZP, and we investigate whether oxygen atoms penetrate in the depth direction of the stainless steel. During this process, we observed serious OZP, meaning the ozone concentration at the outlet of the ozone generator is almost zero for 40–50 h continuously following the gradual decrease in ozone concentration. The penetration of oxygen atoms into the stainless-steel bulk is considered as the start of the collapse of the original passivation film covering on the surface of stainless steel. After the process, i.e., the cessation of the OZP, the formation of a new thin layer instead of the passivation film is observed with the coexistence of a strong oxidizer, i.e., ozone and atomic oxygen and the heat produced by discharge in the ozone generator. However, the recovered ozone concentration is realized up to half of the peak value in the measurement. This process corresponds to the recovery of the ozone concentration after the OZP. Hence, we concluded that the OZP is advanced by the thermal decomposition of ozone accompanied by the deterioration of the stainless-steel surface by ozone oxidation.

Synthesis, Characterization and Gas Sensing Study of ZnO-SnO2 Nanocomposite Thin Films

Thin nanocomposite films composed of ZnO and SnO2 at 0.5–5 mol.% concentrations were synthesized by a new solid-phase low-temperature pyrolysis under the developed protocols. This hetero-oxide material was thoroughly studied by X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) techniques to be compared with electrical and gas-sensing properties. We have found that the films have a poly-nanocrystal structure of ZnO and SnO2 crystals with characteristic grain sizes at 10–15 nm range. When comparing the chemiresistive response of the films with varied tin dioxide content, the sample of Sn:Zn optimum ratio taken as 1:99 yields 1.5-fold improvement upon to 5–50 ppm NO2 exposure at 200 °C. We argue that these remarkable changes have matured from both a reducing the intergrain potential barrier down to 0.58 eV and increasing the concentration of anionic vacancies at this rational composite. The results demonstrate that solid-phase low-temperature pyrolysis is a powerful technique for adjusting the functional gas-sensing properties of hetero-oxide film via modifying the ratio of the oxide components.

Investigation of the selectivity-mechanism of copper (I) sulfide (Cu2S) as a dopant-free carrier selective contact for silicon solar cells

Carrier selective contacts based on dopant free materials are receiving increased attention. Copper(I) sulfide (Cu2S), earth-abundant and non-toxic, shows potential for use in silicon (Si) solar cells, though its carrier selectivity mechanism remains unclear. We present a detailed investigation of the selectivity mechanisms behind thermally evaporated Cu2S on Si. Deposited Cu2S layers are studied by X-ray photoelectron spectroscopy, Auger electron spectroscopy, X-ray diffraction and UV/VIS (ultraviolet–visible) methods. From X-ray photoelectron spectroscopy and Auger electron spectroscopy, only sulfur related Cu(I) bonds are observed in the deposited film. X-ray diffraction measurements indicate that Cu1.95S (djurleite) may also exist in the film. The indirect and direct bandgaps are determined to be 1.2 eV and 2.2 eV, respectively. Band bending of ~0.6 eV is calculated for Cu2S/n-Si (~5 Ω·cm), while it is significantly lower (~0.07 eV) for Cu2S/p-Si (~2.25 Ω·cm). Current-voltage measurements indicate that the carrier selectivity originates from an induced junction at the Cu2S/n-Si interface, and not from a large band-offset of the conduction band. The Cu2S/p-Si structure displays no carrier selectivity, a finding attributed to the insufficient band bending at the interface.

Low-temperature carburized high-alloyed austenitic stainless steels in PEMFC cathodic environment

Austenitic stainless steels are promising materials for bipolar plates in polymer electrolyte membrane fuel cells (PEMFC). In this study, we explore the possibility to apply low-temperature carburized high-alloyed (high Cr, Ni, Mo) steels as bipolar plate materials. The electrochemical properties and the microstructural characteristics of the modified surfaces were analyzed by optical microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and Auger electron spectroscopy. The carburizing treatment (Kolsterising®, Bodycote) induced the formation of a carbon-stabilized expanded austenite layer. The amount of carbon dissolved in the metal matrix was dependent on the alloy composition, in particular on the amount of Mo. Additionally, surface carbides were found at the surface of low-Ni containing steels. The interfacial contact resistance (ICR) measured in a simulated PEMFC was reduced after carburizing as a consequence of thinner oxide layer and change in oxide composition. Potentiodynamic tests revealed nobilitation of all the steels when carbon was present in solid solution. The occurrence of surface carbides, however, was highly detrimental to the corrosion properties. The ICR of carburized materials in aged condition was higher than the corresponding untreated alloys. The presence of localized corrosion in carburized materials could be responsible for this effect.