X-ray Photoemission Spectroscopy Research Articles

Nanoconfinement-Enabled Resistance to Water Matrix Components for Selective Degradation of Micropollutants.

Despite recent substantial advances in water treatment, the ability to selectively degrade trace micropollutants in real waters with complex matrix components remains a grand challenge. Here we report rational crafting of graphene oxide (GO)-wrapped defective TiO2 composite catalysts that creates nanoscopic confinement over the TiO2 surface within GO, thereby enabling the selective degradation of micropollutants through effectively excluding natural organic matter (NOM) and anions from the nanoconfined catalytic sites. In contrast to unconfined counterparts, the nanoconfined composite catalysts retain high degradation efficiency when exposed to various concentrations of NOM and anions, even in real water samples. Oxygen vacancies in TiO2 promote electron separation and oxygen adsorption, leading to a 4.9-fold increase in hydroxyl radical concentration within the nanoconfined space compared to the bulk solution. In-situ X-ray photoemission spectroscopy and Raman spectroscopy unveil the nanoconfined catalytic sites on the TiO2 surface, where micropollutants smaller than the pores of GO are effectively degraded, while NOM with a larger size is excluded by GO. Furthermore, the formation of toxic disinfection byproducts is well controlled due to the exclusion of NOM. This work provides a simple yet viable strategy for designing 2D material-wrapped catalysts to selectively degrade target micropollutants in complex real waters.

A synaptic transistor with a stacked layer of SiNx and SiO2 deposited from hexamethyldisiloxane/O2

Herein, we employed inductively coupled plasma enhanced chemical vapor deposition using a hexamethyldisiloxane/O2 precursor to deposit SiO2 with electrical double layer capacitance on SiNx forming SiO2/SiNx stacked films as a dielectric layer, achieving high-performance synaptic transistors. The effect of O2 concentration during SiO2 deposition on the transistor performance was investigated. The results of Fourier transform infrared spectroscopy and x-ray photoemission spectroscopy confirm that increasing O2 concentration during deposition boosts the amounts of protons moving between the bridging oxygen in the Si–O–Si network, improving the electrical double layer capacitance of SiO2. Furthermore, SiNx in the stacked structure exhibits a higher relative permittivity than SiO2, resulting in a more concentrated electric field within the SiO2 layer, facilitating proton ionization. SiO2/SiNx stacked film with SiO2 deposited at the oxygen flow rate of 150 sccm exhibited the maximum capacitance of 2.87 μF/cm2 at 4 Hz. The transistor with SiO2 deposited at the oxygen flow rate of 150 sccm achieved the maximum paired pulse facilitation index of 132.9% and the maximum A50/A1 index of 155.4%. This work demonstrates that SiO2 deposited via inductively coupled plasma enhanced chemical vapor deposition using a hexamethyldisiloxane/O2 precursor for application potential in artificial neuromorphic computing.

Operando study of Ni-22Cr oxidation dynamics with nanoscale resolution in an X-ray photoemission electron microscope

Operando study of Ni-22Cr oxidation dynamics with nanoscale resolution in an X-ray photoemission electron microscope

Rocksalt-type heavy rare earth monoxides TbO, DyO, and ErO exhibiting metallic electronic states and ferromagnetism.

Solid-phase rare earth monoxides have been recently synthesized via thin film epitaxy. However, it has been difficult to synthesize heavy rare earth monoxides owing to their severe chemical instability. In this study, rocksalt-type heavy rare earth monoxides REOs (RE = Tb, Dy, Er) were synthesized for the first time, as single-phase epitaxial thin films. The REOs were characterized by hard X-ray photoemission spectroscopy, X-ray absorption spectroscopy, resonant photoemission spectroscopy, and magnetization measurements. These REOs showed metallic electronic states with the almost localized 4f states, indicating the 4fn5d1 electronic configurations of Tb, Dy, and Er ions. X-ray magnetic circular dichroism measurements of TbO evidenced the magnetic ordering of the 4f spins below the Curie temperature (TC). The TC was evaluated to be 233 K for TbO, 142 K for DyO, and 88 K for ErO, where the TC decreased with the 4f electron number, approximately proportional to the de Gennes factor.

Investigation of the origin of atomic-like emission at 4.09 eV from h-BN by correlating PL and XPS spectra

Deep ultraviolet (UV) photoluminescence (PL) and x-ray photoemission spectroscopy (XPS) were employed to investigate the origin of the atomic-like emission line at 4.09 eV from hexagonal boron nitride (h-BN) single crystals. High resolution XPS spectra analyzed by correlating PL spectra of the h-BN samples with and without the sharp emission line at 4.09 eV showed that carbon is bonding to both boron and nitrogen in the sample that has the 4.09 eV emission line. Our results showed that the defect responsible for the origin of the 4.09 eV line from h-BN is carbon related and it suggests that the defect structure has elemental carbon occupying both boron (CB) and as nitrogen (CN) sites.

Investigating Dopant Effects in ZnO as an Electron Transport Layer for Enhanced Efficiency in Organic Photovoltaics

AbstractThe power conversion efficiencies of organic solar cells greatly depend on the device architecture and choice of charge transporting materials. Improved power conversion efficiency (PCE) for inverted organic solar cells is observed when using Sn‐doped ZnO as the electron transporting layer. By doping the elements with different numbers of valence electrons (Al3+ and Sn4+ ions) into the ZnO matrix, device conversion efficiencies of 8.69% and 9.21%, respectively, are achieved. Conductive atomic force microscopy (CAFM) observations reveal that the Sn‐doped ZnO film exhibits better conductivity due to its larger number of carrier charges. X‐ray photoemission spectroscopy (XPS) indicates larger oxygen vacancies (OV) in Sn‐doped ZnO. Electrochemical characterization exhibits that there is a reduction in series resistance and charge transfer (CT) resistance for SZO, indicating the optimal charge transport capability of the electron transport layer (ETL). Ultrafast time‐resolved studies further show that, in comparison with Al‐doped ZnO and un‐doped ZnO, the elevated carrier concentration in Sn‐doped ZnO plays a significant role in augmenting the photocurrent. Thus, it is determined how dopants in ETL influence CT mechanisms, enhancing the photovoltaic conversion efficiency, thus contributing to the development of cost‐effective and efficient photovoltaic technologies.

Electronic structure of 2(5H)-thiophenone studied by UPS and soft x-ray spectroscopy

Abstract The electronic structure of 2(5H)-thiophenone in the gas phase was investigated by ultraviolet photoelectron spectroscopy and x-ray photoemission spectroscopy (XPS) and near edge x-ray absorption fine structure (NEXAFS) spectroscopy at the C 1s, O 1s, and S 2p edges. All assignments of the experimental results are supported by both ab-initio electron propagator outer-valence Green’s function (OVGF) calculations for the valence photoemission bands and density functional theory (DFT) and relativistic time dependent DFT calculations for the core levels XPS and NEXAFS spectra. Overall good agreement between experiment and theory is observed; this is especially true for core electron excitations which has permitted an unambiguous assignment of the observed spectral features in terms of single-particle excitations to virtual molecular orbitals. The assignment of the valence band spectra based on OVGF calculations, although satisfactory, points to the importance of electron correlations effects that partially break the single particle picture of ionization.

Engineering 2D Materials from Single-Layer NbS2.

Starting from a single layer of NbS2 grown on graphene by molecular beam epitaxy, the single unit cell thick 2D materials Nb5/3S3-2D and Nb2S3-2D are created using two different pathways. Either annealing under sulfur-deficient conditions at progressively higher temperatures or deposition of increasing amounts of Nb at elevated temperature result in phase-pure Nb5/3S3-2D followed by Nb2S3-2D. The materials are characterized by scanning tunneling microscopy, scanning tunneling spectroscopy, and X-ray photoemission spectroscopy. The experimental assessment combined with systematic density functional theory calculations reveals their structure. The 2D materials are covalently bound without any van der Waals gap. Their stacking sequence and structure are at variance with expectations based on corresponding bulk materials highlighting the importance of surface and interface effects in structureformation.

Protection Materials on III-V Semiconductors for Photoelectrochemical CO Reduction.

Tantalum oxide (TaO x ) and amorphous titanium dioxide (TiO2) are employed as protection materials for commercial GaInP/GaAs/Ge triple-junction solar cells to facilitate the unbiased photoelectrochemical reduction of carbon monoxide on nanostructured copper particles. It has been found that a photoelectrode protected by a 150 nm-thick layer of TiO2, capped with 8 nm TaO x , and decorated with copper nanocubes in the size of 150 nm can successfully drive the photoelectrochemical conversion of carbon monoxide to ethylene. Implemented into a photoelectrochemical flow reactor, which continuously supplies the active interface with CO-saturated electrolyte, the device achieves a faradaic efficiency of 24% under AM1.5G conditions. Direct attachment of the copper nanocubes to a protection layer of TiO2 in the absence of TaO x results in a strong hydrogen evolution reaction (HER) and no CO reduction products are found. This unexpected loss in selectivity is studied via post-operando X-ray photoemission spectroscopy and ion-scattering spectroscopy. No modifications in the redox state of TiO2 or signs of H intercalation are found, while the preferential redeposition of small Cu nanoparticles is considered possible. This increase in HER appears specific for TiO2, as additional, purely electroanalytical experiments using tantalum oxide or carbon as a support layer for Cu nanocubes can produce ethylene effectively.

Combined Chemical and Heat Treatment of Graphite from Spent Zn-C Batteries for Li-Ion Batteries

Lithium-ion batteries (LIBs) play a crucial role in the functioning of electric vehicles, portable gadgets, and grid storage systems. One of the primary obstacles presented by the growing demand for LIBs is the scarcity of raw materials required for their production. One economical strategy involves the use of graphite recovered from spent zinc-carbon (Zn-C) batteries as the negative electrode material. Recycling not only solves the environmental issues related to disposal of spent Zn-C batteries, but also leads to attaining inexpensive raw materials, value-adding the waste materials, and ultimately creating circular material utilization. In this work, a facile and applicable recycling procedure is proposed as the combination chemical and heat treatment of the recovered graphite. Firstly, the graphite is chemically treated with different concentrations (0.1, 1.0, and 10.0 M) of KOH under different temperatures (30, 60, and 90 ˚C). Then, the resulting graphite is neutralized and heated at different temperatures (700, 800, and 900 ˚C) under N2 or H2/N2 atmosphere. After microstructural characterizations of X-ray fluorescence (XRF), X-ray diffraction (XRD), Raman spectroscopy, Near Edge X-Ray Absorption Fine Structure spectroscopy (NEXAFS), X-ray photoemission spectroscopy (XPS), and Scanning electron microscopy (SEM), the best graphite samples in terms of crystallinity and purity are chosen for electrode preparation. The composite graphite electrodes are composed of the treated graphite, carbon black, and sodium alginate. Note that sodium alginate is a bio-based binder and can be dissolved in water, making the preparation process towards green direction. Li-ion battery half-cells containing the graphite electrodes, Li metal, and a standard electrolyte of 1 M LiPF6 in 1:1 v/v EC:DMC are subject to electrochemical characterizations, e.g. galvanostatic cycling, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) so as to investigate the battery performance and efficiency. The battery cells with the best-conditioned graphite are capable of delivering 300 mAh·g-1 at 0.1C for more than 100 cycles. Accordingly, this encourages a feasible recycling procedure of the waste materials for the upcoming battery industries in the foreseeable future.

Complementary Analysis on the SEI of Thin Film Siox Using X-Ray Photoemission Spectroscopy and X-Ray Reflectivity Methods

Silicon materials are expected as a high-capacity anode material for lithium-ion batteries. However, the life of the cell with such silicon materials tends to be short due to the pulverization of silicon associated with its large volume change, and electrolyte consumptions associated with the continuous growth of solid electrolyte interphase (SEI). Compared to pure silicon anodes, silicon oxide (SiOx) has been reported to mitigate such issues and extend the life of the battery1,2. In this study, we combined ex situ XPS (X-ray photoemission spectroscopy) and operando XRR (X-ray reflectivity) methods to investigate the phase transformations in the thin-film SiOx and the nature of SEI during the first lithiation/delithiation cycle to obtain the insights to improve the cycle performances.Using ex situ XPS, we examined the depth profile of the thin-film SiOx sample (Figure 1) at some representative potentials during the first cycle. This elucidated the evolution of chemical nature and thickness of the SEI, and simultaneously the irreversible phase changes in the SiOx. In recent years, the operando XRR method has been successfully applied to the pure silicon thin films3,4, revealing the nature (like thickness and electron density) of top and bottom SEI layers in early cycles. In this study, XRR was applied to thin-film SiOx for the first time. The insight from XPS and that from XRR were integrated for a comprehensive understanding on the evolution of the SEI layer and the SiOx electrode. A systematic comparison was made using the electrolytes with FEC and without FEC to better understand the importance of FEC. It was found out that the SEIs in both systems commonly show breathing behaviors, but the thickness of the SEI is almost always smaller in the FEC containing system. These findings can be a foundation for the high-performance batteries.1. Chen, T.; Wu, J.; Zhang, Q.; Su, X. Recent Advancement of SiOx Based Anodes for Lithium-Ion Batteries. J Power Sources 2017, 363, 126–144.2. Hsu, C.-H.; Chen, H.-Y.; Tsai, C.-J. Stoichiometry Dependence of Electrochemical Behavior of Silicon Oxide Thin Film for Lithium Ion Batteries. J Power Sources 2019, 438, 226943.3. Cao, C.; Steinrück, H.-G.; Shyam, B.; Stone, K. H.; Toney, M. F. In Situ Study of Silicon Electrode Lithiation with X-Ray Reflectivity. Nano Lett 2016, 16 (12), 7394–7401.4. Cao, C.; Steinrück, H.; Shyam, B.; Toney, M. F. The Atomic Scale Electrochemical Lithiation and Delithiation Process of Silicon. Adv Mater Interfaces 2017, 4 (22), 1700771. Figure 1

Origin of Persisting Photoresponse of One-Year Aged Two-Dimensional Lead Halide Perovskites Stored in Air under Dark Conditions.

Two-dimensional halide perovskites are promising for advanced photonic, optoelectronic, and photovoltaic applications. However, their long-term stability is still a critical factor limiting their implementation into further commercial applications. Here, we present an environmental stability analysis of BA2(MA)n-1PbnI3n+1 (BA = C4H12N+, MA = CH6N+) two-dimensional perovskites with the lowest quantum well thicknesses of n = 1 and n = 2, after 1 year of aging under ambient humidity, oxygen content, and light conditions. We observed that both crystal phases (n = 1 and 2) degraded similarly, resulting in the removal of organic components and crystal decomposition into PbI2, Pb oxides, and Pb hydroxides. However, we have found a significant difference between their aging under ambient light and dark conditions, affecting their degraded morphology and photoactivity. Both crystal phases exposed to ambient light aged into a morphology characterized by the formation of several pinholes and voids, accompanied by photoluminescence degradation. Samples stored under dark conditions surprisingly preserved their photoluminescence activity, which morphologically aged into microrod structures. We conclude that the observed loss of photoactivity of 2D perovskites aged under ambient light is attributed to photoaccelerated degradation processes causing faster crystal surface photo-oxidation accompanied by a creation of multiple I vacancies and hydration of the inner crystal. The retainment of photoactivity in 2D perovskites aged under dark conditions is attributed to slower surface oxidation processes into Pb salts, as confirmed by X-ray photoemission spectroscopy. The formed surface layer even allows for a layer-by-layer degradation and acts as a protection barrier against further additional loss of I atoms and the consequent hydration of the inner part of samples. We demonstrate that light is the most critical external factor accelerating 2D perovskite degradation processes in ambient air and thus affecting their long-term stability. We conclude in this work that perovskite material structural engineering together with their surface passivation or encapsulation strategical techniques applied is an essential step for their further application into long-term stable commercial devices.

DFT + U Study of Plutonium Hydrides with Occupation Matrix Control.

The magnetic order of plutonium hydrides (PuHx) has long been a subject of controversy, both experimentally and theoretically. The magnetic, structural, electronic, and thermodynamic properties of PuHx are investigated using Hubbard-corrected density functional theory (DFT + U), with U derived from linear response calculations. To address the issue of electronic metastable states within DFT + U, we employ an occupation matrix control method as well as allowing 5f orbitals to break the structural symmetry. This advanced computational approach establishes that the ground-state magnetic order for PuH2 is antiferromagnetic and that for PuH3 is ferromagnetic, consistent with Faraday and nuclear magnetic resonance experiments. Using the conventional hydrogen-vacancy model for PuHx, the hydrogen-content-induced magnetic transition and anomalous variation of the magnetic moment are successfully reproduced. In particular, the calculated transition point of x matches the experimental findings. Furthermore, the electronic configuration of the Pu atom in PuHx is determined to be 5f5, which is consistent with observations from X-ray photoemission spectroscopy. Our calculated values for enthalpy of formation, heat capacity, and entropy are in good agreement with experimental data, thereby validating the robustness of our theoretical framework.

Multiplet XPS analysis of the Mn 2p for Mn3O4 thin films

In this work, we performed a detailed analysis of the x-ray photoemission spectroscopy (XPS) of the Mn 2ppeak for Mn3O4(001) thin films. This is a challenging task since Mn3O4is composed of two different cations, Mn2+at tetrahedral and Mn3+at octahedral sites, which both contribute to the XPS spectra. The oxide spectra consist of many multiplets arising from the angular momentum coupling of the open Mn 2pand 3dshells, thus increasing the spectrums' complexity. Moreover, the energy spacing and intensities of the different multiplets also reflect the covalent mixing between Mn 3dand O 2pshells. However, we show that a detailed analysis, which provides relevant information about the cations in the oxide structure, is possible. We prepared experimentally different Mn3O4films on Au(111), and their structure was monitored with the diffraction pattern obtained with low-energy electron diffraction. The Mn 2pspectra were fit, guided by cluster model theoretical predictions, and checked for films prepared at different oxygen partial pressures. Therefore, we could observe the Mn2+and Mn3+cations' relative concentration in the Mn 2pmains peaks.

Nonlinear optical properties of La3+-Doped tellurite-zinc glasses: Impact of chemical bonding and physical properties via Raman and XPS

Understanding the connection between the local environments of lanthanum ions in tellurite glasses and their nonlinear optical (NLO) properties is essential for various technological applications. Rare earth ions can serve as probes for the local environments of the host material if the structure-property correlations are well understood. In this study, we investigated glasses with compositions 70TeO2 - (30-x)ZnO - (x)La2O3 (mol%) (x = 0, 5, 7, 9) fabricated by the melt-quenching technique. The capabilities of combined Raman and X-ray photoemission (XPS) spectroscopy were used to identify these glasses and define spectral deconvolution for distinguishing them in the formation of bridging oxygens (BO) and non-bridging oxygens (NBO). NLO properties were evaluated using open-aperture (OA) and closed-aperture (CA) Z-scan measurements with femtosecond (fs) laser pulses (∼220 fs, 750 Hz) at wavelengths ranging from 600 to 1500 nm. Raman spectra revealed a shift to higher frequencies from 731 to 746 cm−1, with increasing of La3+ ions, indicating the conversion of TeO4 polyhedra to TeO3 structural units, affecting the Te-O- Zn2+ or Te=O bonds and resulting in a variation of the polarizability. Besides the conventional analysis of oxidation state and chemical shifts of the core-level peaks, XPS spectroscopy included a careful analysis of the type oxygen bridges and metal-oxygen bond length to distinguish otherwise similar spectral contributions of different TZL glasses. Glasses with a high fraction of Zn2⁺ ions bonded with oxygen form NBO and modify the local structure of the glass network, while La³⁺ ions coordinate with oxygen atoms or interact with the lone pairs of tellurium atoms. By analyzing the correlation in different concentrations of La3+ ions, the Te-O bonds and NBO/(BO + NBO) ratio were clearly demonstrated. These findings suggest charge compensation between the Zn2⁺ and La³⁺ ions, for maintaining structural stability within the glass network. This study also reveals an enhancement of NLO properties as a function of La3+ ions concentration in TZL glasses under fs laser excitation due to resonant nonlinearity. The third-order optical nonlinearities showed an increase in the two-photon absorption coefficient (β) from 0.26 × 10−2 cm GW−1 (TZL5) to 0.62 × 10−2 cm GW−1 (TZL9), along with an increase in the nonlinear refractive index (n2) from 0.32 × 10−18 m2 W−1 to 0.65 × 10−18 m2 W−1. This enhancement is attributed to the increased number of NBOs and the high polarizability of La3+ ions. For all-optical switching (AOS) applications, two figures of merit were applied using the n2, α0, and β coefficients. The results suggest that the TZL glasses studied are potential candidates for AOS devices. Thus, this work not only elucidates the factors underlying the NLO properties but also highlights the promising potential of these glasses for use in AOS devices.

Unravelling the effect of crystal lattice compression on the supercapacitive performance of hydrothermally grown nanostructured hollandite α-MnO2 induced by incremental growth time

Manganese oxide (α-MnO2) nanoparticles are highly recognised for their use in supercapacitor applications. This study demonstrates the successful synthesis of flower-like and nanorods hollandite α-MnO2 by a simple one-pot hydrothermal technique at various reaction times. The synthesised nanoparticles were characterised by various physicochemical and electrochemical characterisation techniques. The influence of the various reaction times on the structural and morphological properties was evaluated by X-ray diffraction (XRD) and scanning electron microscope. XRD patterns revealed that the synthesized MnO2 nanoparticles are tetragonal structures with crystallite sizes ranging from 13.69 to 20.37 nm estimated from the Williamson–Hall method. Moreover, the functional groups and surface area were examined by Fourier transform infrared spectroscopy and Bruner–Emmert–Teller, respectively. Furthermore, the compositional elements were studied by X-ray photoemission spectroscopy and energy-dispersive X-ray spectroscopy. Finally, the electrochemical performances were studied using cyclic voltammetry, galvanostatic charge–discharge and electrochemical impedance spectroscopy (EIS). The GCD characteristics revealed that the optimised α-MnO2 has a good capacitive behaviour, which predicts the potential application in energy storage. Electrochemical studies revealed that the 3 h-MnO2 sample exhibited a superior electrochemical behaviour and demonstrated a high specific capacitance of 132 F/g at a current density of 1A/g.

Double exchange interaction in Mn-based topological kagome ferrimagnet

Recently discovered Mn-based kagome materials, such as RMn6Sn6 (R = rare-earth element), exhibit the coexistence of topological electronic states and long-range magnetic order, offering a platform for studying quantum phenomena. However, understanding the electronic and magnetic properties of these materials remains incomplete. Here, we investigate the electronic structure and magnetic properties of GdMn6Sn6 using x-ray magnetic circular dichroism, photoemission spectroscopy, and theoretical calculations. We observe localized electronic states from spin frustration in the Mn-based kagome lattice and induced magnetic moments in the nonmagnetic element Sn experimentally, which originate from the Sn-p\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$p$$\\end{document} and Mn-d\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$d$$\\end{document} orbital hybridization. Our calculations also reveal ferromagnetic coupling within the kagome Mn-Mn layer, driven by double exchange interaction. This work provides insights into the mechanisms of magnetic interaction and magnetic tuning in the exploration of topological quantum materials.

Hydrogenation of graphene on Ni(111) by H2 under near ambient pressure conditions

Graphene hydrogenation on Ni(111) in the mbar region has been investigated by combining Near Ambient Pressure X-ray Photoemission Spectroscopy and Density Functional Theory calculations. A complete and nearly perfect graphene single layer and an incomplete defective monolayer were exposed to a methanation mixture (H2 + CO and H2 + CO2, respectively) with a large excess of H2. The observed behavior is quite different for the two systems. In the former case, the C 1s spectrum of the initially strongly interacting graphene shows the appearance of new components corresponding to hydrogenated C atoms and their first nearest neighbors. The defective carbon layer, grown in the presence of sulfur contamination and consisting of a mixture of strongly and weakly interacting graphene with a significant amount of dissolved C, initially shows the same C species and then evolves with the formation of sp3 carbon and patches of Ni oxide/hydroxide. NiO forms by CO2 dissociation, while sp3 carbon is indicative of a rumpling of the graphene adlayer induced by hydrogenation. Both species disappear when annealing in H2. Dissociation of H2 and graphene hydrogenation is possible thanks to the presence of the Ni substrate which makes the reaction weakly exothermic and significantly reduces the barrier for H2 dissociation.

Investigation on electronic and magnetic properties of Cr doped V2O5 thin films prepared by chemical solution deposition method

The present study examines the role of Cr doping on the electronic and magnetic behaviour of V2O5i.e. V2-xCrxO5 (x = 0, 0.05, and 0.10) thin films, prepared by chemical-solution deposition technique on Si (111) substrate. X-Ray diffraction technique shows the purity of the films and confirms no secondary phase formation. The atomic force microscopy was used to confirm the roughness of the films. A morphological investigation is done using High-resolution scanning electron microscopy associated with Energy dispersive X-Ray mapping of each element of the film. Fourier transform Infrared spectroscopy is utilised to identify functional groups that are present in obtained samples. The band-gap of these obtained samples is in the range of 0.8–0.6 eV, as examined by UV–Vis i.e., its value is decreasing with Cr doping. Using vibrating sample magnetometer, it is clear that samples shows ferromagnetic (FM) behaviour with saturation magnetization 0.3–0.6 μB/cc consistent with Langevin function fitting. It concludes the presence of FM behaviour of films and magnetization increases with carrier density, consistent with the carrier-induced origin of the ferromagnetism. X-ray photoemission spectroscopy (XPS) is utilised to understand its electronic properties. Core level spectra measurements suggest that V is in mixed state of 5+ and 4+. However Cr is in 3+ states. XPS and UV–Vis measurements imply that oxygen vacancies significantly contribute to the declination of the band gap and the promotion of FM-like behaviour. This discovery offers a promising pathway for engineering novel devices.

Pushing the Thickness Limit of the Giant Rashba Effect in Ferroelectric Semiconductor GeTe.

Ferroelectric Rashba semiconductors (FERSCs) such as α-GeTe are promising candidates for energy-efficient information technologies exploiting spin-orbit coupling (SOC) and are termed spin-orbitronics. In this work, the thickness limit of the Rashba-SOC effect in α-GeTe films is investigated. We demonstrate, using angle-resolved photoemission spectroscopy (ARPES) and first-principles calculations performed on pristine GeTe, that down to 1 nm, GeTe(111) films on a Sb-covered Si(111) substrate continuously exhibit a giant Rashba effect characterized, at 1 nm, by a constant of 5.2 ± 0.5 eV·Å. X-ray photoemission spectroscopy (XPS) allows the understanding of the persistence of the Rashba effect by evidencing a compensation of Ge vacancy defects resulting from the insertion of Sb interfacial atoms in the early stage growth of the GeTe(111) films.