Ultraviolet Photoelectron Spectroscopy Research Articles

2D-3D heterostructure of PtS2-x/Ga2O3 and their band alignment studies for high performance and broadband photodetector.

For deep ultraviolet (UV-C) photodetectors, Gallium oxide (Ga2O3) is a suitable candidate owing to its intrinsic ultra-wide band gap and high stability. However, its detection is limited within the UV-C region, which restricts it to cover a broad range, especially in visible and near-infrared (NIR) region. Therefore, constructing a heterostructure of Ga2O3 with an appropriate material having a narrow band gap is a worthwhile approach to compensate for it. In this category, PtS2 group-10 transitional metal dichalcogenide (TMDC) stands at the top owing to its narrow band gap (0.25-1.65 eV), high mobility, and stability for heterostructure synthesis. Moreover, heterostructure with Ga2O3 sensing in UV and PtS2 broad response in visible and IR range can broaden the spectrum from UV to NIR and to build broadband photodetector. In this work, we fabricated a 2D-3D PtS2-x/Ga2O3 heterostructure based broadband photodetector with detection from UV-C to NIR region. In addition, the PtS2-x/Ga2O3 device shows a high responsivity of 38.7 AW 1 and detectivity of 4.8×1013 Jones under 1100 nm light illumination at 5V bias. A fast response of 90 ms /86 ms illustrates the device's fast speed. An interface study between the PtS2-x and Ga2O3 was conducted using X-ray photoelectron spectroscopy and Ultraviolet photoelectron spectroscopy (UPS) which confirmed type-I band alignment. Finally, based on their band alignment study, a carrier transport mechanism was proposed at the interface. This work offers a new opportunity to fabricate large-area high-performance 2D-3D heterostructures based photodetectors for future optoelectronics devices.

N-Heterocyclic Carbene Monolayers on Metal-Oxide Films: Correlations between Adsorption Mode and Surface Functionality.

N-Heterocyclic carbene (NHC) ligands have been self-assembled on various metal and semimetal surfaces, creating a covalent bond with surface metal atoms that led to high thermal and chemical stability of the self-assembled monolayer. This study explores the self-assembly of NHCs on metal-oxide films (CuOx, FeOx, and TiOx) and reveals that the properties of these metal-oxide substrates play a pivotal role in dictating the adsorption behavior of NHCs, influencing the decomposition route of the monolayer and its impact on work function values. While the attachment of NHCs onto CuOx is via coordination with surface oxygen atoms, NHCs interact with TiOx through coordination with surface metal atoms and with FeOx via coordination with both metal and oxygen surface atoms. These distinct binding modes arise due to variances in the electronic properties of the metal atoms within the investigated metal-oxide films. Contact angle and ultraviolet photoelectron spectroscopy measurements have shown a significantly higher impact of F-NHC adsorption on CuOx than on TiOx and FeOx , correlated to a preferred, averaged upright orientation of F-NHC on CuOx.

Synthesis of the composites of carbon quantum dots and metal organic framework and their application in hydrogen evolution

The Ti-MIL-125 metal-organic framework (MOF) functions as a nanoreactor, producing carbon quantum dots (CQDs) within its structure and forming CQD/MOF composites. Similarly, a Pt-CQD/MOF three-component composite is synthesized. Their properties, along with those of CQDs and MOF-free-CQDs (mf-CQDs) enclosed within the MOF, undergo assessment and comparison. Integrating CQDs and Pt minimally alters the MOF structure but reduces specific surface areas due to incorporation. The emitted wavelength of CQD/MOF (570 nm) differs from pristine CQDs (450 nm) and mf-CQDs (496 nm), indicating MOF influence on CQDs' growth and photoluminescence. HOMO and LUMO levels of CQDs/MOF, measured via ultraviolet photoelectron spectroscopy and low-energy inverse photoelectron spectroscopy, are more positive than those of the MOF, suggesting heterogeneous junction formation, aiding electron separation. CQD/MOF exhibits a modest photocatalytic hydrogen evolution rate of 20.4 μmol/g/h. Conversely, Pt-CQD/MOF significantly boosts the rate to 2213 μmol/g/h, underscoring Pt's pivotal catalytic role.

Flexible Copper Films Modification via Spontaneous Reduction of Aryldiazonium Gold Salts: Unraveling Surface Properties and Energy Profile.

In this study, we report the modification of flexible copper films via the spontaneous reduction of aryldiazonium gold salts [X-4-C6H4N≡N]AuCl4 (X═COOH, NO2). The electroless modification involves dipping of flexible copper films in the aryldiazonium gold solutions for a few seconds, under ambient conditions, followed by a washing step with deionized water to obtain a mechanically robust gold-aryl coating. The chemical composition, morphology, electronic structure, and optical properties of the gold-aryl layer and the flexibility of the modified copper films are supported by the results from X-ray photoelectron spectroscopy (XPS), electrochemistry, contact angle, scanning electron microscopy (SEM), and ultraviolet photoelectron spectroscopy (UPS). XPS surface analysis showed metallic gold in addition to C-C, C-O/C-N, and C═O functional groups from the grafted aryls. Cu 2p showed metallic copper as a major component and a small amount of Cu(II) ions. Wettability studies showed that Au-COOH@Cu increased the contact angle of the bare copper films from 68.0 ± 0.7° to 82.0° ± 0.7°, while Au-NO2@Cu increased the contact angle to 134.0° ± 0.3°. UPS energy profile analysis of [HOOC-4-C6H4N≡N]AuCl4 (valence band maximum = 1.91 eV) exhibited greater reducibility than [O2N-4-C6H4N≡N]AuCl4 (valence band maximum = 2.91 eV). The lower ionization potential of [HOOC-4-C6H4N≡N]AuCl4 (IP = 4.33 eV) enhanced the reactivity upon copper film contact, potentially inducing efficient energy level alignment, compared with [O2N-4-C6H4N≡N]AuCl4 (IP = 5.62 eV). UPS results were further supported by electrochemistry investigation which revealed that [HOOC-4-C6H4N≡N]AuCl4 is easily reducible compared with [O2N-4-C6H4N≡N]AuCl4. The findings presented here hold significant implications for developing flexible copper films and pave the way for future advancements in electronic material modification for industrial applications.

The Fabrication and Property Characterization of a Ho2YSbO7/Bi2MoO6 Heterojunction Photocatalyst and the Application of the Photodegradation of Diuron under Visible Light Irradiation.

A novel photocatalytic nanomaterial, Ho2YSbO7, was successfully synthesized for the first time using the solvothermal synthesis technique. In addition, a Ho2YSbO7/Bi2MoO6 heterojunction photocatalyst (HBHP) was prepared via the hydrothermal fabrication technique. Extensive characterizations of the synthesized samples were conducted using various instruments, such as an X-ray diffractometer, a Fourier transform infrared spectrometer, a Raman spectrometer, a UV-visible spectrophotometer, an X-ray photoelectron spectrometer, and a transmission electron microscope, as well as X-ray energy dispersive spectroscopy, photoluminescence spectroscopy, a photocurrent test, electrochemical impedance spectroscopy, ultraviolet photoelectron spectroscopy, and electron paramagnetic resonance. The photocatalytic activity of the HBHP was evaluated for the degradation of diuron (DRN) and the mineralization of total organic carbon (TOC) under visible light exposure for 152 min. Remarkable removal efficiencies were achieved, with 99.78% for DRN and 97.19% for TOC. Comparative analysis demonstrated that the HBHP exhibited markedly higher removal efficiencies for DRN compared to Ho2YSbO7, Bi2MoO6, or N-doped TiO2 photocatalyst, with removal efficiencies 1.13 times, 1.21 times, or 2.95 times higher, respectively. Similarly, the HBHP demonstrated significantly higher removal efficiencies for TOC compared to Ho2YSbO7, Bi2MoO6, or N-doped TiO2 photocatalyst, with removal efficiencies 1.17 times, 1.25 times, or 3.39 times higher, respectively. Furthermore, the HBHP demonstrated excellent stability and reusability. The mechanisms which could enhance the photocatalytic activity remarkably and the involvement of the major active species were comprehensively discussed, with superoxide radicals identified as the primary active species, followed by hydroxyl radicals and holes. The results of this study contribute to the advancement of efficient heterostructural materials and offer valuable insights into the development of sustainable remediation strategies for addressing DRN contamination.

Efficient photocatalytic CO2 reduction achieved by constructing Bi4O5Br2/Bi-MOF Z-scheme heterojunction

Building efficient catalysts is an urgent issue in the field of photocatalytic CO2 reduction, and Z-scheme heterojunction structures can availably suppress the recombination of photo generated carriers and improve photocatalytic performance. This study successfully prepared a new type of Bi4O5Br2/Bi-MOF composite photocatalyst through self-assembly method. After 5h of simulated sunlight exposure, the optimized sample 50-Bi4O5Br2/Bi-MOF photocatalytic reduction of CO2 to CO efficiency (23.78 μmol·g-1·h-1) was 5.09 times higher than pure Bi4O5Br2, and the CH4 yield (5.39 μmol·g-1·h-1) was 2.52 times that of pure Bi-MOF. In addition, in the cyclic experiment, the catalyst had high stability and reusability. The Z-scheme charge transfer mechanism was confirmed through band structure analysis, Electron spin resonance (ESR), Ultraviolet photoelectron spectroscopy (UPS) and other related characterizations. This work provided an important strategy for designing efficient Z-scheme heterojunction photocatalysts.

Na0.6Co3O4- La/Pr co-Doped Ceria as Semiconductor-Ionic Heterostructure Material for Fuel Cell Application

Functional Sodium-doped cobalt oxide (Na0.6Co3O4, NCO) was incorporated to regulate and improve the electrochemical performance of La/Pr co-doped ceria (LCP) electrolytic materials with good operative stability, forming an p-n heterostructure electrolyte (LCP-NCO) for low-temperature solid oxide fuel cell (LTSOFC) application. LCP-NCO is a new potential semiconductor-ionic material, achieving a maximum power density of 1075 mW cm−2 along with a high open-circuit voltage of 1.061 V at 520 °C. Scanning electron microscopy combined with transmission electron microscopy unveiled the crystallographic microstructure of heterostructure interface between LCP and NCO. Raman spectra and Fourier transform infrared spectroscopy spectra were analyzed to distinguish the functional groups and the vibrational properties. Ultraviolet–visible absorption and ultraviolet photoelectron spectroscopy have determined the accurate band edge positions of LCP and NCO and p-n heterojunction nature. Built-in electric field in semiconductor heterostructure and more oxygen vacancies created through the variation of Co3+/Co2+ ratio in LCP-NCO during the fuel cell test, contributed to the enhanced ionic transport. Characteristic of competent conductivity of 0.26–0.42 S cm−1 at 400 °C–520 °C, and the improved cell duration, revealed that the LCP-NCO as a hybrid oxygen ion and protonic conductor would be a potential electrolyte for LTSOFC.

High‐Performance of Self‐Powered UV–Visible CdS (PVP)/PbI2 Heterojunction Photodetector

Herein, the Polyvinyl pyrrolidone (PVP)‐assisted CdS/PbI2 heterojunction UV–visible photodetector is constructed by the sol–gel spin coating method. The X‐ray diffraction, scanning electron microscopy, and energy dispersive spectrometer demonstrate the synthesis and successful complexation of PVP, CdS, and PbI2. The UV–visible absorption spectroscopy and UV photoelectron spectroscopy measurements of CdS and PbI2 are carried out to prove that the CdS and PbI2 form a type II heterojunction. Compared with pure CdS film photodetector, the CdS (PVP)/PbI2 heterojunction photodetector has self‐powered characteristics, and exhibits excellent photoconductivity in the UV–visible with higher switching ratios, detection rates, and faster response times of 1.1 × 105, 9.77 × 1011 Jones, and 20 ms, respectively, which has great potential in the field of UV–visible self‐powered photodetector.

Moderately Reconstructed Ternary Metal Nitride Nanoparticles for Highly Efficient and Robust Freshwater and Seawater Oxidation under Industrial Current Density

Transition metal nitrides (TMNs) electrocatalysts experience rapid performance degradation during oxygen evolution reaction (OER) due to severe and irreversible electrochemical reconstruction, impeding their practical application in electrochemical water splitting. To address this issue, ternary metal (Ni, Fe, Cr) nitride nanoparticles on spongy nitrogen‐doped disordered carbon skeleton electrocatalyst (NFCN/C) is synthesized using a novel one‐pot pyrolysis of eutectic mixture method. The ionomer‐free NFCN/C electrode, which undergoes moderate electrochemical reconstruction, demonstrates high OER performance in both alkaline freshwater and seawater solutions, achieving a current density of 250 mA cm−2 with low overpotentials of 349 and 364 mV, respectively. The NFCN/C anode with Pt/C cathode delivers 10 mA cm−2 at a low cell voltage of 1.49 V and exhibits long‐term durability of 450 h at 500 mA cm−2. In situ Raman spectroscopy and ultraviolet photoelectron spectroscopy (UPS), along with pre‐ and post‐characterizations, elucidate that both high electrocatalytic activity and robustness of NFCN/C for OER stem from the proposed intrinsic strategy integrating physical and electronic structures. This work paves the way for designing highly efficient and robust TMNs electrocatalysts with moderate electrochemical reconstruction for industrial freshwater and seawater electrolysis.

Fabrication of soy protein nanoparticles based on metal-phenolic networks for stabilization of nano-emulsions delivery system

The use of soy protein isolate (SPI) nanoparticles as a stabilizer in nano-emulsion systems has garnered significant interest. While metal-phenolic networks (MPNs) have been explored for their multifunctional surface modification capabilities, their integration with food protein-based delivery systems remains less explored. In this study, we attempt to develop a novel strategy to encapsulate cinnamaldehyde using MPNs (EGCG-Fe3+) with self-assembling soy protein nanoparticles (SE-Fe NPs) as a stabilizer for nano-emulsions. UV, Raman, and X-ray photoelectron spectroscopy analyses demonstrated that SE-Fe NPs were generated through metal−phenolic coordination and covalent interactions. SE-Fe NPs had a narrower particle size distribution and enhanced radical scavenging (up to 3.35-fold), as well as thermal stability. Furthermore, the smaller droplet size, higher modulus, higher cinnamaldehyde encapsulation efficiency (from 63.5% to 84.2%), and improved bio-accessibility of SE-Fe NPs stabilized nano-emulsions delivery system demonstrated in this study shows promising future applications in the food industry.

Enhanced visible light photocatalytic degradation of dyes by the oxygen-rich vacancy-assisted S-scheme heterojunction Al2O3/BiOBr: Catalytic mechanism and performance evaluation

A heterojunction Al2O3/BiOBr composite photocatalyst, characterized by an S-scheme structure and enriched with oxygen vacancies, was synthesized through a solvothermal reaction coupled with an in situ growth approach. Oxygen vacancies on the catalyst surface, enhanced by the robust coupling between Al2O3 and BiOBr, were corroborated by X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR). Techniques such as UV–vis diffuse reflectance spectroscopy (DRS), UV photoelectron spectroscopy (UPS), Mott–Schottky characterization, and experimental radical trapping experiments collectively validated the pathways for migrating photogenerated carriers. The interplay between the surface oxygen vacancies and the S-scheme Al2O3/BiOBr heterojunction, which possesses potent redox capabilities, significantly improved the photocatalytic degradation. This enhancement was particularly evident in the outstanding visible photocatalytic degradation performance against rhodamine B (RhB), methyl orange (MO), and basic fuchsin (BF). The synthesized composite photocatalysts demonstrated 92% retention of degradation efficiency after five recycling cycles, indicating their considerable stability.

Utilizing Constant Energy Difference between sp-Peak and C 1s Core Level in Photoelectron Spectra for Unambiguous Identification and Quantification of Diamond Phase in Nanodiamonds.

The modification of nanodiamond (ND) surfaces has significant applications in sensing devices, drug delivery, bioimaging, and tissue engineering. Precise control of the diamond phase composition and bond configurations during ND processing and surface finalization is crucial. In this study, we conducted a comparative analysis of the graphitization process in various types of hydrogenated NDs, considering differences in ND size and quality. We prepared three types of hydrogenated NDs: high-pressure high-temperature NDs (HPHT ND-H; 0-30 nm), conventional detonation nanodiamonds (DND-H; ~5 nm), and size- and nitrogen-reduced hydrogenated nanodiamonds (snr-DND-H; 2-3 nm). The samples underwent annealing in an ultra-high vacuum and sputtering by Ar cluster ion beam (ArCIB). Samples were investigated by in situ X-ray photoelectron spectroscopy (XPS), in situ ultraviolet photoelectron spectroscopy (UPS), and Raman spectroscopy (RS). Our investigation revealed that the graphitization temperature of NDs ranges from 600 °C to 700 °C and depends on the size and crystallinity of the NDs. Smaller DND particles with a high density of defects exhibit a lower graphitization temperature. We revealed a constant energy difference of 271.3 eV between the sp-peak in the valence band spectra (at around 13.7 eV) and the sp3 component in the C 1s core level spectra (at 285.0 eV). The identification of this energy difference helps in calibrating charge shifts and serves the unambiguous identification of the sp3 bond contribution in the C 1s spectra obtained from ND samples. Results were validated through reference measurements on hydrogenated single crystal C(111)-H and highly-ordered pyrolytic graphite (HOPG).

Bismuth-Based Perovskite Derivates with Thermal Voltage Exceeding 40 mV/K.

Heat is an inexhaustible source of energy, and it can be exploited by thermoelectronics to produce electrical power or electrical responses. The search for a low-cost thermoelectric material that could achieve high efficiencies and can also be straightforwardly scalable has turned significant attention to the halide perovskite family. Here, we report the thermal voltage response of bismuth-based perovskite derivates and suggest a path to increase the electrical conductivity by applying chalcogenide doping. The films were produced by drop-casting or spin coating, and sulfur was introduced in the precursor solution using bismuth triethylxanthate. The physical-chemical analysis confirms the substitution. The sulfur introduction caused resistivity reduction by 2 orders of magnitude, and the thermal voltage exceeded 40 mV K-1 near 300 K in doped and undoped bismuth-based perovskite derivates. X-ray diffraction, Raman spectroscopy, and grazing-incidence wide-angle X-ray scattering were employed to confirm the structure. X-ray photoelectron spectroscopy, elemental analysis, scanning electron microscopy, and energy-dispersive X-ray spectroscopy were employed to study the composition and morphology of the produced thin films. UV-visible absorbance, photoluminescence, inverse photoemission, and ultraviolet photoelectron spectroscopies have been used to investigate the energy band gap.

High–Quality and Stable Quasi‐2D Perovskite Film Prepared by Introducing Alkali Metal Ion Additive

AbstractDue to the excellent stability, researchers have shown great interest in quasi two–dimensional (2D) perovskite in recent years. However, the poor film quality and low photoelectric conversion efficiency (PCE) of 2D perovskite solar cells are still a major issue that restricts them from catching up with three–dimensional (3D) perovskite. Herein, we introduce sodium iodide as an additive to improve the surface coverage of 2D perovskite ((BA)2(MA)3Pb4I13) films and reduce the number of grain boundaries. Steady–state photoluminescence (PL) and ultraviolet photoelectron spectroscopy (UPS) indicate that non–radiative defects are suppressed and the band alignment is regulated. After modified by NaI, the film surface coverage enhances and the number of holes decreases. As a result, the PCE of device with NaI increases from 13.63 % to 16.40 % at optimal concentration, and the hysteresis effect is also suppressed. Besides, the humidity and thermal stability of perovskite are enhanced. The device with NaI modification can keep 80 % of initial efficiency, compared to 30 % for reference device after stored 30 days under ambient air condition. This work provides a simple method to improve the quality of quasi 2D perovskite films.

The space-charge region at CsPbBr3 NC⊆Pb-MOF p-n junction by self-sacrificing MOFs to selective detect NH3·H2O or Fe3+

The rational design of p-n heterojunction is highly desirable to optimize electron distribution and photocarriers’ transfer pathway at space-charge region, which would influence the fluorescence detection. Herein, the inorganic perovskite CsPbBr3 nanocrystals (CPB NCs) have been encapsulated into Pb-centered MOFs via simple wet-chemical self-sacrifice to construct a “turn-off” sensor for the sensitive detection of NH3·H2O or Fe3+ in aqueous solution. The Mott-Schottky plots (M-S), ultraviolet photoelectron spectroscopy (UPS) and density functional theory (DFT) calculation have proved the formation of p-n junction between the derived CsPbBr3 and parent Pb-MOF. The CPB⊆Pb-MOF heterojunction has provided a strong platform to maintain high fluorescence performance and stability in aqueous solution as sensor. It is found that the static quenching process has affected the detection of Fe3+. More importantly, the occurrence of dynamic quenching with electron transfer is also verified by fluorescence lifetime, in-situ X-ray photoelectron spectroscopy (XPS) analysis. The phase transfer has taken major reason when being introduced by NH3·H2O. Fortunately, the 0.4CPB⊆Pb-MOF has exhibited best analytical performance for NH3·H2O or Fe3+. What’s more, it has been manufactured for the visual detection for NH3·H2O or Fe3+ in the real environmental water samples. Thereby, this perovskite based water detection system would broaden the application in point-to-point precise diagnostics.

ZnxFe3-xO4–ZnO heterojunction interfaced with poly(L-DOPA) electron transfer mediator layer for enhanced visible light photocatalytic activity

Z-scheme heterojunctions comprising ZnxFe3-xO4@poly(L-DOPA)@ZnO (ZF@PD@ZnO) were synthesized using solvothermal and precipitation techniques. The study aimed to investigate the impact of the poly(L-DOPA) electron transfer mediator on the photocatalytic performance of ZnxFe3-xO4@ZnO (ZF@ZnO) nanocomposites under visible light irradiation. X-ray diffraction (XRD) and HRTEM analysis confirmed the formation of heterostructures, identifying the crystalline phases of both ZnO and zinc ferrite. BFTEM images revealed a polyhedral shape for all samples, with a tendency toward mild agglomeration. The partial inversion of the zinc ferrite cubic spinel structure was evidenced by FT-IR, XPS, and VSM analyses. Zinc ferrite was found to be ferromagnetic, with cation distributions between tetrahedral (A) and octahedral (B) positions as [Zn0.62+Fe0.43+]A[Fe0.42+Fe1.63+]BO4. The samples exhibited notable photocatalytic activity against Rhodamine B, serving as a model contaminant. Furthermore, the stability and reusability of the samples were examined. Additionally, the study elucidated the photocatalytic mechanism produced by the ternary Z-scheme ZF@PD@ZnO, involving spin-polarized charge carriers. Energy band alignment was evaluated by combining ultraviolet photoelectron spectroscopy (UPS) with UV-Vis spectroscopy. The interplay between band alignment and reactive oxygen species (ROS) generation was discussed in correlation with EPR results. Enhanced ROS generation under visible light illumination, observed in the ZF@PD@ZnO nanocomposite, is mainly due to the addition of the conductive poly(L-DOPA) layer, acting as an electron transfer mediator in the Z-scheme heterojunction, ensuring enhanced charge separation.

Etching and Compositional Ratio Effect on the Surface Properties of Bismuth Telluride Thin Films

Bismuth telluride has garnered considerable attention owing to its versatile properties applicable in thermoelectric and antibacterial domains, as well as its intriguing topological insulating properties. In this work, our group fabricated bismuth telluride thin films with various ratios using radio frequency magnetron sputtering. The surface properties of these thin films were thoroughly analyzed by employing a diverse array of analytical techniques, including X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), four-point probe and contact angle (CA) measurements. Specifically, our XPS findings indicated that Bi is more susceptible to oxidation than Te following Ar+-ion etching. Pure Te thin films exhibited the highest Rq value of 31.2 nm based on AFM and SEM results due to their larger grain sizes. The XRD patterns revealed a peak at 27.75° for thin films with 20% Te, attributed to its rhombohedral structure. Moreover, thin films with 30% Te yielded the highest weighted average work function with a value of 4.95 eV after etching. Additionally, pristine Bi and Te thin films demonstrated the most robust hydrophobic properties compared to intermediate-composition thin films, as determined by CA measurements.

Electronic structure of superconducting VN(111) films

Vanadium nitride (VN) is a transition-metal nitride with remarkable properties that have prompted extensive experimental and theoretical investigations in recent years. However, there is a current paucity of experimental research investigating the temperature-dependent electronic structure of single-crystalline VN. In this study, high-quality VN(111) films were successfully synthesized on α\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\alpha$$\\end{document}-Al2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_2$$\\end{document}O3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_3$$\\end{document}(0001) substrates using magnetron sputtering. The crystal and electronic structures of the VN films were characterized by a combination of high-resolution X-ray diffraction, low-energy electron diffraction, resonant soft X-ray absorption spectroscopy, and ultraviolet photoelectron spectroscopy. The electrical transport measurements indicate that the superconducting critical temperature of the VN films is around 8.1 K. Intriguingly, the temperature-dependent photoelectron spectroscopy measurements demonstrate a weak temperature dependence in the electronic structure of the VN films, which is significant for understanding the ground state of VN compounds.

Observations on Valence‐Band Electronic Structure and Surface States of Bulk Insulators Based on Fast Stabilization Process of Sample Charging in UPS

AbstractThe valence‐band electronic structure is one of the most basic properties of materials and ultraviolet photoelectron spectroscopy (UPS) is the most commonly used technique for its measurement. To obtain credible UPS spectra on insulator surfaces, eliminating the charging effects at the surfaces is essential but is very difficult. Here, a reliable measurement for the valence‐band structure of bulk insulators is shown. It has been observed that, during UPS measurements without any charge compensation, the charging on irradiated insulator surfaces reaches its steady state very quickly and the fluctuation of the charging‐induced surface potential is very small. Therefore, the whole UPS spectrum undergoes just a parallel shift and can be calibrated by comparison with the corresponding X‐ray photoelectron spectroscopy (XPS) spectrum even though XPS often has a poorer resolution than UPS. From the calibrated valence‐band spectra, it is found that noticeable electronic energy levels (i.e., the “surface states”) exist in the bandgap, and based on the density of states (DOS) calculations, the surface states are attributed to the truncation of the bulk periodic structure at the surfaces. This work is anticipated to provide a way to obtain the valence band structure and the surface states of bulk insulators which play crucial roles in many physical processes.

On the combination of ultraviolet photoelectron spectroscopy with optical absorption studies to investigate Cu2O||TiO2 direct Z-scheme junctions with different Cu2O loading

Among the electronic properties, the positions of the electronic band edges and the work function are essential parameters for determining the potential of a photocatalyst and its ability to function in a solar conversion system. A novel type of photocatalysts, called direct Z-schemes, possesses many advantages over conventional heterojunctions, which all benefit the catalytic performance under solar light. As oxidation and reduction reactions are greatly affected by the electrical characteristics of the material, ultraviolet photoelectron spectroscopy (UPS) is a powerful tool to determine and quantify important electronic parameters of previously fabricated TiO2‖Cu2O junctions. TiO2 nanotubes modified with Cu2O nanoparticles exhibit a reduction in the value of the work function (WF = 3.67 ± 0.01 eV) and ionization potential (IP = 6.01 ± 0.04 eV) with respect to the TiO2 substrate (WF = 4.29 ± 0.02 eV and IP = 7.65 ± 0.05 eV). By varying the electrodeposition time, an optimized amount of deposited Cu2O nanoparticles was proven to reduce the WF and IP to facilitate the excitation of electrons, which could be correlated to the improved absorbance in the visible wavelength range. This work proposes a valuable methodology for band diagram tracing from UPS spectra and provides new insights in the relationship between synthesis, electronic properties and visible light absorption of titania based Z-schemes for photocatalytic applications with a combination of surface sensitive techniques and optical absorption studies.