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Influence of the Cation on the Surface Electronic Band Structure and Magnetic Properties of Mn:ZnS and Mn:CdS Quantum Dot Thin Films
摘要： The effects of doping Mn into ZnS and CdS quantum dots are reported. Scanning tunneling spectroscopy spectra show a reduction in the electronic band gap in both CdS and ZnS upon incorporation of the Mn dopant. Mn:ZnS exhibits a rigid band shift toward higher bias which is reminiscent of a hole doping effect. This rigid band shift in Mn:ZnS is argued, with the help of X-ray photoelectron spectroscopy, to be due to a hole-doping mechanism caused by the favorable formation of Zn vacancies and a reduction in S vacancies compared to undoped ZnS films. In CdS no rigid band shift is observed even though the presence of Cd vacancies can be confirmed by photoemission and magnetic measurements. A strong sp-d hybridization is observed in the Mn:CdS film upon introducing the Mn dopant. d0 ferromagnetism is observed in both undoped ZnS and CdS quantum dot thin films at room temperature. Upon doping of Mn into ZnS the magnetization is reduced suggesting an antiparallel alignment of Mn-Mn or Mn-Zn vacancies nearest neighbors. Density Functional Theory supports the experimental results indicating the nearest neighbor Mn atoms prefer antiparallel alignment of their magnetic moments with preferred ground state of Mn in 3+ oxidation state.
关键词： CdS,Mn doping,quantum dots,magnetic properties,scanning tunneling spectroscopy,electronic band structure,X-ray photoelectron spectroscopy,density functional theory,ZnS
更新于2025-09-11 14:15:04
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revealed by resonant photoelectron spectroscopy
摘要： Resonant photoelectron spectroscopy at the Co and Mn 2p core absorption edges of half-metallic Co2MnGe has been performed to determine the element-speci?c density of states (DOS). A signi?cant contribution of the Mn 3d partial DOS near the Fermi level (EF) was clari?ed by measurement at the Mn 2p absorption edge. Further analysis by ?rst-principles calculation revealed that it has t2g symmetry, which must be responsible for the electrical conductivity along the line perpendicular to the ?lm plane. The dominant normal Auger contribution observed at the Co 2p absorption edge indicates delocalization of photoexcited Co 3d electrons. The difference in the degrees of localization of the Mn 3d and Co 3d electrons in Co2MnGe is explained by the ?rst-principles calculation. Our ?ndings of the element-/orbital-speci?c electronic states near EF will pave the way for future interface design of magnetic tunneling junctions to overcome the temperature-induced reduction of the magnetoresistance.
关键词： first-principles calculation,magnetic tunneling junctions,normal Auger contribution,half-metallic Co2MnGe,magnetoresistance,Resonant photoelectron spectroscopy,Mn 3d partial DOS,element-speci?c density of states,electrical conductivity
更新于2025-09-11 14:15:04
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High Resolution Photoelectron Spectroscopy of Cryogenically-Cooled NO <sub/>3</sub> ˉ
摘要： High-resolution anion photoelectron spectra of cryogenically cooled NO3ˉ anions obtained using slow photoelectron velocity-map imaging are presented and provide new insight into the vibronic structure of the corresponding neutral radical. A combination of improved spectral resolution, measurement of energy-dependent intensity effects, temperature control, and comparison to theory allows for full assignment of the vibronic features observed in this spectrum. We obtain a refined electron affinity of 3.9289(14) eV for NO3. Further, the appearance of Franck-Condon forbidden transitions from vibrationally cold anions to neutral states with excitation along the NO3 v4 mode confirms that these features arise from vibronic coupling with the ? 2 B E excited state of NO3 and are not hot bands as has been suggested. Together, the suite of experimental and simulated results provides clear evidence that the v3 fundamental of NO3 resides near 1050 cm?1, addressing a long-standing controversy surrounding this vibrational assignment.
关键词： vibronic structure,High-resolution photoelectron spectroscopy,NO3ˉ anions,electron affinity,vibronic coupling
更新于2025-09-11 14:15:04
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Influence of oxygen vacancy on the response properties of TiO2 ultraviolet detector
摘要： In this paper, the effect of sputtering distance between target and substrate (DTS) on the structural, morphological and optical properties of TiO2 films were investigated. X-ray diffraction (XRD) and scanning electron microscopy (SEM) revealed that crystallite size and surface morphology were strongly dependent on DTS. The X-ray photoelectron spectroscopy (XPS) results showed that obvious three peaks including C1S, Ti2p and O1s could be clearly observed and binding energy was 285, 458 and 531 eV, respectively. For each sample, four peaks at about 386, 462, 527 and 595 nm in photoluminescence (PL) spectrum were observed and produced by intrinsic recombination, F center, F+ center and electrons transferred from 3d Ti3+ states to the deep levels OH?, respectively. Finally, photoresponse properties of UV detector based on TiO2 films were further analyzed and TiO2 UV detector prepared by DTS of 80 mm showed a high responsivity of 2.02 ×10-4 A/W and photosensitivity of 32.25, also, exhibited a fast response with a rise time (τr) of 0.98 s and fall time (τf) of 3.14 s.
关键词： UV detector,oxygen vacancy,TiO2 thin films,X-ray photoelectron spectroscopy
更新于2025-09-11 14:15:04
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Vacuum-UV of polyetheretherketone (PEEK) as a surface pre-treatment for structural adhesive bonding
摘要： Polyetheretherketone (PEEK) is known for its poor wettability and poor adhesive properties. Hence, for the creation of reliable high-strength structural adhesive bonded joints, surface treatment of PEEK is required. In this work high strength bondable PEEK surfaces were achieved through a vacuum-UV (VUV) treatment. Samples of amorphous and semi-crystalline PEEK films were exposed to different VUV radiation doses. Additionally oxygen low-pressure plasma (LPP) and untreated (as received) PEEK samples were investigated for comparison. Surfaces were characterized using x-ray photoelectron spectroscopy (XPS), contact angle measurements (CA), atomic force microscopy (AFM) and confocal laser scanning microscopy (CLSM). Tensile tests of the PEEK films were carried out, to investigate changes in the mechanical properties in the bulk of the PEEK films due to the VUV exposure. The adhesive bond strength of treated specimen was determined through two different test methods (tensile and shear). These strengths were compared to the created surface properties. A strong correlation between the contact angle and the creation of functional groups was observed. VUV radiation appears as a suitable pre-treatment method for PEEK, as adhesive bonds of high strength were achieved after 5 seconds. Additionally, the usage of a VUV excimer lamp is simple, cheap and easy for automation.
关键词： X-ray photoelectron spectroscopy,Vacuum-UV (VUV),contact angles,chemical surface functionalization,structural adhesive bonding,Polyetheretherketone (PEEK),atomic force microscopy
更新于2025-09-11 14:12:44
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Bulk and surface characterisation of micrometer-thick cobalt ferrite films grown by IR PLD
摘要： We have studied micrometer-thick cobalt ferrite films deposited on Si (100) single crystal substrates by nanosecond pulsed laser deposition at 1064 nm.The thickness of the deposited films (1.3 μm) was monitored by AFM. The chemical and structural characterisation of the films was carried out by Raman spectroscopy and transmission M?ssbauer spectroscopy at 300 and 26 K. For comparison purposes, transmission M?ssbauer data at these two temperatures were also recorded from a commercial cobalt ferrite powder and the home-made target used to grow the films. The surface characterisation was performed by X-Ray Photoelectron Spectroscopy (XPS) and Integral Low Energy Electron Spectroscopy (ILEEMS). XPS showed Co and Fe to be present as Co2+ and Fe3+, as expected for cobalt ferrite. The Raman spectra showed the lines characteristic of cobalt ferrite. The M?ssbauer spectra, both in the transmission and backscattering modes, were fitted to two sextets whose hyperfine parameters are in good agreement with those expected from Fe3+ cations occupying the tetrahedral and octahedral sites in the spinel-related structure. No significant differences were observed in the relative areas of the two sextets in the transmission and ILEEMS spectra, suggesting that the cation distribution at the surface and the bulk are not too different. However, the relative areas of the two components changed drastically with temperature both in the spectra of the films as in those recorded from the cobalt ferrite standards. We discuss the possible origin of the evolution with temperature of those relative areas.
关键词： X-ray photoelectron spectroscopy,Raman spectroscopy,Cobalt ferrite,M?ssbauer spectroscopy,Pulsed laser deposition
更新于2025-09-10 09:29:36
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Cross-Section Analysis of the Composition of Sprayed Cu <sub/>2</sub> ZnSnS <sub/>4</sub> Thin Films by XPS, EDS, and Multi-Wavelength Raman Spectroscopy
摘要： A detailed cross-section analysis of the chemical composition of sprayed Cu2ZnSnS4 thin films is presented. X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy (with near-IR, visible, and UV-lasers) are used to demonstrate that while CZTS effectively forms within the bulk of the film, there is some degree of element segregation, formation of undesirable secondary phases, and the presence of a disordered kesterite structure across the film. Different penetration depths of the excitation signals correspond to the many different surface sensitive techniques employed in this work. XPS results reveal that the surface of Cu4ZnSnS4 (CZTS) films presents a high concentration of tin and zinc and a low sulfur concentration, while being highly depleted in copper. EDS, XRD, and infrared Raman spectroscopy confirm that the composition of as-sprayed and sulfurized films is close to stoichiometric Cu2ZnSnS4. Resonant UV-Raman spectroscopy helps to identify secondary phases located at the external surface of sprayed and sulfurized CZTS films (mainly ZnS, ZnO), while VIS-Raman spectroscopy helps to identify a disordered kesterite structure close to the surface. Secondary phases need to be chemically etched when aiming at incorporating kesterite films obtained by spray pyrolysis into photovoltaic devices.
关键词： multi-wavelength Raman spectroscopy,X-ray photoelectron spectroscopy,spray pyrolysis,thin films,kesterite
更新于2025-09-10 09:29:36
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The Self-Reaction of <i>ortho</i> -Benzyne at High Temperatures Investigated by Infrared and Photoelectron Spectroscopy
摘要： Ortho-benzyne, a Kekulé-type biradical is considered to be a key intermediate in the formation of polycyclic aromatic hydrocarbons (PAH) and soot. In the present work we study the ortho-benzyne self-reactions in a hot micro-reactor and identify the high-temperature products by IR/UV spectroscopy and by photoion mass-selected threshold photoelectron spectroscopy (ms-TPES) in a free jet. Ms-TPES confirms formation of ortho-benzyne as generated from benzocyclobutendione, as well as benzene, biphenylene, diacetylene and acetylene, originating from the reaction o-C6H4 → HCC-CCH + C2H2 , and CH3. PAH molecules like naphthalene, 2-ethynylnaphthalene, fluorene, phenanthrene and triphenylene are identified based on their IR/UV spectra. By comparison with recent computations their formation starting from ortho-benzyne can be readily understood and supports the importance of the biradical addition (1,4-cycloaddition followed by fargmenation) pathway to PAH molecules, recently proposed by Comandini et al.
关键词： photoelectron spectroscopy,Ortho-benzyne,high-temperature reactions,IR/UV spectroscopy,biradical addition,polycyclic aromatic hydrocarbons,PAH,soot
更新于2025-09-10 09:29:36
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Silicon Oxide-Rich Diamond-Like Carbon: A Conformal, Ultrasmooth Thin Film Material with High Thermo-Oxidative Stability
摘要： Silicon oxide-containing diamond-like carbon (a-C:H:Si:O) films are a promising class of protective coatings for environmentally-demanding applications owing to their lower residual stresses and superior thermal stability and oxidation resistance relative to undoped diamond-like carbon. However, existing versions of a-C:H:Si:O deposited by traditional methods such as plasma-enhanced chemical vapor deposition (PECVD) undergo substantial degradation and oxidation at temperatures above 250 °C. This, together with the difficulty of PECVD in depositing conformal coatings on complex geometries such as high-aspect-ratio features, has limited the applicability of a-C:H:Si:O. Here, the unique capabilities of plasma immersion ion implantation and deposition (PIIID) to grow silicon oxide-rich diamond-like carbon materials that are ultrasmooth, continuous, and conformal on high-aspect-ratio topographies are explored. The high concentration of silicon and oxygen in PIIID-grown films (23 ± 5 at.% and 11 ± 4 at.%, respectively) is unrivalled for this class of materials, and drastically increases the resistance to oxidation at high temperatures, compared with PECVD-grown films. The results open the path for using a-C:H:Si:O in applications involving exposure of materials to extreme environments.
关键词： ultrasmooth films,X-ray photoelectron spectroscopy (XPS),diamond-like carbon,NEXAFS,thermal stability
更新于2025-09-10 09:29:36
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Water Dissociation and Hydroxyl Ordering on Anatase
摘要： We studied the interaction of water with the anatase TiO2e001T surface by means of scanning tunneling microscopy, x-ray photoelectron spectroscopy, and density functional theory calculations. Water adsorbs dissociatively on the ridges of a (1 × 4) reconstructed surface, resulting in a (3 × 4) periodic structure of hydroxyl pairs. We observed this process at 120 K, and the created hydroxyls desorb from the surface by recombination to water, which occurs below 300 K. Our calculations reveal the water dissociation mechanism and uncover a very pronounced dependence on the coverage. This strong coverage dependence is explained through water-induced reconstruction on anatase TiO2e001T-e1 × 4T. The high intrinsic reactivity of the anatase TiO2e001T surface towards water observed here is fundamentally different from that seen on other surfaces of titania and may explain its high catalytic activity in heterogeneous catalysis and photocatalysis.
关键词： x-ray photoelectron spectroscopy,scanning tunneling microscopy,anatase TiO2,hydroxyl ordering,density functional theory,water dissociation
更新于2025-09-10 09:29:36