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oe1(光电查) - 科学论文

11 条数据
?? 中文（中国） ▾

  • Laser-induced graphitized periodic surface structure formed on tetrahedral amorphous carbon films

    摘要： Femtosecond laser-induced periodic surface structure (LIPSS), graphitization and swelling observed on ultra-hard, hydrogen-free tetrahedral amorphous carbon (ta-C) films are examined and compared with those on hydrogenated amorphous carbon (a-C:H) films, nitride films, and glassy carbon plates. The threshold fluence for LIPSS formation on ta-C is approximately twice as high as that for other specimens, and the LIPSS period Λ near the threshold is very fine at ca. 80 nm. Λ gradually increases with increasing fluence, and rapidly increases to ca. 600 nm at a high fluence. The ablation rate also increases rapidly at this fluence. In addition, ta-C and a-C:H are graphitized by irradiation and expand in volume. The surface layer of ta-C film changes to nanocrystalline graphite as the fluence increases and the crystallinity is improved; however, at higher fluence, the crystallinity deteriorates suddenly similar to that at low fluence. At high fluence, the rapid increase in Λ and the ablation rate, and the sudden deterioration in crystallinity are determined as common phenomena for these disordered carbons. LIPSS formation and swelling over a large area by scanned spot irradiation produces submicron height flat hills with conductivity and surface functionality on the insulating surface.

    关键词： Graphitization,Swelling,Laser-induced periodic surface structure,Femtosecond-laser processing,Nanocrystalline graphite,Tetrahedral amorphous carbon

    更新于2025-09-23 15:21:01

  • Influence of pore size of Ti substrate on structural and capacitive properties of Ti/boron doped diamond electrode

    摘要： This work is aimed at understanding the influence of pore size of titanium (Ti) substrate on the capacitive properties of boron doped diamond (BDD) electrode. BDD films were deposited on Ti substrates with five different pore sizes - 2.5, 5.0, 20.0, 30.0, 50.0 mm - using hot filament chemical vapor deposition (HFCVD). The pore size of substrate was found to cause significant variations in surface structure and capacitive properties of the Ti/BDD electrodes. The optimum pore size that resulted in best surface structure and capacitive properties was found to be 30.0 mm. The Ti30.0/BDD electrode was found to possess higher sp2-C bonds content, sp3-C bond with doped boron atom, more closely interlaced grains and bigger specific surface area than other electrodes. The maximum capacitance obtained for Ti30.0/BDD electrode was 53.3 mF cm-2, with minimum impedance value Rct of 4.8 U. The minimum capacitance of 1.07 mF cm-2 was obtained for the Ti50/BDD electrode, and the maximum impedance value Rct of 290 U was obtained by the Ti20.0/BDD electrode. Furthermore, the Ti30/BDD electrode possessed a favorable electrochemical stability of capacitance retention of 89.3% after 2070 cycles. A mechanism by which pore size affects the capacitance properties of the Ti/BDD electrode is proposed and discussed in this paper.

    关键词： Capacitive property,Porous titanium substrate,Boron doped diamond,Surface structure

    更新于2025-09-23 15:21:01

  • Broadband models and their consequences on line shape analysis in vibrational sum-frequency spectroscopy

    摘要： Vibrational sum-frequency generation (SFG) spectroscopy can provide valuable qualitative and quantitative information about molecular species at surface and buried interfaces. For example, the resonance frequency of a particular chemical function group is revealing of the surface environment, especially when compared to what is observed in bulk IR absorption or Raman scattering spectra. Furthermore, the amplitude of the mode can be related to the molecular orientation, providing a detailed quantitative account of the surface structure. Each of these attributes, however, requires fitting the spectra to some vibrationally resonant line shape. This is particularly challenging when the modes of interest co-exist with broad resonance features, such as water O–H stretching. In this perspective, we examine the merits and consequences of different approaches to fitting homodyne SFG data. We illustrate that, while any model can provide a useful description of the data, no model can accurately and consistently provide even the relative phase deeply encoded in homodyne data without the use of additional information.

    关键词： Vibrational sum-frequency generation,homodyne data,surface structure,molecular orientation,line shape analysis,SFG spectroscopy

    更新于2025-09-23 15:21:01

  • Hydrogen order at the surface of ice I <sub/>h</sub> revealed by vibrational spectroscopy

    摘要： Among numerous crystalline phases of ice, the Ih phase is the most stable above 72 K at atmospheric pressure. It is well established that the orientations of water molecules in the bulk of ice Ih are statistical without long-range order. However, the orientational order of water at the surface of ice Ih has been enigmatic. Here we show that the surface of ice Ih at 100 K has hydrogen order with the OH group pointing upward to the air (‘‘H-up’’ orientation). We applied nonlinear optical spectroscopy and theoretical modeling to the surface of isotopically pure and diluted ice Ih and observed OH stretch vibrational signatures attributed to H-up ordering. Furthermore, we found that this hydrogen order takes place despite a more inhomogeneous microenvironment at the surface than in the bulk. Our results suggest the prominent role of the surface to allow the reorientation of water molecules for hydrogen ordering that is virtually prohibited in the bulk.

    关键词： surface structure,ice Ih,hydrogen order,nonlinear optical spectroscopy,vibrational spectroscopy

    更新于2025-09-23 15:19:57

  • Growth mode in heteroepitaxial system from nano- and macro- theoretical viewpoints

    摘要： Growth mode in semiconductor heteroepitaxial system such as InAs/GaAs is systematically investigated from nano- and macro-theoretical viewpoints, where ab initio, empirical interatomic potential, and phenomenological macroscopic theory are used. The nanoscopic theories clarify that the misfit dislocation (MD) formation energy depends on orientation such as 1.14 eV/? for (001), 0.96 eV/? for (110), and 0.68 eV/? for (111)A. On the basis of these calculated results, growth mode boundary between two-demensional with MD formation (2D-MD) and three-dimensional Stranski-Krastanov island (3D-SK) growth modes is successfully determined as funcions of surface energy and degree of strain relaxation. The region of 3D-SK growth mode is the largest for (001) while (111)A has the largest 2D-MD region and that for (110) is in between. Using surface energy obtained by ab initio calculations and the degree of strain relaxation estimated by continuum elasticity theory, it is found that (001) favors the 3D-SK growth mode while 2D-MD growth mode appears for (110) and (111)A. It shoud be noted that the (110) data stay near the growth mode boundary between 3D-SK and 2D-MD growth modes. Reflecting this, growth mode transition from 3D-SK to 2D-MD occurs for (110) due to In0.25Ga0.75As layer insertion at the interface that decreases surface energy from 50.9 meV/?2 to 49.1 meV/?2. Versatility of this approach is discussed by comparing with experimental findings.

    关键词： A1 Computer simulation,A1 Growth models,B2 Semiconducting indium compounds,A3 Molecular beam epitaxy,A1 Surface structure

    更新于2025-09-19 17:15:36

  • Enhances surface sensitivity of X-ray photoelectron holography through the example of Bi2Te3(111) surface

    摘要： X-ray photoelectron holography (XPH) is new tool in surface science capable to visualize in real space coordination of the atom of interest (emitter). To study surface phenomena the ultimate and variable (in the range of 1-5 ML) surface sensitivity is needed. Here we discuss possibilities to improve surface sensitivity of XPH by the example of Bi2Se3 (111) surface where different coordinations of the same kind of atoms are present in different layers. To reach ultimate surface sensitivity we used both lower electron kinetic energy and partial analysis of hologram related to grazing angle photoemission. Using calculations of diffraction patterns based on EDAC code and reverse reconstruction of the real space within SPEA-MEM formalism we evaluate the contribution of each atomic layer into diffraction pattern and found that the surface relaxation could be directly visualised at the kinetic energy less than 100 eV, whereas the contribution of the second quintuple layer can be vanished at 200 eV or below. The same effect can be achieved by partial analysis of hologram at grazing detection angles more than 55° to the surface normal. This approach enables broader practical applications of the XPH to various materials in applied surface science.

    关键词： surface structure,photoelectron holography

    更新于2025-09-11 14:15:04

  • Electron induced nanoscale engineering of rutile TiO <sub/>2</sub> surfaces

    摘要： Electron stimulated modifications of the rutile TiO2(110) surface have been investigated using scanning tunnelling microscopy tip pulses and electron beam irradiation. Tip pulses on the ‘as-prepared’ surface induce local surface reconstruction and removal of surface hydroxyls in a region around the reconstruction. A defocused beam from an electron gun as well as tip pulses have been used to generate a number of oxygen deficient surfaces. All tip pulse features display an oval profile, which can be attributed to the anisotropic conductivity of the TiO2(110) surface. A novel oxygen deficient phase with well-ordered defective ‘nano-cracks’ has been identified, which can be produced by either electron beam irradiation or low flash anneal temperatures (～570 K). Annealing such surfaces to moderate temperatures (～850 K) leads to mixed 1×1 and 1×2 surfaces, until now only achievable by annealing in oxygen or ageing by repeated sputter/anneal cycles. Heating to normal preparation temperatures (1000 K) reforms the clean, well-ordered 1×1 surface termination. Our results demonstrate the potential of electron induced processes to modify the oxygen composition and structure of the TiO2(110) surface in a controllable and reversible way for selective surface patterning and surface reactivity modification.

    关键词： electron beam,STM,reconstruction,surface structure,tip pulse,TiO2,point defects

    更新于2025-09-10 09:29:36

  • Trimer bonding states on the surface of the transition-metal dichalcogenide

    摘要： We report a comprehensive study on the surface structural and electronic properties of TaTe2 at room temperature. The surface structure was investigated using both low energy electron diffraction intensity versus voltage and density functional theory calculations. The relaxed structures obtained from the two methods are in good agreement, which is very similar to the bulk, maintaining double zigzag trimer chains. The calculated density of states indicates that such structure originates from the trimer bonding states of the Ta dxz and dxy orbitals. This work will further provide new insights towards the understanding of the charge density wave phase transition in TaTe2 at low temperature.

    关键词： surface structure,low energy electron diffraction,density functional theory,charge density wave,TaTe2

    更新于2025-09-10 09:29:36

  • Tailoring the surface structure of silicon carbide support for copper catalyzed ethanol dehydrogenation

    摘要： The production of acetaldehyde through biomass-derived ethanol dehydrogenation is a sustainable alternative compared to the fossil-feedstock based process, for which Cu-based catalysts are considered to be the most efficient. Herein, we modified the surface of silicon carbide (SiC) to alter the properties of the interface from SiO2-rich to C-rich, and we prepared a series of Cu-supported catalysts (Cu/SiC, Cu/SiO2/SiC, and Cu/C/SiC) with the aim of insight into the effect of the interface structure and composition on catalytic dehydrogenation of ethanol. At 280 °C, the Cu/SiO2/SiC catalyst exhibits high ethanol conversion due to the excellent dispersion of Cu nanoparticles promoted by SiO2-rich interface. In contrast, Cu nanoparticles dispersed on C/SiC shows somewhat lower activity but excellent acetaldehyde selectivity with trace amounts of by-products under identical reaction conditions. This difference is attributed to the fast removal of acetaldehyde because of its low affinity for the relatively inert C-rich interface (C/SiC). This work provides an in-depth understanding of Cu-Si-C multi-interfacial structure and the ethanol dehydrogenation behavior, which may shed light on the design of novel catalysts with tailored interfacial structures.

    关键词： dehydrogenation,ethanol,SiC,copper,surface structure

    更新于2025-09-10 09:29:36

  • Rationalizing and Controlling the Surface Structure and Electronic Passivation of Cesium Lead Halide Nanocrystals

    摘要： Colloidal lead halide perovskite nanocrystals (NCs) have recently emerged as versatile photonic sources. Their processing and luminescent properties are challenged by the lability of their surfaces, i.e. the interface of the NC core and the ligand shell. On the example of CsPbBr3 NCs, we model the nanocrystal surface structure and its effect on the emergence of trap states using density functional theory. We rationalize the typical observation of a degraded luminescence upon aging or the luminescence recovery upon post-synthesis surface treatments. The conclusions are corroborated by the elemental analysis. We then propose a strategy for healing the surface trap states and for improving the colloidal stability by the combined treatment with didodecyldimethyl ammonium bromide and lead bromide and validate this approach experimentally. This simple procedure results in robust colloids, which are both highly pure and exhibit high photoluminescence quantum yields of up to 95-98%, retained even after 3-4 rounds of washing.

    关键词： trap states,didodecyldimethyl ammonium bromide,luminescence recovery,photoluminescence quantum yields,lead bromide,CsPbBr3 NCs,density functional theory,Colloidal lead halide perovskite nanocrystals,surface structure

    更新于2025-09-09 09:28:46