微晶硅薄膜的表面粗糙度及其生长机制的X射线掠角反射研究

采用等离子体增强化学气相沉积技术沉积一系列处于不同生长阶段的微晶硅薄膜.通过同步辐射X射线掠角反射技术研究微晶硅薄膜的表面粗糙度随时间等的演化，探讨微晶硅薄膜的生长动力学过程及其生长机制.研究结果表明，在衬底温度为200 ℃，电极间距为2 cm，沉积气压为6.66×1０² Pa，射频功率密度为0.22 W/cm²，氢稀释度分别为99%和98%的沉积条件下，在玻璃衬底上生长的微晶硅薄膜生长指数β分别为0.21±0.01和0.24±0.01.根据KPZ模型，微晶硅薄膜的生长机制为有限扩散生长. 关键词： X射线掠角反射 微晶硅薄膜 表面粗糙度 生长机制     

直流磁控溅射制备AlN薄膜的结构和表面粗糙度

采用直流磁控反应溅射法,在Si(111)基底上成功制备了多晶六方相AlN薄膜.研究了溅射过程中溅射气压对薄膜结构和表面粗糙度的影响.结果表明:当溅射气压低于0.6 Pa时,薄膜为非晶态,在傅里叶变换红外光谱中,没有明显的吸收峰;当溅射气压不低于0.6 Pa时,薄膜的X射线衍射图中均出现了六方相的AlN(100)、(11...     

Effect of surface roughness on the electron-stimulated desorption of D from microporous D2O ice

The electron-stimulated desorption (ESD) of D⁺ from microporous D₂O ice films condensed on Pt(111) has been investigated. The total D⁺ yield as a function of temperature from 90–180 K depends sensitively on the film roughness, surface temperature and ice phase. In particular, we observe an irreversible increase in the cation yield as the microporous thin film is heated from 90–120 K, which we associate with a decrease in surface roughness as the micropores collapse. We present evidence which suggests that the number of surface sites available for emission, the surface roughness, and reneutralization or reactive scattering of the D⁺ desorbate play major roles in determining the ion yield. A simple model which qualitatively addresses the role of surface roughening on ESD ion yields shows good agreement with the data.     

Grazing‐incidence synchrotron‐radiation 57Fe‐Mössbauer spectroscopy using a nuclear Bragg monochromator and its application to the study of magnetic thin films

Energy‐domain grazing‐incidence ⁵⁷Fe‐Mössbauer spectroscopy (E‐GIMS) with synchrotron radiation (SR) has been developed to study surface and interface structures of thin films. Highly brilliant ⁵⁷Fe‐Mössbauer radiation, filtered from SR by a ⁵⁷FeBO₃ single‐crystal nuclear Bragg monochromator, allows conventional Mössbauer spectroscopy to be performed for dilute ⁵⁷Fe in a mirror‐like film in any bunch‐mode operation of SR. A theoretical and experimental study of the specular reflections from isotope‐enriched (⁵⁷Fe: 95%) and natural‐abundance (⁵⁷Fe: ～2%) iron thin films has been carried out to clarify the basic features of the coherent interference between electronic and nuclear resonant scattering of ⁵⁷Fe‐Mössbauer radiation in thin films. Moreover, a new surface‐ and interface‐sensitive method has been developed by the combination of SR‐based E‐GIMS and the ⁵⁷Fe‐probe layer technique, which enables us to probe interfacial complex magnetic structures in thin films with atomic‐scale depth resolution.     

Metal‐nanoparticle‐coating‐induced enhancement and weakening of resonant Raman scattering in ZnO: effect of surface electric field

Effects of Ag and Ti nanoparticle coatings on resonant Raman scattering in various ZnO thin films are presented. The longitudinal optical (LO) phonons, irrespective of the ZnO quality, exhibit an enhancement and a weakening by the Ag and Ti nanoparticle coatings, respectively. The enhancement (weakening) is always accompanied by a reduced (an increased) intensity ratio of the second to first‐order LO phonons, which can be associated with changes in the electron‐phonon coupling strength in the probed area of ZnO. Angle‐resolved X‐ray photoelectron spectroscopy provides evidence for the bending of the surface energy bands and their changes induced by the metal coatings. The effect of metal nanoparticle coatings on the Raman scattering of ZnO is thus attributed to the changes in the surface electric field. Copyright © 2011 John Wiley & Sons, Ltd.     

Beam‐size‐related phenomena and effective normalization in energy‐dispersive EXAFS for the study of heterogeneous catalysts,powder materials and the processes they mediate: observations and (some) solutions

The effects of focal spot size and the nature of powder samples (such as heterogeneous catalysts) on the quality of data obtainable from a dispersive EXAFS experiment are characterized at ID24 of the ESRF. Using examples of supported Pd catalysts, it is shown that, for a given photon flux, massive improvements in data quality can be achieved by increasing the size of the dispersive beam in the vertical, whilst concurrently applying a methodology to account for scattering effects emanating from the samples under study. These improvements are demonstrated using progressively practical and demanding examples. Questions regarding optimal beam dimensions for the study of such materials, how to counter undesirable effects that arise from the coherence of the source, how to obtain similar results consistently across the 5–30 keV bandwidth of ID24, and whether a methodology for simultaneous normalization in dispersive EXAFS is of significant utility in such circumstances are discussed.     

Surface‐enhanced Raman scattering investigations on silver nanoparticles deposited on alumina and titania nanotubes: influence of the substrate material on surface‐enhanced Raman scattering activity of Ag nanoparticles

Silver nanoparticles deposited on various ‘inert’ porous materials (mainly Al₂O₃ and TiO₂) are often used as substrates for surface‐enhanced Raman scattering (SERS) measurements. In this study, we used the sputter deposition technique to cover tubular arrays of Al₂O₃ and TiO₂ with Ag nanoparticles. Raman spectra of pyridine (as a probe molecule) and of two selected dyes (5‐(4‐dimethylaminobenzylidene)rhodanine and 5‐(4‐(dimethylamino)benzylidene)‐3‐(3‐methoxypropyl)rhodanine) adsorbed on fabricated Ag/TiO₂‐n/Ti and Ag/Al₂O₃‐n/Al substrates were measured. We found that the SERS spectra of pyridine adsorbed on Ag nanoparticles deposited on an Al₂O₃‐n/Al substrate are distinctly different from those measured for an Ag/TiO₂‐n/Ti composite. Similar effects were observed for dyes adsorbed on the surface of both composites. The spectral differences between two kinds of composites (Ag/TiO₂‐n/Ti and Ag/Al₂O₃‐n/Al) are discussed in terms of (1) the modified electronic structure of the Ag nanoparticles due to their interaction with different substrate materials and (2) the different atomic topology of the metal particles thus deposited on the surfaces of the substrates. Composite samples were also studied with the aid of scanning electron microscopy (SEM) and Auger electron spectroscopy (AES) to reveal their characteristic morphological and chemical features. Copyright © 2012 John Wiley & Sons, Ltd.     

Surface‐enhanced Raman spectroscopy (SERS) on silver colloids for the identification of ancient textile dyes: Tyrian purple and madder

Surface‐enhanced Raman spectroscopy (SERS) was used for the identification of natural organic dyes belonging to indigoid and anthraquinone classes in archeological samples, and good agreement with the corresponding reference commercial materials was found. Special attention was paid to the well‐known problem of anomalous bands that arise sometimes in the SERS spectra on colloids: as suggested in the literature, this problem could be reduced by the use of poly‐L ‐lysine and ascorbic acid as aggregating agents, but we observed that also the addition first of the analyte and subsequently of suitable electrolytes to the colloid in an inverted order compared to the most widely used method can be of help in limiting the intensity of such spurious bands. This procedure allowed us to obtain, for the first time, the SERS spectra of both modern and ancient Tyrian purple and to solve a specific problem observed in the analysis of archeological wool samples dyed with madder lake, i.e. the competition in the SERS response between the dye and other compounds possibly deriving from the degradation of the peptide chain during the hydrolysis treatment during the extraction of the dye from the wool fiber. Copyright © 2009 John Wiley & Sons, Ltd.     

Mechanism for crystalline Si surface passivation by the combination of SiO2 tunnel oxide and µc‐SiC:H thin film

This work demonstrates that the combination of a wet‐chemically grown SiO₂ tunnel oxide with a highly‐doped microcrystalline silicon carbide layer grown by hot‐wire chemical vapor deposition yields an excellent surface passivation for phosphorous‐doped crystalline silicon (c‐Si) wafers. We find effective minority carrier lifetimes of well above 6 ms by introducing this stack. We investigated its c‐Si surface passivation mechanism in a systematic study combined with the comparison to a phosphorous‐doped polycrystalline‐Si (pc‐Si)/SiO₂ stack. In both cases, field effect passivation by the n‐doping of either the µc‐SiC:H or the pc‐Si is effective. Hydrogen passivation during µc‐SiC:H growth plays an important role for the µc‐SiC:H/SiO₂ combination, whereas phosphorous in‐diffusion into the SiO₂ and the c‐Si is operative for the surface passivation via the Pc‐Si/SiO₂ stack. The high transparency and conductivity of the µc‐SiC:H layer, a low thermal budget and number of processes needed to form the stack, and the excellent c‐Si surface passivation quality are advantageous features of µc‐SiC:H/SiO₂ that can be beneficial for c‐Si solar cells. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Surface chemistry and catalysis of oxide model catalysts from single crystals to nanocrystals

Fundamental understandings of surface chemistry and catalysis of solid catalysts are of great importance for the developments of efficient catalysts and corresponding catalytic processes, but have been remaining as a challenge due to the complex nature of heterogeneous catalysis. Model catalysts approach based on catalytic materials with uniform and well-defined surface structures is an effective strategy. Single crystals-based model catalysts have been successfully used for surface chemistry studies of solid catalysts, but encounter the so-called “materials gap” and “pressure gap” when applied for catalysis studies of solid catalysts. Recently catalytic nanocrystals with uniform and well-defined surface structures have emerged as a novel type of model catalysts whose surface chemistry and catalysis can be studied under the same operational reaction condition as working powder catalysts, and they are recognized as a novel type of model catalysts that can bridge the “materials gap” and “pressure gap” between single crystals-based model catalysts and powder catalysts. Herein we review recent progress of surface chemistry and catalysis of important oxide catalysts including CeO₂, TiO₂ and Cu₂O acquired by model catalysts from single crystals to nanocrystals with an aim at summarizing the commonalities and discussing the differences among model catalysts with complexities at different levels. Firstly, the complex nature of surface chemistry and catalysis of solid catalysts is briefly introduced. In the following sections, the model catalysts approach is described and surface chemistry and catalysis of CeO₂, TiO₂ and Cu₂O single crystal and nanocrystal model catalysts are reviewed. Finally, concluding remarks and future prospects are given on a comprehensive approach of model catalysts from single crystals to nanocrystals for the investigations of surface chemistry and catalysis of powder catalysts approaching the working conditions as closely as possible.