New relaxation phenomena in the outer atomic layers of Fe{211}

A low-energy electron diffraction analysis of a {211} surface of body-centered cubic iron reveals relaxations in the directions perpendicular and parallel to the surface plane. Both relaxations alternate in successive layers. The perpendicular relaxation goes from contraction of 10.5% to expansion of 5% to contraction of 1%. The parallel relaxation goes from a shift of the first layer of 0.24Å (10% of the nearest neighbor distance) toward more symmetrical registration with the second layer, to an opposite shift of 0.035 Å of the second layer with respect to the third.     

Structural analysis of oxygen segregated Nb(110) surface by photoelectron diffraction

The atomic structure of the Nb(110) surface with oxygen segregated from bulk by annealing at 1500K in UHV has been analyzed by electron and photoelectron diffraction techniques. The observed LEED patterns indicate the modulation of topmost Nb layer in [11ˉ0] direction. Relation of unit cells of substrate and overlayer was determined. The surface component in the Nb 3d photoelectron spectra has a chemical shift of 1.6eV corresponding to that of NbO. The thickness of Nb oxide overlayer is estimated to be about one or two atomic layers. The Nb 3d spectra collected at 4945 different directions are fitted with bulk and surface components. Photoelectron diffraction patterns from Nb atoms within overlayer as well as bulk are successfully extracted. Topmost oxygen atoms are found to be located at about 1.2 Å above the Nb plane. Presented at the X-th Symposium on Suface Physics, Prague, Czech Republic, July 11–15, 2005.     

Surface morphology and local magnetic properties of electrodeposited thin iron layers

Thin iron layers with different thickness were prepared by electrodeposition on the polycrystalline substrate. The surface morphology of the layers, their structure and local magnetic properties were studied using scanning tunneling microscopy (STM), X-ray diffraction (XRD) and conversion electron Mössbauer spectroscopy (CEMS). STM studies revealed the granular structure of the surface of the electrodeposited iron layers with the roughness up to 10 nm. XRD analysis proved that these layers were highly strained. The CEMS spectra showed an in-plane magnetic anisotropy in the iron layers. Isomer shift of the electrodeposited iron was different than that of the -Fe. This difference was attributed to the internal stresses existing in the electrodeposited layers.     

Structure and composition of the NiPd(1 1 0) surface

The NiPd(1 1 0) alloy surface was studied using low energy electron diffraction to measure the structure and composition of the first three atomic layers. The surface layer is highly enriched in Pd and has a significantly buckled structure. The second layer is also buckled, with displacements even larger than the surface layer. The second layer also exhibits intralayer segregation (chemical ordering), with alternate close-packed rows of atoms being Ni enriched and Pd enriched. The third layer has a structure and composition close to that of the bulk alloy. These results are compared with results for the other low index faces of NiPd, the extensive literature on NiPt alloy surfaces, and the growing body of theoretical literature for NiPd alloy surfaces.     

Unusual Multilayer Surface Alloy: Al(100)-c(2 x 2)-2Li

An unusual multilayer surface alloy is formed by adsorption of one monolayer Li on Al(100). It is shown by low energy electron diffraction that the first three layers consist of a mixed Al-Li layer, a pure Al layer, and a second Al-Li layer. Thus the alloy has the same layer stoichiometry as the (100) surface of the metastable Al(3)Li bulk alloy. However, the relative orientation of the two mixed layers is the same as that in the Al(3)Ti-type structure. These findings are confirmed by total-energy calculations, which lead further to the prediction that the bulk Al(3)Li alloy has a faulted, Al(3)Ti-type surface.     

The structure of the Pt(100) surface

The atomic arrangement in the first two layers of the clean Pt(100) surface is described from a Fourier analysis of low energy electron diffraction (LEED) intensities. The Fourier transform and sensible platinum-platinum bond lengths require that the top layer is corrugated, the corrugation “step” being approximately 0.4 Å. The structure of the first layer is partly described by a hcp rearrangement from the bulk fcc structure. The rearrangement is related to geometrical and electronic properties of the metals. Some qualitative and quantitative comments are made on the general value of Fourier methods in surface crystallography.     

Using electron backscatter diffraction to investigate the influence of mechanical polishing on the state of the surface of diamond

Electron backscatter diffraction is used to determine the influence of mechanical polishing on the surface state of a two-layer structure made from diamond. It is found that the process of polishing does not lead to significant degradation of the surface, while the thickness of the amorphous layer formed due to polishing does not exceed a few atomic layers.     

多晶铁电薄膜的相变——应力和晶粒尺寸效应

用掠入射X射线衍射法观察到钛酸铅多晶铁电薄膜表面层与体内的相变温度不同,表面层的结构参数也有异于体内;唯象地把多晶铁电薄膜抽象为一个表面层为细晶粒、低应变层,体内为粗晶粒、高应变层的两层结构,根据应力和晶粒尺寸效应对铁电相变的影响,解释了钛酸铅多晶铁电薄膜的相变特征 关键词：     

Cu偏析诱导Co团簇结构及性质异常的动力学模拟

采用分子动力学结合镶嵌原子势方法,模拟研究了Cu原子分别分布于基体Co团簇内层和表面构成Cu-Co合金团簇的结构和热力学性质,研究表明,相同数目的 Cu原子掺杂到基体中因掺杂层的不同,会诱导内层Co团簇和外层Co团簇结构、能量及熔点表现出巨大差异;Cu原子在团簇各层掺杂位置的差异,会导致原子向低能态位置偏移,但相对移动后后续原子的补位,使团簇结构随温度呈相对无扩散度相变;Cu原子由内层向表面偏析是内层Co团簇与相同原子数比例的外层Co团簇熔点产生巨大差异的主要原因.     

The atomic structure of alloy surfaces: Ni3Al{001}

The atomic structure of the {001} surface of Ni₃Al has been determined by LEED (low-energy electron diffraction) intensity analysis to correspond to simple truncation of the bulk structure with the Ni-Al mixed layer on top rather than the pure Ni layer. The first interlayer spacing is essentially equal to the bulk interlayer spacing between {001} planes. First-principles calculations of the cohesive energies of slabs terminating in the two types of layers also indicate that the mixed layer termination is more stable.     

P110钢CO2腐蚀产物膜的XPS分析

为了确定CO2腐蚀产物膜的组成及不同层次结构中成分和含量的差异,采用P110钢在高温高压腐蚀静态釜中制备CO2腐蚀产物膜,利用SEM观察了腐蚀产物膜的表面和断面形貌,结合XRD分析结果,通过XPS研究了两层结构膜的化学组成差异。结果表明,腐蚀产物膜断面呈现双层结构;膜层的主要成分是FeCO3,还有少量的CaCO3和铁的氧化物,但内层CaCO3较多且夹杂着Fe3C和单质Fe,外层氧化物稍多;通过内外层Ca^2＋含量差异推断出内层腐蚀膜优先形成。     

Simulation of X-ray diffraction profiles in multilayers by direct wave summation: Application to asymmetric reflections

A novel algorithm for the simulation of the X-ray diffraction profiles in multilayers is developed, which can be applied to any multilayered structure, with no limitations. The simulation program in the MATLAB format is based on the direct summation of waves scattered by individual atomic planes. It takes into account the strain and concentration-induced fluctuations of interplanar spacings, interface roughness and buried amorphous layers, and enables adding the diffuse scattering contributions of the Gaussian or Lorentzian types.The summation over individual layers can be done coherently or incoherently, depending on the interface structure. In order to visualize the steps of the fitting procedure, the contribution of each layer can be plotted separately.In this paper the simulation routine is described with a focus on handling asymmetric reflections. We stress that in this case, the effective thickness of the layers, participating in the formation of diffraction signals, can be very different for low or high X-ray incidence angles. We also show that in contrast to symmetric reflections, when treating the asymmetric ones, an additional phase shift depending on the distance between the sample and detector, should be taken into account. The simulation program is applied to fit experimental diffraction profiles, symmetric and asymmetric, taken from the MOVPE-grown heterostructures and superlattices of practical importance, based on the InGaAsP/InP materials system.     

Auger electron spectroscopy depth profiling of Fe-oxide layers on electromagnetic sheets prepared by low temperature oxidation

Auger electron spectroscopy depth profiling was applied to characterize the Fe-oxide layers prepared by low temperature oxidation of Fe electromagnetic sheets produced on an industrial line for applications in the field of electrical motors. In addition the surface morphology, layer composition and layer structure were analysed by electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction techniques. We found that the oxide layers on Fe-sheets with good adhesion between the oxide layer and Fe-substrate, consist mainly of magnetite and to a smaller extent of haematite; the layers are typically thinner than 1 μm and the interface between the oxide layer and the Fe-substrate is relatively broad, i.e. up to 0.3 μm. On the contrary, a decrease of adhesion between the oxide layer and the Fe-substrate was found when the layer is thicker than 1 μm and the layer/substrate interface is narrow and contaminated by foreign elements.     

磁控溅射沉积铝/贫铀与金/贫铀镀层的界面研究

采用磁控溅射技术沉积制铝/贫铀/铝(Al/DU/Al)、金/贫铀/金(Au/DU/Au) "三明治" 薄膜样品. 利用高分辨扫描电镜、 X射线衍射仪、X射线光电子能谱仪、 扫描俄歇微探针对Al/DU/Al, Au/DU/Au样品的Al/DU, Au/DU界面行为进行表征与研究. 结果表明: 沉积态DU层以柱状晶生长; Al/DU界面扩散明显, 物理扩散过程中伴随着Al, DU化学反应形成Al₂U, Al₃U金属化合物; 金属化合物的形成导致界面处Al 2p电子结合能向高能端移动, U 4f电子向低能端移动; 微量O在Al/DU界面处以Al₂O₃及铀氧化物形式存在; DU镀层中以铀氧化形式存在; 沉积态的Au/DU界面扩散为简单的物理扩散, 团簇效应导致Au/DU界面处Al 2p, U 4f电子结合能均向高能端移动; 在Au/DU界面及DU镀层中, 微量O以铀氧化物形式存在; Al/DU界面扩散强于Au/DU; 相同厚度的Al, Au保护镀层, Al镀层保护效果优于Au镀层. 关键词： Al/DU界面 Au/DU界面 磁控溅射 界面扩散     

A new structural model of bivalve ligament from Solen grandis

It is widely accepted that the structure of bivalve ligament contains two layers: outer organic lamellar and inner aragonite fibrous layer. However, by using scanning electron microscopy (SEM), X-ray diffraction (XRD), and infrared spectroscopy (FTIR), we found an additional protein fibrous layer in the Solen grandis ligament. The ligament consists of three layers: an outer layer (OL), middle layer (ML), and inner layer (IL). OL consists of lamellar protein, oriented normal to dorsal edge. ML has unique spring-like protein fibers (ca. 120 nm in diameter) structure, stretching continuously from the left to right valve. Interestingly, IL comprises of aragonite fibers (ca. 100 nm in diameter) oriented posteriorly and inclined at an angle about 26° to dorsal edge at dorsal part; then they turn gradually to ventral part, showing striking zigzag structure vertical to ventral surface (VS). The ligament presents a new three-layered structural model different from previous reports; it may inspire not only in materials synthesis and mechanical design, but also in bivalve classification and evolution.     

Tailoring the structure of water at a metal surface: a structural analysis of the water bilayer formed on an alloy template

Recent studies show that structures based on the traditional "icelike" water bilayer are not stable on flat transition metal surfaces and, instead, more complex wetting layers are formed. Here we show that an ordered bilayer can be formed on a SnPt(111) alloy template and determine the structure of the water layer by low energy electron diffraction. Close agreement is found between experiment and the structure calculated by density functional theory. Corrugation of the alloy surface allows only alternate water molecules to chemisorb, stabilizing the H-down water bilayer by reducing the metal-hydrogen repulsion compared to a flat surface.     

Dispersion of surface plasmons in dielectric-metal coatings on concave diffraction gratings

Anomalies in the intensity ofp-polarized light from concave diffraction gratings (Wood's anomalies) have been used to obtain surface plasmon dispersion curves for dielectric-metal layers on the grating surface. These include a 350 Å MgF₂ layer and Al₂O₃ layers varying from a few angstroms to over 800 Å on an Al substrate. The wavelength range of the incident and diffracted light is from the visible to the vacuum ultraviolet (7,500?500 Å). Anomalous polarization peaks for Al₂O₃ layers in the vacuum ultraviolet (at ～ 1,600 Å) are shown to shift significantly to longer wavelengths for only a few angstroms (up to 50 Å) of oxide thickness, while for thicknesses greater than ～ 50 Å any further shift is small. In the visible region (> 4,000 Å), on the other hand, the wavelength shifts are small for dielectric thicknesses up to ～ 50 Å, but are large for thicknesses of several hundred angstroms. These results are in substantial agreement with the theoretical dispersion curves for these cases. Also considered are some of the effects of diffusion pump oil.     

The structure of Mo/Si multilayers prepared in the conditions of ionic assistance

The influence of a negative substrate-applied bias potential on the structure of periodic Mo/Si multilayer compositions has been investigated by means of cross-sectional electron microscopy, small-angle X-ray reflectivity, X-ray diffraction and by modeling the small-angle spectra. It is known that the crystalline structure of molybdenum layers is the main source of interface roughness. In the absence of a bias potential application, the interface roughness tends to develop from the substrate towards the surface of a Mo/Si multilayer composition. A negative bias potential (up to -200 V) applied to a substrate during silicon layer deposition leads to smoother interfaces and improves the layer morphology. After increasing the bias potential over -200 V a considerable growth of an amorphous interlayer transition zone can be observed at Si-on-Mo interfaces. By raising the bias potential during the deposition of Mo layers a development of roughness at Mo-on-Si interfaces as well as growing interlayer thicknesses were found. PACS 61.10.Kw; 68.37.-d; 68.65.Ac     

Impact of rough silicon buffer layer on electronic quality of GaAs grown on Si substrate

The electronic and the structural properties of n-GaAs layers grown on rough surface of silicon substrate by molecular beam epitaxy (MBE) has been investigated by photoluminescence (PL), time resolved photoluminescence (TRPL) and high resolution X-ray diffraction (HRXRD). The relationship between electronic and structural properties of the n-GaAs layer was checked, showing that the defect density is a strong cause for trapping the minority carriers. The impact of introducing intermediate rough silicon layer between silicon substrate and n-GaAs layer on the electronic properties was observed, showing that the structure grown on rough Si involves higher lifetime than those developed on flat silicon substrate. Such structure could be used for economic solar cells fabrication.     

Evidence for subsurface atomic displacements of the GaAs(110) surface from LEED/CMTA analysis

The low-energy electron diffraction constant momentum transfer average (LEED/CMTA) technique is applied to the GaAs(110) surface. In addition to verifying our earlier model of the top layer atomic displacements, atomic displacements in the first subsurface layer, opposite in direction to those in the top layer, are suggested. Best estimates for atomic positions in the surface and first subsurface layers are given.