Oxidation of Si and GaAs in air at room temperature

The oxidation of Si and GaAs single-crystals, both cleaved and etched, has been studied at room temperature in air. We found experimentally that the oxidation of GaAs follows the direct exponential law at least within a 2 years time interval. The same also holds for both cleaved and etched Si single-crystals until the oxide film reaches a thickness of about 35–40 Å: beyond this thickness the cubic law starts to dominate the oxidation rate. An interpretation of the observed experimental results is given.     

X-ray reflectivity and photoelectron spectroscopy of superlattices with silicon nanocrystals

The structural properties and features of the chemical composition of SiO _x N _y /SiO₂, SiO _x N _y /Si₃N₄, and SiN _x /Si₃N₄ multilayer thin films with ultrathin (1–1.5 nm) barrier SiO₂ or Si₃N₄ layers are studied. The films have been prepared by plasma chemical vapor deposition and have been annealed at a temperature of 1150°С for the formation of silicon nanocrystals in the SiO _x N _y or SiN _x silicon-rich layers with a nominal thickness of 5 nm. The period of superlattices in the studied samples has been estimated by X-ray reflectivity. The phase composition of superlattices has been studied by X-ray electron spectroscopy using the decomposition of photoelectron spectra of the Si 2p, N 1s, and O 1s levels into components corresponding to different charge states of atoms.     

Oxidation of nickel studied by UV and X-ray photoelectron spectroscopy

The nature of argon-ion bombarded nickel surfaces (polycrystalline, and (111), (110) and (100) single crystals) and their subsequent interaction with oxygen at ordinary temperatures have been studied using X-ray and UV photoelectron spectroscopy, including angular variation measurements and the determination of work function changes, in combination in the same apparatus. Variations between the HeI spectra of the four clean substrates were taken to confirm the presence of substantial order within the depth sampled by UPS. The four surfaces exhibited similar but not identical behaviour during oxidation, resembling that reported by other workers from studies of both annealed single crystals and evaporated polycrystalline films. The initial process was deduced to be essentially dissociative chemisorption: no evidence supporting a previous suggestion of associative adsorption at low coverages was found. Oxygen commenced to penetrate below the surface of all samples before oxygen equivalent to a monolayer had been taken up (~10 L exposure) and further substantial uptake followed resulting in the formation of a stable film (~18 Å) of nickel oxide by ~100 L exposure. This oxide layer was not stoichiometric nickel(II) oxide: it was characterized by the presence of two distinct O 1s signals, the relative intensities of which depended on the crystallographic nature of the surface. It is tentatively suggested that the oxygen signal with the higher BE be associated with Ni^III. Comparison of the X-ray and UV spectra suggests that the oxide film is very non-uniform in thickness, some Ni metal remaining very close to the surface.     

Growth of Fe on Ge(1 1 1) at room temperature studied by X-ray photoelectron diffraction

The growth of ultrathin Fe films of various coverages on Ge(1 1 1) at room temperature using molecular beam epitaxy (MBE) was studied via X-ray photoelectron diffraction (XPD or XPED) together with low energy electron diffraction (LEED) and X-ray photoelectron spectroscopy (XPS). All experimentally observed XPD patterns suggested local order structures of the Fe layers for all thicknesses studied. The short-range order of the resulting structures was found to be enhanced for thinner layers whereas the long-range order was gradually lost with increasing Fe thicknesses. At a very low coverage of 0.8 Å Fe and Ge tend to react to the partly ordered structure in which Fe atoms were located in local environments similar to those for higher Fe coverages. Comparison of theoretical and experimental XPD patterns, along with XPS results, showed that intermixing between Fe and Ge occurred during the pseudomorphic growth with a stacking fault near the interface for all Fe coverages under study. Nevertheless, small percentage of domains without the stacking fault was also found to coexist with those with the stacking fault by performing a quantitative analysis of a reliability factor R of the Fe2p pattern for 5.4 Å. The orientation changes of the Ge2p and Ge3d XPD patterns with Fe thickness were unambiguously explained in terms of their different dependencies on the overlayer thickness due to the different inelastic mean free path lengths used in the simulations. Also, Fe got increasingly enriched in the grown layers with increased Fe coverage. The resulting structures and intermixing are discussed in detail.     

Oxidation of ultra-thin Ti films on Mo(100): Soft X-ray photoelectron spectroscopy study

Titanium oxide films grown on Mo(100) have been investigated by low-energy electron diffraction (LEED) and soft X-ray photoelectron spectroscopy (PES). The film was grown by Ti deposition on Mo(100) and subsequent oxidation of the film by 12 L of O₂ exposure at room temperature. As the film was annealed at 700–1000 °C, the film in which the Ti atoms were in a Ti³⁺ oxidation state was formed. As the film was annealed at 1100–1500 °C, the oxidation state of Ti in the film was converted to Ti²⁺. The valence electronic structure of the film was measured under the condition that the emission from the Mo substrate was minimized due to a Cooper minimum of the Mo 4 d photoionization cross sections (hν = 100 eV). It was found that the Ti 3 d band in normal-emission spectra was increased in intensity when the film was annealed at 1100–1500 °C. As the film was annealed at 1300 °C for 10 s and 20 s, the film-covered Mo(100) gave (2 × 2) and (4 × 1) LEED patterns, respectively. The two-dimensional band structure of the (2 × 2) system was investigated by angle-resolved PES, and it was found that the film with a (1 × 1) periodicity with respect to the Mo(100) substrate existed in the (2 × 2) system.     

Oxidation studies of niobium thin films at room temperature by X-ray reflectivity

We report the results of growth kinetics of oxidation process on niobium thin film surfaces exposed to air at room temperature by using a surface sensitive non-destructive X-ray reflectivity technique. The oxidation process follows a modified Cabrera-Mott model of thin films. We have shown that the oxide growth is limited by the internal field due to the contact potential which develops during the initial stage of oxidation. The calculated contact potential for 100 and 230 Å thick films is 0.81 ± 0.14 and 1.20 ± 0.11 V respectively. We report that 40% increase in the contact potential increases the growth rate for the first few mono layers of Nb₂O₅ from ∼2.18 to ∼2790 Å/s. The growth rates of oxidation on these samples become similar after the oxide thicknesses of ∼25 Å are reached. We report on the basis of our studies that a protective layer should be grown in situ to avoid oxidation of Nb thin film surface of Nb/Cu cavities.     

X-ray photoelectron spectroscopy (XPS) of adsorbate valence bands

The CO valence levels for a monolayer of CO adsorbed on the basal (001) face of ruthenium have been observed by XPS. The assignment of the observed peaks is discussed.     

The growth of manganese layers on Si(1 0 0) at room temperature: A photoelectron spectroscopy study

The combination of spin-and charge based electronics in future devices requires the magnetic doping of group IV semiconductors, and the formation of ferromagnetic contacts. The doping of Mn with Si is one of the material systems which is discussed in this context. The present study focuses on the growth of Mn on a Si(100)(2x1) surface, and the evolution of the surface was observed as a function of Mn coverage with synchrotron-based photoelectron spectroscopy. The reaction of Mn with the Si(100) surface at room temperature leads the formation of silicide at the boundary between the Si substrate and the Mn-overlayer, presumably with MnSi stoichiometry. The residual sub-oxide reacts with the Mn and therefore incorporates a few percent of Mn-O-Si at the interface. The analysis of the sub-oxide composition indicates that the Si⁺¹ component is the most reactive oxidation state. The overlayer is dominated by Mn, either as Mn-metal or as a Mn-rich silicide phase, and the metallic layer introduces a band bending in Si. As a consequence of our observations, including information from a recent STM study, the formation of ferromagnetic contacts which require ideally a flat and compositionally homogenous overlayer, cannot be achieved through room temperature deposition of Mn on the Si(100) (2x1) surface. The influence of residual oxides and surface defects on the growth process will be further investigated.     

Charge transfer-transitions and X-ray photoelectron spectroscopy of copper(II) complexes

Satellite structure in the X-ray photoelectron (Cu 2p) spectra of some squareplanar cupric complexes has been compared to electron paramagnetic resonance and electronic spectra results on the electronic structure of these complexes. It is shown that these satellites can be assigned to various ligand → metal 3d or ligand → ligand* transitions within the monopole selection rules of the sudden approximation.     

Creating room temperature Ohmic contacts to 4H-SiC: studied by specific contact resistance measurements and X-ray photoelectron spectroscopy

The use of a silicon interface pre-treatment to produce low resistance Ohmic nickel contacts to 4H-SiC, circumventing the need for contact post annealing, is reported. The effects of two different SiC pre-metal deposition surface preparation techniques: RCA cleaning (control sample) and a silicon interlayer pre-treatment (SIP), are discussed. Electrical characterization of contacts on treated surfaces, using circular transfer length measurements (CTLM), revealed that contacts to RCA cleaned samples were Schottky in nature, unless annealed at temperatures greater than 700 °C. In contrast, contacts formed on SIP SiC surfaces exhibited Ohmic behaviour directly after fabrication, without the need for post metallisation annealing. Average contact resistances as low as 1.3E−05 Ω cm² have been recorded for SIP samples. This fabrication process has distinct technological advantages compared to standard techniques for forming Ohmic contacts to SiC. To consolidate our findings the chemical and electrical nature of the SIP nickel-SiC interface, as it was sequentially formed and annealed, was examined using X-ray photoelectron spectroscopy (XPS). Based on these results, a model is proposed to explain the as-deposited Ohmic contact nature of the SIP sample.     

Effects of surface roughness on surface analysis via soft and ultrasoft X-ray fluorescence spectroscopy

A model for calculating surface roughness effect on the intensity of emitted X-rays in the soft and ultrasoft X-ray region is presented and discussed. The results of calculations based on this model are compared to the results obtained experimentally using Al gratings as models for rough surfaces. It is shown that the correspondence between calculated and experimental intensities for Al–K is sufficient to corroborate the use of this model as a means of estimating maximum allowable surface roughness without a significant loss in intensity. It is also shown that this maximum allowable roughness estimate can be calculated with a knowledge of only the sample density and wavelength of the X-ray emission.     

双原子填充式skutterudite化合物的结构及X射线光电子能谱分析

用高温熔融、淬火、扩散退火结合放电等离子烧结(SPS)法合成了Ca和Ce复合填充的单相Ca_mCe_nFe_xCo_4-xSb₁₂(m=0.17—0.27，n=0.05—0.25，x=1.5)化合物，并结合Rietveld结构解析以及X射线光电子能谱(XPS)分析研究了两种原子复合填充skutterudite化合物的结构与填充状态.Rietveld结构解析表明，Ca_mCe_nFe_1.5Co_2.5Sb₁₂化合物具有skutterudite结构，Ca和Ce原子填充到了Sb的二十面体空洞中，填充原子热振动参数B_Ca/Ce远大于框架原子的热振动参数B_Fe/Co和B_Sb.XPS元素窄区谱分析结果表明，Sb原子在结构中有五种化学状态，每种化学状态的相对含量主要由总填充分数决定，填充原子Ca在Sb的二十面体空洞出现概率有三种可能，但在中心位置出现的概率最大. 关键词： skutterudite化合物 双原子复合填充 结构 X射线光电子能谱分析     

(II) Infrared and X-ray photoelectron spectroscopy of some transition metal dithiocarbamates and xanthates

Measurements are presented for the binding energy variations of (a) (Ni, Cu) 2p_{$\text{3}\text{2}$}, S 2p and N 1s core levels in a series of Ni and Cu disubstituted dithiocarbamates and (b) (Ni, Cu) 2p_{$\text{3}\text{2}$}, and S 2p core levels in a series of Ni xanthates. These shifts, which are observed to be negative and quite large for the S 2p levels, are then correlated with the infrared absorption frequency variations for the associated intramolecular stretching vibrations of the same series. The results are interpreted in terms of a model based on atomic charges and their potential effects on both variations. The functional relationships between the binding energy and infrared frequency variations are shown to be in good agreement with the experimental results.     

NiTi合金薄膜厚度对相变温度影响的X射线光电子能谱分析

采用X射线衍射和X射线光电子能谱实验手段对不同厚度的NiTi薄膜相变温度的变化进行了分析.结果表明在相同衬底温度和退火条件下,3?μm厚度的薄膜晶化温度高于18?μm厚度的薄膜.衬底温度越高,薄膜越易晶化,退火后薄膜奥氏体相转变温度As越低.薄膜的表面有TiO₂氧化层形成,氧化层阻止了Ni原子渗出;膜与基片的界面存在Ti₂O₃和NiO.由于表面和界面氧化层的存在,不同厚度的薄膜内层的厚度也不同,因而薄膜越薄,Ni原子的含量就越高.Ni原子的含量的不同会影响薄膜的相变温度. 关键词： NiTi合金薄膜 X射线衍射 相变 X射线光电子能谱     

X-ray photoelectron (XPS) and Auger (XAES) spectroscopy study of rhodium dispersed on carbon substrate

Photoelectron 3d_5/2 binding and Auger M₅VV kinetic energies of dispersed rhodium have been measured. For the smallest deposition of Rh the shifts 0·6 eV and -2·5 eV of 3d_5/2 and M₅VV lines respectively have been found. Electron core level energy, Auger kinetic energy and Fermi edge shifts have been interpreted by a model based on electrostatic relaxation mechanism in metal particles and initial state contribution of surface atoms. Intensity and background height analysis indicate only surface distribution of Rh.I wish to express my gratitude to Dr. Zdenk Bastl for helpful discussions.     

Experimental evaluation of a simple model for quantitative analysis in X-ray photoelectron spectroscopy

A simple model is described for calculating the relative intensities of photoelectron peaks for the different elements in a homogeneous solid sample. U