Analysis of interface layers by spectroscopic ellipsometry

We investigate the relative validity of the Bruggeman effective-medium approximation and several alloy models to describe interfaces in the analysis of spectroscopic ellipsometric data of laminar samples, using data obtained on an Al_xGa_1−xAs multilayer sample fabricated specifically for this purpose. The investigation highlights the types of errors that result from the use of inappropriate models. Optimum results are obtained with the alloy model where the graded-composition regions are approximated with multilayer stacks.     

Study of aerosol particle transport by means of particulate-matter elemental composition

Summary Results of two measurement campaigns on particulate-matter concentration and composition aimed at studying dispersion and transport of aerosol particles in areas of different typology are reported. Local and regional aerosol transport affects particulate-matter concentration in a rural prealpine area, in particular the regional background is a main component of sulphur compounds. A long-range transport episodic event has been also detected. In the urban area of Milan, under good mixing conditions, the concentration of particulate matter has been found to be nearly constant up to 100 metres. The measurements of elemental-concentration values for a time series of particulate-matter samples collected simultaneously at different sites or altitudes proved to be an effective method for the investigation of transport phenomena. Paper presented at the IX Congresso del Gruppo Nazionale per la Fisica dell'Atmosfera e dell'Oceano, June 8–10, 1992, Rome.     

Preparation of ultrathin metal-oxide layers by means of Langmuir-Blodgett films

Langmuir-Blodgett (LB) films of fatty acid salts (Y-stearate, Y-arachidate, Cu-arachidate, Ba-stearate) were thermally oxidized. As a result one obtains ultrathin (a few Å thick) metal-oxide films at the substrate. The surface of the metal-oxide films was found to be rather inhomogeneous. Y and Cu ions remain quantitatively at the substrate despite the heating procedure. A linear dependence between area density of the metal ions in the oxidized films and the number of monolayers of the LB films was observed. The preparation of a mixed metal-oxide film containing Y, Ba, Cu with a given stoichiometry was found to be difficult due to the effect of counter ion exchange. The samples were investigated by means of plasma-desorption and spontaneous-desorption mass spectrometry, by Rutherford back-scattering and electron microscopy.     

Studying variations in the elemental composition of annual layers in microsections of lake teletskoye sediments by means of scanning X-ray fluorescent microanalysis using synchrotron radiation

SR scanning XRF is used to analyze the annual elemental layers of bottom sediments from Lake Teletskoye. Scanning is conducted with a pitch of 0.1 mm at energies of 16, 24, and 38 keV. The content of more than 15 elements are determined: K, Ca, Ti, Mn, Fe, V, Cr, Ni, Cu, Zn, As, Rb, Sr, Y, Zr, Cd, Sn, I, and Ba (range of concentrations, 0.005–10%). A cross section containing (1) the upper part of an underlying layer, (2) the total annual layer, (3) one more complete layer, and (4) the lower part of an overlapping layer is measured. Geochemical indicators reflecting the rhythm of annual precipitation are found.     

Characterization of various aluminium oxide layers by means of spectroscopic ellipsometry

This paper reports the characterization of both barrier type and porous type anodic oxide films on aluminium by means of spectroscopic ellipsometry (SE). In order to show the capabilities of the technique for quantitative determination of the layer characteristics, results based on ellipsometric data are correlated with complementary information from the analytical techniques transmission electron microscopy (TEM) and Auger electron spectroscopy (AES). It is concluded that ellipsometry yields an accurate characterization for the thicknesses and the interfacial properties of both the barrier layer and the porous layer. The porosity of the porous layer, determined with SE, is found to be in good agreement with the results obtained from TEM.     

Control of polarity of heteroepitaxial ZnO films by interface engineering

Control of polarity of heteroepitaxial ZnO films has been examined by interface engineering. ZnO films were grown by plasma-assisted molecular beam epitaxy on Ga-polar GaN template and c-plane sapphire substrates. Polarity of all the samples is determined by coaxial impact collision ion scattering spectroscopy. Zn- and O-polar ZnO films have successfully grown by Zn- and O-plasma pre-exposures on Ga-polar GaN templates prior to ZnO growth. High-resolution transmission electron microscopy revealed formation of a single-crystalline monoclinic Ga₂O₃ interface layer by O-plasma pre-exposure on Ga-polar GaN templates, while no interface layer was observed for Zn pre-exposed ZnO films. The polarity of ZnO films grown under oxygen ambient on c-plane sapphire with MgO buffer is revealed as O-polar. Fabrication of polarity inverted ZnO heterostructure has been studied: polarity of ZnO films on Ga-polar GaN templates was changed from Zn-polar to O-polar by inserting a MgO layer. High-resolution transmission electron microscopy revealed atomically flat interfaces at both lower and upper ZnO/MgO interfaces and no inversion domain boundaries were detected in the upper ZnO layer.     

Photoelectric characteristics of isotype nInSb-nGaAs heterojunction with distinct or smooth interface

Spectral Characteristics of isotype nInSb-nGaAs heterojunctions (Hjs) having either distinct or smooth transition boundary are considered in the paper. Photovoltaic characteristic of the sharp-boundary Hjs reverses its sign at a certain wavelength of the incited radiation. The wavelength value depends on the applied voltage. No such phenomenon was observed in Hjs with smooth boundary, while their photo-sensitivity spectrum was significantly narrower and shifted to shorter wavelengths. The obtained results are used in design of infrared pyrometers.     

pn结电容-电压法测量应变SiGe禁带宽度

利用应变SiGe/Si异质pn结电容-电压（C-V）特性确定SiGe禁带宽度的技术.该技术根据SiGe/Si异质pn结C-V实验曲线，计算出 pn结接触电势差，并得到SiGe/Si的价带偏移量和导带偏移量，进而求得SiGe禁带宽度.该技术测试方法简便，其过程物理意义清晰，既适用于分立的SiGe/Si异质pn结，也可直接分析SiGe/Si异质结器件中的SiGe 禁带宽度.实验结果与理论计算及其他相关文献报道的结果符合较好. 关键词： SiGe/Si 异质pn结 C-V 禁带宽度     

Characterization of oxide layers and interface layers of ferrite stainless steel (SUS430) by57Fe CEMS

The oxide layers on stainless steel formed by heating at various high temperatures and by dipping in LiF + BeF₂ molten (Flibe) bath at 600 °C were characterized by CEMS. Hematite was a major iron product at 600 °C and fine oxides with paramagnetic Fe(III) species were produced at the higher temperatures than 700 °C. The interface of stainless steel beneath oxide films was characterized as the hyperfine field distributions. Paramagnetic Fe(III) species were produced on Cr depleted layers in the Flibe bath. CEMS is effective for simultaneous characterization of both oxide surface and interface layers of the ferritic stainless steel.     

Microscopic investigation of the band discontinuities at the silicon-germanium heterojunction interface

The formation of interface energy band discontinuities has been directly monitored on Ge-covered Si(111) surfaces with photoemission spectroscopy using synchrotron radiation. The final magnitude of the band discontinuities is not consistent with the linear combination of dipole-layers which leads to the “electron affinity rule”. Strong modifications of the local density of states occur during the formation of the heterojunction and the experiments indicate that the interface is abrupt on a microscopic scale.     

Determination of the reduced thickness of surface layers by means of the substrate method

Layers on solid surfaces have a marked influence on the results of quantitative XPS analysis. Since knowledge of the total thickness of such layers is necessary in compensating for this influence, the substrate method with variation of the take-off angle must be applied. An analysis of (a) XPS data, (b) calculations performed for rough surfaces, and (c) XRFA data leads to the conclusion that at small take-off angles it is uncertainties in the measurements (count-statistics, take-off angle) that predominate, whereas at large angles, it is surface roughness. An evaluation procedure is developed and discussed on the basis of these results.     

Development of novel materials through interface engineering

The impact of interfaces in the processing and properties of polycrystalline material is briefly discussed. The local properties of the interfacial layer are considered in terms of composition, structure and related properties that differ substantially from those of the bulk phase. It has been postulated that novel materials with desired properties for specific industrial applications may be processed through interface engineering rather than through bulk chemistry. This paper considers the impact of interfaces on the properties of materials for technological applications, such as electrochemical devices for reduction of greenhouse gases, through energy conversion and environmental monitoring. The procedures that may be applied for the modification of interfacial chemistry are considered.     

异质结界面电荷对突变InP/InGaAs异质结双极晶体管热场发射影响研究

异质结界面电荷的存在改变了异质结的内建势, 这引起了界面势垒尖峰高度和形状的扰动, 从而使异质结界面载流子的输运产生相应的变化, 最终导致异质结双极晶体管 (HBT) 性能的改变. 基于热场发射-扩散模型, 对异质结界面电荷对InP/InGaAs HBT性能的改变做了研究, 得到结论是正极性的界面电荷有利于InP/InGaAs HBT的直流和高频特性的改善, 而负极性的界面电荷则使器件的直流和高频特性变差. 关键词： InP/InGaAs异质结双极晶体管 界面电荷 内建势 热场发射     

A study of electronic states near the interface in ferroelectric-semiconductor heterojunction prepared by rf sputtering of PbTiO3

Interface states in the ferroelectric-semiconductor junction have been investigated from analyses of DLTS andC-V data. Two trap levels are located at 0.21 and 0.36 eV below the conduction band near the silicon side of the interface in the MFS (Metal-Ferroelectric-Semiconductor) structure. The interface states density has been drastically reduced by putting an oxide layer between ferroelectric and semiconductor with certain heat treatment in H₂ atmosphere at 500 °C. It has been found that the MFMOS (Metal-Ferroelectric-Metal-Oxide-Semiconductor) structure shows the least interface states density (less than 10¹¹cm^–2eV^–1) with the maximal dielectric constant of PbTiO₃ thin films.     

Measurement of the thickness of semiconducting layers by means of an SHF-waveguide with a flange

This article examines an electrodynamic model of an SHF-waveguide with a flange designed to measure the thickness of superconducting layers on conducting substrates. The method of generalized scattering matrices is used to find expressions that make it possible to obtain the distribution of the field in the waveguide and determine the response of the system to a change in the parameters of the superconducting medium. A numerical analysis is performed to select the method of measurement, and sources of random error are examined in an evaluation of the thickness of superconducting layers by the chosen method. It is shown that it is possible to account for the effect of the doping profile of the superconducting layers in measurements. Tomsk University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii. Fizika, No. 5, pp. 12–16, May, 1996.     

Tailoring the photoluminescence of PbS-nanoparticles layers deposited by means of the pulsed laser ablation technique

In this article, we report on the room-temperature pulsed laser deposition (PLD) of lead sulfide (PbS) nanoparticles (NPs) layers onto various substrates. It is particularly shown that the average size of PbS NPs can be controlled by varying the number of laser ablation pulses. The pulsed laser deposited PbS NPs are found to be of high-crystalline quality and their photoluminescence (PL) to blue shift significantly from 1420 to 880 nm, as their average diameter is decreased from 8.5 to 2.5 nm, thereby confirming the quantum size effect. The latitude of our PLD process is shown to permit the achievement of multilayered PbS-NPs structures of which the overall PL emission spectrum can be tailored through the appropriate stack of individual PbS-NPs layers.     

Simulation of interface broadening of sputter profiled isotopic silicon layers

Abstract

The experimental SIMS profiles of Si³⁰/Si²⁸ multilayers depth profiled using 2–10 KeV Ne⁺, Ar⁺ and Xe⁺ (K. Wittmaack and D. B. Poker, Nucl. Instr. Meth. B47 (1990) 224) have been simulated using a diffusion approximation to ion mixing. Both the leading and trailing edges of peaks in the depth profiles could be fitted for all ion energies by mixing efficiencies of 25, 40 and 65 Å⁵ eV^?1 respectively. These values are larger than the estimates of 5, 11 and 15 Å⁵ eV^?1 from ballistic mixing. The additional contributions to the mixing, 20, 29 and 50 Å eV^?1, scale with cascade energy density, suggesting that stimulated motion in thermal spikes is important. A simple spike model in which cascade defects are trapped at fixed sinks agrees with the experimental mixing efficiencies.     

Surface and interface properties of thin pentacene and parylene layers

To improve Organic Thin Film Transistor (OTFT) properties we study OTFT semiconductor/dielectric interfacial properties via examination of the gate dielectric using thin Parylene C layer. Structural and morphology properties of pentacene layers deposited on parylene layer and SiO₂/Si substrate structure were compared. The surface morphology was investigated using atomic force microscopy (AFM) and scanning electron microscopy (SEM). AFM topography of pentacene layer in non-contact mode confirmed the preferable pentacene grain formation on parylene surface in dependence on layer thickness. The distribution of chemical species on the surfaces and composition depth profiles were measured by secondary ion mass spectroscopy (SIMS) and surface imaging. The depth profiles of the analyzed structures show a homogenous pentacene layer, characterized with C or C₂ ions. Relatively sharp interface between pentacene and parylene layers was estimated by characteristic increased intensity of CCl ions peak. For revealing the pentacene phases in the structures the Micro-Raman spectroscopy was utilized. Conformal coatings of parylene and pentacene layers without pinholes resulted from the deposition process as was confirmed by SIMS surface imaging. For the pentacene layers thicker than 20 nm, both thin and bulk pentacene phases were detected by Micro-Raman spectroscopy, while for the pentacene layer thickness of 5 and 10 nm the preferable thin phase was detected. The complete characterisation of pentacene layers deposited on SiO₂ and parylene surface revealed that the formation of large grains suggests 3D pentacene growth at parylene layer with small voids between grains and more than one monolayer step growth. The results will be utilized for optimization of the deposition process.