A. Sulyok

Interdiffusion in amorphous Si/Ge multilayers by Auger depth profiling technique

It has been shown by the Auger depth profiling technique that the concentration profile at the initially sharp Si/Ge interface in amorphous Si/Ge multilayers shifted but remained still sharp after a heat treatment at 680 K for 100 h. At the same time the fast diffusion of Si resulted in the formation of an almost homogeneous Ge(Si) amorphous solid solution, while there was practically no diffusion of Ge into the Si layer. This is direct evidence on the strong concentration dependence of the interdiffusion coefficient in amorphous Si/Ge system, and it is in accordance with the previous indirect result obtained from the measurements of the decay of the small angle Bragg peaks, as well as with finite difference simulations.

Surface excitation effects in electron spectroscopy

AbstractAnalysis for surface chemistry uses electron spectroscopy: AES, XPS and REELS. The excitation and electron emissionprocesses are affected by the competitive surface excitation. Impinging and escaping electrons suffer losses in the solidsurface region, producing surface plasmons. The surface excitation is characterized by the surface excitation parameter P se .A new experimental procedure is described for the determination of P se . It is based on REELS–EPES, using the elastic peakas reference. The procedure is valid for materials having surface and volume plasmon loss peaks, like Si, In, and Sb. It canbe applied for estimating P se on materials exhibiting a surface loss peak decreasing with energy, like Ag. The ratio of theintegrated surface and volume loss peaks is composed and compared with the elastic peak. Experimental results in theEs0.2–5 keV energy range are presented for several solids. q2001 Elsevier Science B.V. All rights reserved. Keywords: Electron spectroscopy; Surface chemistry; Excitation

Recoil effect in carbon structures and polymers

Abstract The recoil effect on quasi-elastic scattering of electrons has been described by Boersch. The Rutherford type scattering on the nucleus produces a shift of the elastic peak maximum of Δ E em , proportional to 1/ M (atomic mass) and electron energy. Laser et al. studied the recoil effect for exact calibration of the energy scale for XPS. The other effect is broadening of the elastic peak. Reflection electron energy loss spectra were studied by an electron spectrometer ESA 31 of high energy resolution. Various modifications of C (electrode and reactor graphite, glassy C, powder) and conducting polymers (polyacetylene, polyaniline, polythiophene) have been studied with varying composition of C, O, H, S, Pd etc. In the case of the samples containing different elements the complex nature of the elastic peaks (consisting of the sum of components having different intensities and shifts) was clearly observed. Possible explanations for the recoil effects detected are reviewed.

Determination of the inelastic mean free path of electrons in GaAs and InP after surface cleaning by ion bombardment using elastic peak electron spectroscopy

Abstract The inelastic mean free path (IMFP) of electrons is an important material parameter needed for quantitative AES, EELS and non-destructive depth profiling. The distinction between the terms for IMFP and the attenuation length (AL) has been established by ASTM standards. A practical experimental method for determining values of the IMFP is elastic peak electron spectroscopy (EPES). In this method, experimentally determined ratios of elastically backscattered electrons from test surfaces and from a Ni reference standard are compared with the values evaluated theoretically. The present paper reports systematic measurements of the IMFP by EPES for GaAs and InP. They are carried out in two laboratories using two different electron spectrometers: a CMA in Budapest and DCMA in Warsaw. Prior to measurements, the samples were amorphized by high-energy Ar + ions (100–400 keV), and the surface composition was determined by quantitative XPS. Argon cleaning produces enrichment of samples in the surface layer in Ga (80%) and In (70%), respectively. The experiments refer to a such modified sample surface that was considered in Monte Carlo calculations. The experimental data were analyzed using calibration curves from Monte Carlo calculations which account for multiple elastic scattering events. This approach has been used previously for elemental solids and is now extended to amorphized binary compounds. The experimental values of IMFP obtained in both laboratories exhibited a reasonable agreement with the available literature data in the 0.1–3.0 keV energy range. With respect to the information depth of EPES, the experimental results refer to the bulk composition within a reasonable extent.

Some problems of electron spectroscopy (AES, EPES) using a retarding field analyser

Abstract The retarding field analyser (RFA) proved to be advantageous in electron spectroscopy due to its high luminosity and by providing LEED simultaneously with AES and EPES. RFA is very efficient for determining the inelastic mean free path of electrons by EPES. Dolinski et al measured the elastic peak by repelling the electron beam using a bias potential on the sample. In this paper a further development of this procedure is described supplying the true percentage of elastically scattered electrons collected by RFA. The percentage has been determined by our RFA with optimized bias potential of the sample for primary energies between 100 and 2000 eV. It was deduced from the high energy side of the elastic peak because the background affects the detected signal on the low energy side. The experimental curve of elastic reflection coefficient is presented for indium. The measured elastic peak is distorted by the analyser. The spectrometer response of an RFA was determined by analysing the peak shape of deflected electrons after optimization of the bias voltage of the sample. The peak shape shows asymmetry since the low energy side differs from the Gaussian like high energy side. The distortion produced by RFA is similar to that observed by Taylor. It is enhanced by the background adjacent to the elastic peak. A computer algorithm was elaborated for reconstruction of the elastic and Auger peaks. Corrected curve is presented for indium Auger peak.

Determination of the mean free path of electrons in solids from the elastic peak - II. Experimental results

The simple theoretical model described in Part I [1] is applied to evaluate experimental results determined by elastic peak electron spectroscopy and published previously. The inelastic mean free path λ determined from the elastic backscattering probabilityPe of 2.2 and 3.1 keV electrons on C, Si, Ge and Mo are in reasonable agreement with results of Seah and Penn. In the evaluation σeff elastic backscattering cross sections calculated with the Thomas—Fermi—Dirac potential model have been applied. This model, however, is not suitable for W and Au high atomic number elements. A detailed discussion is given on the problems associated with the measurement ofPe taking into consideration the CMA response, deconvolution and angular distribution of electron spectra. Another method for determining λ is given by comparing the elastic peaks of two elements and their σeff backscattering cross sections. Experimental results are presented for Al, Si, Ge, GaAs, GaP, InSb, GaSb, Sb, InP, SiO2 and Si3N4, atomic clean surfaces measured with a CMA atEP=1, 1.5, 2 and 3 keV at normal incidence. Good agreement was found with literature data collected by Ashley for Al−Si, Ge−GaAs. The IMPF λ of GaP and GaSb proved to be 10% larger than those of GaAs, results not available in the literature. New results as well are published for λ of Sb, InSb and InP. The good agreement with literature data justifies the application of the simplified model described in Part I.

AUGER ELECTRON SPECTROSCOPY DEPTH PROFILING OF GE/SI MULTILAYERS USING HE+AND AR+ IONS

Various Ge/Si layer structures (multilayers with 2 and 3 nm layer thicknesses, step function transition, and 1 nm Si imbedded between thick Ge layers) were depth profiled by using 1 keV He+ and Ar+ sputtering with angle of incidence of 83°. The specimen was rotated during sputtering. The depth resolution determined on the step function transition weakly depended on the type of projectile used. Similarly there was not a strong deviation of depth profiles recorded on the imbedded Si layer (thickness 1 nm) if Ar+ or He+ projectile was used. In contrast a serious difference between the depth profiles measured by Ar+ and He+ sputtering was observed in the case of the multilayer systems. Based on these observations we concluded that the depth resolution (determined according to the standard) is not a sufficient characterization of a depth profiling device. It is proposed that depth profiling of some standardized multilayer structure, with layer thicknesses of 1–2 nm should also be added to the characterization ...

Auger in‐depth profiling of Mo–Si multilayers

Auger in‐depth profiles were measured on a Mo–Si multilayer structure, consisting of 45 periods of 3.3 nm molybdenum and 3.6 nm silicon layers, by means of Ar ion bombardment with rotated specimen and a glancing incidence ion beam probe. The relative sputtering yield of Si and Mo is determined in the ranges of 2–6 keV ion energy and 80°–87° incidence angle with respect to the surface normal. It is shown that the depth resolution depends strongly on the ion energy. The depth resolution changes immediately when the ion energy is changed. This observation is explained by the fact that the depth resolution in our experiment is limited by ion mixing and not by surface roughening. Attempts to determine the initial structure from the measured profile through application of Liau’s model on ion sputtering were not completely successful.

Determination of the mean free path of electrons in solids from the elastic peak - I. A simplified theoretical approach

AbstractThe inelastic mean free path λ of electrons is an important material parameter for quantitative AES and EELS. Instead of the usual methods, requiring a very delicate sample preparation procedure, λ can be determined by elastic peak electron spectroscopy. Beside geometrical parameters, the elastic peak is given by the product of λ and σeff backscattering cross section. A simple method is described for evaluating experimental elastic backscattering probability results using theoretical σeff data. σeff was calculated by integrating the differential electron scattering cross sections assuming a single scattering process and using three types of the atomic potential: the Thomas-Fermi, the Thomas-Fermi-Dirac and the Hartree-Fock models. Tabulated