M. Menyhard

Amorphisation and surface morphology development at low-energy ion milling

Abstract Amorphisation and surface morphology development of Si and GaAs was studied by means of XTEM after ion bombarding at various low energies in our novel ion milling unit. In this device, the specimen is rotated and the ion energy can be reduced down to 0.12 keV. It was shown that the thickness of the amorphised layer is about 1 nm for Si/0.25 keV, and not observed for GaAs/0.25 keV and Si/0.12 keV. This amorphisation is much thinner than those measured at higher energies, e.g. 5 nm, 2.1 nm for Si/3 keV, GaAs/1.6 keV. Dynamic TRIM simulation could be successfully applied for the description of amorphisation. It will be shown for the first time that the interface roughness also decreases with decreasing ion energy.

TEM sample preparation by ion milling/amorphization

Abstract Artefacts evolved during TEM sample preparation by ion milling are discussed. Possibilities are given to minimise the amorphization/damage of the ion milled samples. A new type of low energy ion gun is applied in the ion milling device; ion beam induced artefacts are minimised, as shown for samples of GaAs and Si.

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.

Determination of the inelastic mean free path (IMFP) of electrons in germanium and silicon by elastic peak electron spectroscopy (EPES) using an analyser of high resolution

Abstract The IMFP of electrons is a fundamental material parameter of surface analysis by AES, XPS, EPES and EELS. In surface analysis calculated IMFP values are used. Their experimental determination is rather difficult. The IMFP of amorphous Ge and polycrystalline Si was determined by comparing the elastic peak intensity ratios with electrolytic Ni reference sample of 1 nm surface roughness, achieved by dedicated Ar+ ion bombardment cleaning and examined by STM. Experimental results obtained with a hemispherical analyser type ESA 31 developed by ATOMKI Debrecen have been evaluated by Monte Carlo analysis, based on Jablonskis differential elastic scattering cross sections and elaborated for the HSA analyser angular window. Due to the 5 × 10−5 energy resolution of the ESA 31 no spectrometer correction was needed. The ratio of the background to the elastic peak was

Experimental determination of the inelastic mean free path (IMFP) of electrons in Cr, Mo, Ge and Si based on the elastic peak intensity ratio with a Ni reference sample

Abstract The inelastic mean free path (IMFP) of electrons has been determined for selected elemental solids using elastic peak electron spectroscopy (EPES) and a Ni standard. The IMFP was evaluated for the range of 500–3000 eV on Cr, Mo, Ge and Si materials. The Ni standard surface has been prepared by electrolysis and HV vapour deposition. Its quality was verified by AES and STM. The theoretical model relating the elastic peak intensity to the value of the IMFP was based on relativistic scattering cross sections and the multiple elastic scattering events were simulated by a Monte Carlo procedure. Reasonable agreement of the obtained IMFP values and their dependence on the energy with the data by Tanuma et al. and by Ashley et al. was found.

Experimental determination of the inelastic mean free path for Cu, Ag, W, Au and Ta, in the energy range 500-3000 eV by elastic peak electron spectroscopy and using Ni reference sample

Abstract The inelastic mean free path (IMFP) is the most important electron transport parameter. The value of IMFP can be determined by electron reflection experiments (EPES) supported by the Monte Carlo theory with the multiple elastic scattering events considered. The values of IMFP for the high atomic number elements obtained from such a model and applying AI standard were found to be in reasonable agreement with the theoretical values. Recently, Ni has been proved to be a more adequate reference sample due to the lack of inelastic losses appearing in the vicinity of the elastic peak. In the present work the energy dependence of the IMFP for Cu, Ag, W, Ta and Au using Ni standard was evaluated by EPES in the energy range 500–3000 eV. The Ni standard of high quality was used, where its surface roughness was verified by scanning tunnelling microscopy. Reasonable agreement with Tanuma et al. results was obtained in the energy range 500–2000 eV. Above 2000 eV the obtained results were in agreement with the values by Ashley and Tung.

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

Surface morphology development during ion sputtering: roughening or smoothing?

We report on STM studies of ion-sputtered surfaces, applying sputtering conditions which were shown to produce a relatively smooth surface. The height correlation function was calculated for the nickel layer in both the as-received and sputtered conditions. The large-scale roughness of the as-received specimen was reduced by ion sputtering according to expectations derived from Auger depth profiling. On the other hand, the small-scale roughness was increased due to sputtering. Self-affine scaling regions are identified, and the exponents are compared to theoretical and numerical results.

Backscattering spectra of medium energy electrons

Backscattering spectra of medium energy electrons (1–10 keV) are very important in Auger electron spectroscopy. Backscattered electrons compose the background and contribute to the excitation of Auger transitions.TheN(E) backscattering spectra were determined by an Auger spectrometer with a CMA analyzer operated in DC mode using an isolation amplifier system.TheN(E) backscattering spectra of electrons were studied on graphite, Si, stainless steel, Ge, Mo, W and Au in the 0.7–3 keV range. The backscattering spectra are presented. Our main results can be summarized as follows:- the backscattering coefficientrB was determined by integratingN(E) above 272 eV (effective for Auger excitation of low energy peaks);-rB is little affected by the primary energyEp and strongly increasing withZ;- the elastic peakN(Ep) is decreasing withEp and strongly increasing with Z;- the distributionN(E) exhibits a drastic change withZ, going from Fe to Si;- the percentage of elastically reflected electrons was determined.

On the performance of the TRIM simulation for the evaluation of auger depth profiles

Thin-film structures several monolayers thick can be observed by Auger depth profiling if specimen rotation, grazing angle of incidence and low ion energy are used. To evaluate depth profiles measured on such features, we developed a trial-and-error type of evaluation technique. First we simulated the depth profile for an arbitrary in-depth distribution using a dynamic TRIM code and then the Auger signal was calculated from the output of the TRIM simulation. It will be shown that using a single fitting parameter all depth profiles measured on various layer structures could be properly evaluated. Based on our evaluation technique we can predict that a depth profile taken on a step-function-like transition is not sensitive to the quality of the interface. On the other hand, small changes in the interface of thin-layer structures result in clearly visible changes in the Auger depth profile.