B. M. Reichl

Segmentation and scatter diagram analysis of scanning Auger images : a critical comparison of results

SummaryIn surface science, Scanning Auger Microscopy (SAM) is an important method for investigating the chemical composition of surfaces and obtaining information about the spatial distribution of chemical elements. Images obtained by SAM give a qualitative impression of the concentration of the selected elements on the surface. For the systematic characterization of inhomogeneous materials the evaluation of multispectral SAM-images can be facilitated by image processing techniques. Two methods, classification and segmentation, are applied to SAM images and the results are compared. Scatter diagrams have been used to classify the number and coverage of different surface phases. In SAM-literature (e.g. [1]) it is demonstrated that classification is a valuable and easy to use tool to interpret the content of multispectral images. Segmentation decomposes the images into homogeneous connected regions of similar surface composition, based on the information contained in the elemental maps. Segmentation makes it possible to extract statistical and topological features of single objects, whereas scatter diagram analysis gives information only about different surface phases.

Kinetics of surface segregation during linear programmed heating

An analysis of the experimentally investigated kinetics of surface segregation can be used to obtain information on the diffusion properties of the system near the surface. A promising way for an efficient experimental analysis of the temperature dependence of the effective diffusion coefficients is the investigation of surface segregation with linearly programmed heating (LPH), in which the temperature is increased linearly with time during the experiment. Model calculations of the segregation kinetics during LPH have been performed on the basis of a modified KTBIM (kinetic tight-binding Ising model) for dilute binary and ternary systems to investigate the general segregation kinetics and the applicability of this method in real systems. The results allow one to determine the conditions under which experimental data can be used to obtain the Arrhenius parameters of the effective diffusion coefficients of the segregating elements in real systems. Additional model calculations performed to describe the segregation kinetics of N and S in polycrystalline Fe and Sn at the Cu(111) surface show excellent agreement with experimental results and demonstrate the sensitivity of this model.

SAM investigations of temperature programmed surface segregation of impurities in α-iron

The time development of the surface concentration of impurities such as sulphur and nitrogen in high-purity polycrystalline α-iron samples has been investigated by means of Auger Electron Spectroscopy (AES) and Scanning Auger Microscopy (SAM) during linearly increasing the temperature from about 100 to 850°C. The subsequent segregation of N and S revealed strong differences in the segregation kinetics of these elements — especially with respect to the contribution of the dominating transport mechanism (grain boundary diffusion and bulk diffusion). Calculating the effective diffusion coefficient of S from two subsequent segregation runs, strongly differing values were found. An interpretation of the change in the diffusion properties of sulphur is given based on SIMS (Secondary Ion Mass Spectroscopy) investigations performed before and after the thermal treatment.

Investigation of the diffusion properties of impurities in polycrystalline α-iron by means of AES

Abstract The time development of the surface concentrations of impurities such as sulphur, oxygen and nitrogen in high-purity polycrystalline α-iron samples has been investigated by means of Auger electron spectroscopy (AES) and scanning Auger microscopy (SAM) during linearly increasing the temperature from about 200 to 830°C. The subsequent segregation of N and S revealed strong differences in the segregation kinetics of these elements — especially with respect to the contribution of the dominating transport mechanism (grain-boundary diffusion and bulk diffusion). Assuming an Arrhenius behaviour, the segregation kinetics was used to determine both the pre-exponential factor and the activation energy of the effective diffusion coefficient of the segregating sulphur. The results are compared with values obtained by other methods and with model calculations performed on the basis of a layer-by-layer segregation model.

Investigation of the segregation on a Fe-3.5at% Si bicrystal with AES and SAM

A fundamental investigation of transport phenomena involved in the surface segregation in polycrystalline systems has been performed, studying a Fe-3.5at% Si bicrystal with one (001) and one (011) oriented surface, separated by an asymmetric grain boundary. The segregation kinetics of Si, P and S was investigated by means of AES (Auger electron spectroscopy). A combined mechanism of bulk diffusion and diffusion across the grain boundary was found to be responsible for the complex segregation behaviour.

A multisource image processing environment in surface analysis

To use data from a number of different surface analytical instruments (such as SAM, SIMS, STM, EPMA, AFM)1 in a synergistic manner, the problem of interchangeability of surface analytical data as well as that of multi-method analysis has to be solved. Starting from the measured images being stored in a standardized format, a preliminary set of low-level data processing routines based on the software packages Khoros [1] and HDF2 [2] has been implemented. The aim is to standardize the storage as well as the processing of the images or spectra. A first version is presented.

Model calculations of temperature programmed surface segregation

The investigation of the kinetics of surface segregation can reveal important information on the diffusion properties of the system near the surface. A promising way for an efficient experimental analysis of the temperature dependence of the effective diffusion coefficients is the temperature programmed segregation (TPS), in which the temperature is increased linearly with time during the experiment. Model calculations of the segregation kinetics during TPS have been performed on the basis of the KTBIM (kinetic tight binding Ising model) for dilute binary and ternary systems to investigate the applicability of this method in real systems. The results give hints on the conditions under which experimental results can be used to obtain the Arrhenius parameters of the effective diffusion coefficients of the segregating elements in real systems.

Model calculations of interface segregation in dilute systems

Using a discrete model for the segregation kinetics based on the Darken theory of diffusion and on the regular solution model (RSM), one and two dimensional simulations of interface segregation in binary and ternary systems have been performed. The aim of the calculations was to investigate the kinetics of segregation sequences in ternary systems, the segregation kinetics in discrete systems during the initial phase and finally the kinetics of surface segregation in the region of a grain boundary intersected by the surface.