We propose a description of the sampling depth (λ) of total electron yield experiments (TEY) in terms of kinetic Auger electron energies. This empirical response results from literature data 1-6 on low energy (<2 keV) and from our own experiments performed on thin layers of Cu on Fe substrates and on thin layers of Al x Ga 1-x As on GaAs substrates at energies of approximately 5 to 8 keV. From these investigations we estimate a sampling depth of 74 nm for Ga KLL Auger electrons in Al x Ga 1-x As. For comparison, the sampling depth of x-ray fluorescence analysis (XRF) for Al Kα radiation in Al x Ga 1-x As is 400 nm

Investigation of thin films by soft X‐ray fluorescence and by total electron yield measurements

An irradiation of solid samples with x-rays causes an electron emission from the sample surface, owing to photoabsorption. These electrons can be detected under vacuum conditions and are photo, Auger and secondary electrons. Due to inelastic collisions most of these electrons have lost some of their original kinetic energy along the path from the atom of origin to the surface. With nondispersive electron detection the total electron yield (TEY) is observed. For measurements performed with a tunable x-ray monochromator information on the qualitative composition can be obtained by the following procedure. The photon energy has to be timed from below to above of one of the absorption edges of a given element. In case of its presence in the specimen an increase of the TEY-signal can be observed.

Total Electron Yield (TEY) A New Approach for Quantitative X-ray Analysis

The theoretical concepts of the two methods are similar. Consequently, comparable fundamental parameter algorithms can be developed and applied to quantitative analysis of bulk specimens and to investigation of thin layers by TEY and by XRFA. Whereas the sampling depth of XRFA is determined by photoelectric absorption, for TEY the escape probability of electrons reduces this quantity to values of less than 100 nm. Thus, TEY is practically a surface analytical method with sampling depths between x-ray photoelectron spectrometry and XRFA. The decrease of fluorescence yields with decreasing atomic number Z is responsible for a significant reduction of the elemental sensitivity of XRFA in the range of low Z elements. On the other hand, the elemental sensitivity of TEY increases with decreasing Z as a consequence of the dominating contribution of KLL- and LMM-Auger electrons to measured TEY jumps. The possibility to quantify submonolayers and layers of nm-thickness buried under nm-layers, a nearly linear dependence of TEY signals versus elemental concentration of multielement specimens and the EXAFS and XANES information which is contained in measured TEY responses are valuable features of TEY. A disadvantage of TEY is the time consuming sequential data accumulation of TEY spectra when compared to energy dispersive XRFA. But due to progress in instrumentation TEY is no longer reserved to synchrotron radiation sources. ABSORPTION-EDGE JUMPS OF TEY TEY deals with the quantification of x-ray induced electron emission. Measurements are performed with tunable monochromatic x-ray sources and nondispersive electron detection.

Quantitative analysis by X-ray induced total electron yield (TEY) compared to XRFA

Resonant electrons below 60 eV which are detected during conversion-electron Mossbauer spectroscopy (CEMS) provide surface-specific signals which decrease exponentially with application of metallic overlayers up to 5.0 nm in thickness. Nonresonant electrons below 60 eV, arising from straggling and multiple-scattering events deep within the film, decrease only slightly in intensity with overlayer thickness. Using this noted difference, two different empirical procedures have been developed/adapted to extract the CEMS spectrum of a 0.3 nm oxide surface layer from a bulk iron target. Collection of low-energy electrons offers the advantages of short data acquisition times and increased surface sensitivity compared to established procedures relying on the collection of electrons near 7.3 keV. These techniques should prove useful for studies of surface reactivity, buried interfaces and surface magnetism.

Depth deconvolution of 57Fe conversion-electron Mössbauer spectra using electrons below 60 eV

The possibility of improving the depth selectivity of conversion-electron Mossbauer spectroscopy by mathematical processing of the initial experimental results is demonstrated. The method constructs Mossbauer spectra for electrons from a thin layer of matter localized at an arbitrarily chosen depth of a specimen by a linear combination of the initial Mossbauer spectra. It is shown that the method allows to a higher depth resolution to be obtained than by conventional instrumentational method.

A method for improving the depth selectivity of conversion-electron Mössbauer spectroscopy

The electron escape functions for various final energies of electrons are measured under the conditions of interaction of characteristic CuKα radiation with a germanium specimen. The energy analysis is carried out by a proportional gas counter of electrons with energy resolution ≈ 18%. The measurements are carried out by using two independent techniques: the method of „calibrated amorphous layers” and the new method of „total external reflection”. The features of the second method are: the universality with respect to the specimen structure (the method can be applied to single-crystalline, polycrystalline, and amorphous samples) and the high speed of measurements.



[Russian Text Ignored].

Experimental Determination of Electron Escape Weight Functions by Using the Methods of ``Calibrated Amorphous Layers'' and ``Total External Reflection''

A method is proposed for extracting information on thin layers of material by means of the superposition of the original signals obtained from thick, initially nonlocalized layers. If the statistical error is below 3%, a subsequent data processing makes it possible to achieve a sixfold narrowing of the analyzed layer.



Es wird ein Verfahren vorgeschlagen fur die Gewinnung von Informationen aus dunnen lokalisierten Materialschichten durch Superposition der Signale, die aus dicken unlokalisierten Schichten gewonnen werden. Fur den Fall, das der statistische Fehler der primaren Ergebnisse nicht hoher als 3% ist, gibt die nachfolgende Datenverarbeitung die Moglichkeit einer sechsfachen Verschmalerung der untersuchten Schicht.

A. I. Chumakov

Papers

Experimental Determination of Electron Escape Weight Functions by Using the Methods of ``Calibrated Amorphous Layers'' and ``Total External Reflection''

On the Possibility of Multiple Increase of the Resolution of Layer‐by‐layer Analysis of Materials