Use of the direct energy spectra in Auger electron spectroscopy

Abstract

The approach to quantitative AES via background subtraction is discussed. Because the knowledge of the transmission function is very important, a possible method for its determination is described. Respective contributions of primary, secondary and inelastic Auger electrons to the background are then theoretidy Bspessed and application to the evaluatioo of peak-to-background and tail-to-peak ratios is brietly outlined. A method to normalize the spectra intensities using the background is presented. Fmlly, spectra combination is proposed as an alternative to background subtraction for quantitative AES. This last method provides information on in-depth homogeneity and chemical effects. INTRODUCTIONAlthough the differential energy spectrum is still widely used as a recording mode for AES, the development of counting techniques together with the availability of computers to record and process data has led to an increasing number of spectra now to be collected in the direct mode. In addition to the customary argument in favour of the direct energy spectrum that the area under the Auger peak can be related to physical parameters, it must be highlighted that the information specifically contained in the background can thus also be obtained.To date, the most frequently used analytical procedures involve a background removal routine before displaying the Auger electron peaks. Several background subtraction methods have already been published,' leading to different values for the relative areas under the peaks.In this paper, a simple theoretical treatment will be discussed to assess the respective contributions of primary, secondary and inelastic Auger electrons to the background. Examples of some analytical procedures will be given to illustrate which type of information can be extracted from an energy spectrum. Finally, methods based on normalization of the spectra via the use of the background will be presented. In particular, an alternative for quantitative Auger analysis will be proposed with spectra combination. CONTRIBUTIONS TO THE ENERGY SPECTRUMThroughout this paper, only the energy distribution of electrons produced after the irradiation of a target by an incident electron beam will be discussed in detail.An experimental measurement is always the convolution of the 'true' signal by the instrumental transmis- sion. Therefore, a precise assessment of the different contributions to the energy spectrum cannot be made without the knowledge of the electron spectrometer's transmission properties. Transmission of the electron spectrometerThe most popular electron spectrometer used in AES is the cylindrical mirror analyser (CMA). Although electron multiplier effects should be taken into account,' it is generally assumed that the transmission of a CMA simply varies as the energy of the emitted electrons E. Hence, the recorded electron distribution is EN(E) and can thus be used as a reference to determine other analyser transmissions when unknown. However, it must be pointed out that such a method can only be used provided ...

XPS survey spectra simulation of nano‐structured surfaces

“…Then the contribution of each element or compound of the model is calculated and the contributions are added to produce the complete simulated spectrum. Linear combination of spectra has already been proposed by Langeron [11] as a general method for Auger quantification and more recently by Basile et al for XPS. [12] GOSSIP extends this method to the analysis of nano-structured samples.…”

Determination of trace elements by electron spectroscopic methods

“…10. AES measurements of single-crystal Na P-alumina demonstrating electron-induced Na ion migration to the surface: (a) spectrum of the as-inserted sample acquired with relatively low beam current density: (b) spectrum acquired after short Ar bombardment ('sputtering') removing mainly carbon surface contamination, and (c) the spectrum resulting from several minutes of relatively high current electron bombardment done after (b) [I11 …”