Emission-Depth-Selective Auger Photoelectron Coincidence Spectroscopy

The collision statistics of the energy dissipation of Auger and photoelectrons emitted from an amorphized Si(100) surface is studied by measuring the Si $2p$ photoelectron line as well as the first plasmon loss peak in coincidence with the Si-$LVV$ Auger transition and the associated first plasmon loss. The Si $2p$ plasmon intensity decreases when measured in coincidence with the Si-$LVV$ peak. If measured in coincidence with the Si-$LVV$ plasmon the decrease is significantly smaller. The results agree quantitatively with calculations accounting for surface, volume, and intrinsic losses as well as elastic scattering in a random medium. In this way one can determine the average emission depth of individual electrons by means of Auger photoelectron coincidence spectroscopy, which therefore constitutes a unique tool to investigate interfaces at the nanoscale level.

Figure 1

(a) Partial escape distribution, or depth distribution function (DDF), ${\varphi }_{n_X}(z,{\theta }_o)$ for the Si $2p_{1/2}$ transition. These data were simulated by means of a Monte Carlo model [15] for normal x-ray incidence, and with the Auger and photoelectron detected at an off-normal emission angle of 60°, as indicated in the inset. (b) Same as (a), for Si-$LVV$ Auger electrons. (c) Reduced double differential partial intensities for bulk inelastic scattering ${\gamma }_{n_X,n_A}=C_{n_X,n_A}/C_{n_X=0,n_A=0}$ calculated from the curves in (a) and (b) using Eq. (1). The dashed curve represents the Si $2p$ singles partial intensities for bulk scattering.

Figure 2

Experimental Si-$LVV$ singles spectrum [15] (dash-dotted line). The same spectrum subjected to a Partial Intensity Analysis [1, 13, 17] is represented by open circles.

Figure 3

Si $2p$ spectrum measured in coincidence with the background in the Si-$LVV$ spectrum (open circles, see arrows marked “background” in Fig. 2), as well as with the peak of the Si-$LVV$ Auger line (open triangles, arrow marked “peak” in Fig. 2). The filled circles are the corresponding singles intensities. The solid and dotted lines represent results of model calculations with the SESSA software (Simulation of Electron Spectra for Surface Analysis) [15] (see text). The data were normalized at the peak maximum. The inset shows an expanded view of the BG and PK spectra.