The CoESCA station at BESSY: Auger electron-Photoelectron coincidences from surfaces demonstrated for Ag MNN

TL;DR

This paper introduces the CoESCA station at BESSY for electron-electron coincidence spectroscopy, demonstrating its capability to analyze Auger electron-photoelectron coincidences from silver surfaces with detailed 6D data collection and analysis.

Contribution

The paper presents a novel coincidence spectroscopy setup capable of detailed 6D electron data collection and analysis, applied to Auger and photoelectron coincidences from surfaces.

Findings

Successful separation of Auger spectra from different core levels.

Determination of two-hole state energy distributions for Auger decay.

Demonstration of the system's capability with silver surface experiments.

Abstract

In this work, we present the CoESCA station for electron-electron coincidence spectroscopy from surfaces, built in a close collaboration between Uppsala University and Helmholtz-Zentrum Berlin at the BESSY II synchrotron facility in Berlin, Germany. We start with a detailed overview of previous work in the field of electron-electron coincidences, before we describe the CoESCA setup and its design parameters. The system is capable of recording shot-to-shot resolved 6D coincidence datasets, i.e. the kinetic energy and the two take off angles for both coincident electrons. The mathematics behind extracting and analysing these multi-dimensional coincidence datasets is introduced, with a focus on coincidence statistics, resulting in fundamental limits of the signal-to-noise ratio and its implications for acquisition times and the size of the raw data stream. The functionality of the CoESCA station is demonstrated for the example of Auger electron - photoelectron coincidences from silver surfaces for photoelectrons from the Ag 3d core levels and their corresponding MNN Auger electrons. The Auger spectra originating from the different core levels, 3d$_{3/2}$ and 3d$_{5/2}$ could be separated and further, the two-hole state energy distributions were determined for these Auger decay channels.