The Measurement of Auger Electron-Ion Coincidence Events from Surfaces

Abstract

The recent activity in the area of desorption induced by electronic transitions has resulted in evermore complex and detailed models for the desorption event [1,2]. The gains in conceptual framework for desorption has been matched by advances in the experimental capabilities, e.g.,angle resolved techniques, photon stimulated desorption, the detection of neutral species (sometimes in a state selective way), to name a few. The challenging physics of the desorption event will require a continual improvement in the sophistication of our techniques, so that the range of questions we can pose and eventually answer keeps expanding. Much of what we now believe to be true regarding desorption mechanisms came from inferences from desorption threshold and near edge structure measurements. In these, the characeristic energy of a threshold or a peak in a desorption yield curve is related to an excitation, which can be directly to a desorbing state, or can subsequently decay to yield desorption via a more complex final state. Another technique which is often used in the gas phase is to measure coincidence between electrons emitted during the formation of the desorbing state, and the emitted ion. In this way one can directly determine the nature of the electronic configuration leading to desorption. This experiment has never been done from surfaces because the surface presents formidable problems; it acts as a source of secondary electrons, there are numerous simultaneous sources of ions, it is difficult to efficiently collect ions or electrons from a surface, and reneutralization and recapture occur readily, so that emitted electrons which in the gas phase would be accompanied by ions, are instead in most events accompanied by a recapture or reneutralization event on surfaces. Here we describe an attempt to measure coincident events between Auger electrons from a surface and ions which are desorbed from the Auger final state.