Positron Annihilation Induced Auger Electron Spectroscopy and Its Use in the Measurement of the Dopler Broadened Annihilation Spectra of Individual Core Levels

Alex Weiss

Positron spectroscopy has found wide application in the study of open volume defects and the electronic structure of bulk materials. In this talk I will focus on new applications of positrons developed in our laboratory for the characterization of surfaces: Positron Annihilation Induced Auger Electron Spectroscopy (PAES). A low energy beam is used to place positrons into an image-correlation well at the surface. A few percent of the positrons trapped in this well annihilate with core electrons resulting in highly excited atoms that relax via the emission of (Auger) electrons. Because the core holes are created via matter-antimatter annihilation, (and not through impact with an energetic electron), PAES spectra can be obtained using very low-incident beam energies. This makes it possible to eliminate the large impact induced secondary electron background that plagues conventional electron induced Auger spectroscopy (EAES). In addition, unlike EAES, which averages over several atomic layers, PAES has a very high degree of top layer selectivity due to the fact that the positrons are trapped just outside the surface prior to annihilation. Case studies will be used to demonstrate how the extremely low background, and increased surface sensitivity of PAES can be used to shed new light on the behavior of positrons at surfaces and to provide new information regarding the composition of the top-most atomic layer. In addition, I will discuss recent gamma-Auger electron coincidence measurements and their relevance for gamma-gamma measurements of the chemical environment of open volume defects in bulk materials.

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