Positron Annihilation Induced Auger Spectroscopy

Shafaq Amdani, Anat Eshed, Nail Fazleev, and Alex Weiss Physics Department, The University of Texas at Arlington 

In this chapter we will provide a brief introduction to the PAES technique including a discusion of the PAES mechanism, the advantages and applications of PAES in surface analysis, and an outline of the theory underlying calculation of PAES intensities. In addition, this chapter will include the first atlas of PAES spectra of the elements in which the intensities have been plotted using a comon normalization method (based on a new analysis of original data) so as to permit direct comparison of relative PAES intensities. The reader is refered to previous PAES reviews for additional PAES examples, applications, and references [4-7]. 

Ey are the binding energies of the electron removed to form the original 

Electron induced Auger Electron Spectroscopy (EAES) makes use of high-energy electrons to remove core electrons via impact-ionization. However, in many instances the utility of EAES is limited by problems associated with the large secondary electron background and the lack of surface specificity inherent in the EAES excitation process [2, 8]. 

The enhanced surface selectivity of PAES stems from the fact that positrons implanted into a metal or semiconductor at low energies have a high probability of diffusing to the surface and becoming trapped in an image-correlation well before they annihilate [3, 9]. The positrons in this well are localized at the surface and annihilate almost exclusively with atoms at the surface. As a result almost all of the Auger electrons originate from the 

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A.H. Weiss, Positron Annihilation Induced Auger Spectroscopy, Chapt. 45 in The Handbook of Surface Imaging and Visualization, Arthur T. Hubbard, Ed., CRC Press, Boca Raton, Florida (1995) ISBN 0-8493-8911-9, pp. 617— 633. 

A. Weiss, Positron-annihilation-induced Auger electron spectroscopy, in Positron Spectroscopy of Solids, Proceedings of the International School of Physics "Enrico Fermi," IOS Press, Amsterdam, (1995), ISBN 90 5199 203 3 and ISBN 4 274 90028 2 C3042, pp. 259-284. 

Weiss AH, Yang G, Kim JH, Nangia lA, Fazleev NG. (1996) Application of positron annihilation induced Auger electron spectroscopy to the study of surface chemistry. J Radioanal Nucl Chem 210 423—433. 

The PAES mechanism, first demonstrated in 1987 [1], can be outlined as follows (1). A positron implanted at low energy diffuses to and gets trapped at the surface. (2). A few percent of the trapped positrons annihilate with core electrons leaving atom in excited state. (3). The atom relaxes via emission of an Auger electron. The PAES mechanism is contrasted with that of electron induced Auger Spectroscopy (EAES) in Figurel2.1. 

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