Positron Annihilation Auger Electron Spectroscopy

Acronyms PAES positron annihilation Auger electron spectroscopy. 

A beam of low energy positrons is shone onto the sample. Some of the positrons annihilate core electrons of the surface atoms, leaving them in an excited state, which decays by Auger emission of an electron. The energies of the Auger electrons are characteristic of the atoms involved and so measurement of the electron energies reveals information about the elemental composition of the sample surface. 

The position beam comes from radioactive emission (e. g. Na) or a high intensity dedicated positron beam source. 

UHV compatible materials. PAES may be used on insulators or dehcate samples, such as weakly physisorbed molecules that cannot be studied easily with conventional AES. 

Elemental composition of the topmost atomic layer with peak shapes that are free of data manipulation artefacts. 

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PAES (positron annihilation Auger electron spectroscopy) is another technique for producing true AES peak shapes that are free of the secondary electron background. PAES is identical to conventional Auger electron spectroscopy except that the sample excitation is done with a low energy beam of positrons rather than a higher energy beam of electrons. 

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. 

Apart from the theoretical approaches, electronic energy spectra of carbides and nitrides have been studied using a variety of experimental techniques X-ray emission and photoelectron spectrosopy, optical and Auger spectroscopy, electron energy loss and positron annihilation spectroscopy, etc. However, interpretation of the results obtained requires, as a rule, use of the computational methods of the band theory of solids and quantum chemistry. Moreover, the data provided by theoretical methods are important by themselves, because they give much more detailed information on the electron states and chemical bonding than any of the experimental methods. They also allow us to model theoretically... 

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