AES and core level photoemission in the study of a-C and a-C:H

The state of the art in the use of two probes of the occupied electron states, namely C KVVAuger emission and C 1 s photoemission, in the study of a-C and a-C:H is reviewed, with particular attention to the issue of deriving the sp(2) fraction. The local character of the two probes justifies decomposition of the relative spectra into an sp(2) and an sp(3) component. While however decomposition of the C Is spectrum relies upon a theoretical basis and allows accounting for disorder effects in the amorphous state, no theory is available to support C KVV spectrum decomposition which has therefore to rely upon a purely empirical basis. In addition, the introduction of disorder related effects is not straightforward for this spectrum. A real validation of the sp(2) fraction measurement is lacking for both techniques, though there are indications that both allow qualitative or even semi-quantitative (C 1s spectrum) understanding of the electronic structure of amorphous carbon systems. Beside the sp(2) fraction evaluation, other pieces of information, concerning the spatial organization of the sp(2) sites, are possibly extracted from these spectra. (c) 2004 Elsevier B.V. All rights reserved.