The effect of the structural properties on the SEY of C materials

Abstract

We review here the dependence of the secondary electron yield (SEY) of carbon materials on the structural ordering of the C lattice and surface damage. We followed the SEY evolution during the thermal graphitization of thin amorphous carbon layers and during the amorphization of highly oriented pyrolytic graphite by means of Ar+ bombardment. C1s core level and valence band spectroscopy, used to follow the structural modification, were measured in parallel with SEY curves. In the first case the SEY decrease observed with the progressive conversion of sp3 hybrids into six-fold aromatic domains was related to the electronic structure of the C-films close to the Fermi level. We found that a moderate structural quality of the C layer, corresponding to aromatic clusters of limited size, is sucient to obtain a SEY as low as ~1. For the bombarded graphite, the strong lattice damaging remains limited to the near surface layer, where the high density of defects reduces the transport of incoming and secondary electrons. Then, the SEY curves resulted dierently modified in the low and high primary energy regions, but their maximum values remained favorably low. Our findings demonstrate that SEY, besides being an indispensable means to qualify technical materials in many technological fields, can be also used as a flexible and advantageous diagnostics to probe surfaces and interfaces.