An STM and atomic force microscopy study of the effects of 1.8 MeV electron bombardment on the surface of graphite

Abstract

Highly oriented pyrolitic graphite was irradiated with 1.8 MeV electrons at 45° and near-grazing (86°) angles of incidence. For doses up to 1016 cm-2 electrons the surface of the samples subjected to 45° incidence, observed by both STM and atomic force microscopy (AFM) remained the same as the original sample showing only the usual periodic atomic corrugation, with an atomic spacing of 0.246 nm. For near-grazing incidence, at a dose of 5×1012 cm-2 electrons, features of nanometre size are observed, some elongated along the direction of the beam incidence. These are attributed to the effects of single electron–carbon interactions in the top surface layers. At a dose of 5×1014 cm-2 electrons (near grazing incidence) both STM and AFM observations show an anomalously large (period 2.5–17 nm) superperiodicity superimposed on the normal 0.246 nm atomic spacing of graphite. This Moiré-like pattern suggests that the corrugations are electronic as well as topographic in origin. We propose that near-grazing incidence electron irradiation causes break-up of the surface layers into fragments, largely retaining six-fold atomic rings, that rotate by a small angle resulting in the observed pattern due to interaction with deeper bulk-structure layers. © 1998 Kluwer Academic Publishers