Electron-beam-induced fragmentation in ultrathinC60films onSi(100)−2×1−H:Mechanisms of cage destruction

Abstract

We demonstrate that irradiation of ultrathin (1--4 monolayer) films of ${\mathrm{C}}_{60}$ grown on $\mathrm{Si}(100)\ensuremath{-}2\ifmmode\times\else\texttimes\fi{}1\ensuremath{-}\mathrm{H}$ with 3.3 and 0.5 keV electron beams leads to substantial modification of the fullerene molecules and their ultimate destruction. The fragmented fullerenes coalesce under continued electron irradiation to form an amorphous material with graphitic local structure. No measurable desorption of fullerene or derived fragments is observed under the irradiation conditions used. At electron doses below those at which complete fullerene destruction occurs we observe evidence indicating polymerization, due to electronic excitation of the molecules, and fullerene hydrogenation by atomic hydrogen liberated by the incident electron beam. An examination of possible fragmentation mechanisms resulting from larger electron doses leads to the conclusion that decay of electronic excitations into vibrational modes of the molecule is the most likely route through which cage destruction occurs.