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Relaxation of a stepped (ill) diamond surface is studied using an accurate, total-energy tightbinding inethod. We determined that the bare surface will become Sp bonded near a step. This spontaneous graphitization is accompanied by a large increase in spacing between the surface layers. Band structures of the ideal and relaxed surfaces indicate that surface states are removed from the gap upon relaxation, but additional gap states arise from the lower layers. Addition of hydrogen to the surface will force the C atoms to revert back to sp bonding. These results are significant towards the understanding of the behavior of a stepped surface under conditions of film growth or even the possibility of diamond nucleation from graphite.Even cleaved and polished diamond surfaces in reality are not flat, but are rough, and may contain height variations of hundreds of angstroms. It is not surprising then that the C(111) surface of diamond films, grown by chemical vapor deposition (CVD), contain grooves, i hillocks, and steps.Hu et al. used reflection elec-

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Chemical vapor deposition (CO) of polycrystalline flms of diamond has improved dramatica1.y during the past six years. During this time there have been parallel developments in modeling chemical processes at a diamond surface, with many of the first-principle studies being carried out within the density functional framework. We review our work on furthering the understanding of chem:cal processes that may be important in the growth process, which requires knowledge of first, the surfaces themselves and second, adsorption of hydrocarbon radicals to add more layers. Studies of both clean and hydrogenated ( 111). (IOO), and (110) surfaces of diamond show that clean surfaces tend to undergo strong relaxation and reconstruction while hydrogenation results in inen surfaces. Modeling interactions of various hydrocarbon radicals with diamond surfaces provides energies and geometries of viable processes while eliminating from furlher consideration processes that are found to be unfavorable. We also discuss briefly recent investigation of behavior at a step on a clean diamond surface, which may indicate a process leading to graphitization of the diamond surface.