Halogenation of diamond (100) and (111) surfaces by atomic beams

Abstract

Diamond (100) and (111) surfaces have been exposed to beams of atomic and molecular fluorine and chlorine in an ultrahigh‐vacuum environment. X‐ray photoelectron spectroscopy, low‐energy electron diffraction, and thermal desorption techniques have been used to elucidate the chemistry involved. F atoms add to both the diamond (100)‐(1×1) and (111)‐(2×1) surfaces to form a carbon‐monofluoride species which reaches a saturation level of approximately three‐quarters of a monolayer at 300 K. In other aspects of their behavior, the diamondsurfaces differ. On the (111) surface, the rate of fluorine atom uptake is, to first order, proportional to the open site concentration. Adsorption produces a dimming of the half‐order electron‐diffraction spots, suggesting the breaking of surface π‐bonded chains to form regions of the bulk 1×1 reconstruction. The (100) surface uptake rate, though, is second order with respect to open site concentration and no electron‐diffraction pattern is observed. This difference in behavior between the two surfaces is ascribed to the difference in bonding geometry, leading to severe steric hindrance to ordered adsorption on the (100) surface. The thermal desorption data show fluorine desorption over a wide temperature range (500–1200 K) on both surfaces indicating binding sites with a range of energies. Limited mass spectrometric data indicates that atomic fluorine is the major desorption product. These results imply that atomic fluorine will act in a fashion similar to hydrogen atoms in that they will break surface dimer bonds, desorb from the surface at an appropriate temperature without etching diamond, and abstract any surface hydrogen in deposition systems utilizing halocarbon species. The much larger chlorine atoms weakly chemisorb on the diamond (100) surface, producing a saturation coverage of less than half a monolayer at 300 K. The adlayer neither shows a distinct C‐Cl peak in the x‐ray photoelectron spectra nor exhibits any electron‐diffraction pattern. In addition, thermal desorption studies indicate that the concentration of chlorine atoms monotonically decreases to virtually zero as the substrate is heated from 223 to 423 K. A small residual chlorine concentration remains up to 600 K, presumably due to binding at defect sites. This behavior implies that atomic chlorine will exhibit a less significant role in the surface chemistry of diamond deposition systems.