Adsorption of fluorine and chlorine on the diamond(100) surface

The reduction in the substrate temperature achieved by low-pressure diamond deposition from halogenated precursors is believed to involve surface processes including halogen adsorption, desorption, and reaction with adsorbed hydrogen. In this work we studied the adsorption of fluorine and chlorine on a diamond (100) single-crystal surface in UHV using thermal desorption spectroscopy (TDS), Auger electron spectroscopy (AES) and low-energy electron diffraction (LEED). Elemental halogens were dosed by solid-state electrolysis of either lanthanumtrifluoride or silver chloride, respectively; at elevated temperatures. The single crystal was regularly cleaned by pretreatment in a hydrogen plasma and showed clear reflexes of a (2 x 1) reconstructed surface in LEED. In AES, upon successive halogen dosing, a linear increase in the intensity of the halogen Auger signal and a simultaneous decrease in the intensity of the 272 eV carbon signal could be seen initially. No LEED overstructures could be observed upon adsorption on C (100). TDS shows that fluorine desorbs at temperatures above 830 degrees C, whereas chlorine desorbs completely in the temperature range between 500 and 700 degrees C. Halogen uptake of the diamond surface can be increased either by thermally activating the surface or by dosing of atomic hydrogen prior to halogen adsorption. (C) 1998 Elsevier Science B.V. All rights reserved.