Hydrogenation of amorphous C : H surfaces by thermal H (D) atoms

Abstract

C : H films of several monolayers thickness have been prepared by ion beam deposition of ethane ions of 160 eV kinetic energy at Pt surfaces covered with a monolayer of graphite. These C : H films typically exhibit a H C ratio of 0.5 and contain about equal amounts of carbon atoms in the sp 2 (graphitic) and sp 3 (diamond) hybridization states. The hybridization states of surface CH x groups have been characterized by means of vibrational spectroscopy (HREELS). The spectra revealed the presence of aliphatic sp 3-CH x ( x = 1, 2, 3), graphitic sp 2-CH and terminal sp-CH groups at the surface of C : H films deposited at 350 K. Thermal treatment of the films successively destroys sp ( T≈500 K), sp 3 ( T≈850 K), and sp 2 ( T = 1150 K) related CH groups, which is paralleled by the evolution of hydrogen and hydrocarbon species from the film. Exposing these films to thermal H (D) atoms at 350 K causes hydrogenation of sp and sp 2 hybridized CH groups resulting in sp 3-CH x group formation. The same phenomena are observed at surfaces of C : D films deposited from fully deuterated ethane. The results provide a microscopic description of the primary reaction steps of graphite erosion by H atoms and allow for an understanding of rate determining steps in low pressure chemical vapor deposition of diamond or diamond-like carbon.