The correlation between surface conductivity and adsorbate coverage on diamond as studied by infrared spectroscopy

A high-resolution analysis of C-H vibrational modes on a single crystal diamond(100) surface using Fourier-transform infrared (FTIR) spectroscopy in combination with conductivity measurements is reported. On a plasma-hydrogenated diamond(100) surface, the IR spectra measured in the multiple internal reflection mode reveal three absorption lines. Two of them at 2921 and 2854 cm(-1) vanish in air at an annealing temperature of 190 degreesC and are assigned to the antisymmetric and symmetric CH, stretching modes of a physisorbed hydrocarbon species, respectively. The third band at 2897 cm(-1) has a width of 16 cm(-1), is stable up to 230 degreesC and is associated with the stretching frequency of C,H, monohydride units on the C(100)2 x 1:2H surface. Upon annealing in air at temperatures lower than 200 degreesC, the surface conductivity is reversibly reduced by up to five orders of magnitude. After cooling down to room temperature, it recovers the value of 1 x 10(-5) Ohm (-1) measured immediately after the plasma hydrogenation with a time constant of several days. Annealing at 230 degreesC destroys the surface conductivity irreversibly and yields conductance values below the measurement limit of 5 x 10(-12) Ohm (-1). We show that the chemisorbed hydrogen in the C2H2 configuration, together with at least one physisorbed species, is responsible for the surface conductivity of hydrogen-terminated diamond(100). (C) 2001 Elsevier Science B.V. All rights reserved.