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 dia mond(100) surface using Fourier-transform infrared (FTIR) spectroscopy in c ombination with conductivity measurements is reported. On a plasma-hydrogen ated diamond(100) surface, the IR spectra measured in the multiple internal reflection mode reveal three absorption lines. Two of them at 2921 and 285 4 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 physi sorbed 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 su rface. Upon annealing in air at temperatures lower than 200 degreesC, the s urface 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 c onductivity irreversibly and yields conductance values below the measuremen t limit of 5 x 10(-12) Ohm (-1). We show that the chemisorbed hydrogen in t he C2H2 configuration, together with at least one physisorbed species, is r esponsible for the surface conductivity of hydrogen-terminated diamond(100) . (C) 2001 Elsevier Science B.V. All rights reserved.