The absolute absorption strength and vibrational coupling of CH stretching on diamond C(111)

This research investigates the infrared absorption intensity and isotope-dependent frequency shifts of CH stretching on diamond C(111) single-crystal surfaces by Fourier transform infrared spectroscopy (IRS). By employing single-pass direct absorption and in situ surface oxidation methods, a single sharp feature at nu(m)=2832.2+/-0.9 cm(-1) with a FWHM of Gamma approximate to 6 cm(-1) is observed at 800 K. Systematic measuring of how band intensity depends on hydrogen etching time indicates that a well hydrogen-terminated C(111)-1 X 1 can be prepared only after prolonged exposure of the surface to H, generated by hot W filaments, at 1100 K. A study of the band intensity at saturation, and assuming an electronic polarizability of alpha(e)=0.65 Angstrom(3) for the CH bond as that in CH4, yields an integrated cross section <(sigma)over bar>z=5.5X10(-18) cm for the CH stretching motion along the internuclear axis. Additional measurements of band position as a function of mixed isotope concentrations afford a stretching frequency of nu(i)=2816.2+/-0.9 cm(-1) for a single CH isolated in a monolayer of CD oscillators at 800 K. The frequency shift of nu(m)-nu(i)=16.0 cm(-1) is too large for dipole coupling theories to explain. The implications of the present findings with regard to applying IRS for quantitatively characterizing CVD diamondlike carbon films are discussed. (C) 1997 American Institute of Physics.