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

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Abstract
This research investigates the infrared absorption intensity and isotope-dependent frequency shifts of CH stretching on diamond C(111) single-crystalsurfaces by Fourier transform infrared spectroscopy (IRS). By employing single-pass direct absorption and in situsurface oxidation methods, a single sharp feature at ν m =2832.2±0.9 cm −1 with a FWHM of Γ≈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)-1×1 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 α e =0.65 Å 3 for the CH bond as that in CH 4 , yields an integrated cross section σ̄ z =5.5×10 −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 ν 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 ν m −ν 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.