Surface Chemical Analysis on Diamond C(111) by IR Sum Frequency Generation and Second Harmonic Generation Spectroscopy

Infrared sum frequency generation (SFG) and second harmonic generation (SHG) has found widespread use as surface sensitive probes [1]. As second order nonlinear processes, SFG and SHG are forbidden in the bulk of centrosymmetric media but allowed at its interface where the symmetry is broken. We have used the techniques to study adsorption of H and CH X on diamond. In particular, with the help of a tunable infrared laser, the infrared-visible SFG allows us to measure in-situ surface vibrational spectra and hence identify the adsorbed species. The results provide us with useful insight about possible mechanisms governing the chemical vapor deposition (CVD) process for diamond growth.