OPTICAL 2ND-HARMONIC GENERATION ON THE DIAMOND C(111) SURFACE

Hydrogen adsorption on and desorption from a diamond C(111) surface we re probed by optical second-harmonic generation (SHG). The hydrogen de sorption monitored in real time at temperatures above 1200 K under ult rahigh vacuum conditions demonstrates that SHG is applicable at the hi gh temperatures present in diamond CVD. A distinct peak of the second- harmonic intensity during desorption indicates dangling bonds prior to the formation of the reconstructed hydrogen-free surface. In contrast with desorption, no dangling bonds are detected by SHG during the ads orption of hydrogen, indicating that adsorption is not a mere reversal of desorption. Experiments at various azimuthal angles suggest that c ontributions to the signal from steps and terraces are of equal import ance.