K-induced surface structural change of Si(1 1 1)-7 7 probed by second-harmonic generation

The growth of thin K films on Si(1 1 1)-7 7 has been investigated by selecting the input and output polarizations of second-harmonic generation (SHG) at room temperature (RT) and at an elevated temperature of 350 8C. The SH intensity at 350 8C showed a monotonic increase with K coverages up to a saturated level, where low energy electron diffraction (LEED) showed a 3 1 reconstructed structure. The additional deposition onto the K-saturated surface at 350 8C showed only a marginal change in the SH intensity. These variations are different from the multicomponent variations up to 1 ML and orders of magnitude increase due to excitation of plasmons in the multilayers at RT. The variations of SHG during desorption of K at 350 8C showed a two-step decay with a marked shoulder which most likely corresponds to the saturation K coverage of the Si(1 1 1)-3 1-K surface. The dominant tensor elements contributing to SHG are also identified for each surface.