THE DIFFERENCE OF THE SINGLET TRIPLET CONVERSION EFFICIENCY BETWEEN K/SI AND K/TA SURFACES THROUGH OXIDATION PROCESS

The oxidation processes of potassium ultrathin films adsorbed on Si(100)2 x 1 and polycrystalline tantalum surfaces were studied by metastable de-excitation spectroscopy (MDS). At the surface of 1 ML K/Si(100)2 x 1, the singlet-triplet conversion efficiency increases with oxidation. On the other hand, in the case of 1 ML K/Ta, it decreases with oxidation. These experimental facts were explained as follows: the 1 ML potassium on Si(100)2 x 1 forms a filled-band structure for the top band which is the same as that of semiconductors. Since this band structure makes it infeasible that a singlet 2s electron tunnels resonantly into the sample, the singlet triplet conversion efficiency is small at 1 ML K/Si(100)2 x 1. This efficiency increases because of the flowing out of potassium electrons into oxygen atoms with oxidation.