Study of the electronic and adsorption structure of Cs and H coadsorption on Si(100)2×1

The coadsorption structure and electronic states of Cs and H on Si(100)2×1 were investigated by means of MDS (metastable de-excitation spectroscopy) and TDS (thermal desorption spectroscopy). The both systems of Cs/H/Si and H/Cs/Si have the same TDS profile, which indicates that Si dangling bonds are partly terminated with H atoms in both systems and CsH formed at the Cs coverages above about 0.4 ML is dissociated into H and Cs, resulting in H2 desorption at about 20°C. On the other hand, MDS spectra for the H/Cs/Si system differ from those for Cs/H/Si one, i.e., Cs–H bonds can be clearly seen in case of the H/Cs/Si systems, while not in case of the Cs/H/Si systems. The difference in MDS spectra between both systems can be explained as follows: in case of the Cs/H/Si systems, all hydrogen atoms including Cs–H bonds are located between Cs layer and Si substrate, while in case of the H/Cs/Si systems, some of the hydrogen atoms forming Cs–H bonds are on the outermost surface.