Phase transition induced surface electronic states on Pb/Si(111) surface

It is known that the 1$\times $1 phase of a monolayer Pb on Si(111) surface at room temperature may undergo a phase transition into a $\surd $7x$\surd $3 phase at a low temperature below 250K. We use scanning tunneling spectroscopy to study electronic structures on both 1$\times $1 and $\surd $7x$\surd $3 phases. Our observation reveals that the electronic structures of Pb overlayer are significantly affected because of phase transition. In tunneling spectra there appears two distinct peaks on $\surd $7x$\surd $3 phase but they disappear on 1$\times $1 phase, indicating that the phase transition can induce the formation of the surface electronic states on $\surd $7x$\surd $3 phase. Moreover, the peak intensity is location-dependent and the relative strength at the low-energy peak can be reversed at the high-energy peak. These phenomena can be qualitatively explained by Kronig-Penney model.