Visualizing buried silicon atoms at the Cd-Si(111)- 7×7 interface with localized electrons

We report the atomic-scale imaging of the buried Cd-Si(111)-$7\ifmmode\times\else\texttimes\fi{}7$ interface with a low temperature scanning tunneling microscopy (STM). The Cd(0001) films grown on Si(111)-$7\ifmmode\times\else\texttimes\fi{}7$ reveal the electronic growth mode, and manifest a series of quantum-well states. In the low-bias STM images, not only the $7\ifmmode\times\else\texttimes\fi{}7$ reconstruction but also individual Si adatoms buried by thick Cd islands are clearly visible. The two successive layers of Cd islands exhibit the distinct contrasts due to the quantum size effect. Moreover, we found a small gap appeared at Fermi level owing to the Anderson localization induced by interface scattering. The perfect transparency of Cd films can be attributed to the anisotropic electron motion, i.e., lateral electron localization and transverse motion like free-electron.