Occupied electronic structure of Au and Ag on Ge(111).

Abstract

The surfaces formed by the vapor deposition of Au and Ag on c(2\ifmmode\times\else\texttimes\fi{}8)Ge(111) were probed with the technique of synchrotron-radiation angle-resolved photoelectron spectroscopy (ARPES), as well as low-energy electron diffraction and Auger-electron spectroscopy. Depositions were performed with the substrate at room and elevated temperatures (T\ensuremath{\approxeq}300--350 \ifmmode^\circ\else\textdegree\fi{}C) and both the valence and core states were sampled with ARPES. Extensive studies were made of the occupied electronic structure of the (\ensuremath{\surd}3 \ifmmode\times\else\texttimes\fi{} \ensuremath{\surd}3 )R30\ifmmode^\circ\else\textdegree\fi{} surfaces, which are formed by the deposition of small amounts of Au or Ag onto an elevated-temperature Ge(111) substrate. The results of these experiments indicate that the d states of the metal overlayer are atomiclike and that specific occupied electronic states can be associated with the (\ensuremath{\surd}3 \ifmmode\times\else\texttimes\fi{} \ensuremath{\surd}3 )R30\ifmmode^\circ\else\textdegree\fi{} surface structure. Investigation of the electronic structure of surfaces formed by deposition onto a room-temperature substrate indicates that a bulklike metallic valence-band structure is developing by coverages of 5 or more monolayers. These results and the subtle variations between the Au and Ag systems are discussed.