Unoccupied electronic states of 2D Si on Ag-3-Si(111)

Optimizing substrate characterization to grow 2D Si layers on surfaces is a major issue toward the development of synthesis techniques of the promising silicene. We have used inverse photoemission spectroscopy (IPES) to study the electronic band structure of an ordered 2D Si layer on the3×3-Ag/Si(111) surface (3-Ag). Exploiting the large upwards band bending of the3-Ag substrate, we could investigate the evolution of the unoccupied surface and interface states in most of the Si band gap. In particular, thek_∥-dispersion of the3-Ag free-electron-likeS₁surface state measured by IPES, is reported for the first time. Upon deposition of ∼1 ML Si on3-Ag maintained at ∼200 °C, the interface undergoes a metal-insulator transition with the complete disappearance of theS₁state. The latter is replaced by a higher-lying stateU₀with a minimum at 1.0 eV aboveE_F. The origin of this new state is discussed in terms of various Si 2D structures including silicene.