Effect of a subnanometer thin insulator layer at the Ag/Si(111) interface through the observation of quantum well states

The ``two-step'' growth technique has been used to grow atomically uniform Ag films on $7\ifmmode\times\else\texttimes\fi{}7$ Si(111) and $8\ifmmode\times\else\texttimes\fi{}8 \ensuremath{\beta}{\text{-Si}}₃{\text{N}}₄$(0001)/Si(111) surfaces. Angle-resolved photoemission spectroscopy reveals the formation of $sp$ quantum well states in the Ag films with distinct properties in the two cases. It is shown that the valence electrons in silver can be confined in the fundamental gap of a less than 1-nm-thin nitride layer, effectively decoupling the Ag and Si states.