Understanding the insulating nature of alkali-metal/Si(111):B interfaces

We have recently revisited the phase diagram of alkali-metal/Si(111):B semiconducting interfaces previously suggested as the possible realization of a Mott?Hubbard insulator on a triangular lattice. The insulating character of the surface reconstruction observed at the saturation coverage, i.e.?0.5?ML, has been shown to find its origin in a giant alkali-metal-induced vertical distortion. Low energy electron diffraction, photoemission spectroscopy and scanning tunneling microscopy and spectroscopy experiments coupled with linear augmented plane-wave density functional theory calculations allow a full understanding of the k-resolved band structure, explaining both the inhomogeneous charge transfers into an Si?B hybridized surface state and the opening of a band gap larger than 1 eV. Moreover, , 3???3 and surface reconstructions observed as a function of coverage may reveal a filling-controlled transition from a half-filled correlated magnetic material to a strongly distorted band insulator at saturation.