Scanning tunneling spectroscopy investigation of the (√3×√3)R30° Sn/Si(1 1 1) α and γ surfaces

Scanning tunneling spectroscopy (STS) has been used to investigate the electronic structure of the 1/3 ML Sn1−xSix/Si(1 1 1) 2D alloy at 300 K for the two limiting cases of x≈0 and x=0.5 corresponding to the α and γ (or mosaic) phases of the Sn induced (√3×√3)R30° structure. Spectra of the α-surface compare well with k∥ resolved photoemission and inverse photoemission spectra reported in the literature, but less well, in the empty state region, with theoretical band structure calculations. The surface is metallic (or semiconducting with a small gap of order 100 meV) and there are two main structures above and below the Fermi level. STS of the γ phase also shows metallic (or similar semiconducting) behaviour of the surface, in contrast to the related semiconducting γ-Pb/Si(1 1 1) and γ-Pb/Ge(1 1 1) phases.