Surface phase transitions of Ge(100) from temperature-dependent valence-band photoemission

Valence-band photoemission at a photon energy of 32 eV has been carried out on Ge(100) from below room temperature to 1173 K. The c(4×2)->2×1 phase transition is accompanied by a shifting of a back-bond-derived surface state. The high-temperature 2×1?1×1 transition is apparent in the discontinuity in the measured emission intensity of both a bulk and a surface electronic state. A further discontinuity occurs in both of these features and of the Fermi level intensity at higher temperature, approximately 1075 K, indicating the presence of a further reversible phase transition whose nature is discussed.