Phase transition and stability of Si(111)-8 x '2'-In surface phase at low temperatures

Scanning tunneling microscopy (STM) has revealed several intermediate stages during a phase transition from the Si(111)-4 x 1-In surface phase to the 8 x '2'-In phase by cooling below room temperature, showing a gradual and inhomogeneous redistribution in surface electronic density, and also the influence of impurity adatoms. By depositing tiny amounts of adsorbates (less than 0.05 ML of group III atoms or about 0.1 ML of Ag atoms) on the low temperature (LT) 8 x '2'-In phase at around 100 K, the surface reverted to the high-temperature 4 x 1-In phase, accompanied with an increase in electrical conductivity. LT STM observations showed that the deposited Ag atoms locally destroyed the 8 x '2'-In phase, while the deposited In atoms totally destroyed the phase to return the surface wholly into the 4 x 1-In phase. Such a quenched 4 x 1-In phase at LT was quite stable against further adsorptions of these impurity atoms. These results suggest that the impurity atoms act as 'perturbers' which electronically disturb the 8 x '2' phase to revert to the 4 x 1 phase. In other words, the phase transition of the 4 x 1-In --> 8 x '2'-In by cooling is electronically driven. (C) 2001 Elsevier Science B.V. All rights reserved.