Ground state of the Si(001) surface revisited - is seeing believing?

The stable structure of clean Si(0 0 1) surface around 100 K is the c(4 x 2) arrangement constructed by buckled dimers. This structure was widely accepted as the ground state in 1990's. The view was challenged at the beginning of 2000's by the observations of a p(2 x 1) structure below 20 K with scanning tunneling microscopy (STM). Recent experimental studies confirm that the dimer is buckled below 30 K. Large tip-surface interaction, and/or tunneling current induced dynamical effect are now experimentally evident in the STM images at low temperatures. Moreover, a current induced structure transformation is discovered below 40 K even in the study by low energy electron diffraction. Dynamical electronic and vibrational effects are theoretically studied for accounting the observation of a p(2 x 1) structure below 20 K. (C) 2004 Elsevier Ltd. All rights reserved.