The influence of thermal fluctuations on electronic and structural properties of Ge(001) surface

We present a theoretical study (within the density functional theory) of the influence of thermal fluctuations of the Ge(0 0 1) structure on its electronic properties, mainly in the context of possible metallization of this surface observed in experiment. Analysis is based on the results of three series of long-time molecular dynamics (MD) simulations performed for p(1 x 2), c(2 x 4) and p(2 x 4) surface unit cells. We have found that for the p(1 x 2) unit cell thermal fluctuations lead to the appearance of a sharp peak in the density-of-states distribution at the Fermi level, and consequently, to metallization of the germanium surface, while the energy structure of the c(2 x 4) reconstructed surface remains non-metallic even at high temperatures. This result is in an agreement with recently published scanning tunneling spectroscopy data. Our MD simulations show that, depending on the translational symmetry of the surface, thermal fluctuations may modify its electronic structure in quite a distinct way. The obtained results also indicate that the observed Ge(0 0 1) surface metallization is an averaged effect of the variations of the local density of states caused by thermal fluctuations. (c) 2007 Elsevier B.V. All rights reserved.