Monte Carlo simulation of temperature dependence of X-ray diffraction intensity of Ge(001) surface with defects

We perform Monte Carlo simulations (MCS) to study the influence of surface defects on the order-disorder phase transition of Ge(0 0 1) surface. Coupli ng constants among the buckling of the dimers given by the recent first-pri nciples calculations are used in the MCS. The feature of the phase transiti on is remarkably changed by a low density of defect. The magnitude of the l ong-range order parameter is much reduced at low temperatures as compared t o the defect-free system. The temperature dependence of the X-ray diffracti on intensity for the quarter-order spot specific to the c(4 x 2) structure becomes broad. The influence of defects on the formations of local domains of Ge(0 0 1) is well understood by analogy with that of Si(0 0 1). The expe rimental temperature dependence of the X-ray diffraction intensity is well reproduced by the present MCS. (C) 2001 Elsevier Science B.V. All rights re served.