The low-temperature c(4×2) structure of Ge(001) undergoes an order-disorder phase transition at temperatures in the range 174–194 K depending on the quality of the starting structure. The critical exponents β and γ have been experimentally determined with x-ray diffraction measurements and found to be consistent with the mean-field approximation. Surface contamination from the residual gas tends to pin the ordered structure causing increased critical temperatures and rounding of the transition. © 1996 The American Physical Society.

• Received 6 March 1996

DOI:https://doi.org/10.1103/PhysRevB.54.5581