Using low energy electron microscopy, we have investigated the (2×1)-(1×1) phase transition occurring above 925 K on Ge(001). Dimer breakup has been identified as the physical origin of this transition. A quantitative description of the dimer concentration during the transition involves configuration entropy of random monomers within the dimer matrix. The dimer formation energy amounts to 1.2±0.3 eV. Dimer breakup promotes reversible surface disorder by step proliferation and irreversible surface roughening above 1130 K.
van Vroonhoven, E., Zandvliet, H. J. W., & Poelsema, B. (2003). (2x1)-(1x1) Phase Transition on Ge(001): Dimer Breakup and Surface Roughening. Physical review letters, 91(11), 116102-1-116102-4. https://doi.org/10.1103/PhysRevLett.91.116102