High-resolution angle-resolved photoemission and low-energy electron diffraction studies were reported which investigate the relationship between a metallic or nearly metallic surface state and an order-disorder transition on Ge(001). Careful and systematic studies of this state’s angle- and temperature-dependent photo-emission intensity lead to conclusions concerning the real-space character of the elementary excitation in this transition and the driving force for formation of the ordered c(4 x 2) low-temperature state. Comparisons to changes in the low-energy electron diffraction pattern relate the onset of the metallic intensity to the formation of a phase in which surface dimers were randomly oriented with respect to each other. The data were most consistent with the flipping of a single dimer as the elementary excitation in the disordering transition. Evidence for a short-range driving force, probably involving interactions between dangling bonds on nearest neighbouring dimers, was presented. The conclusions allow direct measurement of the fraction of flipped dimers on the surface as a function of temperature.

Surface States and Reconstruction on Ge(001). S.D.Kevan: Physical Review B, 1985, 32, 2344-50