Behavior of single adatoms on the Ge(111) surface above the 1050 K phase transition

The intensity of the quasielastic peak in He atom time-of-flight spectra reveals that, upon the 1050 K phase transition, the Ge adatom concentration on the Ge(lll) surface rises from the 25% expected at T < T-c. to about 31% at T > T-c. The wave vector dependence of the energetic broadening of the same peak indicates that above T-c, the adatoms jump to neighboring sites on a structurally well-defined.. substrate with a liquidlike diffusion coefficient of D approximate to 1.2 x 10(-4) cm(2)/s. These new results reconcile previous conflicting descriptions of the Cc high-temperature phase and provide the first information on the dynamical behavior of single adatoms on a semiconductor surface close to its melting point. [S0031-9007(99)08938-3].