Time-resolved structural study of the Ge(111) high-temperature phase transition

The dynamic behavior of the Ge(111) high-temperature phase transition has b een investigated using 100 ps time-resolved reflection high-energy electron diffraction (RHEED). A laser pulse heats the surface while a synchronized electron pulse is used to obtain the surface diffraction pattern at some ti me during and after the heating laser pulse. For slow heating, the RHEED re sults show that the high-temperature phase transition spreads from similar to 1020 K to similar to 1070 K. For 100 ps laser heating, the time-resolved RHEED measurements show that the phase transition occurs in the transient temperature range from 1083 +/- 23 K to 1138 +/- 32 K. The time-resolved RH EED results are in agreement with incomplete melting in which only the topm ost layer melts during the phase transition. Thus, overheating of the topmo st bilayer beyond the onset temperature of incomplete melting by 63 +/- 23 K was observed for 100 ps laser heating. (C) 1999 Elsevier Science B.V. All rights reserved.