Time-resolved structural study of low-index surfaces of germanium near itsbulk melting temperature - art. no. 085410

The structure of the low-index surfaces of germanium near its bulk melting temperature is investigated using 100-ps time-resolved reflection high-ener gy electron diffraction. The surface is heated by 100-ps laser pulses while a synchronized electron beam probes the structure. Ge(111) was observed to remain in its incomplete melting structure up to at least T-m + 134 +/- 40 K when heated by a 100-ps laser pulse. Both the Ge(100) and Ge(110) surfac es are observed to melt near the bulk melting temperature when heated with 100-ps laser Pulses, Because of the low-diffraction intensity-to-background ratio at high temperatures and because of the temperature uncertainty in t he time-resolved experiments, we are unable to accurately identify the melt ing point of Ge(100) and Ge(110) when heated with a 100-ps laser pulse. The results, however, favor the lack of surface superheating of Ge(100) and, t o some extent, Ge(110). The superheating of the incomplete melting state of Ge(111) could be due to the metallization of the top germanium bilayer and its interaction with the solid underneath causing an energy barrier suffic ient to allow for transient surface superheating.