DYNAMICAL CHANGE OF STEP AND DOMAIN-STRUCTURES ON THE SI(111) SURFACEWITH HEAT-TREATMENT OBSERVED BY A LOW-ENERGY-ELECTRON MICROSCOPE

In situ observation of surface structures of the Si(111) clean surface has been carried out in real time by a low-energy electron microscope (LEEM) with varying temperature across the phase transition between 7 X 7 and 1 X 1. Contrast changes of atomic steps and 7 X 7 domain boun daries were observed during the phase transition between 800 degrees C and 850 degrees C. Furthermore the structural conversion from metasta ble ''1 X 1'' to 7 X 7 for a surface quenched from above 1000 degrees C was observed with annealing at 700-800 degrees C. The 7 X 7 domain b oundaries were observed with a dark contrast while the phase transitio n was progressing. The contrast changes of steps and domain boundaries observed by LEEM during the phase transition are explained by the dif fraction contrast. The domain boundaries and the metastable ''1 X 1'' structure observed by STM are illustrated in order to understand the S i(111) surface structure at the atomic scale.