HIGH-TEMPERATURE SCANNING-TUNNELING-MICROSCOPY (STM) OBSERVATION OF METASTABLE STRUCTURES ON QUENCHED SI(111) SURFACES

High temperature scanning tunneling microscopy (STM) observation has been performed to investigate the energetic stability of metastable structures of Si(111) surfaces. Upon supercooling from 1100 degrees C, 5 x 5 and 9 x 9 structures have been observed at 600 degrees C, as well as the reconstructed 7 x 7 and disordered 1 x 1 areas. The 5 x 5 and 9 x 9 areas shrink to disappear as a consequence of the growth of 7 x 7 domains. The smaller domain size; and the faster shrinking speed of the 9 x 9 structure indicate its lower stability compared to the 5 x 5 structure. The 11 x 11 and 13 x 13 DAS structures were occasionally observed at above 500 degrees C, however, suggesting lower stability than the (2n + 1) x (2n + 1) DAS structures with smaller n. The root 3 x root 3 structures also appear at high-temperatures below 550 degrees C, whereas the 2 x 2, c2 x 4, and c2 x 8 structures are observed only at room temperatures. Clear STM images of the root 3 x root 3 structure can rarely be obtained at temperatures higher than 600 degrees C, which is considered to be due to the thermally excited random motion of Si adatoms