THERMAL-DESORPTION OF NA FROM NA SI(111)3X1 - IN-SITU OBSERVATION OF THE 3X1-TO-7X7 STRUCTURAL TRANSFORMATION USING A HIGH-TEMPERATURE SCANNING TUNNELING MICROSCOPE/

The Na-stabilised Si(111)3 X 1 phase has been investigated upon anneal ing. At temperatures between 410 and 540 degrees C the Na desorbs grad ually, resulting in a structural transformation to the 7 x 7 reconstru ction. The use of a high-temperature STM enabled the in situ observati on of this morphological transition, revealing a variety of intermedia te Si(111) reconstructions such as 2 X 2, c4 X 2, root 3 X root 3 R30 degrees, 5 X 5, 7 X 7 and 9 x 9 on Na-free areas, before the entire su rface reconstructed to the 7 x 7 structure at higher temperatures (800 degrees C). The transition is accompanied by a pronounced mass transp ort and can be explained in terms of the removal of excess Si atoms fr om local Na-free 3 X 1 formations.