Phase transition of silicon-nitride monolayer on Si(111) surface observed by scanning tunneling microscopy

Phase transition of a silicon-nitride (SiN) monolayer on a Si(111) surface was observed by ultrahigh vacuum scanning tunneling microscopy (UHV-STM). T he STM image showed an 8/3 x 8/3 regular array of dots on the Si(111)-8 x 8 surface. After annealing at 1030 degreesC, the image changed to a 3/4 x 3/ 4 regular array of dots, which corresponds to the quadruplet surface. The r otation angle of one of the four quadruplet domains was directly measured a nd found to be about 10 degrees with respect to the crystallographic struct ure of the Si(111) surface. Further annealing at 1050 degreesC changed the 3/4 x 3/4 structure to the 7 x 7 structure, which means that the SiN monola yer decomposed and was removed from the surface completely. Overall anneali ng behavior observed in our STM experiments,vas consistent with low-energy electron diffraction (LEED) and electron energy loss spectroscopy (EELS) da ta reported previously.