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). The STM image showed an 8/3×8/3 regular array of dots on the Si(111)-8×8 surface. After annealing at 1030°C, the image changed to a 3/4×3/4 regular array of dots, which corresponds to the quadruplet surface. The rotation angle of one of the four quadruplet domains was directly measured and found to be about 10° with respect to the crystallographic structure of the Si(111) surface. Further annealing at 1050°C changed the 3/4×3/4 structure to the 7×7 structure, which means that the SiN monolayer decomposed and was removed from the surface completely. Overall annealing behavior observed in our STM experiments was consistent with low-energy electron diffraction (LEED) and electron energy loss spectroscopy (EELS) data reported previously.