High resolution REM studies of Si(5 5 12) surfaces and their roughening phase transition

High resolution reflection electron microscopy has been applied to studies of a high index Si(5 5 12) surface at a sub-unit cell resolution. Lattice fringes with different widths were found to be directly corresponding to the subunits of the (5 5 12) surface. Defects on the surface were resolved as nano-facets with close orientation to (5 5 12). (13 13 31) and (7 7 17) facets were identified based on the subunit arrangement. An incommensurate structure (q=a*bk/2.43) was revealed at a temperature just below the roughening transition. Formation of an incommensurate structure as well as defects was discussed in terms of surface steps.