VARIABLE LOW-TEMPERATURE SCANNING-TUNNELING-MICROSCOPY STUDY OF SI(001) - NATURE OF THE 2X1-]C(2X4) PHASE-TRANSITION

We have studied the Si(001) surface from 120 K to room temperature usi ng a variable low-temperature scanning tunneling microscope, Complemen tary investigations were carried out on two distinctly different types of surfaces: first, the normal 2 x 1 surface and second, the 2 x n (4 <n<12) surface. For the 2 x 1 surface, the defects are scattered rando mly, By plotting out the fraction of buckled dimers as a function of t emperature, we find a slow transition from predominantly c(2 x 4) at l ow temperature to mostly 2 x 1 at room temperature for a defect concen tration of about 8.5%. For the 2 x n surface, the much larger number o f surface vacancies form long-range ordered chains, dividing the surfa ce into many short dimer segments. These dimer segments predominantly appear to be unbuckled at room temperature. Upon cooling to 190 K, we observe very little change in the amount of buckling. The implications of this result are discussed. (C) 1996 American Vacuum Society.