STRUCTURES OF ATOMIC STEPS ON THE 7X7 RECONSTRUCTED SI(111) SURFACE

We have carried out a systematic study of the structures of mono bilay er atomic steps on the 7X7 reconstructed Si(111) surface whose step ed ges are parallel to the unit-cell boundary. Atomic steps in all possib le 14 step groups have been observed; thus a complete picture of the s tep structure is presented. The upper step edges of ten groups termina te at unit-cell boundaries, while the remaining four groups do not. Th e step structure formed is the result of two factors competing to mini mize the surface free energy: the structural integrity of the upper st ep edge and the width of the transition region at the lower terrace. T here is evidence that step formation is influenced by the annealing me thod used.