Comparison of LEED and STM measurements of vicinal Si(111)

LEED beam-profile and STM measurements have been used in combination to study the ordering of stepped Si(111) surfaces misoriented by 4° toward the [***211] direction. LEED measurements show that ordering of the surface steps is dependent on the thermal history of the sample, but give little clue about the reasons. An initial cleaning at 1250°C followed by slow cooling is required to obtain a well-ordered step structure. STM measurements show that cleaning at a lower temperature (850°C) results in a surface containing highly disordered patches which are possibly correlated with residual carbon. These disordered regions evidently inhibit step order. STM images of rapidly quenched surfaces show a very different sort of disorder consisting of long wavelength (5–10 nm) corrugations of rms vertical amplitude 2 nm.