NATURE OF THE STEP-HEIGHT TRANSITION ON VICINAL SI(001) SURFACES

The Si(001)2 x 1 surface is expected to undergo a phase transition from single- to double-atomic-height steps with increasing angle of miscut. Here we show that this transition is quite different than previously believed, involving something like a "devil's staircase" of transitions in a mixed phase consisting of a complex sequence of single and double steps. Even at low angles, where only single steps occur, the areas of 2 x 1 and 1 x 2 regions are unequal, in agreement with recent experimental results.