STEP-HEIGHT MIXTURES ON VICINAL SI(111) SURFACES

Scanning tunneling microscopy (STM) and high resolution low-energy electron diffraction measurements on vicinal (stepped) Si(111) surfaces reveal mixtures of single- and triple-layer-height steps, with the density of triples increasing with total step density. The diffraction signature of the step mixtures is an incommensurate spacing; however, the STM data show no periodic sequence of singles and triples. Instead, there is a random sequence with specific ratios of the lengths of terraces bounded by steps of different heights, quantitatively consistent with the energetic ground state for elastically interacting steps.