ErSi2-x nanowires (NWs) were grown on Si(0 0 1). The orientation relationships between ErSi2-x and Si(0 0 1) were determined to be ErSi2-x[0 0 0 1]//Si[1 1 0], ErSi2-x(1 1 0 0)//Si(0 0 1) and ErSi2-x[1 1 2 0]//Si[1 1 0], ErSi2-x(1 1 0 0)//Si(0 0 1). Due to the anisotropy of lattice matches on Si(0 0 1), ErSi2-x has a preferred direction of growth. Since Si is expected to be the dominant diffusing species during intermixing, the observation of NWs surrounded by recessed silicon steps is attributed to the release of Si atoms causing retreat of the steps. Owing to the difference in growth shape and Er deposition rate, the vacancy ordering structure along c-axis is more ordered in NWs than in thin-film system. The analysis indicates that the variation of vacancy ordering structures depends on the strain relaxation on the surface. (c) 2004 Elsevier B.V. All rights reserved.