Analysis of mesoscopic patterns formed by the Au-induced faceting of vicinalSi(001)

Abstract

Vicinal Si(001) surfaces with ≈4° miscut toward [110] consist of ordered terraces that are separated by a double step every 4 nm. Adsorptionof Au at 800–900 °C changes the step morphology dramatically: after a critical Au coverage of1/3 ML is reached, Au condenses from an initially formed lattice gas into a(5 × 3.2) reconstruction on newly formed (001) terraces. The steps of the vicinal surface areaccumulated in irregular step bunches to conserve the macroscopic miscut. With increasingAu coverage the step bunches are transformed into well defined facets. The ultimate facetorientation depends on the adsorption temperature, although at temperatures aboveT = 800 °C only (001) terraces and (119) facets are observed. Depending on the depositiontemperature, the terraces and facets exhibit a periodicity from 200 nm to4 µm and a structural length of up to several millimetres. Illumination with white light undergrazing incidence results in a colourful striped pattern in an optical microscope. Anovel in situ light diffraction experiment is presented, that is perfectly matched tothe mesoscopic dimensions of the faceted surfaces. Illumination with a He–Nelaser during and after deposition results in complex diffraction patterns that canbe used to estimate the length of the terraces. The temperature dependence ofthe terrace length shows an Arrhenius behaviour with an activation energy ofEA≈2.8 eV during the initial stages of the faceting; atT = 825 °C the terraces extend with a constant velocity of30 µm s−1. This value is in excellent agreement with earlier low energy electron microscopymeasurements.