Structural Correlation among Different Phases in the Initial Stage of Epitaxial Growth of Au on Si(111)

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Abstract
Structures created on the Si(111) substrate in the presence of Au atoms corresponding to coverages (θ; Au) of ∼0.7–1.4 monolayers (ML) are discussed on the basis of the observed scanning tunneling microscopy images. At small θ; Au's ( ∼0.7–1.0 ML), a √3×√3 phase and a less-ordered phase coexist, the fractional area of the latter being increased with increasing θ; Au, and at larger θ; Au's (\stackrel>∼ 1.1 ML), a 6×6 phase appears as a single phase, in agreement with previous reports. It is shown that the less-ordered phase coexisting with the √3×√3 phase already has a close relation to the 6×6 phase in structure. The most fundamental structure of the 6×6 phase is seen at a large θ; Au of ∼1.4 ML, in which a layer of Au atoms sits on the Si(111) substrate incommensurately. As θ; Au decreases, some Au atoms appears to be removed with a periodicity of 6×6. The Au coverage of the √3×√3 phase seems to be ∼2/3 ML.