Observation of the Ag/Si(111) system using a high-resolution ultra-high vacuum scanning electron microscope

Abstract

Abstract Secondary electron (SE) imaging with a new ultra-high vacuum scanning electron microscope (UHV-SEM) has been employed to study the Ag/Si(111) system. Domains of the 3 × 3 -Ag or 6 × 1(3 × 1)-Ag structure partially covering a Si(111) surface are clearly contrasted against the 7 × 7 region. No sample bias is applied. Two-dimensional (2D) domain morphology differs completely between 3 × 3 - Ag and 6× 1(3× 1)-Ag. The 3 × 3 - Ag nucleates at any of (1) the steps, (2) the steps plus phase boundaries, and (3) the steps plus phase boundaries plus mid-domains, of the Si(111)-7 × 7 substrate, depending on both the step spacing and the substrate temperature. An SE image for Ag deposition at ∽ room-temperature shows regular arrangements having the same periodicity as the 7 × 7 unit meshes. This implies that 2D Ag clusters, ∽ 2.3 nm in size and composed probably of 36 Ag atoms, resulting from the preferential Ag deposition onto faulted halves of the 7 × 7 unit meshes are observed. In our previous papers, the presence of areas with three sorts of brightness for samples with the 7 × 7 and the 3 × 3 - Ag structure were reported. This is shown to be caused by the remaining 1 × 1 domains among the 7×7 domains, resulting from quenching during the substrate cleaning. Difference between 1 × 1 and 7 × 7 domains and contrast due to steps are observed even without Ag deposition.