In this study, low energy electron diffraction (LEED), valence band, and core-level photoemission were used to establish the correct Sn 4d line shape of both the v3 × v3 and 3 × 3 phases of Sn/Ge(111). It was found that the Sn 4d and valence band spectra of these phases are similar.

An evolution of an apparent 3 × 3 low-energy electron diffraction (LEED) pattern has been observed for the Sn1-xSix/Si(1 1 1) v3 × v3 surface alloy. The origin of this additional diffraction has been investigated in detail by scanning tunneling microscopy (STM). The 3 × 3 diffraction, which appears after annealing, is associated with the arrangement of the Sn and substitutional Si atoms in the surface layer, forming many local structures such as honeycombs, hexagons, and atomic lines. As revealed by Fourier-transforms of the STM-images, these local structures are the origins of the 3 × 3 diffraction and a weak 23×3 streaky background superposed on the 3 × 3 LEED pattern. © 2003 Elsevier Science B.V. All rights reserved.

The √3×√3, √39×√39, and 6×6 phases of Ag/Ge(111) have been studied by angle-resolved photoemission and low-energy electron diffraction. The √3×√3 surface, formed at a one-monolayer (ML) Ag coverage, shows a metallic behavior with two partially occupied surface bands resulting from a tiny amount of extra Ag atoms on the surface. The √3×√3 surface transforms into a √39×√39 periodicity, below ∼250 K, when a small amount of Ag is added to the surface. The presence of the additional Ag atoms leads to an increased filling of two partially occupied surface bands. By depositing ∼0.2 ML of Ag on the √3×√3 surface, it transforms into a 6×6 periodicity. We observe an interesting transition from the metallic √3×√3 and √39×√39 phases to a semiconducting phase for the 6×6 surface, with a gap of around 0.2 eV with respect to the Fermi level. On the 6×6 surface, the lower band of the partially occupied surface bands is pulled down entirely below the Fermi level while the upper band is missing in the photoemission spectra. These changes result in the observed band gap.

The α-√3×√3, β-√3×√3, and 6×6 surfaces of Au/Si(111) have been studied by angle-resolved photoelectron spectroscopy (ARPES). The α-√3×√3 surface shows four surface state bands, one of which is a dispersing metallic band. Except for one nondispersing band near the Fermi level, the β-√3×√3 surface shows surface bands that are similar to those of α-√3×√3. Eight surface state bands have been found on the 6×6 surface instead of two as reported in the literature. Seven of these surface states are broadened into three, when the 6×6 phase is transformed into the quenched β-√3×√3 phase just by annealing followed by quick cooling. The transition between the 6×6 and quenched β-√3×√3 phases is consistent with a crystal-glass transition.

A √21×√21 reconstruction can be formed by either Ag or Au adsorption on the Ag/Si(111) √3×√3 surface. The electronic structures determined by angle-resolved photoemission from these two √21×√21 surfaces show clear similarities. The presence of the extra Ag or Au adatoms results in a metallic surface with two surface state bands near the Fermi level. Only one of these bands crosses the Fermi level instead of two as reported in the literature. A tiny amount of Ag deposited onto the √21×√21-Ag surface below 100 K transforms it into a 6×6 periodicity. The additional Ag leads to an interesting transition from the metallic √21×√21 surface to a semiconducting 6×6 surface with a gap of about 0.2 eV with respect to the Fermi level.

Submonolayer coverages of Au on Si(111), known as the 5×2, α-√3×√3, β-√3×√3, 2√21×2√21, and 6×6 surfaces, have been investigated by low-energy electron diffraction and photoelectron spectroscopy. Three Si 2p surface components on the 5×2 surface, and four surface components on the α-√3×√3, quenched β-√3×√3, and 6×6 surfaces have been identified by surface sensitive high resolution core-level spectroscopy. The photoemission data of the α-√3×√3, the 6×6 and the quenched β-√3×√3 phases are discussed in terms of extra Au adatoms on the √3×√3 surface described by the ideal 1 ML conjugate honeycomb chained trimer model. The similarity between the 6×6 and the quenched β-√3×√3 surface is obvious from the decomposition of the Si 2p spectra, suggesting an order-disorder relation.

A small amount of Au atoms deposited at room temperature transforms the Ag/Ge(1 1 1)v3 × v3 surface into a v 39 × v39 surface. The presence of the Au atoms leads to downward shifts and modifications of the surface state bands compared to the initial v3 × v3 surface. Further deposition of Au on the v39 × v39 surface changes it into a 6 × 6 periodicity. At the same time the surface electronic structure changes from a metallic to a semiconducting phase with a gap of around 0.2 eV with respect to the Fermi-level. Finally, the 6 × 6 phase transforms into a new 2v3 × 2v3 phase when more Au is added, and the surface switches back to a metallic state. © 2003 Elsevier Science B.V. All rights reserved.

The 6 × 6 and v39 × v39 phases on Ag/Ge(1 1 1) have been studied by scanning tunneling microscopy (STM). Four types of 6 × 6 configurations are found which all consist of a v3 × v3 layer with six extra Ag adatoms per 6 × 6 unit cell. These reconstructions show either mirrored or complementary relations. We observe interesting transitions between the different 6 × 6 reconstructions. The v39 × v39 surface appears to have five extra Ag atoms per unit cell. By using various tip biases, we show that the v39 × v39 domain orientation can be changed. Surface structure models of the v39 × v39 and 6 × 6 phases are proposed based on the HCT structure of the underlying v3 × v3 surface. © 2003 Elsevier Science B.V. All rights reserved.

The 6×6 and v39×v39 phases of Ag/Ge(1 1 1) have been studied by scanning tunneling microscopy (STM). Surface atomic structures of the 6×6 and the v39×v39 phase are proposed in terms of additional Ag adatoms on top of a v3×v3 layer described by the honeycomb-chain-trimer (HCT) model. By varying the STM tip bias, the reconstruction can be changed reversibly between the v39×v39 and the 6×6 phase. Besides the switching between two different phases, it is also possible to flip the domain orientation of the v39×v39 phase. The mechanisms of the reconstruction transformation have been discussed in terms of the role of the STM tip. © 2003 Elsevier B.V. All rights reserved.