Hanmin Zhang

Experimental study of the relationship between temperature and adhesive forces for low-alloyed steel, stainless steel, and titanium using atomic force microscopy in ultrahigh vacuum

Experimental study of the relationship between temperature and adhesive forces for low-alloyed steel, stainless steel and titanium using atomic force microscopy in ultra-high vacuum

Surface electronic structure of K- and Cs-induced √21×√21 phases on Ag∕Si(111)√3×√3

Surface electronic structure of K and Cs-induced sqrt21xsqrt21 phases on Ag/Si(111)sqrt3xsqrt3

Surface structure of Si(100) with submonolayer coverages of C

Abstract We report a combined STM, LEED and AES study of Si(100) surfaces prepared by coevaporation from two MBE-sources with Si and SiC, respectively. The flux from the SiC source contains 10% C, enabling studies of deposited layers with C-concentrations in the range 0–10%. After room temperature deposition, the structures have been annealed at 600 °C to generate a c(4×4) reconstruction. This has previously been reported to contain from 0.0 to 0.5 monolayers (ML) of C. Annealing at 800 °C irreversibly transforms the c(4×4) surface to a 2×1-reconstructed surface that contains precipitates of SiC. Since only 0.07 ML of C is needed to have 98% of the surface covered with the c(4×4) reconstruction, we conclude that the c(4×4) reconstruction is impurity-induced rather than having C-atoms in well defined positions within each unit cell. The c(4×4) reconstruction is attributed to a basic structure containing buckled parallel ad-dimers, which in approximately 50% of the reconstructed unit cells is decorated with perpendicular dimers.

HIGH-RESOLUTION Si2p CORE-LEVEL STUDY OF THE K/Si(111)-(3 × 1) SURFACE

The structure of the K/Si(111)-(3 × 1) surface was studied by high-resolution core-level photoelectron spectroscopy. Five surface components were observed in the Si 2p core-level spectra. Compared to the bulk component, three components are shifted to lower and two to higher binding energies. The two components with the lowest binding energies are assigned to the top-layer Si atoms bonded to the K atoms with different configurations. The component with highest binding energy has a contribution from the π-bonded Si atoms of the top layer. The two other components originate from the Si atoms of the second and third layers.

Surface electronic structure of the √3 × √3, √39 × √39 and 6 × 6 surfaces of Ag/Ge(111): observation of a metal to semiconductor transition

Deposition of 1 monolayer (ML) of Ag on the clean Ge(1 1 1) surface, followed by annealing at 300°C for 2 min, results in a sharp √3 x √3 low-energy electron diffraction (LEED) pattern. This surface transforms into a √39 x √39 surface, as observed by LEED, due to a tiny amount of additional Ag atoms when the temperature is below approximately -20°C. The presence of the additional Ag leads to an increased filling of two partially occupied surface bands. By depositing approximately 0.2 ML of Ag on the √3 × √3 surface, it transforms into a 6 x 6 periodicity. The addition of Ag leads to an interesting transition from the metallic surfaces (√3 x √3 and √39 x √39) to the semiconducting 6 x 6 surface with a gap of around 0.2 eV with respect to the Fermi-level. On the 6 x 6 phase, the lower one of the partially occupied surface bands of the √3 x √3 and √39 x √39 surfaces seems to be entirely pulled down below the Fermi-level, while the upper one is missing. The electronic structures of the different Ag/Ge(1 1 1) surfaces are also discussed in comparison with the Ag/Si(1 1 1) surfaces.

Structural Investigation of the So-Called Ca/Si(111)-(5×1) Surface

We have investigated the geometric structure of the so-called Ca/Si(111)-(5×1) surface using low-energy electron diffraction (LEED) and high-resolution core-level photoelectron spectroscopy. In LEED, dim extra spots besides the ×5 spots were observed after cooling the sample to 100 K. The positions of these dim spots reveal that this phase has a ×2 periodicity along its one-dimensional (1D) chains. In Si 2p core-level spectra, we observed five surface components. By considering the energy shift and intensity of each surface component and the 0.3 ML Ca coverage, we propose a structural model of this surface.

High-resolution Si 2p core-level and low-energy electron diffraction studies of the Ca/Si(1 1 1)-(3 × 2) surface

We have investigated the surface structure of the Ca/Si(1 1 1)-(3 × 2) surface using low-energy electron diffraction (LEED) and high-resolution core-level photoelectron spectroscopy. Weak ×2 streak ...

Surface electronic structures of Au-induced reconstructions on the Ag/Ge(111)sqrt3xsqrt3 surface

Surface electronic structures of Au-induced reconstructions on the Ag/Ge(111)sqrt3xsqrt3 surface

High-resolution core-level study of the Ca/Si(1 1 1)-(2×1) surface

We have investigated the geometric structure of the Ca/Si(1 1 1)-(2×1) surface using low-energy electron diffraction (LEED) and high-resolution core-level photoelectron spectroscopy. A clear (2×1) ...

Origin of 3 × 3 diffraction on the Sn1-xSix/Si(1 1 1) v3 × v3 surface

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.