Kinetics in surface reconstructions on GaAs(001)

We have successfully controlled the surface structures of GaAs(001) by changing incident As-molecular species. Under As4 fluxes, the c(4 x 4) reconstruction with Ga-As dimers [c(4 x 4)alpha structure] is obtained, but the formation of three As-As dimer structures [c(4 x 4)beta structure] is kinetically limited. On the other hand, the structure change from the (2 x 4), through c(4 x 4)alpha, to c(4 x 4)beta phases is observed under As2 fluxes. We found that the c(4 x 4)alpha structure is energetically metastable and provides a kinetic pathway for the structure change between the (2 x 4) and c(4 x 4)beta phases under As2 fluxes.     

New Ga-enriched reconstructions on the GaAs(001) surface

To prepare structure-ordered GaAs(001) surfaces at low temperatures, GaAs(001) surfaces coated with native oxides were exposed in an atomic hydrogen flow in the temperature range 280–450 °C. The new Ga-enriched GaAs(001) surfaces with the (4 × 4) and (2 × 4)/c(2 × 8) reconstructions were prepared and studied by the methods of X-ray photoelectron spectroscopy, low-energy electron diffraction, and high-resolution characteristic electron energy loss spectroscopy. For the GaAs(001)-(2 × 4) surface, the structure of the Ga-stabilized surface has been proposed and ab initio computed within the (2 × 4) Ga-trimer unit cell model.     

Surface reconstructions of MnAs grown on GaAs(001)

During epitaxial growth of MnAs on GaAs(001) by molecular-beam epitaxy (MBE) the surface exhibits various reconstructions depending on the growth conditions. These reconstructions have been studied during growth by reflection high-energy electron diffraction (RHEED) and reflectance difference spectroscopy (RDS). A feature sensitive to the surface structure was identified in the RD spectra. After growth, the (1×2) and (1×1) reconstructions were cooled down to room temperature and imaged in ultrahigh vacuum with a conventional scanning tunneling microscope (STM). Atomic-scale images of these surfaces are presented.     

Mn/GaAs(001)的表面再构与Mn的磁矩研究

通过第一性原理计算，系统地研究了Mn/GaAs(001)表面的各种再构和相应的局域电子态密度分布，以及表面上Mn的磁矩与各种再构间的对应关系.结果发现，Mn的行为类似电荷施主，将向GaAs表面提供电子，数量依表面的需求而定；直接与Mn的磁矩相联系的d轨道，既可以向GaAs表面施予电子，以弥补Mn的s电子的不足，又可以吸纳因GaAs表面饱和而富余的s电子.这些概念可有效地简化对金属引起的半导体表面再构的理论描述. 关键词： 表面再构 Mn/GaAs(001) 第一性原理计算     

(4×2) and (2×4) reconstructions of GaAs and InP(001) surfaces

Received: 21 March 1997/Accepted: 12 August 1997     

Atomic reconstructions and electronic states on the GaAs(001) surface with the adsorbed Sb and Cs layers

In experiments on the adsorption and thermal desorption of Cs on GaAs(001) surfaces with various atomic reconstructions and compositions including those enriched in the cation (gallium) and in the anions (arsenic and antimony), the correlation in the behavior of the atomic structure and the surface electronic states, which determine the band bending, has been established. The cesium adsorption on the anion-rich surfaces results in both the similar disordering of the atomic structure and in the close dose dependences of the band bending, while the adsorption on the Ga-rich surface is ordered and results in the qualitatively different dose dependence, which has several maxima and minima. In the Cs desorption and the subsequent adsorption-desorption cycles, the stabilizing effect of Sb on the atomic structure and the electronic states of the Cs/Sb/GaAs(001) surface has been revealed.     

The GaAs (001)−c(4×4) and (2×4) reconstructions: A comparative photoemission study

Surface sensitive photoemission measurements of As(3d) core levels give new experimental evidence that the MBE-grown GaAs (0 0 1)?c(4×4) surface is richer in As than the 2×4 surface and that it is produced by an As overlayer chemisorbed onto the As atoms terminating the polar GaAs(0 0 1) surface. A study of As thermal desorption shows that the c(4×4) structure persists over a broad range of surface stoichiometry.     

Immobilization of avidin on (001) GaAs surface

To reliably immobilize different biomoieties on surfaces of III-V semiconductors is one of the most critical issues in the development of biodetector devices based on the optical/electronic properties of these materials. Herein we demonstrate the successful immobilization of avidin, a robust and well-studied protein, on a (001) GaAs surface. The immobilization was investigated via specific binding to biotin, which was connected to the GaAs surface through commercially available long- or short-chain amino group terminated alkanethiols (HS(CH₂)₁₁NH₂ or HS(CH₂)₂NH₂), or through a biotinylated thiol synthesized in our laboratory. The immobilization performance was evaluated by photoluminescence and fluorescence microscopy measurements. We found that the biotinylated thiol mixed with a diluent thiol provides the highest avidin immobilization efficiency. PACS 81.05.Ea; 82.65.+r; 87.14.Ee     

Atomic structures of gallium-rich GaAs(001)-4×2 and GaAs(001)-4×6 surfaces

Scanning tunneling microscopy is applied for the first time to an atomic-resolution investigation of the 4×2 and 4×6 phases on a gallium-rich GaAs(001) surface obtained by molecular-beam epitaxy and migration-enhanced epitaxy. A unified structural model is proposed with consideration of the results of experiments and first-principles calculations of the total energy. In this model the 4×2 phase consists of two Ga dimers in the top layer and a Ga dimer in the third layer, and the 4×6 phase is matched to periodically arranged Ga clusters at the corners of a 4×6 unit cell on top of the 4×2 phase. Zh. éksp. Teor. Fiz. 111, 1858–1868 (May 1997)     

Vickers indentation of thin GaAs (001) samples

Thin GaAs (001) samples have been deformed using a Vickers indenter at temperatures around 350°C under loads ranging between 0.4 and 2.35?N. Optical microscopy, optical interferometry and transmission electron microscopy were used to obtain a better understanding of the plastic flow through the specimens. Anisotropic plastic flow through the thin foils could be detected at the face opposite to the indented face under large loads. In this case pile-up at the indented surface progressively vanished. An α-dislocation-based model describing the material flow through the samples is proposed.