L. Smit

Ion scattering determination of the atomic arrangement at polished diamond(111) surfaces before and after reconstruction

The technique of medium-energy ion scattering combined with shadowing and blocking is used to obtain information on the positions of atoms at (111) diamond surfaces, both as-polished and after thermally induced reconstruction. The data for the unreconstructed (hydrogen-terminated) surface show that the outermost atomic monolayer is relaxed inward by ≈ 0.05 A, rather less than has been predicted. After heating to the reconstruction temperature of 950°C, the surface exhibits a predominantly single domain (2 × 1) LEED pattern, and ion scattering reveals that two monolayers of surface atoms have acquired large displacements. Of the various models which have been proposed for this reconstruction, only the π-bonded chain model is compatible with the data, detailed consideration of which indicates that alternate pairs of chain atoms must also be strongly dimerized. A large enhancement of thermal vibration amplitudes is found at both surfaces.

The relaxed GaAs(110) surface: Are bond-lengths conserved?

Abstract Medium-energy ion scattering on the relaxed GaAs(110) surface measures a value of 29° ± 3° for the rotation of the top Ga-As atomic chains. Measurements in a scattering geometry especially sensitive to the surface-parallel displacements concomitant with such a bond rotation, show that bond-lengths in the relaxed surface remain unchanged.

Determination of atomic positions in the GaSb(110) and InAs(110) surfaces by medium-energy ion blocking

Abstract In medium energy ion scattering measurements on cleaved GaSb(110) and InAs(110) backscattering contributions from both elements in the compound are resolved. Measurements of blocking directions for each signal provide an independent, real-space determination of the surface relaxation. Bonds connecting first-layer atoms are rotated through an angle ω = 28.5° ± 2.6° out of the (110) plane for GaSb and through ω = 30.0° ± 2.4° for InAs.Bond lenghts are essentially conserved. The root-mean-square thermal vibration amplitudes of the surface atoms are enhanced by a factor 1.6–1.7.

Interface electronic structure of Pb on GaAs(001)

The electronic structure of two‐dimensional, ordered Pb overlayers in submonolayer coverages on MBE grown GaAs(001) surfaces has been studied by angle‐resolved photoemission using synchrotron radiation. A Pb(6s) derived interface state of Δ1 symmetry has been identified in the heteropolar gap of GaAs at an energy of −8.3 eV below the valence‐band maximum. Two surface resonances of dangling bond character and of inplane character ( px−py) are located near the top of the valence bands, at −0.4 eV and −2.0 eV, respectively. High resolution studies of Ga(3d), As(3d), and Pb(5d) core levels show that there is no significant chemical interaction between the overlayer and the substrate.

Ion-beam crystallography of the GaSb (110) surface

Abstract We report the first successful structure determination of a reconstructed compound semiconductor based on mass-resolved RBS. For the GaSb (110) surface blocking directions have been determined for ions backscattered from the Ga atoms and from the Sb atoms in the near-surface region. The reconstruction is characterised by a rotation of the bond between toplayer Sb and Ga atoms. We find a bond rotation angle of (29.5±1.5)°, which is close to a ELEED value recently reported for this surface. The rms vibrational amplitude of surface atoms is enhanced by a factor 1.5 with respect to the bulk value.

Core level binding energy shifts for reconstructed GaAs(001) surfaces

Abstract With the use of surface-sensitive photoemission spectroscopy 3d-core level binding energy shifts have been determined for surface atoms in reconstructed MBE-grown GaAs (001) surfaces. An analysis of As(3d) shifts suggests that the C(4×4) structure is produced by chemisorption of arsenic on the As-rich 2×4 reconstructed surface.

Disordering effect of Al clusters on GaAs(110) measured with medium-energy ion scattering

Abstract The effect of room-temperature adsorption of Al on the surface structure of GaAs(110) has been investigated with medium-energy ion scattering using shadowing and blocking. For the coverage range studied (0 to 2.8 × 1015 Al atoms cm-2) we have observed the formation of three-dimensional islands. In between clusters the surface relaxation is identical to that of the atomically clean surface. Under the clusters the number of substrate atoms visible to the incident ion beam has increased by an amount equivalent to one monolayer. This indicates a local chemical interaction which leaves the substrate in a disordered state.

Atomic Geometry and Dynamics of the InAs(110) Surface

The structure of the relaxed InAs (110) surface has been determined by massresolved Rutherford backscattering of He+ ions. Measurements of ion blocking angles identify the relaxation as a bond-length conserving rotation of the In-As surface bond by an angle of ω = 29° −4° +5° out of the surface plane. The r.m.s. vibration amplitudes of surface atoms are enhanced by a factor 1.6 with respect to the bulk values.