A. A. Williams

The influence of Sb as a surfactant on the strain relaxation of Ge/Si(001)

We have investigated by the use of surface x‐ray diffraction the initial strain relaxation of Ge on Si(001) when a ‘‘surfactant’’ layer of Sb [0.7 monolayers (ML)] is present. Due to the high sensitivity of the technique to lateral strain in the overlayer, we have been able to observe directly the onset of strain relaxation at a coverage of 9–10 ML. This strain relief proceeds gradually as a function of coverage, but unlike the case without an Sb surfactant, it was not possible to relax the overlayer fully. No bulklike Ge was seen even up to a coverage of ≊55 ML. Concurrent specular reflectivity measurements also showed that the overlayer formed in a layer‐by‐layer mode up to the same level. These results differ quite markedly from those obtained without the surfactant layer, where several stages of island formation and strain relaxation are seen. They show dramatically how the modification of surface energies by the presence of a surfactant can affect the morphology of, and strain in, a lattice mismatched overlayer. In addition, they are direct confirmation that the initial strain relaxation mechanism in operation when a surfactant is not present is the formation of coherent Ge islands, rather than that of dislocations.

X-ray reflectivity study of surface-initiated melting: Density profile at the Pb(110) surface

The angular dependence of the X-ray reflectivity was measured on the Pb(110) surface as a function of temperature. At temperatures just below the bulk melting point, the measurements reveal on the crystal surface the presence of a thin layer of liquid-like density. The thickness and density change in the quasiliquid layer are determined, as well as the widths of the solid-quasiliquid and quasiliquid-vapor interfaces.

X-ray reflectivity of an Sb delta-doping layer in silicon

X‐ray reflectivity measurements were made on Si(001) crystals containing a delta‐doping layer of Sb atoms a few nanometers below the surface. The measurements show the Sb doping profile to be abrupt towards the substrate side of the sample and to decay towards the surface with a characteristic decay length of 1.01 nm.

Structure determination of the Ge(111)−2×1-Sb surface using X-ray diffraction

Abstract The atomic structure of the 2x1 reconstruction induced by the adsorption of Sb on the Ge(111) surface has been determined by X-ray diffraction. The projection of the adsorption sites onto the surface plane was derived from the in-plane structure factor amplitudes. The heights of the Sb atoms above the surface plane and their precise positions relative to the substrate lattice were obtained from scans along the integer-order rods of scattering perpendicular to the surface. The adsorbed Sb atoms are found to form three domains of zig-zag chains, saturating the dangling bonds of Ge atoms in the top layer. The chains are tilted by 5.6(8)°.

The initial stages of growth of Ge on Si(001) studied by X-ray diffraction

The structure of an ultra-thin epitaxial Ge layer during in situ deposition onto a Si(001) surface has been investigated. Peaks arising from the 2*1 reconstruction disappear at a coverage of approximately=ML. The layer is epitaxial with respect to the substrate up to a coverage of approximately=5 Ml, beyond which the strained layer relaxes gradually. At a coverage of 10 ML the lateral strain is reduced to 2.2% compared with 4.0% in the unrelaxed layer.

Strain Relaxation in Ge/Si(001) Studied Using X-Ray Diffraction

Grazing incidence x-ray diffraction has been utilized to give a direct measure of the lateral strain distribution during in-situ MBE deposition of Ge onto Si(001). Differences in growth conditions and thermal treatment result in significantly different strain relaxation behavior. The results demonstrate the gradual relaxation of strain, which is incomplete at a coverage of 11 monolayers. At this coverage the strain distribution exhibits two components, one of which is almost fully relaxed and the other having a range of lattice spacings intermediate between those for bulk Si and Ge. The results are discussed in terms of current models for strain relaxation.

Surface science lettersX-ray reflectivity study of surface-initiated melting: Density profile at the Pb(110) surface

The angular dependence of the X-ray reflectivity was measured on the Pb(110) surface as a function of temperature. At temperatures just below the bulk melting point, the measurements reveal on the crystal surface the presence of a thin layer of liquid-like density. The thickness and density change in the quasiliquid layer are determined, as well as the widths of the solid-quasiliquid and quasiliquid-vapor interfaces.