Robert E. Martinez

High coverage phases of Pb on the Si(111) surface: structures and phase transitions

Abstract We have studied the high coverage phases of Pb on a Si(111) surface using a scanning tunneling microscope (STM). For annealed samples, 1 ML Pb forms an incommensurate (IC) phase composed of alternating domains of two types of trimer regions and a quasi-1 × 1 region. The detailed morphology of the domains depends sensitively on the stress fields resulting from imperfections on the surface. We observe that the stress fields originating from nearby reconstructions transform the IC phase into a 1 × 1 structure. The transformation involves only small displacements of Pb atoms. We observe that the 1/3 ML √3 phase suppresses the formation of trimers in the 1 × 1 phase, but Pb islands and Pb clusters enhance their formation. The same structural transformation from IC to 1 × 1 can occur at high temperatures. The local transformation temperature depends strongly on surface imperfections nearby. The high coverage phase for room temperature (RT) deposition, Pb/Si-7 × 7, is also resolved. Pb deposition on this phase causes interesting changes in its morphology. The 1 × 1 adatoms in Pb/Si-7 × 7 appear to relax normal to the surface relative to the surrounding unreconstructed regions. The formation of the IC phase for Pb/Si(111) offers a novel system for understanding incommensurate surface reconstructions in a chemisorption system.

Low-temperature homoepitaxial growth on Si(111) mediated by thin overlayers of Au

High quality homoepitaxial growth of Si on Si(111) through an overlayer of Au is shown to occur at 450–500 °C, far below the temperature required for growth of Si of similar quality on bare Si(111). Films of unlimited thickness can be obtained with excellent crystalline quality, as revealed by Rutherford backscattering spectrometry ion channeling measurements (χmin=2.2%). A distinct range of Au coverage (0.4–1.0 monolayer) results in the best quality epitaxy, with no measurable amount of Au trapped at either the interface or within the grown films. Cross‐sectional transmission electron microscopy reveals that in films grown with Au coverages below and above the optimum range, the predominant defects are twins on (111) planes and Au inclusions, respectively.

Surface stresses in atomic reconstructions of lead on silicon (111)

Abstract We have measured the intrinsic surface stresses associated with reconstructions of Pb adsorbed on Si(111). By measuring the stress in two different √3 × √3 reconstructions having 1 3 and 1 6 ML Pb coverage, we find that both Pb and identical surface stresses of 1.75 ± 0.20 eV/1 × 1 cell. This value is in excellent agreement with theoretical calculations for Si adatoms in the √3 × √3 reconstruction. A comparison with calculations for Ga √3 × √3 adatoms shows that the electronic hybridization of the adsorbate atoms is more important than the adatom size in determining the surface stress. We also determine that the rotated incommensurate phase having ~ 1 ML of Pb on Si(111) has a surface stress of 1.24 ± 0.10 eV/1 × 1 cell, which is comparable to that of an incommensurate reconstruction of Ga on Si(111). The similarities in these stresses, despite differences in the two incommensurate structures, indicate that the overlayer is effectively decoupled from the substrate in both incommensurate reconstructions.

Electron transport through strongly coupled AlInP/GaInP superlattices

Using ballistic-electron-emission spectroscopy, electron transport through the principal (Γc,Lc) miniband of an (Al0.5In0.5P)11/(Ga0.5In0.5P)10 superlattice in the strong-coupling regime has been observed. Second derivative spectra of experimental data and Monte Carlo simulations were in agreement.