共查询到20条相似文献,搜索用时 15 毫秒
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J.E. Rowe 《Surface science》1975,53(1):461-472
In order to study the effects of photon-polarization selection rules on chemisorptionbond geometry, we have measured photoelectron spectra as a function of angle of incidence, θi, in the range 28° ? θ ? 80°. A noble-gas UV resonance lamp and cylindrical mirror analyzer were used to measure both bonding and non-bonding surface Orbitals. A large enhancement (200–400%) of the photocmission is found when photon electric field intensity is near the maximum normal to the surface. This indicates a spatial variation of microscopic fields which is approximately independent of adsorbate bonding since it is determined by the optical properties of the substrate. In addition, we observe some effects on adsorbate photoelectron peaks due to different orbital symmetry. The case of atomic hydrogen chemisorption is discussed as an example of this latter effect. 相似文献
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We suggest that dangling electrons at (111) surfaces of group IV semiconductors should have a 2-dimensional excitonic insulator ground state. The higher order reconstructions observed in Si and Ge are accounted for in detail. 相似文献
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Tang SJ Lee CY Huang CC Chang TR Cheng CM Tsuei KD Jeng HT Yeh V Chiang TC 《Physical review letters》2011,107(6):066802
Lattice match is important for epitaxial growth. We show that a competing mechanism, electronic match, can dominate at small film thicknesses for metal-semiconductor systems, where quantum confinement and symmetry requirements may favor a different growth pattern. For Pb(111) on Ge(111), an accidental lattice match leads to a √3 × √3 configuration involving a 30° in-plane rotation at large film thicknesses, but it gives way to an incommensurate (1 × 1) configuration at small film thickness. The transformation follows an approximately inverse-film-thickness dependence with superimposed bilayer oscillations. 相似文献
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The (1 × 1) and (√3 × √3)R30° (T4) structures of Ga and As adatoms on the Ge(111) and Si(111) surfaces are studied using first-principles calculations. The surface energetics predicts, in some cases, a transformation of the T4 structure (surface covered with 1/3 monolayer (ML) of adatoms) into domains of the 1-ML covered (1 × 1) structure and areas of clean reconstructed suface. For As adatoms, such phase separation is favored on both substrates, while for Ga adatoms, it is only preferred on the Ge(111) surfaces. These results compare well with experimental observations. 相似文献
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Toshihiro Ichikawa 《Surface science》1981,111(2):227-259
When submonolayer and monolayer amounts of indium were deposited onto clean Ge(111) surfaces at room temperature and then heated, (13 × 2√3), (12 × 2√3), (11 × 2√3), (10 × 2√3), (4√3 × 4√3) R30°-related, (√31 × √31) R(±9°), (√61 × √61) R(30 ± 4°) and (4.3 × 4.3) structures appeared on the surfaces at fixed In coverages and at fixed surface temperatures. General intensity features of superlattice reflections are derived from intensity estimations by eye of superlattice spots in their RHEED patterns, and some structural characteristics of the superstructures are clarified from the analysis of the general intensity features. The former four superstructures are long-period (2 × 2)-related antiphase structures whose period changes, depending on the coverage. The wavevector characterizing the (13 × 2√3) structure, which appears at the smallest coverage, almost coincides with those of structural fluctuation emerging at the clean Ge(111) (1 × 1) surface around 350°C. The coincidence suggests that the longperiod (2 × 2)-related antiphase structures have a close relationship to the structural fluctuation and, besides, to the (2 × 8) structure in their origin. 相似文献
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The chemical contrast between Si and Ge obtained by scanning tunneling microscopy on Bi-covered Si(111) surfaces is used as a tool to identify two vertical Ge/Si intermixing processes. During annealing of an initially pure Ge monolayer on Si, the intermixing is confined to the first two layers approaching a 50% Ge concentration in each layer. During epitaxial growth, a growth front induced intermixing process acting at step edges is observed. Because of the open atomic structure at the step edges, relative to the terraces, a lower activation barrier for intermixing at the step edge, compared to the terrace, is observed. 相似文献
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We have deposited relatively thick (∼60 nm) Ge layers on Br-passivated Si(111) substrates by thermal evaporation under high
vacuum conditions at room temperature. Ge has grown in a layer-plus-island mode although it is different from the Stranski-Krastanov
growth mode observed in epitaxial growth. Both the islands and the layer are nanocrystalline. This appears to be a consequence
of reduction of surface free energy of the Si(111) substrate by Br-passivation. The size distribution of the Ge nanoislands
has been determined. The Br-Si(111) substrates were prepared by a liquid treatment, which may not produce exactly reproducible
surfaces. Nevertheless, some basic features of the nanostructural island growth are reasonably reproducible, while there are
variations in the details of the island size distribution. 相似文献
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L.N. Surnev 《Journal of Electron Spectroscopy and Related Phenomena》1982,26(1):53-63
Electron energy-loss spectra of a Ge(111) surface covered with Na, K or Cs in the submonolayer range have been measured. The presence of alkali metal (a.m.) causes the empty dangling-bond surface states to vanish and results in the creation of new interface states. The filling of the latter is a decreasing function of the ionicity of the a.m.—Ge bond.It was found that the energy shift of transitions involving a.m. s resonance as the final state is a linear function of a.m. coverage. 相似文献
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The positions of Ge atoms intermixed in the Si(100) surface at very low concentration are identified using empty-state imaging in scanning tunneling microscopy. A measurable degree of place exchange occurs at temperatures as low as 330 K. Contrary to earlier conclusions, good differentiation between Si atoms and Ge atoms can be achieved by proper imaging conditions. 相似文献
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Surface segregation of Sn in Cu is measured at (111) and (100) surfaces by means of AES and LEED. In the case of at temperature measurements and no cosegregation of impurities occurring, equilibrium segregation is accomplished for Sn bulk concentrations between 40 and 4300 at ppm and temperatures of 800 to 1230 K. The maximum segregation level of Sn corresponds to a (√3 × √3)R30° structure for the (111) surface and a p(2 × 2) structure for the (100) surface. For theoretical analysis, the Langmuir-McLean equation has to be modified. No difference in segregation enthalpies for both surface orientations is found within the experimental error. The mean segregation enthalpy is determined to ΔH = ?(53 ± 5) kJ/g-atom. 相似文献
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O. Pulci M. Marsili P. Gori M. Palummo A. Cricenti F. Bechstedt R. Del Sole 《Applied Physics A: Materials Science & Processing》2006,85(4):361-369
We present an ab initio study of two semiconductor surfaces, the α phase of Sn on Ge(111) and the cleavage surface of diamond. The theoretical tools used (density functional theory (DFT) and many-body perturbation theory) are discussed in detail, and the advantages and disadvantages of the two approaches are pointed out. We show that in the case of diamond it is essential to go beyond the DFT single-particle approach, and to introduce quasiparticle effects through the GW approximation. PACS 73.20.-r; 73.20.At; 71.15.Mb 相似文献
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L. Surnev 《Surface science》1981,110(2):458-470
Oxygen adsorption on an alkali metal (a.m.)-covered Ge(111) surface has been studied by means of Auger electron spectroscopy (AES), electron energy loss spectroscopy (ELS), thermal desorption (TD), and work function measurements (WF). It was found that the presence of a.m. results in enhancement of the oxygen adsorption rate. The initial values of the sticking coefficient, S0, are exponential functions of the work function changes caused by the a.m. adsorption. It was shown that no germanium oxide phases are formed on an alkali-covered Ge surface at 300 K. The oxidation rate at high temperatures is limited by the rearrangement processes taking place in the surface GeO layer. The results obtained show that the alkali metal perturbs the GeO bond to a certain extent but no alkali oxide formation was observed at a.m. covertages under investigation. 相似文献
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《Surface science》1986,167(1):127-140
The subsurface strain associated with surface reconstruction was measured for the Ge(001)-c(4×2) and Ge(111)-c(2×8) surfaces using high energy ion scattering. In the case of the Ge(001) surface we find the equivalent of ∼3 monolayers displaced by more than 0.12 Å, in accord with dimer models of the surface reconstruction. For the Ge(111) surface displacements are observed in off-normal incidence, indicating large displacements perpendicular to the surface or other reconstructions, such as a stacking fault configuration. The relationship between subsurface strain and stacking fault models is also discussed. The subsurface strain in these two Ge surfaces is remarkably similar to that of the corresponding Si surfaces, even though the details of the surface reconstruction are different. Measurements at low temperature indicate that the strain is essentially temperature independent, as expected. Measurements of the hydrogen covered surfaces show little change is strain, a surprising result when compared to the behavior of Si(001). 相似文献
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Ballabio G Profeta G de Gironcoli S Scandolo S Santoro GE Tosatti E 《Physical review letters》2002,89(12):126803
Distortions of the sqrt[3]x sqrt[3] Sn/Ge(111) and Sn/Si(111) surfaces are shown to reflect a disproportionation of an integer pseudocharge, Q, related to the surface band occupancy. A novel understanding of the (3 x 3)-1U ("1 up, 2 down") and 2U ("2 up, 1 down") distortions of Sn/Ge(111) is obtained by a theoretical study of the phase diagram under strain. Positive strain keeps the unstrained value Q=3 but removes distortions. Negative strain attracts pseudocharge from the valence band causing first a (3 x 3)-2U distortion (Q=4) on both Sn/Ge and Sn/Si, and eventually a (sqrt[3] x sqrt[3])-3U ("all up") state with Q=6. The possibility of a fluctuating phase in unstrained Sn/Si(111) is discussed. 相似文献