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Bengu E Plass R Marks LD Ichihashi T Ajayan PM Iijima S 《Physical review letters》1996,77(20):4226-4228
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High-resolution electron energy-loss spectroscopy and monochromatic low-energy electron diffraction have been applied to the study of the Si(111)(7 × 7) surface and the thermally-quenched Si(111) (1 × 1) surface. For the (1 × 1) surface, the inelastic continuum, observed for the (7 × 7) surface, due to the Drude absorption of electrons in the dangling-bond surface states is not existent, which indicates that the surface-state band associated with the dangling-bonds of the (1 × 1) surface is insulating. The observed electronic transitions indicate that the (7 × 7) and (1 × 1) surfaces have similar local band geometries and that they differ only in long-range order. The (1 × 1) surface is considered to have a disordered structure. The defect model is favored for the (7 × 7) structure. 相似文献
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Long range orientational order within C60 monolayers on Au(111) is observed with low-temperature scanning tunneling microscopy. A unit cell comprised of 49 molecules which adopt 11 different orientations is found. It can be divided in a faulted and an unfaulted half similar to the (7x7) reconstruction of Si(111). A model is proposed which shows how, through a Moiré-like effect, the substrate induces minute changes in the orientation of the C60 molecules. Intermolecular interactions are shown to play a major role in stabilizing the superlattice. 相似文献
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Electroweak unification is obtained in anSU(7) model at a mass scale 3×1010≦M≦3×1016 GeV's, with left-right symmetric subgroups and sin2 θ w (M)=3/8. BelowM, the model reduces toSU(3) L ×SU(3) R , the flavor sector of the “trinification theory” of Glashow et al., or of theE 6 grand unified theory. This model predicts a natural massless neutrino, and fractionally charged leptons with masses in theM regime. 相似文献
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The oxidation products on Si(111)-(7x7) are investigated at 82 K by means of high-resolution electron energy loss spectroscopy. The isotope-labeled vibrational spectra with 16O2, 18O2, and 16O 18O show that, in the initial stage of the oxidation, an O2 molecule dissociates to form a metastable product with an O atom bonding on top of the Si adatom and the other inserted into the backbond. The metastable product is observed as a dark site in the topographic scanning tunneling microscopy (STM) image and can be transformed to a stable product by the STM manipulation. Our results are in good agreement with recent theoretical calculations. 相似文献
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We propose a natural two-speed model for the phase dynamics of Si(111) 7 x 7 phase transition to high-temperature unreconstructed phase. We formulate the phase dynamics by using phase-field method and adaptive mesh refinement. Our simulated results show that a 7 x 7 island decays with its shape kept unchanged, and its area decay rate is shown to be a constant increasing with its initial area. Low-energy electron microscopy experiments concerned are explained, which confirms that the dimer chains and corner holes are broken first in the transition, and then the stacking fault is remedied slowly. This phase-field method is a reliable approach to phase dynamics of surface phase transitions. 相似文献
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By adsorption and subsequent reduction of oxygen on Pd(110), metastable (1 × 2) and (1 × 3) reconstructed surfaces have been produced. Oxygen was not present after the reduction but a small amount of residual hydrogen (< 0.15 monolayers) remained. However this is not the origin of the reconstruction as adsorption of this amount of hydrogen on the clean surface did not cause reconstruction. The structures were stable up to ˜ 370 K, and at higher temperatures they reverted to (1 × 1). These results are compared with Rh(110) where similar reconstructions have been found. 相似文献
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We report results of a scanning tunneling microscopy and X-ray photoelectron spectroscopy study on the interaction of tetraethoxysilane (TEOS), a precursor for chemical vapor deposition of silicon dioxide, with Si(111)-(7×7) at room temperature. Under these conditions the interaction of TEOS with the surface is predominantly dissociative. The main adsorption products are ethyl- and triethoxysiloxane groups, which probably evolve in a four-center reaction of TEOS with two neighboring surface dangling bonds. Adsorption of the dissociation products is highly site-selective: triethoxysiloxane groups adsorb on the Si adatoms while ethyl groups react with the rest-atom dangling bonds. Center adatoms are over three times more reactive towards this reaction than corner adatoms. This two-fold selectivity is explained within the concept of local electron donor/acceptor properties. 相似文献
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Lantz MA Hug HJ van Schendel PJ Hoffmann R Martin S Baratoff A Abdurixit A Guntherodt H Gerber C 《Physical review letters》2000,84(12):2642-2645
A low temperature scanning force microscope (SFM) operating in a dynamic mode in ultrahigh vacuum was used to study the Si(111)- (7x7) surface at 7.2 K. Not only the twelve adatoms but also the six rest atoms of the unit cell are clearly resolved for the first time with SFM. In addition, the first measurements of the short range chemical bonding forces above specific atomic sites are presented. The data are in good agreement with first principles computations and indicate that the nearest atoms in the tip and sample relax significantly when the tip is within a few A of the surface. 相似文献
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P. Sobotík I. Ošťádal P. Kocán J. Mysliveček T. Jarolímek 《Czechoslovak Journal of Physics》2003,53(1):69-74
Surface diffusion is one of the basic processes determining morphology of a growing film. In the case of metal heteroepitaxy on Si(111)-(7X7) the diffusion is strongly affected by the presence of surface reconstruction, which introduces additional constraints into the motion of deposited atoms. To determine diffusion parameters we used two different approaches: i) interpretation of experimentally observed morphologies by a coarse-grained kinetic Monte Carlo model, ii) direct observation of adatom movement using UHV STM. The attempt frequency and the barrier to hopping of a single Ag atom between half-unit cells of the reconstruction were estimated in both cases. Obtained values are compared and discussed. 相似文献