Surface Corrugation in Rotational and Diffractive Scattering of O2 from LiF (001)

A quantum dynamic calculation on a five-dimensional O₂/LiF (001) model system is performed using the multi-configuration time-dependent Hartree method. The obtained results show that the mechanism of rotational and diffractive excitation in details: Comparison with the rotational excited state, the initially non-rotational state is seen to favor the inelastic scattering in the rotational excitation process. The surface corrugation can damp the quantum interferences and produce a greater amount of rotational inelastic scattering at the expense of the elastic process in the rotational excitation process. The diffraction process and the average energy transferred into the rotational and diffractive mode are also discussed.     

Theory of Diffuse X-Ray Scattering from Surface Blisters

A theory of the diffuse X-ray scattering on randomly distributed surface blisters, which constitute a new type of defects, has been developed. An expression for the amplitude of diffuse X-ray scattering from surface blisters has been obtained within the model of a truncated spherical layer. Scattering intensity distribution maps from surface blisters have been numerically simulated. The effect of the elastic bending of reflecting planes of the lattice of surface blisters on the angular distribution of the scattering intensity in the reciprocal space has been revealed.     

Cu（001）表面CO吸附的电子结构效应

本文应用Ｒｅｃｕｒｓｉｏｎ方法，计算了ＣＯ在Ｃｕ（００１）表面不同位置（顶位、桥位和空位）吸附的电子结构，分析了ＣＯ与Ｃｕ表面原子之间的键作用。分析表明ＣＯ在顶位吸附时，Ｃｐｘ（ｐｙ）－Ｃｕｄｓ（１号）和Ｃｐｘ（ｐｙ）－Ｃｕｄ２（ｄｓ）（２号）之间存在较强的键作用，这有利于ＣＯ在顶位吸附。桥位和空位吸附时，ＣＯ与表面原子形成的键较弱，是不稳定的。计算结果得到了实验的支持。     

Surface vibrations of Na(001) and K(001) surfaces

We present the results of a theoretical study of the dynamics of the atom motion of Na(001) and K(001) surfaces. The total electronic energy is calculated using a pseudopotential approach with a confined electron gas as unperturbed system. With this theory the dynamical matrix can he derived without resorting to empirical parametrizations. Surface phonon dispersion curves are reported for the high symmetry directions of the two-dimensional Brillouin zone for ideal and relaxed configurations. The calculated spectra are compared with the results of semi-empirical force constant calculations. The effects of single and multilayer relaxations on the location and the nature of the main surface bands are examined.     

The Influence of Hydrogen Adsorption on Magnetic Properties of Ni/Cu(001) Surface

Ni/Cu(001) is known as a unique system showing the spin-reorientation transition from an in-plane to out-of-plane magnetization direction when the Ni-overlayer thickness is increased. We investigate different relaxed multilayer structures with a hydrogen adlayer using the full-potential linearized augmented plane-wave method. The relaxed geometries, determined by total energy and atomic force calculations, show that H-monolayer strongly influences the interlayer distance between the Ni-surface and sub-surface layers yielding the outward relaxation of Ni-layer at H/Ni interface. Furthermore, large decrease of local magnetic moments at the top surface area is found for the surface covered by H. The magneto-crystalline anisotropy energies are calculated for fully relaxed H/Ni-films. The spin-reorientation transition critical thickness of 4 ML is found in good quantitative agreement with the experiment.     

Surface stress anisotropy of Ge(001)

By analyzing the equilibrium shape of vacancy islands on the Ge(001) surface we have determined the surface stress anisotropy, i.e., the difference between the compressive stress component along the substrate dimer rows and the tensile stress component perpendicular to the substrate dimer rows. In order to extract the surface stress anisotropy we have used a model recently put forward by Li et al. [Phys. Rev. Lett. 85, 1922 (2000)]. The surface stress anisotropy of the clean Ge(001) surface is found to be 80+/-30 meV/A(2). This value is comparable to the surface stress anisotropy of the closely related Si(001) surface.     

Surface charge-density wave phase transitions on Mo(001) and W(001)

The recently reported phase transitions of Mo(001) and W(001) are discussed in terms of surface charge-density waves. Band structure, surface lattice distortion and possible accompanying surface antiferromagnetism are considered. The expected two-dimensional critical behaviour is also investigated.     

Surface electromigration of metals on Si(001): In/Si(001)

The possibility of surface electromigration (SE) of metals of In, Ga, Sb and Ag on a very flat Si(001)2×1 substrate (single domain 2×1) was examined by SEM, μ-RHEED and μ-AES under UHV conditions. It was found that Ga, Sb and Ag show no SE on Si(001) surface even at DC annealing temperatures for the desorption of these metals. For In on Si(001), a very fast SE (8000 μm/min) towards the cathode side was found that suddenly sets in at 450°C DC annealing, which was related to a surface phase transition. μ-RHEED and μ-AES observation showed that the SE is related to an ordered 4×3-In phase together with two-dimensional In gas phase over the 4×3-In phase and an In-disordered phase at the front end of SE. Single domain 4×3-In phases were found to occur under sequences of In deposition and DC annealing which involve the In SE on Si(001).     

Structure and Dynamic Stability of a Multilayer Na Film on the Cu(001) Surface

Mechanisms of atomic layer-by-layer formation of the equilibrium structure of multilayer Na film on the Cu(001) surface have been studied taking into account relaxation and dynamic (phonon) processes. It has been shown that the atomic rearrangement of the substrate-commensurate с(2 × 2) superstructure of the first Na monolayer to a bcc (110)-oriented structure begins with the second monolayer. The dynamic contribution to the formation of the structure of the growing Na film has been estimated. It has been shown that phonon modes select exponentially observed structures from statically favorable structures. All calculations have been performed with interatomic potentials constructed with the embedded atom method. The comparison of the calculated vibrational frequencies with the existing experimental data has demonstrated their good agreement.

     

Surface bands of the (001) surface of molybdenum

The electronic structure of the ideal (001) surface of Mo is calculated using a parametrized linear combination of atomic orbitals. Surface states and resonances are identified along the high symmetry directions of the two dimensional Brillouin zone. The local density of states near the surface is presented and the main modifications due to the surface states are discussed. Significant surface features are found in the range 0–0.1 Ryd below the Fermi energy in agreement with the experimental findings.     

Scattering of image-potential-state electrons by steps on Cu(001)

Scanning tunneling spectroscopy (STS) reveals a distinct asymmetry in the scattering properties of an isolated step for the n=1 image-potential state on Cu(001). The elastic scattering probability for an electron traveling downstairs is determined from the strength of density oscillations in front of a step edge and is found to be approximately two times higher than for the opposite upstairs direction. A one-dimensional scattering model is extended to the case of asymmetric transmission and reflection coefficients. The calculations using the asymmetry measured by STS explain the dispersion and the decay rate of the n=1 band on Cu(119) measured by two-photon photoemission. In particular, the asymmetry of the decay rate can be described quantitatively with a minimum of adjustable parameters. While the results can also be transferred successfully to the Cu(1115) surface, the limit of applicability is reached for Cu(117) with a step separation of 3.5 nearest-neighbor distances. PACS 73.20.At; 79.60.Bm; 68.37.Ef; 72.10.Fk     

Low photoemission intensity near induced by the surface relaxed structure of CrO2(001)

Based on first principles calculations we find that CrO2(001) will form a relaxed structure at its surface, at which each surface Cr atom is surrounded by four oxygen atoms in a distorted tetrahedral configuration. This tetrahedral environment has important effects on the electronic structure, leading to an inversion of the t2g-eg splitting of Cr 3d orbitals. Two 3d electrons of the surface Cr ion will fully occupy the doublet eg, which becomes lower in energy than the t2g, leaving the t2g orbitals empty. The consequence is that the Fermi level lies in a gap between the eg and t2g for a local electronic structure at the surface. This finding is consistent with and explains the extremely low photoemission intensity near EF at CrO2(001) [K?mper et al., Phys. Rev. Lett. 59, 2788 (1987)].