LEED analysis of the surface structure of Mo(001)

A detailed comparison between theoretical and experimental LEED data for the Mo(001) surface, using the quantitative r-factor method of Zanazzi and Jona, yields a value for the surface layer contraction of 9.5 ± 2.0%, consistent with the 11.5% found previously by Ignatiev et al. Non-structural parameters are also in agreement, although the surface Debye temperature, 230 K, is slightly higher than found before. r-Factors were used to investigate the effects of all the parameters, and show that an energy-dependent inner potential gives better agreement than a fixed value and that the second layer is contracted by about 1% of the bulk layer spacing. The effect of using different ion core potentials is examined and discussed. A superposition potential which models the surface ion environment is found to have a significant effect on the layer displacement concluded.     

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.     

Self-consistent electronic structure for a Mo (001) surface with saturated H adsorption

The band structure for a Mo (001) surface covered with a saturated monolayer of hydrogen is calculated self-consistently using the pseudopotential method in a mixed-basis representation. Two adsorbate bands are found below the bottom of the molybdenum bulk bands. Most of the intrinsic surface states of the clean (001) surface also exist on the hydrogen covered surface at lower energies. The results are used to identify H induced structures observed in recent photoemission studies of hydrogen on W (001).     

Electronic origin of the surface reconstruction and relaxation of the (001) surface of Mo and W

The reconstruction and the relaxation of the (001) surface of Mo and W are studied by using the tight-binding d band and the Born-Mayer repulsive potential. The d band parameters are set to reproduce band energies of ab initio band calculations at high symmetry points in the Brillouin zone and the parameters in the Born-Mayer potential are chosen to obtain the correct equilibrium lattice constant and the bulk modulus of the bulk crystal. First, we give a detailed discussion on the mechanism of the surface relaxation, and then show that the (001) surfaces of Mo and W are unstable to the c(2 × 2) mode but stable with regard to the (2 × 1) mode. By calculating the energy change up to the fourth order of atomic displacement, we determine the stable surface atomic structure which is in fair agreement with experiments.     

Electronic origin of the surface reconstruction of the (001) surface of Cr,Mo and W

The d-band effects on the reconstruction of the (001) surface of Cr, Mo and W are discussed with a tight-binding model. Response functions corresponding to some models for the reconstruction and their q-dependence are calculated by using Haydrock et al.'s recursion method. The present calculation shows that an energy gain by broadening the surface state peak near the Fermi energy is most remarkable for the model proposed by Debe and King, and therefore gives a theoretical support to it. The energy gain is attributed to an enhancement in the bonding property by pairing of surface atoms in the Debe and King model. Response functions without an electron-phonon matrix element (EPME) are also calculated, which show only a very weak q-dependence. Detailed discussions are given on the mode dependence, that is, on the effect of EPME.     

Adhesion at a heterophase interface: First-principles study of Mo(001)/MoSi2(001)

The bonding characteristics, interfacial energetics, and electronic structure associated with adhesion at the Mo-MoSi₂(001) heterophase interface are investigated using the first-principles, self-consistent local orbital method. We found both the adhesive energy and peak interfacial strength for the interface to be 10%-15% smaller than the respective values for cleavage along the (001) planes in crystalline Mo and MoSi₂. The equilibrium interlayer separation between Mo and MoSi₂ is found to lie between the interplanar spacings of crystalline Mo and MoSi₂. The interfacial adhesive bonding is attributable to the combination of a nearly uniform band of charge accumulation at the interface and directional charge accumulation between atoms across the interface. These first-principles calculations demonstrate that the universal-binding-energy relation can be extended to describe adhesion between dissimilar materials.     

The kinetics of CO dissociation on Mo(001)

The thermal dissociation of molecular CO adsorbed on the Mo(001) surface has been studied using ultraviolet photoemission methods. Results derived from isothermal measurements indicate that the conversion to atomic β-CO does not obey simple first order kinetics. The observed rate behavior can be explained, however, by an activation energy which increases with adsorbate coverage from a value of 0.60 eV near half coverage. Adsorbate-induced rearrangement of Mo atoms may be responsible for the coverage-dependent changes in the reaction rate.     

Facetting,steps and reconstruction on GaAs (001)

Assuming that facets develop on a microscopic scale during MBE growth of macroscopically flat GaAs (001) surfaces, models were made for the different structures found for surfaces prepared under UHV conditions as reported in the literature. The deduced surface structures are discussed in connection with data available from experimental work on the composition and structure of the reconstructed surface.     

Surface-enhanced electron-phonon coupling and irreversible reconstruction of MgO(001)

A possible mechanism for the thermally irreversible reconstruction of MgO(001) is presented. The theory is based on the electronic structure and the electron-phonon interaction at the surface. It is suggested that a narrower band gap at the surface enhances the electronphonon coupling and that this leads to an adiabatic potential curve with a metastable and a stable state which can result in the irreversible structural transformation.     

氮离子轰击钼(001)和钼(110)表面形成的有序结构

用能量为1千电子伏,束流为6微安的氮离子轰击含有痕量碳和氧的钼(001)和钼(110)表面10至15分钟,在俄歇能谱中出现了很强的氮的俄歇峰。从室温直到350℃退火,低能电子衍射观察表明,表面是无序层。样品加热到530℃和650℃之间,在钼(001)表面上得到c(2×2)-氮,p(2×2)-氮和(4(2^1/2)×2^1/2)R45°-氮、氧三种结构的低能电子衍射图;在密堆的钼(110)面得到单一结构的c(7×3)-氮的低能电子衍射图。低能电子衍射图与热脱附密切相关 关键词：     

Two-dimensional carbon incorporation into Si(001): C amount and structure of Si(001)-c(4 x 4)

The C amount and the structure of the Si(001)-c(4 x 4) surface is studied using scanning tunneling microscopy (STM) and ab initio calculations. The c(4 x 4) phase is found to contain 1/8 monolayer C (1 C atom in each primitive unit cell). From the C amount and the symmetry of high-resolution STM images, it is inferred that the C atoms substitute the fourth-layer site below the dimer row. We construct a structure model relying on ab initio energetics and STM simulations. Each C atom induces an on-site dimer vacancy and two adjacent rotated dimers on the same dimer row. The c(4 x 4) phase constitutes the subsurface Si(0.875)C(0.125) delta layer with two-dimensionally ordered C atoms.