States of water molecule adsorbed on Si(111) surface

Calculated electronic energy structure of an overlayer of water molecules chemisorbed on Si(111), with a molecular plane perpendicular to the surface, reveals that 3a₁ molecular state is removed upon adsorption, and the resulting state densities cannot be reconciled with the UPS spectrum. These results, and state densities obtained from different atomic configurations are interpreted to rule out the molecular adsorption on Si(111) surface at room temperature.     

Atomic force microscope studies of CuCl island formation on CaF2(111) substrates

We have grown by molecular beam epitaxy (MBE) CuCl thin films at various thicknesses and substrate temperatures on CaF₂(111) substrates. Atomic force microscope (AFM) topographs reveal that islanding is the dominant growth mechanism. Quantitative analysis of the AFM data enabled us to determine the amount of the substrate remaining exposed after the deposition as well as the total amount of CuCl deposited. We calculated the reciprocal-space height correlation function, 〈 | h(q, t) |each of our films and compared them to the predictions of the shadowing growth theory, which enabled us to extract the important kinetic parameter of surface diffusion length for the growth condition of each of the four films.     

Electronic structure of SiO2(111) thin film

The electronic structure of (111) surface of β-crystobalite is investigat ed using the empirical tight binding method. Our calculations identify surface states in the conduction band, band gap and valence band. The surface state formed from silicon-s and p_z orbitals, which is believed to account for the structure in the O K excitation spectra, lies in the band gap. It is seen that oxygen adsorption on the surface removes surface states and gives rise to a sharp peak at about — 3.8 eV below the valence band edge.     

Langmuir evaporation from the (100), (111A), and (111B) faces of GaAs

We have measured the Langmuir evaporation of Ga and As from the (100), (111A), and (111B) faces of GaAs above and below the congruent evaporation temperature T_c. We have found that T_c is lowest for the (111B) face and highest for the (111A) face. These differences can be understood in terms of the different lifetimes of surface Ga on these faces. Furthermore, we have deduced that the evaporation processes are the rate limiting steps in the decomposition of GaAs. Below T_c, decomposition is controlled by the evaporation of Ga; above T_c it is controlled by the evaporation of As.     

Field emission energy distribution from (111) copper

Theoretical calculations of the field emission energy distributions from (111) Cu are presented. Both bulk and surface state contributions are considered, with the latter in particular being predicted to be predominant in part of the accessible energy region. The d-band contribution is also considered and shown to be small but clearly observable.     

Study of Ag/Si(111) submonolayer interface: I. Electronic structure by angle-resolved UPS

Angle-resolved ultraviolet photoelectron spectra have been measured for well defined Ag/Si(111) submonolayer interfaces of (1) $\text{Si(111)(}\text{3}\text{×}\text{3}\text{)R30°-Ag}$, (2) “Si(111)(6 × 1)-Ag”, and (3) Ag/Si(111) as deposited at room temperature. Non-dispersive and very narrow (FWHM ～ 0.4–0.5 eV) Ag 4d derived peaks are found at 5.6 and 6.5 eV below the Fermi level for surface (1) and at 5.3 and 6.0 eV for surface (2). Dispersions of sp “binding” states in the energy range between E_F and Ag 4d states have been precisely determined for surface (1). Electronic structures similar to those of the Ag(111) surface, including the surface state near E_F, have been observed for surface (3).     

Study of Ag/Si(111) submonolayer interface: II. Atomic geometry of Si(111) (√3 × √3 )R30°-Ag surface

Final state diffraction of Ag 3d X-ray photoelectrons from the Si(111) (√3 × √3)R30°-Ag surface has been measured. From a kinematical analysis of the diffraction patterns, it is found that a buried honeycomb framework of Ag atoms is formed on the surface with lateral displacement of the first Si layer.     

About the existence of an antiferromagnetic ground state for the (1× 1) structure of Si(111)

A recent proposal by Duke and Ford (Surface Sci. 111 (1981) L685) of strong correlations at the metastable (1× 1) Si(111) surface is shown to be equivalent to our earlier theory of magnetic or charge instabilities at this surface. It is recalled how this can be discussed from a perturbation analysis. Estimates of the Coulomb parameter U are given using recent theoretical results for dangling bond states in silicon. They support the conclusion of an antiferromagnetic 2 × 1 ground state for this surface.     

Electronic properties of TiC(100) and polar TiC(111) surfaces

The energy bands of films of TiC have been calculated using the linear-combination-of-atomic-orbitals method with parameters obtained by a fit to the bulk band structure. The Madelung potentials and charge redistribution have been determined self-consistently. For the neutral TiC(100) surface, the density of states (DOS) is similar to that of the bulk. For the non-neutral Ti-covered TiC(111) surface, Ti 3d-derived surface states appear around the Fermi energy E_F. The long-range electric field produced by the polar surfaces is screened by the charge redistribution, and the polar surfaces are stabilized. Characteristic features of TiC(111) compared to other surfaces of TiC are attributed to the high surface DOS at E_F.     

Electron states on the (111) surface of copper

A calculation of electronic states at the (111)-surface of Cu in the energy region around E_F is presented. The calculation is based on the empirical pseudopotential method. A proper position of an abrupt potential barrier ensures overall charge neutrality. A surface state is found at 0.13 eV below E_F, being localized midway between atomic layers. The effective mass of the associate bands is 0.39m_e. Our results are in good agreement with directional photoemission data.     

Observation of Si(111) and gold-deposited Si(111) surfaces using micro-probe reflection high-energy electron diffraction

Observations of clean Si(111) and gold-deposited Si(111) surfaces have been performed using micro-probe reflection high-energy electron diffraction. It was found that many atomic steps on a Si(111) surface run in nearly the same direction, about 9° off the [1̄1̄2] direction. When gold was deposited on this surface at a substrate temperature of about 800°C, 5 × 1, diffuse √3 × √3R30°, sharp √3 × √3 R30° structures and Au clusters appeared on the surface with continuation of the deposition. During the deposition process, it was found that one kind of Si(111) 5 × 1 Au domain grew selectively along these atomic steps and nearly covered the entire surface. A phenomenon of gold clusters moving during the deposition was also observed. These clusters all moved in nearly the same direction so as to climb the atomic steps.     

Surface state like bulk band emission in the photoelectron energy spectra of Cu(111)

Using a relativistically calculated band structure the presence in Cu(111) UV photoemission spectra of a prominent 3d peak, previously ascribed to a Tamm type surface state, is explained in terms of bulk band transitions.     

Two-Step Oxidation of Pb（111） Surfaces

We report on a two-step method for oxidation of Pb（111） surfaces, which consists of low temperature （90K） adsorption of 02 and subsequent annealing to room temperature. In situ scanning tunnelling microscopy observation reveals that oxidation of Pb（111） can occur effectively by this method, while direct room temperature adsorption results in no oxidation. Temperature-dependent adsorption behaviour suggests the existence of a precursor state for 02 adsorption on Pb（111） surfaces and can explain the oxidation-resistance of clean Pb（111） surface at room temperature.     

A vibrational study of ammonia chemisorbed on Ni(110) and Ni(111): whither goest the metal-nitrogen stretching mode on FCC (111) surfaces?

The adsorption of ammonia on the Ni(110) and Ni(111) surfaces has been studied with high resolution (≤ 65 cm_?1) electron energy loss spectroscopy (EELS) combined with thermal desorption spectroscopy. The EELS spectra of the initial chemisorbed layer or α state on each surface are very different. Ammonia chemisorbed on the Ni(110) surface exhibits a strong Ni-N stretching mode at 570 cm^?1 which is absent on the Ni(111) surface. The Ammonia adsorption site appears to be different on the Ni(110) and Ni(111) surfaces. We suggest that the absence of the M-N stretching mode on the Ni(111) surface is a general characteristic of the ammonia adsorption site on the (111) surfaces of fcc Group VIII metals.     

Electron energy-loss spectroscopy of alkali-metal-covered Ge(111) surfaces

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.     

Some coadsorption effects on Rh(111)

ESD energy analysis is used to study the reaction products produced during coadsorption of CO-O₂ and CH₄-O₂ on Rh(111). Residence of CO₂ on the surface is confirmed by detection of a CO₂⁺ ionic component with energy of 1.8 eV. Adsorption and dissociation of CH₄ on oxygen- covered Rh(111) is inferred as a result of a low energy component present in the energy spectra of desorbed O⁺.     

Ga- and As-Adatom phases on the Ge(111) and Si(111) surfaces: analogies and differences

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.     

High-resolution photoemission from Ag(100), Ag(110), and Ag(111)

Energy distribution curves of photoelectrons emitted normal to (100), (110), and (111) faces of silver have been obtained at photon energies of 21.22, 16.85, and 11.83 eV. The results are compared with Christensen's relativistic band structure calculation of bulk silver yielding a close correspondence between experiment and theory. A surface state in the L gap immediately below the Fermi level is identified.     

Determination of the E(k6 relation for a surface state on Au(111)

Angle-resolved photoemission measurements have been used to determine the energy versus parallel wave vector (k₆) relations for the surface state on Au(111). The state has its minimum energy 0.5 eV below the Fermi level, and disperses upward with increasing k₆