Band structure of selectively adsorbed atoms on alkali halide surfaces

We present calculations for the band structure of selectively adsorbed atoms, i.e. for energies greater than zero on alkali halide surfaces near the regions of degenerated bands for existing experimental data. The calculated splittings of crossing-bands are in good agreement with experimental data. Also splittings between different bound levels appear in the calculation.     

Electronic structure of carbon nanotubes modified by alkali metal atoms

The electronic structure and parameters of the energy band structure of (n, 0)-type nanotubes modified by alkali metal atoms (Li, Na) and intercalated by potassium atoms are studied. The quantum-chemical semiempirical MNDO method and a model of the covalent cyclic cluster built in via ionic bonding are used to model infinitely long nanotubes. The electronic density of states of modified nanotubes is found. It is shown that semiconductor-metal transitions can occur in semiconductor nanotubes and that semimetal nanotubes can undergo metal-metal transitions.     

XPS satellite spectra for adsorbed atoms

The surface plasmon and electron-hole satellite spectra in core-level XPS of a large adsorbed atom are calculated for an idealised model of a metal surface.     

Electronic structure of semiconducting nanotubes adsorbed on metal surfaces

A total-energy electronic-structure calculation is performed to explore energetics and electronic structures of nanotubes adsorbed on metal surfaces. We find that the charge transfer from metal surfaces to the nanotubes takes place depending on both the electronic structures of the adsorbed nanotubes and the work functions of the metal surfaces. In addition, we also find a substantial hybridization between the electron states of metal atoms and those of the nanotubes, which results in the metal-induced inhomogeneous charge distribution in the nanotubes.     

Scattering length for fermionic alkali atoms

We examine the use of the WKB approximation to determine the p-wave scatteringlength. For this we solve the p partial wave Schrödingerequation and analyse the validity of adopting the semiclassical solution toevaluate the constant factors in the solution. We also calculate the p-wavescattering lengths of ⁶Li and ⁴⁰K for the a³Σ⁺ _u andX¹Σ⁺ _g states respectively using the variable phase method. Thep-wave scattering lengths of ¹³²Cs and ¹³⁴Cs are also calculated.Based on our calculations, the value of the p-wave scattering lengths of⁶Li and ⁴⁰K are -36a_o and -95a_o respectively.     

Polarizability of alkali atoms

The scalar and tensor components of static polarizability of alkali atoms Na, K, and Rb were calculated. The results were compared with available theoretical and experimental data.     

Numerical study of pseudowavefunctions for alkali atoms

Smooth pseudowavefunctions based on known valence and core functions are calculated and displayed for atomic Li, Na and K. These are used to examine some of the approximations employed in pseudopotential calculations; in particular, that of replacing the pseudowavefunction by a constant in the core region. The possibility of neglecting inner core states in pseudopotential calculations is discussed in the light of pseudowavefunctions calculated using only the core state of highest energy.     

Electronic structure of alkali halide surfaces upon ion irradiation

By a careful analysis of the electron loss spectra of some alkali halide crystals after ion irradiation we have demonstrated that defect generation depends on ion energy nonmonotonously. This effect is connected with inelastic interaction between ion and surface atoms.     

Electronic structure of adsorbed sodium on Pt(III)

Using electron energy loss spectroscopy we have investigated excitation of electrons in thin Na layers adsorbed on Pt(III). Transitions from occupied Pt-valence states to unoccupied shifted Na-valence states are reported. With the help of a simple model we obtain information on valence electron structure and charging of the adatom.     

Bombardment of alkali halide crystals with medium-energy atoms

The sputtering characteristics of KCl and NaCl alkali halide single crystals by bombardment with argon and mercury atoms are investigated. The sputtering coefficients are measured in the energy range 0.5–3 keV. Anisotropy is found in sputtering at various incident angles of the beam. The yield of charged particles during bombardment of thin specimens (of the order of 8–20 m) of KCl single crystals is investigated.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 55–59, July, 1984.     

Modeling migration of adsorbed atoms in dense multicomponent adsorbed layers

Within the framework of a simple (i.e., ignoring lateral interactions) lattice model, surface migration of adsorbed atoms of a crystalline substance A is considered for the case in which the surface is densely covered by the adsorbed atoms of a noncrystallized substance B. Simulation of the migration, performed by means of the Monte-Carlo method, demonstrates a sharp decrease in the root-mean-square displacement of the adsorbed atoms of A with an increase in the degree of covering by adsorbed atoms of B in the case where these adsorbed atoms exhibit weak migration mobility. This effect is associated with strong correlations in the directions of individual jumps of an adsorbed atom of A. The results of the simulation are applied to estimate the influence of the degree of covering of a surface with an impurity on the temperature at which a transition is accomplished from an nascent to a stepwise-layered mechanism of growth in silicon in molecular-beam epitaxy. V. D. Kuznetsov Siberian Institute for Technical Physics. Tomsk University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 89–94, June, 1998.     

Electronic structure of PdO studied by photoemission (XPS,UPS)

In this paper we present the results of photoemission studies (XPS and UPS) performed on a polycrystalline surface of PdO. The electron density of states (EDOS) deduced both from XPS and UPS (He_I and He_II) are very similar. The valence band of PdO, which differs significantly from the Pd one, can be built up by four structures located at 0.5 eV, 2.2eV, 4.5 eV and 6.5 eV below E_F. The various electronic contributions (p or d) in the band are considered and, in order to explain our spectra, we discuss several hypothesis taking into account the possible existence of satellite lines or crystal field effects. Our XPS and UPS spectra show that the energy bands of PdO are narrow (～ 2–3 eV), moreover the energy shift of the core levels (|ΔE^F_B| = 2 eV) is important : these results suggest that the correlations between the d electrons may be important in PdO.     

Optical properties and electronic structure of copper atoms adsorbed on a platinum electrode

The optical properties of Cu atoms deposited in the underpotential region from electrolytic solution onto a polycrystalline Pt electrode have been studied by differential reflectance spectroscopy. Spectra of the normalized reflectance change ($\text{ΔR}\text{R}$) have been obtained in the photon energy range between 1.5 and 5.5 eV for p- and s-polarized light as a function of coverage θ and angle of incidence ?₁. Evaluation of the adsorbate optical constants by a simple 3-phasemodel reveals three absorption bands in the range studied, one of them being strongly angular dependent. From an assignment of these transitions the positions of the 3d-, 4s- and 4p-derived levels in the energy level diagram of the Cu adatom is determined. As expected these levels are considerably shifted and broadened in comparison to their unperturbed atomic counterparts. Optical evidence for the occurrence of a structural change in the adsorbate layer at about θ = 0.6 is also presented.     

Electronic structure of solid pyridine and pyridine adsorbed on polycrystalline silver

The electronic structure of the valence bands of polycrystalline films of pyridine (C₅H₅N), including all valence levels extending from initial energies of 4 down to 30 eV (E_VAC = 0), has been determined from photoelectron energy distribution measurements for photon energies 20eV ? hν ? 170 eV, using synchrotron radiation. The valence bands showing a one-to-one correspondence to the gas phase, a rigid relaxation shift of δe_r = 0.3 eV for the vertical binding energies, and a considerable solid state broadening (? 0.5 eV) are assigned in comparison to recent MO calculations. By tuning the photon energy and thereby achieving high surface sensitivity for hν around 45 eV, we have also studied pyridine adsorbed at 120 K (6 Langmuir) on in situ prepared polycrystalline Ag-substrates. Thus, we were able to study in detail the surface electronic structure in the range of the Ag 4d bands. Due to a strong mixing of substrate 4d and pyridine 2b₁ (π), 1a₂ (π) and 7a₁ (n) energy levels, the surface electronic structure is strongly modified in the upper part of the 4d bands, and a strong and sharp (0.4 eV FWHM) surface resonance at an energy of 3.7 e V below E^AG_F is observed, which we attribute to a 4d-7a₁ (n) bonding of the nitrogen lone-pair orbital.     

The Alexander-Anderson problem for two atoms adsorbed on graphene

The Green’s functions for the Alexander-Anderson problem have been obtained using the previously proposed model density of states for graphene. Both the ferromagnetic and antiferromagnetic dimers have been considered. It has been shown that, in order to describe the density of states of the dimer adatom, the density of states of the isolated adatom with two positions of the gravity center of the quasi-level shifted in opposite directions can be used. It has been demonstrated that the approximate method of obtaining the Green’s function of the dimer proposed by us previously and consisting in that the Green’s function of the adatom rather than that of the atom is taken as the seed function gives the same result as the Alexander-Anderson approach. The dependences of the indirect interaction of dimer adatoms on the problem parameters have been evaluated in the limit of low energies.