Friedel oscillations in ytterbium films deposited on the Si(111) 7 × 7 surface

The nonmonotonic dependence of the work function of ytterbium nanofilms deposited on singlecrystal Si(111) on their thickness is experimentally revealed and studied. This dependence is shown to be caused by electron density oscillations in the films (Friedel oscillations), which are generated by the ytterbium-silicon interface. These oscillations originate, in turn, from appreciable charge transfer from the ytterbium film having a low work function to silicon.     

Magnetization-induced anisotropy of second harmonic generation in thin cobalt films

Magnetization-induced effects in the symmetry properties of optical second harmonic generation (SHG) are studied in thin cobalt films. We demonstrate that the application of an external magnetic field leads to the appearance of a strong SHG azimuthal anisotropy from the isotropic Au/Co structure. Symmetry analysis of the SHG dependencies, supported by the SHG interferometry measurements, indicates that the effective magnetic and crystallographic second-order susceptibilities are both of the same order of magnitude.     

Optical second harmonic generation as a surface probe of silver electrodes

Surface second harmonic (SH) signals generated at a polycrystalline silver surface are studied as the electrode undergoes electrochemical cycling in sulfate electrolytes of variable pH. The SH intensity profiles are correlated with the ionic adsorption and surface chemistry occurring at the electrode interface. The dramatic differences in the optical response of these solutions is attributed to the formation of silver oxides. Detection of monolayer coverages of adsorbed sulfate ions demonstrate the inherent sensitivity of this nonlinear optical technique. The effect on the SH efficiency of trace amounts of oxygen in the electrolyte is also discussed.     

Influence of impurities on the surface structures and fault generation in homoepitaxial Si (111) films

In situ LEED studies of the homoepitaxial growth of Si(111) films by uhv sublimation, indicate a strong correlation between the type of surface structure generated and the metallic impurity content of the silicon substrates as estimated from minority carrier lifetimes. The development of the familiar Si (111)−7 × 7 structure is favored by the presence of lifetime-killing impurities in the substrate. Experiments where Fe is introduced on high lifetime substrates prior to annealing and film growth, suggest that this impurity species plays a role in the generation of the 7 × 7 surface structure. Electron microscopy reveals that homoepitaxial Si(111) layers are generally faulted, the number density of which increases progressively as the growth temperature is lowered and the deposition rate increased. Films deposited on high lifetime silicon contain substantially fewer stacking faults than those grown on low lifetime substrates. These results suggest that the faults originate at the substrate surface at microprecipitates consisting of fast diffusing, low solubility impurity species.     

Adsorption of thin films of titanium on tungsten (111) surface

The structural and electronic properties of titanium-covered (111) surface of tungsten are studied via first-principles density-functional calculations. The dominant role played by substrate–adlayer interactions in the formation of thin films of Ti on W(111) explains the observed isomorphous growth for Ti depositions up to a full physical overlayer, with adatoms most favorably arranged in substrate-lattice-continuation sites. The optimized atomic configurations indicate substantial interplane relaxations following the contraction–contraction–expansion pattern, characteristic also of the clean W(111) substrate. Modification of the surface electronic properties of the Ti/W(111) system is examined for increasing adsorbate coverage with emphasis placed on the formation and localization properties of adsorbate-induced resonances.     

Pulsed-laser-deposited epitaxial aluminum nitride films on (111) Si for surface acoustic-wave applications

Epitaxial (001) aluminum nitride (AlN) thin films on (111) Si substrates are prepared using pulsed-laser deposition. The epitaxial structure of the as-prepared thin films is characterized by checking the X-ray-diffraction θ-2 θ scan and pole-figure, using scanning electron microscopy, infrared radiation (IR) spectroscopy and Raman spectroscopy. The surface acoustic-wave resonance at 345 MHz for a 1.5 μm thick AlN film on a (111) Si substrate is observed using an inter-digital electrode. Received: 18 September 2001 / Accepted: 29 January 2002 / Published online: 3 June 2002 RID="*" ID="*"Corresponding author. Fax: +86-25/359-5535, E-mail: liujm@nju.edu.cn     

Group-theoretical analysis of second harmonic generation at (110) and (111) surfaces of antiferromagnets

Received: 20 September 1998     

Submonolayer films on a Si(111) surface under low-energy ion bombardment

The kinetics of deposition for monomolecular submonolayer films on a Si(111) surface is studied via low-energy electron diffraction with measurements of the intensities of diffraction reflection and the elastic background. The degree of structural perfection in growing films is estimated for alkali-metal silicides and silicon from low-energy beams. The optimum energy and dose intervals of silicide film formation are determined.     

Passivation of Si(111) surfaces with electrochemically grafted thin organic films

Ultra thin organic films (about 5 nm thick) of nitrobenzene and 4-methoxydiphenylamine were deposited electrochemically on p-Si(111) surfaces from benzene diazonium compounds. Studies based on atomic force microscopy, infrared spectroscopic ellipsometry and x-ray photoelectron spectroscopy showed that upon exposure to atmospheric conditions the oxidation of the silicon interface proceed slower on organically modified surfaces than on unmodified hydrogen passivated p-Si(111) surfaces. Effects of HF treatment on the oxidized organic/Si interface and on the organic layer itself are discussed.     

A leed-aes study of thin Pd films on Si(111) and (100) substrates

A system Pd (deposit)-Si (substrate) has been studied by LEED and AES. Pd₂Si formed on Si(111) became epitaxial after a short time of annealing at a temperature between 300 and 700°C, while the Pd₂Si formed on Si(100) did not, in both cases the surfaces of the Pd₂Si being covered with a very thin Si layer. A sequence of superstructures (3√3 × 3√3), (1 × 1), and (2√3 × 2√3) was observed successively in Pd/Si(111) as the annealing temperature was increased. A (√3 × √3) structure was obtained by sputtering the 3√3 surface slightly. It was found that the √3 structure corresponds to Pd²Si(0001)-(1 × 1) grown epitaxially on Si(111), and that the 3√3 structure comes from the thin Si layer accumulated over the silicide surface, while the 2√3 and 1 structures arise from a submonolayer of Pd adsorbed on Si(111). Superstructures observed on a Pd/Si(100) system are also studied.     

Magnetic properties of Co films grown on the modified Si(111) surface

The magnetic properties and domain structure of epitaxial Co films grown on a modified Si(111) surface were studied. First, the processes of growth of copper silicide nanostructures on the Si(111) surface were investigated. Copper silicide clusters were formed on the Si(111)-5.55 × 5.55-Cu surface at a substrate temperature of ～550°C. It was established that the nanostructures formed have a perfect faceting, and the lateral edges and long wire side are oriented along the Si〈110〉 crystallographic directions. Then, Co films were deposited on the formed structures. The investigation of the coercive force and reduced remanent magnetization showed that the Co(111) films have the sixth-order crystalline anisotropy. It was found that the coercive force of the Co films deposited on the Cu buffer layer is approximately six times less than that of the Co films deposited on the Si(111)-5.55 × 5.55-Cu surface and Si(111)?5.55 × 5.55-Cu/(Cu-Si) cluster surface.     

Magnetic relaxation in very thin films of Dy deposited onto crystalline Cu(111)

Magnetic relaxation measurements of very thin Dy films of thickness 20 Å and 40 Å have been performed in the temperature range 1.8 K–20 K. Below the blocking temperature, the magnetic viscosity decreases when decreasing the temperature and becomes non-thermal below a few Kelvins.     

Properties of Si nanostructural modification on Si (111) surface

Si nanostructures (Si-NSs) epitaxially grown or adsorbed on Si (111) surface, with various shapes including pit-like, bars, islands, hill-like, diamond-like and double cage, were studied theoretically using density-functional theory (DFT) calculations. The electronic and optical properties of these Si-NSs were calculated, showing that the designed Si-NSs modifications can enhance the optical absorption for Si surface.     

Plasma resonance absorption in interfacial photoemission from very thin silver films on Cu(111)

Very thin silver films deposited on a Cu(111) substrate were studied with the photoemission-into-electrolyte technique. The optical resonance absorption at the silver bulk plasma frequency was observed for films thicker than two monolayers. The correlation between optical absorption and photoemission intensities depends in a complicated fashion on the photon energy as well as the film thickness.