Electronic structure of dysprosium silicide films grown on a Si(1 1 1) surface

The thickness-dependent electronic structures of Dy silicide films grown on a Si(1 1 1) surface have been investigated by angle-resolved photoelectron spectroscopy. Two (1×1) periodic bands, both of them cross the Fermi level, have been observed in the silicide films formed by Dy coverages of 1.0 monolayer and below, and more than five () periodic bands have been observed in thicker films. Taking the () periodic structure of Dy atoms in the submonolayer silicide film into account, the periodicity of the two metallic bands indicate that they mainly originate from the orbitals of Si atoms, which form a (1×1) structure. Of the () periodic bands observed in thick films, four of them are well explained by the folding of the (1×1) bands into a () periodicity. Regarding the other band, the three () periodic bands would originate from the electronic states related to the inner Si layers that form a () structure, and the one observed in the 3.0 ML film only might originate from the electron located at the interface between bulk Si and the Dy silicide film.     

Co-induced nano-structures on Si(1 1 1) surface

The interaction of cobalt atoms with silicon (1 1 1) surface has been investigated by means of scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED). Besides the Co silicide islands, we have successfully distinguished two inequivalent Co-induced reconstructions on Si(1 1 1) surface. Our high-resolution STM images provide some structural properties of the two different derived phases. Both of the two phases seem to form islands with single domain. The new findings will help us to understand the early stage of Co silicide formations.     

Submillimeter measurements of N2 and air broadening of hypochlorous acid

The pressure induced broadening of a several pure rotational transitions of hypochlorous acid, HOCl, have been measured as a function of temperature. This set of rotational transitions is the dominant feature of the submillimeter spectrum in the range where several remote sensing instruments currently operate. Additional features throughout the submillimeter spectrum have been recorded at the full-resolution of the room temperature Doppler linewidth using multiplier chains in the 110- wavelengths.     

Thickness and temperature dependence of the dynamic magnetic behavior in disordered FePt films

We present in this work an investigation of the magnetic behavior of FePt films as a function of film thickness and thermal treatment. The films have been sputter-deposited on oxidized Si (1 0 0) crystals and are ferromagnetic at room temperature. Using ferromagnetic resonance techniques at 9.5 GHz we have studied a series of four films with a thickness in the range . The resonance spectra of these films were measured at and also above room temperature. The high temperature measurements produce irreversible changes in the samples which depend on the maximum temperature reached during the experiment. For relatively low measuring temperatures () the magnetic properties are generally improved, probably due to the release of stress formed during film fabrication. For larger temperatures () the absorption linewidth gradually broadens and the line could be hardly observed at room temperature if the measuring temperature exceeded . This behavior is due to the partial transformation of the metastable FCC phase to the ordered L1₀ high anisotropy phase. These data are consistent with the results found in samples annealed outside the resonant cavity.     

Etching and forward transfer of fused silica in solid-phase by femtosecond laser-induced solid etching (LISE)

We present a femtosecond laser-based technique for etching and forward transfer of bulk transparent materials in solid-phase. Femtosecond laser pulses with were focused through a fused silica block onto an absorbing thin film of Cr. A constraining Si wafer was pressed into tight contact with the Cr film to prevent lift-off of the film. A combination of the high temperature and pressure of the Cr, and compressive stress from the Si, resulted in etching of smooth features from the fused silica by cracking. Unlike in conventional ablative or chemical etching, the silica was removed from the bulk as single solid-phase pieces which could be collected on the Si. Using this so-called laser-induced solid etching (LISE) technique, 1-2 m deep pits and channels have been produced in the silica surface, and corresponding dots and lines deposited on the Si. The threshold fluence for etching was found to be with duration pulses. The morphology of the etched features are investigated as functions of fluence and exposure to multiple pulses.     

Near-infrared diode laser spectroscopy of the HCSi radical

The , , and band spectra of HCSi radical were investigated by means of near-infrared diode laser spectroscopy to determine precise molecular constants for the and states. The detailed analysis of the rotationally resolved band spectra, studied for the first time in the present investigation, leads to the precise determination of molecular constants for the state associated with the Renner-Teller interaction. We obtained −0.15126663(53) and 495.00698(30) cm⁻¹ as the Renner-Teller parameter ε and the bending vibrational frequency ω₂, respectively. Based on the molecular constants for the and states, the rotational levels of the state were analyzed to obtain molecular constants and information on upper state perturbations. Using the available spectroscopic data, valence force fields for both the and states were estimated to aid in understanding the vibrational energy levels of the HCSi radical.     

Structural and luminescent characteristics of non-stoichiometric ZnO films by various sputtering and annealing temperatures

ZnO thin films were prepared by reactive RF magnetron sputtering at various deposition temperatures. They were annealed in oxygen ambient at various annealing temperatures. The microstructures and photoluminescence characteristics of ZnO films were investigated. The grain size of the ZnO thin film that was deposited at room temperature (RT) after annealing exceeded that of the film that was deposited at . Excess Zn atoms were considered to be present in the ZnO film that was deposited at RT, so the film was non-stoichiometric ZnO. No visible emission of either of the ZnO films deposited at the two temperatures was observed before annealing. Following annealing at high temperature, the green emission from the ZnO film that was deposited at RT was stronger than that of the film that was deposited at . The relationship between the non-stoichiometry of the thin film and the visible emission was discussed. The luminescent centers that correspond to green emission are defects; the concentration of defects was higher in the ZnO thin film that was deposited at RT than in the film that was deposited at .     

Observation of internal-conversion electrons induced by inelastic nuclear resonant scattering

Measurements of the internal-conversion electron emission due to the inelastic nuclear resonant excitation are reported. thin films of 20 and 1.3 nm thickness were deposited on Si(1 1 1), and the internal-conversion electrons were measured as a function of the photon energy. From the inelastic part of the spectra, the phonon density of states was obtained. Whereas the phonon density of states of 20-nm thick film resembles that of bulk -Fe, the 1.3-nm thick film revealed an obvious softening of the acoustic mode.     

Formation of multiple nanoscale twin boundaries that emit intense light in indirect-gap AlGaAs epilayers

Parallel twin boundaries arranged at similar intervals of nanometer length, that emitted an intense monochromatic light polarized parallel to the boundaries, were self-organized in an indirect-gap AlGaAs epilayer; the epilayer was grown on a rough As-deficient surface of an AlGaAs(0 0 1) substrate with any lattice constant, by conventional metal-organic chemical-vapor deposition. Most boundaries were of -type on B, and they extended from the interface between the epilayer and the substrate. There existed no compositional fluctuation around the boundaries. The formation mechanism was discussed.     

Dynamics of electrons and holes at surfaces

We present ab initio calculation results for electron-phonon (e-ph) contribution to hole lifetime broadening of the surface state on Al(0 0 1). We show that e-ph coupling in this state is significantly stronger than in bulk Al at the Fermi level. It makes the e-ph decay channel very important in the formation of the hole decay in the surface state at . We also present the results for e-e lifetime broadening in a quantum-well state in 1 ML K/Cu(1 1 1). We show that this contribution is not negligible and is much larger than that in a surface state on Ag(1 1 1).     

High pressure structural studies on SrRuO3

We have performed room temperature high pressure structural studies on the ferromagnetic perovskite SrRuO₃ to 34 GPa. We have also used three different pressure media (silicone fluid, 4:1 methanol:ethanol and argon) to test for possible effects of pressure media on compression data. The orthorhombic perovskite structure is stable to the highest pressure, and the data can be fit with a bulk modulus of with a pressure derivative of for all of the pressure media. We have also examined the high pressure behavior of the RuO₆ octahedra using a model that assumes the octahedra are not distorted. Various tilt angles around the ideal cubic perovskite axes are found and can be used to estimate the Ru-O-Ru bond angle that is known to be directly related to the ferromagnetic Curie temperature. For all pressure media, there appears to be a minimum in the Ru-O-Ru bond angle around 15 GPa. Implications for the observed high pressure magnetic behavior of SrRuO₃ will be discussed.     

Parametric characterization of Mathieu-Gauss beams

Based on the irradiance moments definitions, the expression of factor of truncated zeroth-order Mathieu-Gauss beams (MGBs) is derived analytically. Furthermore, the propagation equation of kurtosis parameter of non-truncated MBGs passing through a paraxial ABCD optical system is established. Particularly, the dependence of factor and kurtosis parameter on the spatial profile of the beam are illustrated numerically and analyzed in details.     

Terahertz spectroscopy of oxygen, O2, in its Σg and Δ electronic states : THz Spectroscopy of O2

High precision rotational spectra of isotopic oxygen O₂ (with or ) in its electronic ground state have been measured in selected frequency regions between 0.4 and 2.0 THz. The main isotopic species, , was also investigated in its first excited electronic state . The new data, analyzed together with previous measurements, yielded improved spectroscopic parameters.     

The first measured Mn I Stark widths

The shapes of the astrophysically interesting neutral manganese (Mn I) resonance spectral lines (403.075, 403.306, 403.448, 279.481, 279.826 and 280.108 nm) have been observed together with six other prominent Mn I lines in the laboratory helium plasma at a 47 000 K electron temperature and electron density. With these plasma parameters the Stark broadening has been found to be an important mechanism in the Mn I line shape formation. Our measured Mn I Stark widths (W) are the first data in the literature. Stark widths are compared with line hyperfine structure splittings (Δ_hfs). At above mentioned helium plasma conditions the line broadening due to hyperfine structure splitting of the lines is less than that of the Stark and Doppler broadening for the case of the Mn I lines under investigation. We estimate that at electron densities below and electron temperatures below 4000 K the components in the hyperfine structure play an important role in the mentioned Mn I line shape formation.     

A half-moment model for radiative transfer in a 3D gray medium and its reduction to a moment model for hot, opaque sources

We present in this paper a new 3D half-moment model for radiative transfer in a gray medium, called the model, which uses maximum entropy closure. This model is a generalization to 3D of the 1D version recently proposed in (J. Comp. Phys. 180 (2002) 584). The direction space Ω is divided into two pieces, Ω⁺ and Ω^-, in a dynamical way by the plane perpendicular to the total radiative flux, and the half moments are defined from these subspaces. The model closure and the integrations of the radiative transfer equation performed on the moving Ω^± spaces are detailed. 1D planar results, which have motivated the extension of the model of (J. Comp. Phys. 180 (2002) 584) to multi-dimensions, are shown. These results are very good. The model is thereafter derived for 3D spherically symmetric geometry, where the correctness of the non-trivial border terms can be checked. Two 3D spherically symmetric problems are numerically solved in order to show the accuracy of the closure and the role of the border terms. Once again, compared to the solution obtained with a ray tracing solver, results are very good. From the 3D half-moment model, a new moment model, called , is derived for the particular case of a 3D hot and opaque source radiating into a cold medium, for applications such as simulations of stellar atmospheres and fires. Two-dimensional numerical results are presented and compared to those obtained solving the RTE and with other moment models. They demonstrate the very good accuracy of the model, its good convergence properties, and better prediction compared to all other existing moment models in its domain of applicability.