266 research outputs found
First-principles characterization of Mg low-index surfaces: Structure, reconstructions, and surface core-level shifts
In this paper, first-principles calculations provide structural characterization of three low-index Mg surfaces - Mg(0001), Mg(1010), and Mg(1120) - and their respective surface core-level shifts (SCLSs). Inspired by the close similarities between Be and Mg surfaces, we also explore the reconstruction of Mg(1120). Through the calculation of surface energies and the use of the angular-component decomposed density of states, we show that reconstructions are likely to occur at the Mg(1120) surface, similarly to what was found earlier for Be(1120). Indeed, the surface energy of some of the explored reconstructions is slightly lower than that of the unreconstructed surface. In addition, because of lattice symmetry, the morphology of the unreconstructed surface (1120) results in a steplike zig-zag chain packing, with topmost chains supporting a resonant, quasi-one-dimensional (1D), partially filled electronic state. As the presence of partially filled quasi-1D bands is a necessary condition for Peierls-like dimerization, we verify that the undimerized surface chain remains stable with respect to it. Some of the reconstructions, namely, the 2
71 and 3
71 added row reconstructions, induce a stronger relaxation of the topmost chains, increasing the coupling with lower layers and thus significantly damping the quasi-1D character of this state. The original approach followed offers a common and general framework to identify quasi-1D bands - even in the case of resonant electronic surface states - and to meaningfully compare calculated and measured SCLSs even in the presence of multicomponent peak contributions
Electrical and Raman-imaging characterization of laser-made electrodes for 3D diamond detectors
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Interplay among work function, electronic structure and stoichiometry in nanostructured VO: X films
The work function is the parameter of greatest interest in many technological applications involving charge exchange mechanisms at the surface. The possibility to produce samples with a controlled work function is then particularly interesting, albeit challenging. We synthetized nanostructured vanadium oxide films by a room temperature supersonic cluster beam deposition method, obtaining samples with tunable stoichiometry and work function (3.7-7 eV). We present an investigation of the electronic structure of several vanadium oxide films as a function of the oxygen content via in situ Auger, valence-band photoemission spectroscopy and work function measurements. The experiments probed the partial 3d density of states, highlighting the presence of strong V 3d-O 2p and V 3d-V 4s hybridizations which influence 3d occupation. We show how controlling the stoichiometry of the sample implies control over work function, and that the access to nanoscale quantum confinement can be exploited to increase the work function of the sample relative to the bulk analogue. In general, the knowledge of the interplay among work function, electronic structure, and stoichiometry is strategic to match nanostructured oxides to their target applications
Electro-chemical deposition of zinc oxide nanostructures by using two electrodes
One of the most viable ways to grow nanostructures is electro deposition. However, most electrodeposited samples are obtained by three-electrode electrochemical cell. We successfully use a much simpler two-electrode cell to grow different ZnO nanostructures from common chemical reagents. Concentration, pH of the electrolytes and growth parameters like potentials at the electrodes, are tailored to allow fast growth without complexity. Morphology and surface roughness are investigated by Scanning Electron and Air Force Microscopy (SEM and AFM) respectively, crystal structure by X-Ray Diffraction measurements (XRD) and ZnO stoichiometry by core level photoemission spectroscopy (XPS)
O2 Loaded Germanosilicate Optical Fibers: Experimental In Situ Investigation and Ab Initio Simulation Study of GLPC Evolution under Irradiation
In this work we present a combined experimental and ab initio simulation investigation concerning the Germanium Lone Pair Center (GLPC), its interaction with molecular oxygen (O2), and evolution under irradiation. First, O2 loading has been applied here to Ge-doped optical fibers to reduce the concentration of GLPC point defects. Next, by means of cathodoluminescence in situ experiments, we found evidence that the 10 keV electron irradiation of the treated optical fibers induces the generation of GLPC centers, while in nonloaded optical fibers, the irradiation causes the bleaching of the pre-existing GLPC. Ab initio calculations were performed to investigate the reaction of the GLPC with molecular oxygen. Such investigations suggested the stability of the dioxagermirane (DIOG) bulk defect, and its back conversion into GLPC with a local release of O2 under irradiation. Furthermore, it is also inferred that a remarkable portion of the O2 passivated GLPC may form Ge tetrahedra connected to peroxy bridges. Such structures may have a larger resistance to the irradiation and not be back converted into GLPC
EP-1370: Stereotactic body radiotherapy in 117 oligometastatic lymph node recurrent prostate cancer patients
HST/NICMOS Observations of NGC 1333: The Ratio of Stars to Sub-Stellar Objects
We present an analysis of NICMOS photometry and low-resolution grism
spectroscopy of low-mass stars and sub-stellar objects in the young
star-forming region NGC 1333. Our goal is to constrain the ratio of low-mass
stars to sub- stellar objects down to 20 Mjup in the cluster as well as
constrain the cluster IMF down to 30 Mjup in combination with a previous survey
of NGC 1333 by Wilking et al. Our survey covers 4 fields of 51.2" x 51.2",
centered on brown dwarf candidates previously identified in Wilking et al. We
extend previous work based on the use of a water vapor index for spectral
typing to wavelengths accessible with NICMOS on the HST. Spectral types were
derived for the 14 brightest objects in our fields, ranging from <M0 - M8,
which at the age of the cluster (0.3 Myr) corresponds to a range in mass of
>0.25 - 0.02 Msun. In addition to the spectra, we present an analysis of the
color-magnitude diagram using pre-main sequence evolutionary models of D'Antona
& Mazzitelli. Using an extinction-limited sample, we derive the ratio of
low-mass stars to brown dwarfs. Comparisons of the observed ratio to that
expected from the field IMF of Chabrier indicate that the two results are
consistent. We combine our data with that of Wilking et al. to compute the
ratio of intermediate-mass stars (0.1 - 1.0 Msun) to low-mass objects (0.03 -
0.1 Msun) in the cluster. We also report the discovery of a faint companion to
the previously confirmed brown dwarf ASR 28, as well as a possible outflow
surrounding ASR 16. If the faint companion is confirmed as a cluster member, it
would have a mass of ~ 5 Mjup (mass ratio 0.15) at a projected distance of 350
AU, similar to 2MASS 1207-3923 B.Comment: 33 pages, 6 figures, accepted for publication by A
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