2,052 research outputs found
Study of the isotropic contribution to the analysis of photoelectron diffraction experiments at the ALOISA beamline
The angular distribution of the intensity in photoemission experiments is
affected by electron diffraction patterns and by a smoothly varying ISO
contribution originated by both intrumental details and physical properties of
the samples. The origin of the various contributions to the ISO component has
been identified since many years. Nonetheless in this work we present original
developement of the ED analysis, which arises from the evolution of
instrumental performance, in terms of analyzers positioning and angular
resolution, as well as collimation and size of X-ray beams in third generation
synchrotron sources. The analytical treatement of the instrumental factors is
presented in detail for the end station of the ALOISA beamline (Trieste
Synchrotron), where a wide variety of scattering geometries is available for ED
experiments. We present here the basic formulae and their application to
experimental data taken on the Fe/Cu3Au(001) system in order to highlight the
role of the various parameters included in the distribution function. A
specific model for the surface illumination has been developed as well as the
overlayer thickness and surface roughness have been considered.Comment: RevTex, nine pages with five eps figures; to be published in J.
Electron Spectrosc. Relat. Pheno
Quality differences in cheeses produced by lowland and highland units of the Alpine transhumant system
The characteristics of ripened cheeses depend on a large number of factors, of which animal feeding plays an important role. Several researches showed influences of factors linked to forage, such as quality or method of conservation (Verdier-Metz et al., 1998)
Dissociation of CH Species on Ni(111):A HREELS Study
The isothermal dissociation rate of CCH and CH on Ni(111) was measured by following, with HREEL spectroscopy, the intensity of the CH stretching peak as a function of time. By repeating the experiment at several different temperatures we obtained an activation energy of 8±3 kcal/mol for the CCH dissociation reaction and of 12±3 kcal/mol for the CH dissociation reaction. Pre-exponential factors were found to be 10^3±1 s-1 in both cases. Independent thermal desorption spectra show a feature at 470 K and a tail extending up to 600 K which can be assigned to the CCH dissociation and the CH dissociation respectively. The two experiments are quantitatively consistent
Spectro-microscopy of single and multi-layer graphene supported by a weakly interacting substrate
We report measurements of the electronic structure and surface morphology of
exfoliated graphene on an insulating substrate using angle-resolved
photoemission and low energy electron diffraction. Our results show that
although exfoliated graphene is microscopically corrugated, the valence band
retains a massless fermionic dispersion, with a Fermi velocity of ~10^6 m/s. We
observe a close relationship between the morphology and electronic structure,
which suggests that controlling the interaction between graphene and the
supporting substrate is essential for graphene device applications.Comment: 10 pages of text, 4 JPEG figure
Making ARPES Measurements on Corrugated Monolayer Crystals: Suspended Exfoliated Single-Crystal Graphene
Free-standing exfoliated monolayer graphene is an ultra-thin flexible
membrane, which exhibits out of plane deformation or corrugation. In this
paper, a technique is described to measure the band structure of such
free-standing graphene by angle-resolved photoemission. Our results show that
photoelectron coherence is limited by the crystal corrugation. However, by
combining surface morphology measurements of the graphene roughness with
angle-resolved photoemission, energy dependent quasiparticle lifetime and
bandstructure measurements can be extracted. Our measurements rely on our
development of an analytical formulation for relating the crystal corrugation
to the photoemission linewidth. Our ARPES measurements show that, despite
significant deviation from planarity of the crystal, the electronic structure
of exfoliated suspended graphene is nearly that of ideal, undoped graphene; we
measure the Dirac point to be within 25 meV of . Further, we show that
suspended graphene behaves as a marginal Fermi-liquid, with a quasiparticle
lifetime which scales as ; comparison with other graphene and
graphite data is discussed
Oscillatory Instabilities of Standing Waves in One-Dimensional Nonlinear Lattices
In one-dimensional anharmonic lattices, we construct nonlinear standing waves
(SWs) reducing to harmonic SWs at small amplitude. For SWs with spatial
periodicity incommensurate with the lattice period, a transition by breaking of
analyticity versus wave amplitude is observed. As a consequence of the
discreteness, oscillatory linear instabilities, persisting for arbitrarily
small amplitude in infinite lattices, appear for all wave numbers Q not equal
to zero or \pi. Incommensurate analytic SWs with |Q|>\pi/2 may however appear
as 'quasi-stable', as their instability growth rate is of higher order.Comment: 4 pages, 6 figures, to appear in Phys. Rev. Let
Assembly and Annotation of Red Spruce (Picea rubens) Chloroplast Genome, Identification of Simple Sequence Repeats, and Phylogenetic Analysis in Picea
We have sequenced the chloroplast genome of red spruce (Picea rubens) for the first time using the single-end, short-reads (44 bp) Illumina sequences, assembled and functionally annotated it, and identified simple sequence repeats (SSRs). The contigs were assembled using SOAPdenovo2 following the retrieval of chloroplast genome sequences using the black spruce (Picea mariana) chloroplast genome as the reference. The assembled genome length was 122,115 bp (gaps included). Comparatively, the P. rubens chloroplast genome reported here may be considered a near-complete draft. Global genome alignment and phylogenetic analysis based on the whole chloroplast genome sequences of Picea rubens and 10 other Picea species revealed high sequence synteny and conservation among 11 Picea species and phylogenetic relationships consistent with their known classical interrelationships and published molecular phylogeny. The P. rubens chloroplast genome sequence showed the highest similarity with that of P. mariana and the lowest with that of P. sitchensis. We have annotated 107 genes including 69 protein-coding genes, 28 tRNAs, 4 rRNAs, few pseudogenes, identified 42 SSRs, and successfully designed primers for 26 SSRs. Mononucleotide A/T repeats were the most common followed by dinucleotide AT repeats. A similar pattern of microsatellite repeats occurrence was found in the chloroplast genomes of 11 Picea species
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