1,728 research outputs found
Quantum size effects in the low temperature layer-by-layer growth of Pb on Ge(001)
The electronic properties of thin metallic films deviate from the
corresponding bulk ones when the film thickness is comparable with the
wavelength of the electrons at the Fermi level due to quantum size effects
(QSE). QSE are expected to affect the film morphology and structure leading to
the low temperature (LT) ``electronic growth'' of metals on semiconductors. In
particular, layer-by-layer growth of Pb(111) films has been reported for
deposition on Ge(001) below 130 K. An extremely flat morphology is preserved
throughout deposition from four up to a dozen of monolayers. These flat films
are shown to be metastable and to reorganize into large clusters uncovering the
first Pb layer, pseudomorphic to the substrate, already at room temperature.
Indications of QSE induced structural variations of the growing films have been
reported for Pb growth on Ge(001), where the apparent height of the Pb(111)
monatomic step was shown to change in an oscillatory fashion by He atom
scattering (HAS) during layer-by-layer growth. The extent of the structural QSE
has been obtained by a comparison of the HAS data with X-ray diffraction (XRD)
and reflectivity experiments. Whereas step height variations as large as 20 %
have been measured by HAS reflectivity, the displacement of the atomic planes
from their bulk position, as measured by XRD, has been found to mainly affect
the topmost Pb layer, but with a lower extent, i.e. the QSE observed by HAS are
mainly due to a perpendicular displacement of the topmost layer charge density.
The effect of the variable surface relaxation on the surface vibration has been
studied by inelastic HAS to measure the acoustic dispersion of the low energy
phonons.Comment: 28 pages (laTex,elsart) and 13 figures (eps); updated reference
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
Exoelectron emission during oxidation of Cs films
During oxidation of thin Cs films, a nonadiabatic surface reaction manifests itself in the emission of electrons. This effect was investigated in detail by combining measurements of the current and of energy distributions of these exoelectrons with studies on the electronic properties of the surface by means of ultraviolet photoelectron spectroscopy and metastable deexcitation spectroscopy. Exoelectron emission occurs via Auger deexcitation of the empty state derived from the O2 affinity level. This process is confined to the stage Cs2O2âCsO2 in which resonance ionization of the affinity level of the impinging O2 molecule upon crossing the Fermi level EF is efficiently suppressed due to the absence of metallic states near EF. A kinetic model based on the successive steps involved in the oxidation of Cs is developed which describes qualitatively well all the experimental findings
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
Singlet-to-triplet conversion of metastable He atoms at alkali-metal overlayers
Energy distributions of electrons emitted from alkali-metal surfaces by impact of metastable He atoms reveal that there is a high probability for transformation of singlet atoms (excitation energy E*=20.6 eV) into triplet atoms (E*=19.8 eV) prior to deexcitation into the ground state. The conversion probability (as expressed by the ratio R of the intensities of valence-band emission due to triplet and singlet He* deexcitation, respectively) increases with increasing alkali-metal coverage on a Ru(0001) substrate, and in turn decreases with increasing oxygen exposure at a fixed alkali coverage. These findings indicate that R is a qualitative measure for the degree of ââmetallizationââ of the adlayer. R also increases with temperature due to broadening of the nearest-neighbor distribution whereby, on the average, a larger part of the adlayer becomes metalliclike. For Cs overlayers exhibiting work functions *â (1s12s2) formation as reflected by the R data as well as by the widths of the electron spectra
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)
The Planck Low Frequency Instrument
The Low Frequency Instrument (LFI) of the "Planck Surveyor" ESA mission will
perform high-resolution imaging of the Cosmic Microwave Background anisotropies
at four frequencies in the 30-100 GHz range. We review the LFI main scientific
objectives, the current status of the instrument design and the on-going effort
to develop software simulations of the LFI observations. In particular we
discuss the design status of the PLANCK telescope, which is critical for
reaching adequate effective angular resolution.Comment: 10 pages, Latex (use epsfig.sty); 4 Postscript figures; Astrophys.
Lett & Comm, in press. Proc. of the Conference: "The Cosmic Microwave
Background and the Planck Mission", Santander, Spain, 22-25 June 199
Sensory quality of meat from lambs fed on different diets
The whole seed of sweet lupin var. Multitalia with a protein content higher than 35% and a low content in alkaloids constitutes a good protein source alternative to soybean meal, today deriving for more than 60% from OGM (Genetically Modified Organisms) cultivation. Moreover, the poor national production and the cost of feeds for animals forces the livestock compartment to utilize alternative biomasses the availability of which highly depends on from the environment and the season
Thermal susceptibility of the Planck-LFI receivers
This paper is part of the Prelaunch status LFI papers published on JINST:
http://www.iop.org/EJ/journal/-page=extra.proc5/jinst .
This paper describes the impact of the Planck Low Frequency Instrument front
end physical temperature fluctuations on the output signal. The origin of
thermal instabilities in the instrument are discussed, and an analytical model
of their propagation and impact on the receivers signal is described. The
experimental test setup dedicated to evaluate these effects during the
instrument ground calibration is reported together with data analysis methods.
Finally, main results obtained are discussed and compared to the requirements.Comment: This is an author-created, un-copyedited version of an article
accepted for publication in Journal of Instrumentation. IOP Publishing Ltd is
not responsible for any errors or omissions in this version of the manuscript
or any version derived from it. The definitive publisher authenticated
version is available online at 10.1088/1748-0221/4/12/T1201
Planck Low Frequency Instrument: Beam Patterns
The Low Frequency Instrument on board the ESA Planck satellite is coupled to
the Planck 1.5 meter off-axis dual reflector telescope by an array of 27
corrugated feed horns operating at 30, 44, 70, and 100 GHz. We briefly present
here a detailed study of the optical interface devoted to optimize the angular
resolution (10 arcmin at 100 GHz as a goal) and at the same time to minimize
all the systematics coming from the sidelobes of the radiation pattern. Through
optical simulations, we provide shapes, locations on the sky, angular
resolutions, and polarization properties of each beam.Comment: On behalf of the Planck collaboration. 3 pages, 1 figure. Article
published in the Proceedings of the 2K1BC Experimental Cosmology at
millimetre wavelength
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