11,866 research outputs found
Endotaxial Si nanolines in Si(001):H
We present a detailed study of the structural and electronic properties of a
self-assembled silicon nanoline embedded in the H-terminated silicon (001)
surface, known as the Haiku stripe. The nanoline is a perfectly straight and
defect free endotaxial structure of huge aspect ratio; it can grow micrometre
long at a constant width of exactly four Si dimers (1.54nm). Another remarkable
property is its capacity to be exposed to air without suffering any
degradation. The nanoline grows independently of any step edges at tunable
densities, from isolated nanolines to a dense array of nanolines. In addition
to these unique structural characteristics, scanning tunnelling microscopy and
density functional theory reveal a one-dimensional state confined along the
Haiku core. This nanoline is a promising candidate for the long sought after
electronic solid-state one-dimensional model system to explore the fascinating
quantum properties emerging in such reduced dimensionality.Comment: 8 pages, 6 figure
One dimensional Si-in-Si(001) template for single-atom wire growth
Single atom metallic wires of arbitrary length are of immense technological
and scientific interest. We describe a novel silicon-only template enabling the
self-organised growth of isolated micrometer long surface and subsurface
single-atom chains. It consists of a one dimensional, defect-free
reconstruction - the Haiku core, here revealed for the first time in details -
self-assembled on hydrogenated Si(001) terraces, independent of any step edges.
We discuss the potential of this Si-in-Si template as an appealing alternative
to vicinal surfaces for nanoscale patterning.Comment: 3 pages, 2 figure
Eco-friendly gas mixtures for Resistive Plate Chambers based on Tetrafluoropropene and Helium
Due to the recent restrictions deriving from the application of the Kyoto
protocol, the main components of the gas mixtures presently used in the
Resistive Plate Chambers systems of the LHC experiments will be most probably
phased out of production in the coming years. Identifying possible replacements
with the adequate characteristics requires an intense R&D, which was recently
started, also in collaborations across the various experiments. Possible
candidates have been proposed and are thoroughly investigated. Some tests on
one of the most promising candidate - HFO-1234ze, an allotropic form of
tetrafluoropropane- have already been reported. Here an innovative approach,
based on the use of Helium, to solve the problems related to the too elevate
operating voltage of HFO-1234ze based gas mixtures, is discussed and the
relative first results are shown.Comment: 9 pages, 6 figures, 1 tabl
Observation of coda signals from regional and local earthquakes recorded from a downhole-uphole couple of broad-band sensors at Mt Etna
Seismic coda of regional and local earthquakes recorded at a couple of broad band seismometers
located at the bottom of a 125 m deep borehole and up-hole at surface show interesting spectral
features. We observe strong similarity between the waveforms recorded from up- and down-hole
sensors at low frequency (0.1 -3 Hz) and measurable differences in the higher frequency limit. We
interpret this observation assuming that at high frequency the up-hole coda is produced by body-tosurface
wave scattering in the near surface. We compare the experimental results with numerical
simulations done using the Monte Carlo scheme of Yoshimoto et al. (2000) carried out in the
assumption of velocity and scattering coefficient which smoothly vary with depth, with the addition of a
body-to-surface wave conversion for the energy particles which reach the surface. The comparison of
the experimental coda envelopes with those obtained through numerical simulation allow for a
quantification of the turbidity parameter at surface
Shear wave splitting changes associated with the 2001 volcanic eruption on Mt. Etna
The time delays and polarizations of shear wave splitting above small earthquakes show variations
before the 2001 July 17–August 9 2001 flank eruption on Mt Etna, Sicily. Normalized
time delays, measured by singular value decomposition, show a systematic increase starting
several days before the onset of the eruption. On several occasions before the eruption, the
polarization directions of the shear waves at Station MNT, closest to the eruption, show 90â—¦-
flips where the faster and slower split shear waves exchange polarizations. The last 90â—¦-flip
being 5 days before the onset of the eruption. The time delays also exhibit a sudden decrease
shortly before the start of the eruption suggesting the possible occurrence of a ‘relaxation’
phenomena, due to crack coalescence. This behaviour has many similarities to that observed
before a number of earthquakes elsewhere
Performance of Optically Readout GEM-based TPC with a 55Fe source
Optical readout of large Time Projection Chambers (TPCs) with multiple Gas
Electron Multipliers (GEMs) amplification stages has shown to provide very
interesting performances for high energy particle tracking. Proposed
applications for low-energy and rare event studies, such as Dark Matter search,
ask for demanding performance in the keV energy range. The performance of such
a readout was studied in details as a function of the electric field
configuration and GEM gain by using a Fe source within a 7 litre
sensitive volume detector developed as a part of the R\&D for the CYGNUS
project. Results reported in this paper show that the low noise level of the
sensor allows to operate with a 2~keV threshold while keeping a rate of
fake-events lesser than 10 per year. In this configuration, a detection
efficiency well above 95\% along with an energy resolution () of 18\%
is obtained for the 5.9 keV photons, demonstrating the very promising
capabilities of this technique
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