1,238 research outputs found
Temperature dependent transport characteristics of graphene/n-Si diodes
Realizing an optimal Schottky interface of graphene on Si is challenging, as
the electrical transport strongly depends on the graphene quality and the
fabrication processes. Such interfaces are of increasing research interest for
integration in diverse electronic devices as they are thermally and chemically
stable in all environments, unlike standard metal/semiconductor interfaces. We
fabricate such interfaces with n-type Si at ambient conditions and find their
electrical characteristics to be highly rectifying, with minimal reverse
leakage current (10 A) and rectification of more than . We
extract Schottky barrier height of 0.69 eV for the exfoliated graphene and 0.83
eV for the CVD graphene devices at room temperature. The temperature dependent
electrical characteristics suggest the influence of inhomogeneities at the
graphene/n-Si interface. A quantitative analysis of the inhomogeneity in
Schottky barrier heights is presented using the potential fluctuation model
proposed by Werner and G\"{u}ttler.Comment: 5 pages, 5 figure
A transfer technique for high mobility graphene devices on commercially available hexagonal boron nitride
We present electronic transport measurements of single- and bilayer graphene
on commercially available hexagonal boron nitride. We extract mobilities as
high as 125 000 cm^2/V/s at room temperature and 275 000 cm^2/V/s at 4.2 K. The
excellent quality is supported by the early development of the nu = 1 quantum
Hall plateau at a magnetic field of 5 T and temperature of 4.2 K. We also
present a new and accurate transfer technique of graphene to hexagonal boron
nitride crystals. This technique is simple, fast and yields atomically flat
graphene on boron nitride which is almost completely free of bubbles or
wrinkles. The potential of commercially available boron nitride combined with
our transfer technique makes high mobility graphene devices more accessible.Comment: 3 pages, 3 figure
Da\phi ne gamma-rays factory
Gamma sources with high flux and spectral densities are the main requirements
for new nuclear physics experiments to be performed in several worldwide
laboratories and envisaged in the ELI-NP (Extreme Light Infrastructure-Nuclear
Physics) project or in the IRIDE (Interdisciplinary Research Infrastructure
with Dual Electron Linacs) proposals. The paper is focalized on an experiment
of gamma photons production using Compton collisions between the DA\Phi NE
electron beam and a high average power laser pulse, amplified in a
Fabry-P\'erot optical resonator. The calculations show that the resulting gamma
beam source has extremely interesting properties in terms of spectral density,
energy spread and gamma flux comparable (and even better) with the last
generation gamma sources. The energy of the gamma beam depends on the adopted
laser wavelength and can be tuned changing the energy of the electron ring. In
particular we have analyzed the case of a gamma factory tunable in the 2-9 MeV
range. The main parameters of this new facility are presented and the
perturbation on the transverse and longitudinal electron beam dynamics is
discussed. A preliminary accelerator layout to allow experiments with the gamma
beam is presented with a first design of the accelerator optics.Comment: 26 pages, 15 figure
Electronic Spin Transport in Dual-Gated Bilayer Graphene
The elimination of extrinsic sources of spin relaxation is key in realizing
the exceptional intrinsic spin transport performance of graphene. Towards this,
we study charge and spin transport in bilayer graphene-based spin valve devices
fabricated in a new device architecture which allows us to make a comparative
study by separately investigating the roles of substrate and polymer residues
on spin relaxation. First, the comparison between spin valves fabricated on
SiO2 and BN substrates suggests that substrate-related charged impurities,
phonons and roughness do not limit the spin transport in current devices. Next,
the observation of a 5-fold enhancement in spin relaxation time in the
encapsulated device highlights the significance of polymer residues on spin
relaxation. We observe a spin relaxation length of ~ 10 um in the encapsulated
bilayer with a charge mobility of 24000 cm2/Vs. The carrier density dependence
of spin relaxation time has two distinct regimes; n<4 x 1012 cm-2, where spin
relaxation time decreases monotonically as carrier concentration increases, and
n>4 x 1012 cm-2, where spin relaxation time exhibits a sudden increase. The
sudden increase in the spin relaxation time with no corresponding signature in
the charge transport suggests the presence of a magnetic resonance close to the
charge neutrality point. We also demonstrate, for the first time, spin
transport across bipolar p-n junctions in our dual-gated device architecture
that fully integrates a sequence of encapsulated regions in its design. At low
temperatures, strong suppression of the spin signal was observed while a
transport gap was induced, which is interpreted as a novel manifestation of
impedance mismatch within the spin channel
Spin dependent quantum interference in non-local graphene spin valves
Spin dependent electron transport measurements on graphene are of high
importance to explore possible spintronic applications. Up to date all spin
transport experiments on graphene were done in a semi-classical regime,
disregarding quantum transport properties such as phase coherence and
interference. Here we show that in a quantum coherent graphene nanostructure
the non-local voltage is strongly modulated. Using non-local measurements, we
separate the signal in spin dependent and spin independent contributions. We
show that the spin dependent contribution is about two orders of magnitude
larger than the spin independent one, when corrected for the finite
polarization of the electrodes. The non-local spin signal is not only strongly
modulated but also changes polarity as a function of the applied gate voltage.
By locally tuning the carrier density in the constriction we show that the
constriction plays a major role in this effect and indicates that it can act as
a spin filter device. Our results show the potential of quantum coherent
graphene nanostructures for the use in future spintronic devices
Surfaces roughness effects on the transmission of Gaussian beams by anisotropic parallel plates
Influence of the plate surfaces roughness in precise ellipsometry experiments
is studied. The realistic case of a Gaussian laser beam crossing a uniaxial
platelet is considered. Expression for the transmittance is determined using
the first order perturbation theory. In this frame, it is shown that
interference takes place between the specular transmitted beam and the
scattered field. This effect is due to the angular distribution of the Gaussian
beam and is of first order in the roughness over wavelength ratio. As an
application, a numerical simulation of the effects of quartz roughness surfaces
at normal incidence is provided. The interference term is found to be strongly
connected to the random nature of the surface roughness.Comment: 18 pages, Journal of Physics D: Applied Physics, volume 36, issue 21,
pages 2697 - 270
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