8,811 research outputs found
Charge transfer and trapping as origin of a double dip in the transfer characteristics of graphene based field-effect transistors
We discuss the origin of an additional dip other than the charge neutrality
point observed in transfer characteristics of graphene-based field-effect
transistors. The double-dip is proved to arise from charge transfer between
graphene and metal electrodes, while charge storage at the graphene/SiO2
interface enhances it. Considering different Fermi energy from the neutrality
point along the channel and partial charge pinning at the contacts, we propose
a model which explains all features in gate voltage loops.Comment: 14 pages, 5 figure
Graphene field effect transistors with Niobium contacts and asymmetric transfer characteristics
We fabricate back-gated field effect transistors using Niobium electrodes on
mechanically exfoliated monolayer graphene and perform electrical
characterization in the pressure range from atmospheric down to 10-4 mbar. We
study the effect of room temperature vacuum degassing and report asymmetric
transfer characteristics with a resistance plateau in the n-branch. We show
that weakly chemisorbed Nb acts as p-dopant on graphene and explain the
transistor characteristics by Nb/graphene interaction with unpinned Fermi level
at the interface.Comment: 10 pages, Research Pape
Field emission from single and few-layer graphene flakes
We report the observation and characterization of field emission current from
individual single- and few-layer graphene flakes laid on a flat SiO2/Si
substrate. Measurements were performed in a scanning electron microscope
chamber equipped with nanoprobes, used as electrodes to realize local
measurements of the field emission current. We achieved field emission currents
up to 1 {\mu}A from the flat part of graphene flakes at applied fields of few
hundred V/{\mu}m. We found that emission process is stable over a period of
several hours and that it is well described by a Fowler-Nordheim model for
currents over 5 orders of magnitude
Solar-like oscillations in the G8 V star tau Ceti
We used HARPS to measure oscillations in the low-mass star tau Cet. Although
the data were compromised by instrumental noise, we have been able to extract
the main features of the oscillations. We found tau Cet to oscillate with an
amplitude that is about half that of the Sun, and with a mode lifetime that is
slightly shorter than solar. The large frequency separation is 169 muHz, and we
have identified modes with degrees 0, 1, 2, and 3. We used the frequencies to
estimate the mean density of the star to an accuracy of 0.45% which, combined
with the interferometric radius, gives a mass of 0.783 +/- 0.012 M_sun (1.6%).Comment: accepted for publication in A&
Tunable Schottky barrier and high responsivity in graphene/Si-nanotip optoelectronic device
We demonstrate tunable Schottky barrier height and record photo-responsivity
in a new-concept device made of a single-layer CVD graphene transferred onto a
matrix of nanotips patterned on n-type Si wafer. The original layout, where
nano-sized graphene/Si heterojunctions alternate to graphene areas exposed to
the electric field of the Si substrate, which acts both as diode cathode and
transistor gate, results in a two-terminal barristor with single-bias control
of the Schottky barrier. The nanotip patterning favors light absorption, and
the enhancement of the electric field at the tip apex improves photo-charge
separation and enables internal gain by impact ionization. These features
render the device a photodetector with responsivity (3 A/W for white LED light
at 3 mW/cm2 intensity) almost an order of magnitude higher than commercial
photodiodes. We extensively characterize the voltage and the temperature
dependence of the device parameters and prove that the multi-junction approach
does not add extra-inhomogeneity to the Schottky barrier height distribution.
This work represents a significant advance in the realization of graphene/Si
Schottky devices for optoelectronic applications.Comment: Research paper, 22 pages, 7 figure
On the measurement of intensity correlations from laboratory and astronomical sources with SPADs and SNSPDs
We describe the performance of detector modules containing silicon single photon avalanche photodiodes (SPADs) and superconducting nanowire single photon detectors (SNSPDs) to be used for intensity interferometry. The SPADs are mounted in fiber-coupled and free-space coupled packages. The SNSPDs are mounted in a small liquid helium cryostat coupled to single mode fiber optic cables which pass through a hermetic feed-through. The detectors are read out with microwave amplifiers and FPGA-based coincidence electronics. We present progress on measurements of intensity correlations from incoherent sources including gas-discharge lamps and stars with these detectors. From the measured laboratory performance of the correlation system, we estimate the sensitivity to intensity correlations from stars using commercial telescopes and larger existing research telescopes. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only
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