559 research outputs found
Charge Detection in Graphene Quantum Dots
We report measurements on a graphene quantum dot with an integrated graphene
charge detector. The quantum dot device consists of a graphene island (diameter
approx. 200 nm) connected to source and drain contacts via two narrow graphene
constrictions. From Coulomb diamond measurements a charging energy of 4.3 meV
is extracted. The charge detector is based on a 45 nm wide graphene nanoribbon
placed approx. 60 nm from the island. We show that resonances in the nanoribbon
can be used to detect individual charging events on the quantum dot. The
charging induced potential change on the quantum dot causes a step-like change
of the current in the charge detector. The relative change of the current
ranges from 10% up to 60% for detecting individual charging events.Comment: 4 pages, 3 figure
Raman spectroscopy on etched graphene nanoribbons
We investigate etched single-layer graphene nanoribbons with different widths
ranging from 30 to 130 nm by confocal Raman spectroscopy. We show that the
D-line intensity only depends on the edge-region of the nanoribbon and that
consequently the fabrication process does not introduce bulk defects. In
contrast, the G- and the 2D-lines scale linearly with the irradiated area and
therefore with the width of the ribbons. We further give indications that the
D- to G-line ratio can be used to gain information about the crystallographic
orientation of the underlying graphene. Finally, we perform polarization angle
dependent measurements to analyze the nanoribbon edge-regions
Quantum capacitance and density of states of graphene
We report on measurements of the quantum capacitance in graphene as a
function of charge carrier density. A resonant LC-circuit giving high
sensitivity to small capacitance changes is employed. The density of states,
which is directly proportional to the quantum capacitance, is found to be
significantly larger than zero at and around the charge neutrality point. This
finding is interpreted to be a result of potential fluctuations with amplitudes
of the order of 100 meV in good agreement with scanning single-electron
transistor measurements on bulk graphene and transport studies on nanoribbons
Tunable Coulomb blockade in nanostructured graphene
We report on Coulomb blockade and Coulomb diamond measurements on an etched,
tunable single-layer graphene quantum dot. The device consisting of a graphene
island connected via two narrow graphene constrictions is fully tunable by
three lateral graphene gates. Coulomb blockade resonances are observed and from
Coulomb diamond measurements a charging energy of ~3.5 meV is extracted. For
increasing temperatures we detect a peak broadening and a transmission increase
of the nanostructured graphene barriers
Coulomb oscillations in three-layer graphene nanostructures
We present transport measurements on a tunable three-layer graphene single
electron transistor (SET). The device consists of an etched three-layer
graphene flake with two narrow constrictions separating the island from source
and drain contacts. Three lateral graphene gates are used to electrostatically
tune the device. An individual three-layer graphene constriction has been
investigated separately showing a transport gap near the charge neutrality
point. The graphene tunneling barriers show a strongly nonmonotonic coupling as
function of gate voltage indicating the presence of localized states in the
constrictions. We show Coulomb oscillations and Coulomb diamond measurements
proving the functionality of the graphene SET. A charging energy of meV is extracted.Comment: 10 pages, 6 figure
Local gating of a graphene Hall bar by graphene side gates
We have investigated the magnetotransport properties of a single-layer
graphene Hall bar with additional graphene side gates. The side gating in the
absence of a magnetic field can be modeled by considering two parallel
conducting channels within the Hall bar. This results in an average penetration
depth of the side gate created field of approx. 90 nm. The side gates are also
effective in the quantum Hall regime, and allow to modify the longitudinal and
Hall resistances
Distribuição de carbono e estabilidade de agregados em amostras indeformadas de diferentes sistemas de rotação de culturas em plantio direto.
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