3,299 research outputs found
Gate Coupling to Nanoscale Electronics
The realization of single-molecule electronic devices, in which a
nanometer-scale molecule is connected to macroscopic leads, requires the
reproducible production of highly ordered nanoscale gaps in which a molecule of
interest is electrostatically coupled to nearby gate electrodes. Understanding
how the molecule-gate coupling depends on key parameters is crucial for the
development of high-performance devices. Here we directly address this,
presenting two- and three-dimensional finite-element electrostatic simulations
of the electrode geometries formed using emerging fabrication techniques. We
quantify the gate coupling intrinsic to these devices, exploring the roles of
parameters believed to be relevant to such devices. These include the thickness
and nature of the dielectric used, and the gate screening due to different
device geometries. On the single-molecule (~1nm) scale, we find that device
geometry plays a greater role in the gate coupling than the dielectric constant
or the thickness of the insulator. Compared to the typical uniform nanogap
electrode geometry envisioned, we find that non-uniform tapered electrodes
yield a significant three orders of magnitude improvement in gate coupling. We
also find that in the tapered geometry the polarizability of a molecular
channel works to enhance the gate coupling
Effects of magnetic field and disorder on electronic properties of Carbon Nanotubes
Electronic properties of metallic and semiconducting carbon nanotubes are
investigated in presence of magnetic field perpendicular to the CN-axis, and
disorder introduced through energy site randomness. The magnetic field field is
shown to induce a metal-insulator transition (MIT) in absence of disorder, and
surprisingly disorder does not affect significantly the MIT. These results may
find confirmation through tunneling experimentsComment: 4 pages, 6 figures. Phys. Rev. B (in press
Self-directed growth of AlGaAs core-shell nanowires for visible light applications
Al(0.37)Ga(0.63)As nanowires (NWs) were grown in a molecular beam epitaxy
system on GaAs(111)B substrates. Micro-photoluminescence measurements and
energy dispersive X-ray spectroscopy indicated a core-shell structure and Al
composition gradient along the NW axis, producing a potential minimum for
carrier confinement. The core-shell structure formed during the growth as a
consequence of the different Al and Ga adatom diffusion lengths.Comment: 20 pages, 7 figure
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Probing Single- to Multi-Cell Level Charge Transport in Geobacter Sulfurreducens DL-1
Microbial fuel cells, in which living microorganisms convert chemical energy into electricity, represent a potentially sustainable energy technology for the future. Here we report the single-bacterium level current measurements of Geobacter sulfurreducens DL-1 to elucidate the fundamental limits and factors determining maximum power output from a microbial fuel cell. Quantized stepwise current outputs of 92(±33) and 196(±20)âfA are generated from microelectrode arrays confined in isolated wells. Simultaneous cell imaging/tracking and current recording reveals that the current steps are directly correlated with the contact of one or two cells with the electrodes. This work establishes the amount of current generated by an individual Geobacter cell in the absence of a biofilm and highlights the potential upper limit of microbial fuel cell performance for Geobacter in thin biofilms.Chemistry and Chemical Biolog
Coulomb Gap and Correlated Vortex Pinning in Superconductors
The positions of columnar pins and magnetic flux lines determined from a
decoration experiment on BSCCO were used to calculate the single--particle
density of states at low temperatures in the Bose glass phase. A wide Coulomb
gap is found, with gap exponent , as a result of the long--range
interaction between the vortices. As a consequence, the variable--range hopping
transport of flux lines is considerably reduced with respect to the
non--interacting case, the effective Mott exponent being enhanced from to for this specific experiment.Comment: 10 pages, Revtex, 4 figures appended as uu-encoded postscript files,
also available as hardcopies from [email protected]
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Imaging of Tissue Micro-Structures using a Multi-Modal Microscope Design
We investigate a microscope design that offers high signal sensitivity and hyperspectral imaging capabilities and allows for implementation of various optical imaging approaches while its operational complexity is minimized. This system utilizes long working distance microscope objectives that enable for off-axis illumination of the tissue thereby allowing for excitation at any optical wavelength and nearly eliminating spectral noise from the optical elements. Preliminary studies using human and animal tissues demonstrate the feasibility of this approach for real-time imaging of intact tissue microstructures using autofluorescence and light scattering imaging methods
Electrically Driven Light Emission from Individual CdSe Nanowires
We report electroluminescence (EL) measurements carried out on three-terminal
devices incorporating individual n-type CdSe nanowires. Simultaneous optical
and electrical measurements reveal that EL occurs near the contact between the
nanowire and a positively biased electrode or drain. The surface potential
profile, obtained by using Kelvin probe microscopy, shows an abrupt potential
drop near the position of the EL spot, while the band profile obtained from
scanning photocurrent microscopy indicates the existence of an n-type Schottky
barrier at the interface. These observations indicate that light emission
occurs through a hole leakage or an inelastic scattering induced by the rapid
potential drop at the nanowire-electrode interface.Comment: 12 pages, 4 figure
Giga-Hertz quantized charge pumping in bottom gate defined InAs nanowire quantum dots
Semiconducting nanowires (NWs) are a versatile, highly tunable material
platform at the heart of many new developments in nanoscale and quantum
physics. Here, we demonstrate charge pumping, i.e., the controlled transport of
individual electrons through an InAs NW quantum dot (QD) device at frequencies
up to GHz. The QD is induced electrostatically in the NW by a series of
local bottom gates in a state of the art device geometry. A periodic modulation
of a single gate is enough to obtain a dc current proportional to the frequency
of the modulation. The dc bias, the modulation amplitude and the gate voltages
on the local gates can be used to control the number of charges conveyed per
cycle. Charge pumping in InAs NWs is relevant not only in metrology as a
current standard, but also opens up the opportunity to investigate a variety of
exotic states of matter, e.g. Majorana modes, by single electron spectroscopy
and correlation experiments.Comment: 21 page
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