102 research outputs found
Periodic negative differential conductance in a single metallic nano-cage
We report a bi-polar multiple periodic negative differential conductance
(NDC) effect on a single cage-shaped Ru nanoparticle measured using scanning
tunneling spectroscopy. This phenomenon is assigned to the unique
multiply-connected cage architecture providing two (or more) defined routes for
charge flow through the cage. This, in turn, promotes a self- gating effect,
where electron charging of one route affects charge transport along a
neighboring channel, yielding a series of periodic NDC peaks. This picture is
established and analyzed here by a theoretical model
Nonadiabatic to Adiabatic Transition of Electron Transfer in Colloidal Quantum Dot Molecules
Electron transfer is an important and fundamental process in chemistry,
biology and physics, and has received significant attention in recent years.
Perhaps one of the most intriguing questions concerns with the realization of
the transitions between nonadiabatic and adiabatic regimes of electron
transfer, as the coupling (hybridization) energy, , between the donor and
acceptor is varied. Here, using colloidal quantum dot molecules, a new class of
coupled quantum dot dimers, we computationally demonstrate how the
hybridization energy between the donor and acceptor quantum dots can be tuned
by simply changing the neck dimensions and/or the quantum dot size. This
provides a handle to tune the electron transfer from the nonadiabatic
over-damped Marcus regime to the coherent adiabatic regime in a single system,
without changing the reorganization energy, , or the typical phonon
frequency, . We develop an atomistic model to account for several
donor and acceptor states and how they couple to the lattice vibrations, and
utilize the Ehrenfest mean-field mixed quantum-classical method to describe the
charge transfer dynamics as the nonadiabatic parameter, , is varied. We
find that charge transfer rates increase by several orders of magnitude as the
system is driven to the coherent, adiabatic limit, even at elevated
temperatures, and delineate the inter-dot and torsional acoustic modes that
couple most strongly to the charge transfer reaction coordinate
Control of charging in resonant tunneling through InAs nanocrystal quantum dots
Tunneling spectroscopy of InAs nanocrystals deposited on graphite was
measured using scanning tunneling microscopy, in a double-barrier
tunnel-junction configuration. The effect of the junction symmetry on the
tunneling spectra is studied experimentally and modeled theoretically. When the
tip is retracted, we observe resonant tunneling through the nanocrystal states
without charging. This is in contrast to previous measurements on similar
nanocrystals anchored to gold by linker molecules, where charging took place.
Charging is regained upon reducing the tip-nanocrystal distance, making the
junctions more symmetric. The effect of voltage distribution between the
junctions on the measured spectra is also discussed.Comment: submitte
Optical Gain from InAs Nanocrystal Quantum Dots in a Polymer Matrix
We report on the first observation of optical gain from InAs nanocrystal
quantum dots emitting at 1.55 microns based on a three-beam, time resolved
pump-probe technique. The nanocrystals were embedded into a transparent polymer
matrix platform suitable for the fabrication of integrated photonic devices.Comment: 8 pages, 3 figures. This second version is excactly the same as the
first. It is resubmitted to correct some format errors appeared in the pdf
file of the first versio
Electrical transport through a single nanoscale semiconductor branch point
ABSTRACT. Semiconductor tetrapods are three dimensional branched nanostructures, representing a new class of materials for electrical conduction. We employ the single electron transistor approach to investigate how charge carriers migrate through single nanoscale branch points of tetrapods. We find that carriers can delocalize across the branches or localize and hop between arms depending on their coupling strength. In addition, we demonstrate a new single-electron transistor operation scheme enabled by the multiple branched arms of a tetrapod: one arm can be used as a sensitive arm-gate to control the electrical transport through the whole system. Electrical transport through nanocrystals, 1 molecules, 2,3 nanowires 4,5 and nanotubes 6,7 display novel quantum phenomena. These can be studied using the single electron transistor approach to successively change the charge state by one, to reveal charging energies, electronic level spacings, an
Optimal metal domain size for photocatalysis with hybrid semiconductor-metal nanorods
Semiconductor-metal hybrid nanostructures offer a highly controllable platform for light-induced charge separation, with direct relevance for their implementation in photocatalysis. Advances in the synthesis allow for control over the size, shape and morphology, providing tunability of the optical and electronic properties. A critical determining factor of the photocatalytic cycle is the metal domain characteristics and in particular its size, a subject that lacks deep understanding. Here, using a well-defined model system of cadmium sulfide-gold nanorods, we address the effect of the gold tip size on the photocatalytic function, including the charge transfer dynamics and hydrogen production efficiency. A combination of transient absorption, hydrogen evolution kinetics and theoretical modelling reveal a non-monotonic behaviour with size of the gold tip, leading to an optimal metal domain size for the most efficient photocatalysis. We show that this results from the size-dependent interplay of the metal domain charging, the relative band-alignments, and the resulting kinetics
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