576 research outputs found
On the Electronic Transport Mechanism in Conducting Polymer Nanofibers
Here, we present theoretical analysis of electron transport in polyaniline
based (PANi) nanofibers assuming the metalic state of the material. To build up
this theory we treat conducting polymers as a special kind of granular metals,
and we apply the quantum theory of conduction in mesoscopic systems to describe
the transport between metallic-like granules. Our results show that the concept
of resonance electron tunneling as the predominating mechanism providing charge
transport between the grains is supported with recent experiments on the
electrical characterization of single PANi nanofibers. By contacting the
proposed theory with the experimental data we estimate some important
parameters characterizing the electron transport in these materials. Also, we
discuss the origin of rectifying features observed in current-voltage
characteristics of fibers with varying cross-sectional areas.Comment: 5 pages, 1 figure, accepted for publication in Phys. Rev. B, Vol.72,
xxxx (2005
Predictive-State Decoders: Encoding the Future into Recurrent Networks
Recurrent neural networks (RNNs) are a vital modeling technique that rely on
internal states learned indirectly by optimization of a supervised,
unsupervised, or reinforcement training loss. RNNs are used to model dynamic
processes that are characterized by underlying latent states whose form is
often unknown, precluding its analytic representation inside an RNN. In the
Predictive-State Representation (PSR) literature, latent state processes are
modeled by an internal state representation that directly models the
distribution of future observations, and most recent work in this area has
relied on explicitly representing and targeting sufficient statistics of this
probability distribution. We seek to combine the advantages of RNNs and PSRs by
augmenting existing state-of-the-art recurrent neural networks with
Predictive-State Decoders (PSDs), which add supervision to the network's
internal state representation to target predicting future observations.
Predictive-State Decoders are simple to implement and easily incorporated into
existing training pipelines via additional loss regularization. We demonstrate
the effectiveness of PSDs with experimental results in three different domains:
probabilistic filtering, Imitation Learning, and Reinforcement Learning. In
each, our method improves statistical performance of state-of-the-art recurrent
baselines and does so with fewer iterations and less data.Comment: NIPS 201
Temperature dependent charge transport mechanisms in carbon sphere/polymer composites
Carbon spheres (CS) with diameters in the range were prepared
via hydrolysis of a sucrose solution at and later annealed in
at The spheres were highly conducting but difficult to process into
thin films or pressed pellets. In our previous work, composite samples of CS
and the insulating polymer polyethylene oxide (PEO) were prepared and their
charge transport was analyzed in the temperature range
Here, we analyze charge transport in CS coated with a thin polyaniline (PANi)
film doped with hydrochloric acid (HCl), in the same temperature range. The
goal is to study charge transport in the CS using a conducting polymer (PANi)
as a binder and compare with that occurring at CS/PEO. A conductivity maxima
was observed in the CS/PEO composite but was absent in CS/PANi. Our data
analysis shows that variable range hopping of electrons between polymeric
chains in PANi-filled gaps between CS takes on a predominant part in transport
through CS/PANi composites, whereas in CS/PEO composites, electrons travel
through gaps between CS solely by means of direct tunneling. This difference in
transport mechanisms results in different temperature dependences of the
conductivity.Comment: 7 pages, 6 figure
Controlled Doping of Graphene Using Ultraviolet Irradiation
The electronic properties of graphene are tunable via doping, making it attractive in low dimensional organic electronics. Common methods of doping graphene, however, adversely affect charge mobility and degrade device performance. We demonstrate a facile shadow mask technique of defining electrodes on graphene grown by chemical vapor deposition (CVD) thereby eliminating the use of detrimental chemicals needed in the corresponding lithographic process. Further, we report on the controlled, effective, and reversible doping of graphene via ultraviolet (UV) irradiation with minimal impact on charge mobility. The change in charge concentration saturates at ~2 x 1012cm-2 and the quantum yield is 10-5 e/photon upon initial UV exposure. This simple and controlled strategy opens the possibility of doping wafer-size CVD graphene for diverse applications
Electrospun Hybrid Organic/Inorganic Semiconductor Schottky Nanodiode
We report on a simple method to fabricate, under ambient conditions and within seconds, Schottky nanodiodes using electrospun polyaniline nanofibers and an inorganic n-doped semiconductor. In addition to being a rectifier, the advantage of our design is the complete exposure of the rectifying nanojunction to the surrounding environment, making them attractive candidates in the potential fabrication of low power, supersensitive, and rapid response sensors as well. The diode parameters were calculated assuming the standard thermionic emission model of a Schottky junction, and the use of this junction as a gas sensor was examined
Field Effect Transistor Behavior in Electrospun Polyaniline/Polyethylene Oxide Nanofibers
Novel transistors and logic devices based on nanotechnology concepts are under intense development. The potential for ultra-low-power circuitry makes nanotechnology attractive for applications such as digital electronics and sensors. For NASA applications, nanotechnology offers tremendous opportunities for increased onboard data processing, and thus autonomous decision-making ability, and novel sensors that detect and respond to environmental stimuli with little oversight requirements. Polyaniline (PANi) is an intriguing material because its electrical conductivity can be changed from insulating to metallic by varying the doping levels and conformations of the polymer chain, and when combined with polyethylene oxide (PEO), can be formed into nanofibers with diameters ranging from approximately 50 to 500 nm (depending on the deposition conditions). The initial goal of this work was to demonstrate transistor behavior in these nanofibers, thus creating a foundation for future logic devices
Graphene Based Reversible Nano-Switch/Sensor Schottky Diode (NANOSSSD) Device
A nanostructure device is provided and performs dual functions as a nano-switching/sensing device. The nanostructure device includes a doped semiconducting substrate, an insulating layer disposed on the doped semiconducting substrate, an electrode formed on the insulating layer, and at least one layer of graphene formed on the electrode. The at least one layer of graphene provides an electrical connection between the electrode and the substrate and is the electroactive element in the device
- …