893 research outputs found
Ballistic transport and electrostatics in metallic carbon nanotubes
We calculate the current and electrostatic potential drop in metallic carbon
nanotube wires self-consistently, by solving the Green's function and
electrostatics equations in the ballistic case. About one tenth of the applied
voltage drops across the bulk of a nanowire, independent of the lengths
considered here. The remaining nine tenths of the bias drops near the contacts,
thereby creating a non linear potential drop. The scaling of the electric field
at the center of the nanotube with length (L) is faster than 1/L (roughly
). At room temperature, the low bias conductance of large
diameter nanotubes is larger than due to occupation of non crossing
subbands. The physics of conductance evolution with bias due to the
transmission Zener tunneling in non crossing subbands is discussed
A Comparison of Application-Level and Router-Assisted Hierarchical Schemes for Reliable Multicast
Two-Dimensional Quantum Model of a Nanotransistor
A mathematical model, and software to implement the model, have been devised to enable numerical simulation of the transport of electric charge in, and the resulting electrical performance characteristics of, a nanotransistor [in particular, a metal oxide/semiconductor field-effect transistor (MOSFET) having a channel length of the order of tens of nanometers] in which the overall device geometry, including the doping profiles and the injection of charge from the source, gate, and drain contacts, are approximated as being two-dimensional. The model and software constitute a computational framework for quantitatively exploring such device-physics issues as those of source-drain and gate leakage currents, drain-induced barrier lowering, and threshold voltage shift due to quantization. The model and software can also be used as means of studying the accuracy of quantum corrections to other semiclassical models
Geometries, Electronic Structures and Electronic Absorption Spectra of Silicon Dichloride Substituted Phthalocyanine for Dye Sensitized Solar Cells
The geometries, electronic structures, polarizabilities, and hyperpolarizabilities of Silicon dichloride substituted phthalocyanine dye sensitizer were studied based on Density Functional Theory (DFT) using the hybrid functional B3LYP. Ultraviolet-Visible (UV-Vis) spectrum was investigated by using a hybrid method which combines the single-excitation configuration interactions (CIS) with DFT, i.e. CIS-DFT(B3LYP). Features of the electronic absorption spectrum in the visible and near-UV regions were assigned based on CIS-DFT calculations. The absorption bands are assigned to n→π* transitions. Calculated results suggest that the three lowest energy excited states of Silicon dichloride substituted phthalocyanine are due to photoinduced electron transfer processes. The interfacial electron transfer between semiconductor TiO2 electrode and dye sensitizer is due to an electron injection process from excited dye to the semiconductor’s conduction band. The role of Silicon dichloride in phthalocyanine geometries, electronic structures and electronic absorption spectra were analysed and these results were concluded that Silicon dichloride substituted phthalocyanine used in Dye Sensitized Solar Cells (DSSC) give a good conversion efficiency
Two Dimensional Quantum Mechanical Modeling of Nanotransistors
Quantization in the inversion layer and phase coherent transport are
anticipated to have significant impact on device performance in 'ballistic'
nanoscale transistors. While the role of some quantum effects have been
analyzed qualitatively using simple one dimensional ballistic models, two
dimensional (2D) quantum mechanical simulation is important for quantitative
results. In this paper, we present a framework for 2D quantum mechanical
simulation of a nanotransistor / Metal Oxide Field Effect Transistor (MOSFET).
This framework consists of the non equilibrium Green's function equations
solved self-consistently with Poisson's equation. Solution of this set of
equations is computationally intensive. An efficient algorithm to calculate the
quantum mechanical 2D electron density has been developed. The method presented
is comprehensive in that treatment includes the three open boundary conditions,
where the narrow channel region opens into physically broad source, drain and
gate regions. Results are presented for (i) drain current versus drain and gate
voltages, (ii) comparison to results from Medici, and (iii) gate tunneling
current, using 2D potential profiles. Methods to reduce the gate leakage
current are also discussed based on simulation results.Comment: 12 figures. Journal of Applied Physics (to appear
Localisation of iron and zinc in grain of biofortified wheat
The dietary contributions of iron (Fe) and zinc (Zn) from cereals are determined by concentrations, locations and chemical forms. A genetically biofortified wheat line showed higher concentrations of Zn and Fe than three control lines when grown over two years. The mineral distributions determined using imaging (histochemical staining and LA-ICP-MS), sequential pearling and hand dissection showed no consistent differences between the two lines. Fe was most abundant in the aleurone layer and the scutellum and Zn in the scutellar epithelium, the endosperm transfer cells and embryonic axis. Pearling fractions showed positive correlations between the concentration of P and those of Zn and Fe in all fractions except the outermost layer. This is consistent with Fe and Zn being concentrated in phytates. Developing grains showed decreasing gradients in concentration from the proximal to the distal ends. The concentrations of Fe and Zn were therefore higher in the biofortified line than the control lines but their locations did not differ
Transmission Through Carbon Nanotubes With Polyhedral Caps
We study electron transport between capped carbon nanotubes and a substrate,
and relate the transmission probability to the local density of states in the
cap. Our results show that the transmission probability mimics the behavior of
the density of states at all energies except those that correspond to localized
states in the cap. Close proximity of a substrate causes hybridization of the
localized state. As a result, new transmission paths open from the substrate to
nanotube continuum states via the localized states in the cap. Interference
between various transmission paths gives rise to antiresonances in the
transmission probability, with the minimum transmission equal to zero at
energies of the localized states. Defects in the nanotube that are placed close
to the cap cause resonances in the transmission probability, instead of
antiresonances, near the localized energy levels. Depending on the spatial
position of defects, these resonant states are capable of carrying a large
current. These results are relevant to carbon nanotube based studies of
molecular electronics and probe tip applications
Understanding edge-connectivity in the Internet through core-decomposition
Internet is a complex network composed by several networks: the Autonomous
Systems, each one designed to transport information efficiently. Routing
protocols aim to find paths between nodes whenever it is possible (i.e., the
network is not partitioned), or to find paths verifying specific constraints
(e.g., a certain QoS is required). As connectivity is a measure related to both
of them (partitions and selected paths) this work provides a formal lower bound
to it based on core-decomposition, under certain conditions, and low complexity
algorithms to find it. We apply them to analyze maps obtained from the
prominent Internet mapping projects, using the LaNet-vi open-source software
for its visualization
Conductance of carbon nanotubes with disorder: A numerical study
We study the conductance of carbon nanotube wires in the presence of
disorder, in the limit of phase coherent transport. For this purpose, we have
developed a simple numerical procedure to compute transmission through carbon
nanotubes and related structures. Two models of disorder are considered, weak
uniform disorder and isolated strong scatterers. In the case of weak uniform
disorder, our simulations show that the conductance is not significantly
affected by disorder when the Fermi energy is close to the band center.
Further, the transmission around the band center depends on the diameter of
these zero bandgap wires. We also find that the calculated small bias
conductance as a function of the Fermi energy exhibits a dip when the Fermi
energy is close to the second subband minima. In the presence of strong
isolated disorder, our calculations show a transmission gap at the band center,
and the corresponding conductance is very small
- …