Electronic transport properties of a-Si:H

To investigate the electron transport properties of hydrogenated amorphous silicon (a-Si:H), a series of quantum simulations and electron transport analyses were performed. The target system is a nano-scale junction of a-Si:H with various hydrogen concentrations sandwiched between two metal electrodes. The density functional based tight binding simulation was conducted to obtain the electronic structure, and the non-equilibrium Green’s function method was adopted to evaluate the electron transmission coefficient and the electric current under a bias field. It is confirmed that the hydrogen atoms passivate a part of defects in amorphous silicon, but the remaining defects realize the energy states in the bandgap; the p orbitals of silicon atoms mainly contribute to the electron transmission. The transport behavior is greatly affected by the hydrogen concentration. The interface between a-Si:H and the metal electrodes also influences the transport behavior through changing the spatial charge density inside the a-Si:H

Hydrolysis of Cellulose in Supercritical Water: Quantum Simulation

Cellulose nanofiber (CNF) is a high-strength nanomaterial made from cellulose fibers. Among several fabrication processes of CNF, we focus on the hydrolysis of cellulose in supercritical water and analyze the reaction mechanism by numerical simulation. In order to deal with the detailed chemical reaction, a series of quantum molecular dynamics simulations were performed based on the density functional theory coupled with the tight binding model. After locating the vapor-liquid critical point with a 100 water molecule system, we explored the hydrolysis reaction of cellulose using a simplified system consisting of a single cellobiose surrounded by 100 water molecules. We observed a cleavage of the 1, 4--glycosidic bond in some cases. Electric charge analysis suggests that the carbon atom at the cleavage site gives the electron to a water molecule approaching to the bond with sufficiently large velocity

Effects of Hydrogen Concentration and Cooling Speed on Fabrication of Hydrogenated Amorphous Silicon: Quantum Simulation

In order to investigate various properties of hydrogenated amorphous silicon (a-Si:H) for improvement of low conversion efficiency and stability of solar cells, a series of quantum simulations based on the density functional theory combined with the tight binding model were performed for a-Si:H with various hydrogen concentrations and cooling rates. The radial distribution function (RDF) for Si-Si pairs indicates that samples with higher H concentration (20% and 25%) give a structure in better agreement with experiments, but the RDF of Si-H pairs suggests that samples with lower H concentration (14%) may give more appropriate structure. The coordination number (Nc) analysis indicates that more defects (dangling bonds and floating bonds) exist in 20% and 25% H concentration samples. Overall, a-Si:H with 14% H concentration gives most preferable structure. The cooling rate has also much effect on the structure. Sample with the slowest cooling rate is slightly more structured based on Si-Si pair RDF and Nc. The electron transport of a-Si and a-Si:H were evaluated and the superiority of a-Si:H was confirmed

Electronic Properties of SiC Nanotubes: Quantum Simulation

We performed a series of quantum simulations for the geometrics, electronic structures and electron transport of various types of silicon carbide nanotubes (SiCNT's). The 1:1 SiCNT's generally show more stable semi-conducting behaviour than carbon nanotubes (CNT's). The SiCNT's exhibit better electronic properties than their bulk crystal and expanded sheets. Next, we found out that these tubes' band gap increases with increasing the tube diameter. Armchair SiCNT's have narrower band gap than zigzag ones, whereas the zigzag SiCNT's possess a direct band gap. Finally, we investigated how adsorbed atoms affect the electronic structure. Three cases of hydrogen atoms adsorbed on different sites were examined, showing different semiconducting properties. These results indicate the potential application of SiCNT's in fields of electronic devices

Time evolution of a thin black ring via Hawking radiation

Black objects lose their mass and angular momenta through evaporation by Hawking radiation, and the investigation of their time evolution has a long history. In this paper, we study this problem for a five-dimensional doubly spinning black ring. The black ring is assumed to emit only massless scalar particles. We consider a thin black ring with a small thickness parameter, $\lambda\ll 1$, which can be approximated by a boosted Kerr string locally. We show that a thin black ring evaporates with fixing its thickness parameter $\lambda$. Further, in the case of an Emparan-Reall black ring, we derive analytic formulas for the time evolution, which has one parameter to be evaluated numerically. We find that the lifetime of a thin black ring is shorter by a factor of $O(\lambda^2)$ compared to a five-dimensional Schwarzschild black hole with the same initial mass. We also study detailed properties of the Hawking radiation from the thin black ring, including the energy and angular spectra of emitted particles.Comment: 28 pages, 6 figure

コロイド粒子の電場配向

An orientation factor for a colloidal particle with positive and negative sites has been obtained by considering the differences of electrophoretic velocity of the particle under an action of electric field. A simple model that many spheres are linearly connected with each other is assumed and the electrophoretic velocity of each part of the particle is estimated from the number of unoccupied sites calculated by Langmuir's adsorption isotherm. The orientation factor we obtained depends on the number of site and the equilibrium constant for adsorption and can be used to explain the field dependence of electric birefringence of polyelectrolytes

Ground-state properties of neutron-rich Mg isotopes

We analyze recently-measured total reaction cross sections for 24-38Mg isotopes incident on 12C targets at 240 MeV/nucleon by using the folding model and antisymmetrized molecular dynamics(AMD). The folding model well reproduces the measured reaction cross sections, when the projectile densities are evaluated by the deformed Woods-Saxon (def-WS) model with AMD deformation. Matter radii of 24-38Mg are then deduced from the measured reaction cross sections by fine-tuning the parameters of the def-WS model. The deduced matter radii are largely enhanced by nuclear deformation. Fully-microscopic AMD calculations with no free parameter well reproduce the deduced matter radii for 24-36Mg, but still considerably underestimate them for 37,38Mg. The large matter radii suggest that 37,38Mg are candidates for deformed halo nucleus. AMD also reproduces other existing measured ground-state properties (spin-parity, total binding energy, and one-neutron separation energy) of Mg isotopes. Neutron-number (N) dependence of deformation parameter is predicted by AMD. Large deformation is seen from 31Mg with N = 19 to a drip-line nucleus 40Mg with N = 28, indicating that both the N = 20 and 28 magicities disappear. N dependence of neutron skin thickness is also predicted by AMD.Comment: 15 pages, 13 figures, to be published in Phys. Rev.

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