Yuichi Hashi

Electronic and transport properties of N-P doped nanotubes

Electronic properties of a doped zigzag nanotube are investigated by a self-consistent tight-binding method. We propose that a doped nanotube with donor atoms on one side and acceptors on the other can function as a nano diode. It is shown that a potential step in the tube, created by two different types of doping in this case, causes the nonlinear rectifying effect.

First-principles studies on magnetism of Ni clusters coated and alloyed with Pd

Abstract First-principles electronic-structure calculations are performed for the Ni clusters coated and alloyed with Pd. For coated clusters, the magnetic moments of the Ni core are reduced as compared to the bared one. Especially, Ni1Ni12Pd6Pd24Pd12 cluster with Oh symmetry consists of the ferromagnetic Ni core, the ferromagnetic Pd and paramagnetic Pd shells, the induced magnetic moment of Pd in the interface is 0.1μB, qualitatively in agreement with experimental results found in Ni particles coated with Pd. The dependence of magnetic moment on Pd thickness displays an oscillatory behavior, similar to that found in Co clusters coated with Cu or Ag and in Ni/Pd multilayers. For the alloyed clusters, the enhanced magnetism is confirmed, and the mechanism is clarified: which is resulted not only due to the large atomic distance of Pd but also due to electron transfers. The explanations are given for the different magnetic behaviors between coated and alloyed clusters.

Molecular dynamics simulation for the cluster formation process of Lennard‐Jones particles: Magic numbers and characteristic features

Cluster formation of Lennard‐Jones particles (65 536 atoms in a unit cell with an overall number density equal to 0.0149) was simulated by molecular dynamics. The temperature was set to decrease linearly with time by various thermostats, starting from a gas state temperature and ending at zero temperature. With the Nose–Hoover thermostat, it was found that the translational temperature of the clusters suddenly decreased almost to zero when the cluster formation drastically increased around a reduced temperature (T*) of 0.5, while the internal temperature decreased linearly. Using the Andersen thermostat, which could simulate the aggregation of particles in an inert gas, both the internal and translational temperatures decreased almost linearly with time. When these thermostats were used, cluster–cluster and cluster–atom collisions did not give any magic number peaks in the size distribution up to 250 atoms/cluster at any temperature. Careful tracing of the cluster growth of 13‐atom clusters showed no diff...

In-situ infrared spectroscopy of a photoirradiated potassium-doped C60 film

Abstract Photodimerization between C 60 molecules in a potassium-doped C 60 film (a mixture of α-C 60 and K 3 C 60 phases) has been investigated using in-situ Fourier-transform (FT) infrared spectroscopy in combination with tight-binding molecular dynamics calculations. A comparison of the experimental spectrum of C 60 dimers, which was found to be a main product in the photoirradiated K-doped film using an FT mass spectrometer, with the theoretical spectra for several isomers of C 120 suggests that C 120 species with structures similar to a bucky peanut were formed in the photoirradiated film.

The effect of segregation and partial order on the thermodynamics of (1 1 1) antiphase boundaries in Ni3Al

Thermodynamic properties of thermal and a-thermal (1 1 1) antiphase boundaries (APB) in Ni3Al are computed from first-principles. The eAect of oA-stoichiometry, partial disordering and segregation are evaluated and a rough estimate of the vibrational contribution to the antiphase boundary energy is given. Although the vibrational eAect is found to be small, the configurational eAects are large, so that at non-zero temperature and in oA-stoichiometric Ni3Al the antiphase boundary energy (APBE) may be only half of that in perfectly ordered stoichiometric Ni3Al at zero temperature. This result points to a discrepancy between electronic structure calculations and experimental measurements. ” 1999 Elsevier Science B.V All rights reserved.

In Situ FTIR, XPS, and STM Studies of the Nano-Structure of a Photopolymerized C60 Film

Abstract The nano-structure of C60 photopolymers has been investigated using in situ Fourier-Transform Infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and scanning tunneling microscopy (STM). The FTTR and XPS studies revealed that the C60 pholopolymer has a cross-linking via a [2+2] cycloaddition four-membered ring and formed a 2D rhombohedral structure when the polymerization was saturated. Using STM, we have successfully observed the direct real-space imaging of the C60 dimers and trimers in a C60 monolayer supported on a clean semiconductor surface.

Cloud Internet of Things Framework for Enabling Services in Smart Cities

In the future internet era, the Internet of Things (IoT) has consolidated its presence in the smart cities with a variety of innovative IoT platforms for the provisioning of relevant services. The provisioning of such services requires ubiquity, reliability, high-performance, efficiency, scalability. In order to accomplish this popular trend is to merge IoT and Cloud concepts by combining multi-Cloud IoT architectures. The introduction of cognition was the first step for the IoT success, as it brought essential self-management and awareness capabilities combined with knowledge-generation functionality. The Cloud-IoT architectural vision is paving the way to the next/vital step for the IoT success and for new business value propositions for the IoT world leveraging cloud principles. Towards this direction, in this effort, a set of challenges have been identified, with a set of different research initiatives that aim to address them. A promising architecture for enabling Cloud-IoT services in smart cities is presented together with a case study that reveals the high potential that Cloud-IoT can achieve in the context of smart cities. The work concludes with the lessons learnt through the study and the elaboration of the Cloud-IoT concepts.

Magnetic properties of nanoscale Fe clusters in Cu

Abstract The magnetic and electronic properties of fcc Fe clusters embedded in a Cu matrix are studied by the first-principles spin-polarized calculations within the local density functional formalism. A single Fe atom in a Cu host is found to have a magnetic moment of 3.05 μ B . Small Fe n clusters ( n ≤ 13) in Cu exhibit high-moment ferromagnetic coupling, while larger clusters ( n ≥ 13) in Cu show low-moment antiferromagnetic coupling. The magnetic properties of embedded fcc Fe clusters in Cu have some features in common with nanoscale fcc Fe/Cu(100) films.

The Nanostructure of C60 Photopolymers

The nanostructure of C60 photopolymers has been investigated using in situ Fourier-Transform Infrared spectroscopy (FTIR), X-ray Photoelectron Spectroscopy (XPS), and Scanning Tunneling Microscopy (STM). FTIR and XPS studies revealed that the C60 photopolymer has crosslinking via a [2+2] cycloadditional four-membered ring and forms a 2D rhombohedral structure when polymerization is saturated. Using STM, we have successfully observed direct real-space image of C60 dimers and trimers in a C60 monolayer supported on a clean semiconductor surface. We obtained a value of 0.90 nm for the intermolecular distance between adjacent C60 molecules in the dimer, which is in good agreement with the XRD value of 0.91 nm for the C120 dumbbell structure, and 0.93 nm for the trimer.

Electronic, Transport and Mechanical Properties of Carbon Nanotubes

This article reviews the electronic properties of plain and doped nanotubes. The effect of doping on transport is then discussed. Novel transport properties are obtained for N-P doped nanotubes. It will be shown that N-P junctions of semiconducting zigzag tubes have a rectifying behavior whereas those of metallic armchair tubes have a negative differential resistance. These effects become more pronounced as the tube radius is reduced. Such interesting and novel properties may be used for designing new nanoscale devices. In a second part, mechanical properties of the tubes and the effect of defects on them will be discussed. This section will be illustrated by the results of molecular dynamics simulations.