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The molecular dynamics simulation method is utilized to investigate the physical characteristics of nanoscale vanadium powder during 3D printing powder bed fusion laser sintering process. The radius of gyration, neck width, and root mean square of different powder size of nanoscale vanadium powder during 3D printing laser sintering process under different heating rate is analyzed and discussed. The neck width and internal lattice changes are also observed.It is observed that the temperature of solid state diffusion decrease with heating rate increasing, but the temperature of that increase with powder size decreasing. It is found that the coalescence temperature of nanoscale vanadium powder is range of between 1600K and 1950K, and the melting temperature of that is range of between 1850K and 1990K.

We develop the tight-binding model to study electronic and optical properties of graphane. The strong sp3 chemical bondings among the carbon and hydrogen atoms induce a special band structure and thus lead to the rich optical excitations. The absorption spectrum hardly depends on the direction of electric polarization. It ex- hibits a lot of shoulder structures and absorption peaks, which arise from the extreme points and the saddle points of the parabolic bands, respectively. The threshold op- tical excitations, only associated with the 2px and 2py orbitals of the carbon atoms, are revealed in a shoulder structure at ?3.5 eV. The first symmetric absorption peak, appearing at ~11 eV, corresponds to energy bands due to the considerable hybridiza- tion of carbon 2pz orbitals and H 1s orbitals. Also, some absorption peaks at higher frequencies indicate the bonding of 2s and 1s orbitals. These results are in sharp contrast to those of the sp2 graphene systems., 16 pages, 5 figures

We have developed the generalized tight-binding model to understand how the electronic structures of ABC-stacked trilayer graphene can be modulated by external fields. A band-like Hamiltonian matrix is used to obtain the electronic properties efficiently. A uniform perpendicular magnetic field gives rise to three groups of Landau levels that can be distinguished from one another by the subenvelope functions of the distinct sublattices. Intergroup Landau-level anticrossings occurring between any two groups and intragroup anticrossings coming from the second group are revealed in the magnetic field-dependent energy spectrum. Such anticrossings are induced by specific interlayer atomic interactions. In the presence of an electric field, each Landau-level group will split into two subgroups, which are characterized by the two different localization centers. The anticrossings in the second group can be suppressed or produced by varying the electric field strength, the reason being the significant modification of the band structures. Furthermore, the intragroup anticrossings arise in two split subgroups of the first group.

The generalized tight-binding model is developed to largely reduce the numerical computation time in calculating optical properties. Modulated electric potentials can control the low-frequency magneto-optical absorption spectra of monolayer graphene. They induce the oscillatory energy dispersions of Landau subbands and the spatial symmetry breaking of the wave function; therefore, the original peaks and extra peaks of different selection rules come into existence simultaneously. Such peaks mainly arise from the band-edge states and/or the middle states. Their number, intensities, frequencies and structures are dominated by the modulation strength and period. More absorption peaks appear with an increase in potential. The extra peaks can relatively easily be observed for higher frequencies and stronger potentials. However, the absorption spectra remain unchanged for a fixed ratio of strength over period.

The microstructure and electrical properties of ZnTe films were investigated by using thermal evaporation with emphasis on the effects of a deposition temperature. Microstructure, crystallinity, carrier concentration, resistivity, and mobility are shown to be dependent on the deposition temperature. The highest carrier concentration of 9.1×1014 cm-3, the lowest resistivity of 9.9 Ω-cm and the largest mobility of 667 cm2V-1S-1 are presented at a deposition temperature of 580oC, respectively. The ZnTe thin films using thermal evaporation can find applications in solar cell or light emitting diodes.

Dissipative particle dynamics (DPD), a mesoscopic simulation approach, has been used to investigate the effect of volume fraction, the different degree of functionalization, and the effect of PE length on the structural property of the immiscible polyethylene (PE)/carbon nanotube (CNT) in a system. In this work, the interaction parameter in DPD simulation, related to the Flory−Huggins interaction parameter, χ, is estimated by the calculation of mixing energy for each pair of components in molecular dynamics (MD) simulation. The immiscibility property of CNT and PE polymer induces the phase separation and exhibits different architectures at different volume fractions. In order to observe the effects of different degrees of functionalization, we change the repulsive interaction parameter to simulate the different degrees of functionalization. In order to observe the effect of volume fraction and different degrees of functionalization, the radius of gyration and order parameter are used to observe the arrang...

Electronic structures of nanotube–graphene hybrid carbon systems are calculated by the tight-binding model. The Lennard-Jones potential is used to determine the optimal geometry between nanotubes and a monolayer graphene. The periodic alignment of nanotubes on graphene results in quasi-one-dimensional physical phenomena. The low-frequency energy dispersions are significantly influenced by the interlayer interactions, such as the removal of subband degeneracy, creation of extra band-edge states, and modulation of energy gaps. The composite systems could be either metals or semiconductors according to the alignment and geometry of nanotubes.

The mechanical behavior of multi-walled carbon nanotubes (MWNTs), being fixed at both ends under uniaxial tensile loading, is investigated via the molecular dynamics (MD) simulation with the Tersoff interatomic potential. It is found that Young's modulus of the MWNTs is in the range between 0.85 and 1.16 TPa via the curvature method based on strain energy density calculations. Anharmonicity in the energy curves is observed, and it may be responsible for the time-dependent properties of the nanotubes. Moreover, the number of atomic layers that is fixed at the boundaries of the MWNTs will affect the critical strain for jumps in strain energy density vs. strain curves. In addition, the boundary conditions may affect “yielding” strength in tension. The van der Waals interaction of the double-walled carbon nanotube (DWNT) is studied to quantify its effects in terms of the chosen potential.

Molecular dynamics simulation was carried out to investigate the behavior of (5,5) and (10,10) armchair carbon nanotubes in water under tensile loading. The water molecules inside a nanoscale tube, unlike inside a bulk tube, have a confined effect. The local density distributions of oxygen and hydrogen atoms inside the carbon nanotubes were calculated to find the confinement effect. Moreover, the mechanical behavior of carbon nanotubes in water was studied under tensile loading. The results show that the Young's modulus of nano-tubes in water remains the same as that in vacuum. However, the tensile stress of nanotube in water is less than that in vacuum.

Buckling strengths, in terms of compressive strain, of single-, double- and triple-walled carbon nanotubes (CNTs) are investigated to study the effects of slenderness ratio (S R ) via the molecular dynamics (MD) simulations with the Tersoff potential. Under constant ratio of slenderness, the CNTs with small S R behave like a continuum shell object. For large S R 'S, multi-walled CNTs exhibit the characteristics of the Euler columns. In addition, smaller nanotubes possess higher buckling-resistance. The buckling strength of multi-walled nanotubes is controlled by the size of their outermost shell.

This study uses molecular dynamics simulations to investigate the intrinsic thermal vibrations of a single-walled carbon nanotube (SWNT) modelled as a clamped cantilever. Using an elastic model defined in terms of the tube length, the tube radius and the tube temperature, the standard deviation of the vibrational amplitude of the tube's free end is calculated and the Young's modulus of the SWNT evaluated. The numerical results reveal that the value of the Young's modulus is independent of the tube length, but decreases with increasing tube radius. At large tube radii, the Young's modulus value approaches the in-plane modulus of graphene, which can be regarded as an SWNT of infinitely large radius. The results also indicate that the Young's modulus is insensitive to changes in the tube temperature at temperatures of less than approximately 1100 K, but decreases significantly at higher temperatures.

This study investigates the electronic properties of finite-length armchair carbon nanotubes in an electric field (E) using a single-pi-band tight-binding model. Three different tip configurations are considered, namely, open ends with hydrogen terminations (H-terminations), one end capped with half of C60 fullerene and the other end open with H-terminations, and both ends capped with half of C60 fullerene. In general, the electronic states and energy gaps of low-energy electronic structures are highly sensitive to changes in the direction and magnitude of the applied electric field and to the tip configuration. The present results show that the electric field induces a strong modulation of the state energies and energy gaps of the current nanotubes, changes their energy spacings, and prompts the occurrence of semiconductor-metal transitions (SMTs). It is found that the SMTs occur more frequently as the direction of the electric field approaches the symmetry axis or when its magnitude becomes sufficiently large. The present results also indicate that the Fermi levels and energy gaps of the three nanotubes considered in this study are strongly influenced by the cap configuration. Finally, the convergent decay behavior of the energy gap which is observed as the length of the nanotube is increased is also strongly dependent on the tip configuration.

This paper investigates the morphological stability of epitaxial films growing heteroepitaxially on ultra-thin substrates. The misfitting strain model is incorporated into the quasi-static mechanical equilibrium system. The interfacial evolution equation between the vapour and film phases is used to solve the film evolution. The perturbation method of normal modes is used to derive the analytical form of the normal-mode growth rate. Additionally, this paper investigates the dynamic behaviour of the vapour–film interface. The results of the study show that a decrease in substrate thickness tends to stabilize the system regardless of whether the stiffness ratio, ρ (i.e. the ratio of film stiffness to substrate stiffness) is less than, equal to or greater than unity. Furthermore, it is found that the effects of a finite substrate thickness on the stability behaviour of the system are quite profound, and that this is particularly true when the film thickness is close to hc with values of stiffness ratio greater than unity.

Using time resolved Fourier transform EPR spectroscopy the photoreduction of duroquinone by triethylamine in methanol solution was investigated. It is found that the spin-polarized (CIDEP) duroquinone triplet deactivates by electron transfer from triethylamine generating duroquinone radical anion and amine radical cation, and by hydrogen transfer from the solvent generating durosemiquinone radical and hydroxymethyl radical, respectively. All radicals are observed at different conditions and are spin-polarized by triplet mechanism and partially by ST0 radical pair mechanism. The time dependence of FT-EPR intensities of radical cation and radical anion on the amine concentration is investigated in the range of 1 to 100 mM triethylamine. The contribution of the triplet mechanism to the spin polarization of radicals changes with different triethylamine concentrations. The durosemiquinone radical is found to be transformed into duroquinone radical anion in the presence of triethylamine in the solution. CIDNP experiments indicate that the hydrogen back transfer between the durosemiquinone radical and hydroxymethyl radical pair has a significant influence on the time behaviour of duroquinone radical anion. The intensity of triethylamine radical cation is found to be decreased with the increase of triethylamine concentration, which is interpreted that the triethylamine radical cation is deprotonated by the amine. Based on the FT-EPR results, a new complete mechanism is proposed.

An appreciable equilibrium isotope effect has been observed for electron transfer from phenothiazine (PT) to the radical cation of its N-15 substituted analogue ([N-15]PT+.), i,e, PT+[N-15]PT+.K reversible arrow PT+.+[N-15]PT via electron paramagnetic resonance analysis of the mixed radical cations formed from mixing the [N-15]phenothiazlne radical cation hexachloroantimonate and phenothiazine in acetonitrile (K=0.77+/-0.10 at 25 degrees C), and by physical separation of the neutral phenothiazines from the radical cation salts in the equilibrium mixture (K=0.83+/-0.10 at 25 degrees C), Infrared and Raman spectra of [N-14]- and [N-15]phenothiazines and their radical cations were measured to assign the vibrational frequency shifts caused by the heavy-atom substitution and radical cation formation, which gave an estimate of the enthalpy change of 441.7 J mol(-1) for the electron transfer process. These results reveal that N-15 substitution of phenothiazine decreases appreciably the ionization potential of the molecule, making it easier to lose an electron to form the corresponding radical cation in solution. (C) 1997 by John Wiley & Sons, Ltd.

A planar octagon monopole UWB band-notched antenna is proposed and experimentally studied. It consists of an octagon patch with a modifed U-shaped notched, which intends to obtain frequency notched for WiMAX. The proposed antenna operates from 1.93 GHz to 11 GHz for return loss of less than -10dB with 5.26-6.4 GHz notched. The notch frequency of the proposed antenna can be adjusted by controlling the location of slot. The measured results are in reasonably good agreement with the simulated results. Details of the proposed antenna design and simulation results for UWB operations are presented and discussed.

This paper proposed the pyramid microstructure (PYM) used on the base of the light guide as the micro-optical components to replace the conventional diffuser dot made by direct etching on the steel stamper. The PYM is made by MEMS technology, which uses silicon wafer as original mold of PYM and to replicate it on Ni micro-mold by using electroforming method. The effective optical design tool is used to find the optimal distribution of the PYM, which integrates the random microstructure generation scheme developed based on the molecular dynamics method and the optical commercial software. The SEM images show the intact PYM can be produced on the Si micro-mold and replicated fully on the Ni micro-mold by the electroforming process. The intact PYM on the base of the light guide can also be produced by the injection molding showing the complete transformation of the Ni micro-mold to the light guide. The luminance measurement of a 2.4 inches backlight module with 4 LEDs shows the average luminance of 4769 nit with 86.3% uniformity for the PYM on the base of light guide, which is 10% higher than that for the diffuser dot microstructure.

Dynamical behavior of water confined inside a capped single-walled carbon nanotube (SWCNT) is investigated at different temperatures via the Molecular Dynamics (MD) Simulation method. Water in a SWCNT behaves in the fashion of random walk and increases amplitudes with temperature. Moreover, the SWCNT’s tip vibrates more significantly as temperature increases. The water molecules embedded nanotubes exhibit less thermal noise amplitude, indicating increases in effective stiffness in the water-nanotube composite. Further, the vibrational amplitude of a water-embedded SWCNT’s tip is more noticeable during the initial transient state at the beginning of our MD simulations, and gradually decays, and reaches a steady state, as MD simulation time increases. The variation of vibrating amplitude of the SWCNT’s tip increases linearly as temperature increases when no water is present inside. The tip vibration exhibits the largest amplitude when temperature is at the boiling point of water. Moreover, the tip vibration increases monotonically as temperature increases, providing information to estimate the effective Young’s modulus of the water-nanotube composite. The diffusion pathways of water inside a SWCNT are also studied in terms of temperature changes.Copyright © 2008 by ASME

We propose a recessed pyramid microstructure (PYM) to be used on the base of the light guide as micro-optical components to replace the conventional diffuser dot made by direct etching on the steel stamper. The PYM is made by microelectromechanical systems technology, which uses a silicon wafer for the original PYM mold, which is replicated on a Ni micromold using the electroforming method. An effective optical design tool is used to find the optimal PYM distribution integrating the random microstructure generation scheme based on the molecular dynamics method into optical commercial software. The scanning electron microscopy images show intact PYMs can be produced on the Si micromold and then replicated fully on the Ni micromold by the electroforming process. An intact PYM on the base of the light guide can then be produced by injection molding, completing the transformation of the Ni micromold for use in the light guide. The luminance measurement of a 2.4-in. backlight module with four LEDs shows an average luminance of 4769 nit with 86.3% uniformity for the PYM on the base of light guide, 10% higher than that of the diffuser dot microstructure.

This paper studies the buckling phenomena and mechanical behavior of single-walled carbon nanotubes (SWNTs) and double-walled carbon nanotubes (DWNTs) via molecular dynamics simulations. The Tersoff interatomic C–C potential is adopted. Using a dimensionless parameter, slenderness ratio (SR, the ratio of length to diameter), we investigate the mechanical behavior of long and short nanotubes under compression through their buckling modes, total strain energy and strain energy density, as well as post-buckling. The curvatures of strain energy provide a means to measure the Young’s modulus of the nanotubes. Moreover, jumps in either the strain energy or strain energy density indicate identical mechanical buckling strains, and are studied in relation to buckling modes. In our simulations, a transition time is observed for short nanotubes to reach stable vase-like buckling mode, indicating a time-dependent property of nanotubes. Furthermore, nanotubes with small SR can bear higher compressive load after their first buckling. In addition, nanotubes with same chirality exhibit roughly the same elastic modulus, regardless of their lengths, when applied compressive strains are less than 5% strain. However, long nanotubes show smaller buckling strength. Effects of temperature at 300 K on buckling strength for SWNT are also discussed in connection to our present study at 1 K.