Solid State Phenomena Vols. 121-123

Abstract: Detailed investigations have been carried out [1,2] on the response of microparticles and nanoparticles to lasers of various pulse durations and energies. A first principles model has been developed that allows the prediction of all thermo-mechanical effects that will be generated from any laser pulse, such as pressure generation and phase changes. This theoretical work also predicts the thermo-mechanical effects transmitted to the surrounding transparent medium that the nanoparticles are immersed in, such as water or a solid polymer. The use of short enough pulses produces shock fronts in the surrounding medium. We calculate how short the laser pulse must be as a function of nanoparticles properties. We also show that measurements of pressure peaks in the medium can be used to determine the thermo-mechanical properties of the absorbing nanoparticles, such as bulk modulus and thermal expansion coefficient. Because the measurements can be made in the surrounding medium, they are easier to perform experimentally. Using this approach on particles of decreasing size, measurements of the pressure in the medium allow the determination of the size at which a nanoparticle is small enough to deviate from its bulk behavior and manifest discrete atom, finite size effects. This allows the prediction of how the thermo-mechanical properties of nanoparticles will change as their size decreases.

Abstract: Based on the higher order Cauchy-Born rule, a nanoscale finite deformation continuum theory, which links interatomic potentials and atomic microstructure of carbon nanotubes to a constitutive model, is presented for analysis of the mechanics of carbon nanotubes. By using of Tersoff-Brenner potential with two sets of parameters, the energy and Young’s modulus of graphite sheet and single-walled carbon nanotubes are studied based on the theory presented. The findings are in good agreement with the existing experimental and theoretical results.

Abstract: A computational model is proposed to analyze the nanoscale self-assembling phenomenon of monolayers on heterogeneous surfaces. Morse potential is used to describe the pairpotential between molecules or atoms. Minimization of free energy is used to regulate different phases and lattices to form optimized heterogeneous structures of different sizes with periodical patterns. A representative volume element (RVE) is first defined and an optimization algorithm is developed to adjust the positions of particles in it to reduce its potential until global equilibrium is reached. The pair-potential distribution in the monolayer and the substrate layers are studied. It is interesting to observe that the pair-potential distribution in the substrate layers resumes uniformity just a few layers away from the interfacial boundary.

Abstract: We investigated the nucleation of SWNTs and the role of metallic catalyst using firstprinciples calculations. To avoid dangling bonds a closed cap forms on a metal surface. 6 pentagonal rings are introduced into the cap, which reduces the strain energy. A unique tube chirality then grows from the cap, which is controlled by the metal lattice at the nucleation stage. We found that chirality of nanotubes affects the bond energies, including dangling bonds, carbon-carbon bonds & carbonmetal bonds.

Abstract: A large area perfect aligned carbon nanotubes (CNTs) thin film was grown directly on a stainless steel substrates by a low cost bias-assisted hot-filament chemical-vapor deposition (BA HF-CVD) technology. The CNT’s / stainless steel field emission array (FEA) cathode (CNT’s/FEA) has been fabricated. The field electron emission behavior of the CNT’s/FEA cathode was characterized in a vacuum condition, a high electron emission of about 10mA/cm2 at a low electric field of 4V/μm implies the promising the application as a cathode of the flat panel display device, so further assembled this cathode in a kind of vacuum device, and the possibility of the operation from a flat panel character (Pictures) display tube FCT has been tested initially.

Abstract: In the present paper, the size and temperature effects on lattice distortion of Ag and Pt nanoparticles have been investigated in terms of atomic mean bond length using the molecular dynamics simulations and the modified analytic embedded atom method. It is found that the lattice contraction ratio decreases linearly with the reciprocal of the particle size. The average value of lattice contraction over the whole system is larger than that of the experimental data, and the average value of lattice contraction in the inner core has a better agreement with the experiment results. This phenomenon is mainly resulted by inhomogeneous lattice distortion. The surface distortion and the size effect on the inner core distortion are remarkable. As the grain size increases to a certain degree, the inhomogeneous surface lattice distortion is mainly localized to the outer shell with a thickness of 2-3 lattice parameters.

Abstract: A molecular dynamics simulation study has been performed for a large-sized system consisting of 106 liquid metal Al atoms to investigate the evolution characteristics of nano-clusters formed during rapid solidification processes. The cluster-type index method (CTIM) has been applied to describe the structural configurations of the basic clusters and nano-clusters. The results show that the icosahedral clusters (12 0 12 0) and their combinations play a critical role in the microstructural transitions. The nano-clusters are mainly formed by combining basic and medium sized clusters through continuous evolution. Their structural configurations are different from the multi-shell structures obtained by gaseous deposition, ionic spray, and so on. The central atoms of basic clusters composing the nano-cluster are bonded with each other, some central atoms are multi-bonded, and others single-bonded.

Abstract: Molecular dynamics simulation of the solidification behavior of liquid nickel nanowires has been carried out based on the embedded atom potential with different cooling rates. The nanowires constructed with a face-centered cubic structure and a one-dimensional (1D) periodical boundary condition along the wire axis direction. It is found that the final structure of Ni nanowires strongly depend on the cooling rates during solidification from liquid. With decreasing cooling rates the final structure of the nanowires varies from amorphous to crystalline via helical multi-shelled structure.

Abstract: The electrical properties of metallic carbon nanotubes (CNT) can rival, or even exceed, the best metals known. It is a potential candidate for future on-chip interconnect, whose performance will be dominant in the next generation integrated circuits. In this paper, a study on the modeling and simulation techniques for the CNT interconnect network is carried out. The frequency-independent models of CNT interconnects in terms of resistance, inductance and capacitance are summarized. A novel frequencydependent circuit model is proposed for CNT for various high-frequency applications. Preliminary analysis shows a good match between numerical simulations and the compact model. The proposed modeling and simulation techniques for CNT interconnect network are expected to play an important role in the future CNT nanotechnology applications.

Abstract: Ab initio molecular dynamics simulations were carried out to study low-k/ultra low-k dielectric systems comprising Cu/Ta/SiLK-like polymer. A study of the motion of single metal atoms of Cu and Ta in the SiLK-like polymer showed that Cu atom motions are effected by jumps between cavities inside the polymer and that Ta is more sluggish than Cu not only because of its larger mass but also because of stronger affinity to the polymer. It was also found that crosslinking of the polymer did not affect the motion of the metal atoms. Simulations of deposition showed that a thin Ta diffusion barrier does not have good structural integrity to prevent Cu-diffusion when directly deposited onto the SiLK; the barrier performance was greatly improved after introducing a Si-based film between the Ta and SiLK.