Tight-binding potential model for Re and W-Re alloy

A tight-binding potential model which goes beyond the Slater-Koster two-center approximation and includes explicit three-center and crystal field expressions is presented. Using carbon and silicon as examples, we show that various bulk structures, surface reconstructions, and the structures of clusters and liquids of C and Si can be well described by the present three-center tight-binding model. These results demonstrate that three-center interaction and crystal field effect are very important for improving the transferability of tight-binding models in describing the structures and properties of materials over a broad range of bonding configurations.

We present a tight-binding model which goes beyond the traditional two-center approximation and allows the hopping parameters and the repulsive energy to be dependent on the binding environment. Using carbon as an example, we show that the approach improves remarkably the transferability of the tight-binding model. The properties of the higher-coordinated metallic structures are well described by the model in addition to those of the lower-coordinated covalent structures. \textcopyright{} 1996 The American Physical Society.

Electronic structures of silicon nitride revealed by tight binding calculations

By performing extensive search of the “compressing liquid” strategy together with the “genetic algorithm” approach, at the level of tight-binding(TB) potential model, the low-lying isomers of medium-sized Gen (n = 35, 40, 45, 50, 55 and 60) are achieved. The selected lower-energy candidates from TB calculations are then fully optimized by the accurate first-principles calculations, the best candidates are identified. We find that the best candidates of germanium clusters undergo a structural transition from the prolate shape to the spherical structure in our concerned size range. This just corresponds to the observation of germanium clusters in ion mobility experiments. Furthermore, we reveal that the vibration entropy contributed to the free energy of an isomer which is useful for understanding the stability of the cluster at finite temperatures. As a result, the stability of the low-lying candidates at zero temperature is maintained at finite temperatures. In addition, the size-dependent HOMO–LUMO gaps have been briefly discussed in this paper. Our findings should be useful for future experiment investigations.

We present an orthogonal tight-binding (TB) potential model for W/Cu binary systems. This model can reasonably predict the electronic structures, elastic properties, and thermodynamics properties of W/Cu systems. Furthermore, by performing the TB Monte Carlo simulations and the TB molecular dynamics simulations, we find that (1) the W(110) surface in the fusion reactor exhibits pre-melting behaviors, (2) W and Cu atoms in a W/Cu binary system prefer to form single element domains, and (3) the interface between a W domain and a Cu domain degrades the transport property of the heat in a W/Cu system significantly.

This article presents a molecular dynamics simulation of the copper reflow process for the recently developed damascene process, in which copper replaces aluminum as the interconnect material. A deposition simulation is performed, and one of the results from this simulation, namely a morphology with a void defect within the filling trench, is used as the initial morphology for the annealing process. The influence of variations in the annealing process parameters on void filling within the trench and on the copper microstructure is investigated. The article establishes a three-dimensional trench model and also provides deposition and reflow models. The annealing procedure is modeled by employing the Langevin technique to simulate heating and cooling of the thermal layer located beneath the Ti barrier layer which covers the trench. The many-body, tight-binding potential model is adopted to simulate the interatomic force between atoms. The results of this study indicate that the duration for which a constant annealing temperature is maintained plays an important role in determining the success of the reflow process. A short duration fails to produce motion of the atoms located in the trench above the void, and this motionless region of atoms prevents atoms from flowing into the trench to fill the void. The motion trace of trench atoms during the reflow process shows that circular motion is evident in the atoms that are located in the region surrounding the void, while atoms in the region above the void migrate for a long distance in the direction of the void. Finally, it is determined that a longer heating duration is beneficial in improving the microstructure of the interconnects.

The disintegration and formation of the C{sub 60} fullerene are studied using molecular dynamics simulations. The interactions between carbon atoms are described with a tight-binding potential model that yields structural and vibrational properties of the molecule in good agreement with experimental data. The simulations show that C{sub 60} is stable against spontaneous disintegration up to 5000 K. The cage formation process is also observed by cooling and compressing 60 carbon atoms from the gas phase. 13 refs., 3 figs., 1 tab.

A molecular dynamics simulation on surface tension of liquid Ni and Cu

The vibrational frequencies of three ${\mathrm{C}}_{84}$ fullerene isomers are calculated with a tight-binding potential model. The differences between the vibrational properties of these isomers are discussed.

The structure and dynamics of C60 buckyball and carbon clusters C n (n=2–90) have been studied with molecular dynamics simulations using a tight-binding potential model. The studies show that it is possible to nucleate a ‘buckyball-like’ cluster by cooling and compressing carbon atoms from the gas phase. The studies also show that there is a transition from one-dimensional linear and cyclic structures to two-dimensional cage structures as the number of carbon atoms reaches n=20. Magic numbers for fullerene formation energy are observed at n=50,60,70 and 84.

The phonon dispersion curves for both ordered and configurationally disordered cubic phases of Cu3Au are calculated using force constants derived from a many-body tight-binding potential. The derived phonon frequency spectra are used to estimate the vibrational contribution to the entropy difference between the two phases. A brief discussion concerning the relative values of interatomic force constants is included.

A kinetic Monte Carlo (kMC) simulation is conducted to study thegrowth of ultrathin film of Co on Cu(001) surface. The many-body,tight-binding potential model is used in the simulation to representthe interatomic potential. The film morphology of heteroepitaxial Cofilm on a Cu(001) substrate at the transient and final stateconditions with various incident energies is simulated. The Cocovered area and the thickness of the film growth of the first twolayers are investigated. The simulation results show that theincident energy influences the film growth and structure. Thereexists a transition energy where the interfacial roughness isminimum. There are some void regions in the film in the final state,because of the influence of the island growth in the first fewlayers. In addition, there are deviations from ideal layer-by-layergrowth at a coverage from 0 ∼ 2 monolayers (ML).

This paper presents the use of molecular dynamics (MD) in simulating thin-film growth on giant magnetoresistance corrugated structures. The simulation model mainly concerns the deposition of Co atoms on a $V$-shape Cu substrate. The many-body, tight-binding potential model is utilized in the MD simulation to represent the interatomic force that exists between the atoms. The interface width is used to quantify the variation of surface roughness at the transient and steady states. The paper investigates the influence of incident energy on the deposited film surface property and on the growing mechanism, for both vertical and oblique deposition. The results demonstrate how the growing characteristics are influenced by different incident energies and by different deposition directions. It is found that at relatively low incident energies the film growth tends to be in a three-dimensional cluster mode and that a void track is formed, whose growing direction is almost equal to the surface normal to the two inclined surfaces. The uneven thickness found along the base of the $V$ shape is mainly due to the deposited atoms that accumulate at the bottom of the $V$ groove when the incident energy is at a relatively high level. It is found that there exists an optimal incident energy that produces the best film surface property. The film surface property can be improved by changing the incident direction relative to the two inclined directions of \ifmmode\pm\else\textpm\fi{}45\ifmmode^\circ\else\textdegree\fi{}. Smaller deviation angles yield better film surface properties for low incident energy. Conversely, higher levels of incident energy result in worse film surface properties.

Effect of lattice defects, hydrogen impurity and temperature on electronic thermal conductivity in first wall tungsten materials

The impact of helium clusters on the electronic thermal transport properties of tungsten plasma-facing materials at finite temperatures