Solid State Phenomena Vols. 121-123

Abstract: Rheological properties of water films nanoconfined in two parallel Au plates are investigated with the aid of molecular dynamics simulations. The density distribution, velocity profile, and diffusion coefficients of the water film in a Couette flow are studied. Shear viscosity and its dependence on the shear rate of the water film are also examined in the present research. It is found that the density of the water molecules near the plates is much higher than that in the other regions. This indicates that many water molecules are adsorbed by the plates and adsorbed layers are formed in the vicinity of the plates. The diffusion of the whole film increases dramatically as the shear rate becomes greater than 1010 s-1. The shear viscosity decreases as the shear rate increases, especially for the water film with a small thickness, which indicates the shear-thinning behavior for viscosity of the nanoconfined film. Moreover, an increase in shear viscosity with a decrease in the film thickness can also be found in the present study.

Abstract: In this work we present a theoretical model that explains the current and voltage oscillations at the Si electrode in HF media. A simulation computer program based on this model is implemented and results are shown. Oscillations of the current and (for the first time) the voltage obtained numerically fit perfectly with experiments. The model allows to obtain more information about the system in the form of maps (accompanied by histograms) of e.g.: oxide thickness distribution, SiO2/HF and Si/SiO2 interfaces morphology, or local voltage losses. Other characteristics of the oxide like capacitance or roughness can also be obtained.

Abstract: By means of the density functional theory on the basis of generalized gradient approximation, the reaction paths of the dehydrogenation from the diamond (100) surface was deduced due to the reaction heat. Moreover, the most stable structure of the hydride diamond (100) surface was obtained. The results indicate that the dehydrogenation is easier to take place at the same C-C dimer and forms the parallel geometries. The parallel 1×1:1.5H, 2×1:H and parallel 2×1:0.5H are the intermediate products during the hydrogen desorption process, while, 2×1:H is the most stable structure of the hydride diamond (100) surfaces. The calculated reaction heat is in accordance with the experimental results.

Abstract: The mode frequency and the quality factor of nanowire cavities are calculated from the intensity spectrum obtained by the finite-difference time-domain (FDTD) technique and the Padé approximation. In the free-standing nanowire cavity with the dielectric constant 6.0 and the length of 5 μm, the quality factors of 130, 159, and 151 are obtained for HE11 with frequency around 798 THz, at the cavity radius of 60nm, 75nm, and 90nm, respectively. The Q-factor of 78 is also calculated in the nanowire with length of 5 μm and radius of 60nm grown on the sapphire substrate with refractive index 1.8. The obtained mode field distribution of the fundamental transverse mode shows that the mode field confined very well by the nanowire cavity even when the radius of nanowire is much smaller than the mode wavelength.

Abstract: Based on the exchange mechanism of metal islands growth on anisotropic metal surfaces, the growth processes of anisotropic Cu islands on the anisotropic Pd (110) surface are investigated by Monte Carlo simulations with realistic growth model and physical parameters. The anisotropic diffusion and anisotropic sticking of Cu adatoms are included in the simulation model after being considered the anisotropy of Pd (110) surface and compared to the experiments. It is found that the larger diffusion rate along the [110] channels of Pd (110) surface gives rise to a slower growth rate of Cu island in this direction, unless special effect of the anisotropic sticking is invoked. The simulation results show that the shape anisotropy of Cu islands is mainly due to the sticking anisotropy rather than the diffusion anisotropy.

Abstract: Chemical mechanical polishing (CMP) is a widely used technique to achieve high level of global and local planarity required in integrate circuit (IC) areas, which pleas for concentrate researches. A preliminary wafer-scale flow model for CMP is presented considering the roughness as well as the porosity and compressibility of the pad. Pressure distributions for three kinds of pad roughness: cosine shape, two-scale cosine shape and actual roughness were given with the help of numerical simulation by solving the corresponding two-dimensional slurry flow model. Pressure fluctuations and peaks can be seen from the results. The model predictions will be conducive to the removal rate and mass transport computation. The research is a qualitative one and will pave the way for further explorations of mechanisms of CMP process.

Abstract: A molecular dynamic simulation study has been performed for a large-sized system consisting of 106 liquid metal Al atoms to deeply investigate the formation and magic number characteristics of various cluster formed during solidification processes. It has been found that the numbers of various types of cluster in the system obviously possess peak values, namely, magic numbers. The first, second, third, .…,and tenth magic numbers are determined in turn in the order of 13, 19, 25(27), 31(33), 38(40), 42(45), 48(51), 55(59), 61(65), 67,…( the numbers in the brackets are the second peak values in the corresponding level of cluster). This magic number serial is in good agreement with the experimental results obtained by Harris et al, and this method determining the magic numbers from the clusters according to the level of basic cluster can be used to afford a primary scientific and reasonable explanation to experimental results.

Abstract: Particle’s behavior in the slurry with power-law viscosity shows great effect on the wafer surface polishing. Hydrodynamic pressure is periodically generated on the surface asperity when particles are passing through it. Fatigue fracture occurs under the effect of periodical pressure and it begins from the top to the bottom of the asperity. Based on the energy-balance fracture theory, the removal rate is calculated and it shows good agreement with experiment data.

Abstract: The behavior of island shape transition and nucleus density evolution in the early stage of epitaxial growth mediated by a monolayer of surfactant is studied by using a kinetic Monte Carlo simulations. The main kinetic processes included in the model are deposition, diffusion of atoms, exchange of adatoms with their underneath surfactant atoms, and reexchange in which an exchanged adatom resurfaces to the top of the surfactant layer. The simulation produces pattern transitions from small compact islands at low temperatures, to fractal-like islands at intermediate temperatures where the deposited adatoms can be easily incorporated into the surfactant layer, and then to regular compact islands at high temperatures where the reexchange becomes active. The island density as a function of temperature exhibits a complex N-shape. These results provide a reasonable explanation for the observed temperature dependence of the growth mode in existing experiments.

Abstract: 2D kinetic Monte Carlo simulation has been used to study the void distribution of nickel thin film prepared by physical vapor deposition, and embedded atom method (EAM) was used to represent the interatomic interaction. Packing density and surface roughness were studied as the functions of deposition rate, substrate temperature and incident angle. The results reveal the existence of critical substrate temperature and critical incident angle, and higher substrate temperature, lower deposition rate and appropriate incident angle are advantaged to prepare the compact thin film with excellent mechanical properties.