Biomedical subjects

Jacques G Amar

Publications and source records attributed to Jacques G Amar.

4 recordsLinked to original sources

PubMed2006

Upper critical dimension for irreversible cluster nucleation and growth in the point-island regime.

We compare the results of kinetic Monte Carlo (KMC) simulations of a point-island model of irreversible nucleation and growth in four dimensions (4D) with the corresponding mean-field (MF) rate-equation predictions for the monomer density, island density, island-size distribution (ISD), capture-number distribution (CND), and capture-zone distribution (CZD), in order to determine the critical dimension d(c) for mean-field behavior. The asymptotic behavior is studied as a function of the fraction of occupied sites (coverage) and the ratio DF of the monomer hopping rate D to the (per site) monomer creation rate F. Excellent agreement is found between our KMC simulation results and the MF rate equation results for the average island and monomer densities. For large D/F, the scaled CND and CZD do not depend on island size, in good agreement with the MF prediction, while the scaled ISD also agrees well with the MF prediction except for a slight difference at the peak values. Coupled with previous results obtained in d = 3 , these results indicate that for growth in the point-island regime, the upper critical dimension for irreversible cluster nucleation and growth is equal to 4.

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PubMed2002

Effects of short-range attraction in metal epitaxial growth.

The effects of short-range attraction in metal epitaxial growth are studied. Our results indicate that even at normal incidence, the short-range attraction of depositing atoms to step edges can significantly increase the selected mound angle and surface roughness for typical energies used in epitaxial growth. Our results also lead to a picture of the process of deposition near step edges that is quite different from the standard downward funneling picture. Results for the dependence of the uphill current on incident atom kinetic energy and substrate temperature are also presented.

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PubMed2002

Dynamical scaling behavior in two-dimensional ballistic deposition with shadowing.

The dynamical scaling behavior in two-dimensional ballistic deposition with shadowing is studied as a function of the angular distribution of incoming particles and of the underlying lattice structure. Using a dynamical scaling form for the surface box number, results for the scaling of the surface fractal dimension are also presented. Our results indicate that, in addition to the usual self-affine universality class corresponding to vertical deposition, there exist at least two additional universality classes characterized by distinct values of the coarsening and roughening exponents p and beta describing the evolution of the lateral feature size and surface roughness with film thickness, as well as the surface fractal dimension D(f). For the case of a uniform angular distribution corresponding to an anisotropic flux, we find p=beta=1 and D(f) approximately 1.7. However, for ballistic deposition with an isotropic flux (corresponding to a "cosine" angular distribution), we find p approximately 2/3 and D(f) approximately 1.5 while the effective roughening exponent beta approximately 0.52-0.64 was found to be slightly lattice dependent. In both cases, anomalous scaling of the height-height correlation function is also observed. In contrast, vertical deposition leads to a self-affine surface with p=2/3, beta=1/3, and D(f)=1. The asymptotic scaling behavior appears to depend on the behavior of the angular distribution at large angles but does not depend on other details. An analysis that clarifies the relationship between the launch angle distribution used in the simulations and the flux distribution is also presented.

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PubMed2002

Scaling behavior of the surface in ballistic deposition.

Using a dynamical scaling form for the surface fractal dimension as well as efficient algorithms for the simulation and analysis of the surface in three-dimensional ballistic deposition, we show that while the top of the surface is self-affine, the complete surface including overhangs has fractal dimension D(f) approximately 3. The existence of such a fractal surface is a consequence of the difficulty of closing off voids in three and higher dimensions. By studying a modified ballistic deposition model in which sticking is allowed with a given probability p, we show that the surface undergoes a phase transition from fractal to compact at a finite value of p. Our results also have implications for understanding the surface morphology in sedimentary rocks and low-temperature thin films.

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