Biomedical subjects

Michael J Aziz

Publications and source records attributed to Michael J Aziz.

3 recordsLinked to original sources

PubMed2006

Continuum theory of nanostructure decay via a microscale condition.

The morphological relaxation of faceted crystal surfaces is studied via a continuum approach. Our formulation includes (i) an evolution equation for the surface slope that describes step line tension, g1, and step repulsion energy, g3; and (ii) a condition at the facet edge (a free boundary) that accounts for discrete effects via the collapse times, t(n), of top steps. For initial cones and t(n) approximately t(n)4, we use t(g) from step simulations and predict self-similar slopes in agreement with simulations for any g = g3/g1 > 0. We show that for g >> 1, (i) the theory simplifies to an equilibrium-thermodynamics model; (ii) the slope profiles reduce to a universal curve; and (iii) the facet radius scales as g(-3/4).

Journal Article↗

PubMed2005

Shocks in ion sputtering sharpen steep surface features.

We report a regime of ion beam sputtering that occurs for sufficiently steep slopes. High slopes propagate over large distances without dissipating the steepest features. Both the propagation velocity and the dynamically selected slope are universal, independent of the details of the initial shape of the surface. The resulting behavior can be understood as the propagation of a shock front that self-selects a stable slope, as has been previously observed in thin-film fluid flows. Experiments confirm predictions of the theory. An important implication of the propagative behavior at high surface slopes is that a pattern can be fabricated at a large length scale and, through uniform ion irradiation, reduced to a smaller length scale while preserving, or even sharpening, the sharpest features.

Journal Article↗

PubMed2005

Synthesis of nearly monodisperse embedded nanoparticles by separating nucleation and growth in ion implantation.

We investigate the formation of nanoparticles of Au in SiO(2) by multiple ion implantation steps and intermediate anneals to isolate nucleation and growth, thereby producing a narrow particle size distribution. We discuss the effects of varying the initial nucleation dose and the growth temperature and establish guidelines for synthesizing nanoparticles with improved size uniformity. By this method, we have obtained a standard deviation of 16% on an average diameter of 1.68 nm, compared to 28% when no attempt is made to isolate nucleation and growth.

Crystallization↗