Kris's Research Notes

December 21, 2012

Thermal Grooving Simulations

Filed under: Grains, KMC, Sintering, Thermal Grooving — Kris Reyes @ 4:23 pm

In this note, we present simulations on thermal grooving for both porous and non-porous media. A bar with grains is allowed to anneal by means of grain growth and surface diffusion. In the case of porous media, this can be seen as a follow-up of the previous sintering simulations, but with a free boundary.

December 18, 2012

Sintering Simulations: Part 2

Filed under: Grains, KMC, Sintering — Kris Reyes @ 8:33 pm

Here, we present simulation results of sintering on a longer time scale than the previous simulations. Average grain size and number of grains are plotted as a function of time.

December 14, 2012

Sintering simulations: Part 1

Filed under: Grains, KMC, Sintering — Kris Reyes @ 4:13 am

In this note, we present preliminary simulations of sintering, by which we mean the evolution of granular, porous material. Grains represent contiguous regions of atoms of a given orientation. A system evolves by surface diffusion of atoms and changes of atom orientation.

September 4, 2012

VLS Nanowire Simulations — Exchange barrier

Filed under: KMC, Nanowire — Kris Reyes @ 6:10 pm

In this note, we continue to study the effect of energy parameters have on the growth modes observed in VLS nanowire growth. Here we consider the energy $\epsilon$, the additive barrier for exchanges at solid/liquid interface. This governs the attachment and detachment kinetics of solid material to and from the interface, and hence roughly measures the mobility of the interface.

August 27, 2012

VLS Nanowire Simulations – C Bonds

Filed under: KMC, Nanowire — Kris Reyes @ 5:30 pm

In this note, we continue to study the effect of energy parameters on VLS nanowire growth. Here we examine the role of the $\gamma(B,C)$ and $\gamma(C,C)$ bonds, the liquid-solid and solid-solid bond strengths, respectively.

August 24, 2012

VLC Nanowire Simulations — B Bonds

Filed under: KMC, Nanowire — Kris Reyes @ 4:40 pm

This note is a follow-up to our previous one, and continues to explore the effect of the energy parameters in the resulting structure after attempting to grow nanowires by VLS method. In this note, we vary the bonds $\gamma(B, B)$ and $\gamma(B, C)$ — i.e. the strength between liquid-liquid and liquid-solid bonds.

August 23, 2012

Reaction Events

Filed under: KMC, Nanowire — Kris Reyes @ 9:53 pm

In this note, we describe a new reaction event which is incorporated in our model in order to correctly simulate VLS nanowire growth.

July 13, 2012

Crystallization on Grooved Substrates

Filed under: GaAs Simulations, KMC — Kris Reyes @ 3:01 am

In this note, we consider liquid Ga droplet formation and crystallization by As on a substrate with a triangular groove. We study the effect of substrate species by considering first a GaAs substrate and second a substrate composed of a third species (nominally Si). In the latter case, nucleation at the liquid/solid interface is not preferred leading to increased surface nucleation as well as a different geometry of the crystallization front.

June 29, 2012

Memoization of Rates

Filed under: Implementation — Kris Reyes @ 4:38 am

In this note, we comment on an implementation detail that accounts for a 10x speed-up to a naive KMC implementation: memoization of rates. Memoization is the act of storing rates computed in the course of the simulated so that they do not have to be re-computed again if needed. We summarize why doing this makes sense in the KMC context and give two consequences of its implementation which improves both performance and memory usage.

June 15, 2012

3D Nanowires — Liquid Droplets

Filed under: Nanowire — Kris Reyes @ 12:31 pm

In 2+1 dimensions, KMC simulations tend to facet easily. This makes sense as more bonds nearest and next-nearest neighbor bonds occur in 2+1 dimensions. Indeed, on the diamond lattice used throughout our 3D simulations, an atom posses 4 nearest neighbor and 12 next-nearest neighbor bonds. If we wish to model nanowire growth by the VLS method, it is desirable for our liquid (which resides on the lattice) to not be faceted. In this note, we describe preliminary results in our search for the correct energy and temperature parameters that allow this to occur.

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