Thermal Diffusion in Molecular Dynamics Simulations of Thin Film Diamond Deposition
Molecular Dynamics simulations of carbon atom depositions
are used to investigate energy diffusion from the impact zone.
Simulations were performed of 50 eV carbon atom depositions onto (111) surface of a 3.8nm x 3.4nm x 1.0nm diamond slab containing 2816 atoms in 11 layers of 256 atoms each.
After the initial transient (200fSec) the impact zone has cooled below 3,000K then near 1,000K by 1pSec. Thereafter the temperature profile decays approximately as described by diffusion theory, perturbed by atomic scale fluctuations.
A continuum model of classical energy transfer is provided by the traditionnal thermal diffusion equation.
The results show that continuum diffusion theory describes well energy diffusion in low energy atomic deposition processes, at distances and time scales larger than 1.5 nm and 1-2 pSec, beyond which the energy decays essentially exponentially.
1. 96 time steps.
Profile of local temperatures in a diamond substrate maintained at 300K, as
a function of time and radius from the impact zone of a 50eV neutral carbon atom.
Predictions of continuum diffusion theory are shown on the left and results of MD simulations on the right.
2. 56 time steps.
Profile of local temperatures for longer times (t>1.13pSec) to show decaying fluctuations.
3. Different Views of Figure 2.
Profile of local temperatures for longer times (t>1.13pSec).Temperatures close to the point of impact have been removed to show the detail between 0.28 and 2.10 nm. The red mesh is the continuum Diffusion Theory.
Click here to see a quicktime animation showing how Figure 2 was extracted from Figure 1.
Click here to see a VRML model of this 3D graph.
B.A. Pailthorpe, D. Mitchell and N.S. Bordes "Thermal diffusion in molecular dynamics simulations of thin film diamond deposition" Thin Solid Films, Volume 332, Nos.1 and 2, pp 109 (February 1999).