From dc8c4ad6e5ce70527a1e97f63e35ed31753fa0b5 Mon Sep 17 00:00:00 2001 From: hackbard Date: Tue, 20 Apr 2010 14:08:53 +0200 Subject: [PATCH] v1 inc temp nearly finished --- posic/thesis/md.tex | 27 +++++++++++++++++---------- 1 file changed, 17 insertions(+), 10 deletions(-) diff --git a/posic/thesis/md.tex b/posic/thesis/md.tex index 8860ce2..4a7524e 100644 --- a/posic/thesis/md.tex +++ b/posic/thesis/md.tex @@ -264,6 +264,7 @@ Due to the limitations of short range potentials and conventional MD as discusse The simulation sequence and other parameters aside system temperature remain unchanged as in section \ref{subsection:initial_sims}. Since there is no significant difference among the $V_2$ and $V_3$ simulations only the $V_1$ and $V_2$ simulations are carried on and refered to as low carbon and high carbon concentration simulations. Temperatures ranging from $450\,^{\circ}\mathrm{C}$ up to $2050\,^{\circ}\mathrm{C}$ are used. + A simple quality value $Q$ is introduced, which helps to estimate the progress of structural evolution. In bulk 3C-SiC every C atom has four next neighboured Si atoms and every Si atom four next neighboured C atoms. The quality could be determined by counting the amount of atoms which form bonds to four atoms of the other species. @@ -285,18 +286,24 @@ Structures that look promising due to high quality values need to be further inv \includegraphics[width=12cm]{tot_pc_thesis.ps}\\ \includegraphics[width=12cm]{tot_ba.ps} \end{center} -\caption[Si-C radial distribution and quality evolution for the low concentration simulations at different elevated temperatures.]{Si-C radial distribution and quality evolution for the low concentration simulations at different elevated temperatures. All structures are cooled down to $20\,^{\circ}\mathrm{C}$. Arrows in the quality plot mark the end of carbon insertion and the start of the cooling down step.} +\caption[Si-C radial distribution and quality evolution for the low concentration simulations at different elevated temperatures.]{Si-C radial distribution and quality evolution for the low concentration simulations at different elevated temperatures. All structures are cooled down to $20\,^{\circ}\mathrm{C}$. The grey line shows resulting Si-C bonds in a configuration if substitutional C in c-Si (C$_\text{sub}$) at zero temperature. Arrows in the quality plot mark the end of carbon insertion and the start of the cooling down step.} \label{fig:md:tot_si-c_q} \end{figure} -Figure \ref{fig:md:tot_si-c_q} shows the radial distribution of Si-C bonds for different temperatures and the corresponding quality evolution as defined earlier. - -Cut-off vanisches, thats a nice win ... - -Further explanation of PC ... - -100 to sub configurations ... - -This is reflected in the qualities obtained for different temperatures. +Figure \ref{fig:md:tot_si-c_q} shows the radial distribution of Si-C bonds for different temperatures and the corresponding quality evolution as defined earlier for the low concentration simulaton, that is the $V_1$ simulation. +The first noticeable and promising change in the Si-C radial distribution is the successive decline of the artificial peak at the Si-C cut-off distance with increasing temperature up to the point of disappearance at temperatures above $1650\,^{\circ}\mathrm{C}$. +The system provides enough kinetic energy to affected atoms, which are able to escape the cut-off region. +Another important observation in structural change is exemplified in the two shaded areas. +In the grey shaded region a decrease of the peak at 0.186 nm and the bump at 0.175 nm and a concurrent increase of the peak at 0.197 nm with increasing temperature is visible. +Similarly the peaks at 0.335 nm and 0.386 nm shrink in contrast to a new peak forming at 0.372 nm as can be seen in the yellow shaded region. +Obviously the structure obtained from the $450\,^{\circ}\mathrm{C}$ simulations, which is dominated by the existence of \hkl<1 0 0> C-Si dumbbells transforms into a different structure with increasing simulation temperature. +Investigations of the atomic data reveal substitutional carbon to be responsible for the new Si-C bonds. +The peak at 0.197 nm corresponds to the distance of a substitutional carbon to the next neighboured silicon atoms. +The one at 0.372 is the distance of the substitutional carbon atom to the second next silicon neighbour along the \hkl<1 1 0> direction. +Comparing the radial distribution for the Si-C bonds at $2050\,^{\circ}\mathrm{C}$ to the resulting Si-C bonds in a configuration of a substitutional carbon atom in crystalline silicon excludes all possibility of doubt. +The resulting bonds perfectly match and, thus, explain the peaks observe for the increased temperature simulations. +To conclude, by increasing the simulation temperature, the \hkl<1 0 0> C-Si dumbbell characterized structure transforms into a structure dominated by substitutional C. + +This is also reflected in the qualities obtained for different temperatures. \begin{figure}[!ht] \begin{center} -- 2.20.1