From: hackbard Date: Wed, 7 Apr 2010 17:25:21 +0000 (+0200) Subject: nearly finished 450 C simulation results X-Git-Url: https://hackdaworld.org/gitweb/?a=commitdiff_plain;h=4401286c0fd9e064939428a601bdf5c28beb9c46;p=lectures%2Flatex.git nearly finished 450 C simulation results --- diff --git a/posic/thesis/md.tex b/posic/thesis/md.tex index 0af5010..45f0195 100644 --- a/posic/thesis/md.tex +++ b/posic/thesis/md.tex @@ -205,16 +205,34 @@ Figure \ref{fig:md:pc_si-c} displays the Si-C radial distribution function for a The first peak observed for all insertion volumes is at approximately 0.186 nm. This corresponds quite well to the expected next neighbour distance of 0.189 nm for Si and C atoms in 3C-SiC. By comparing the resulting Si-C bonds of a C-Si \hkl<1 0 0> dumbbell with the C-Si distances of the low concentration simulation it is evident that the resulting structure of the $V_1$ simulation is dominated by this type of defects. -This is not surpsisingly, since the \hkl<1 0 0> dumbbell is found to be the ground-state defect of a C interstitial in c-Si and for the low concentration simulations a carbon interstitial is expected in every fifth silicon unit-cell ... - -\subsection{Increased temperature simulations} - -It is not only the C-C bonds which seem to be unbreakable. +This is not surpsising, since the \hkl<1 0 0> dumbbell is found to be the ground state defect of a C interstitial in c-Si and for the low concentration simulations a carbon interstitial is expected in every fifth silicon unit cell only, thus, excluding defect superposition phenomena. +The peak distance at 0.186 nm and the bump at 0.175 nm corresponds to the distance $r(3C)$ and $r(1C)$ as listed in table \ref{tab:defects:100db_cmp} and visualized in figure \ref{fig:defects:100db_cmp}. +In addition it can be easily identified that the \hkl<1 0 0> dumbbell configuration contributes to the peaks at about 0.335 nm, 0.386 nm, 0.434 nm, 0.469 nm and 0.546 nm observed in the $V_1$ simulation. +Not only the peak locations but also the peak widths and heights become comprehensible. +The distinct peak at 0.26 nm, which exactly matches the cut-off radius of the Si-C interaction, is again a potential artifact. + +For high carbon concentrations, that is the $V_2$ and $V_3$ simulation, the defect concentration is likewiese increased and a considerable amount of damage is introduced in the insertion volume. +The consequential superposition of these defects and the high amounts of damage generate new displacement arrangements for the C-C as well as for the Si-C pair distances, which become hard to categorize and trace and obviously lead to a broader distribution. +Short range order indeed is observed but only hardly visible is the long range order. +This indicates the formation of an amorphous SiC-like phase. +In fact the resulting Si-C and C-C radial distribution functions compare quite well with these obtained by cascade amorphized and melt-quenched amorphous SiC using a modified Tersoff potential \cite{gao02}. + +So why is it amorphous? +Short range bond order potentials show overestimated interactions. +Indeed it is not only the C-C bonds which seem to be unbreakable. Also the C-Si pairs, as observed in the low concentration simulations, are stuck. This can be seen from the horizontal progress of the total energy graph in the continue-step. -Higher time periods or alternatively higher temperatures to speed up the simulation are needed. +Higher time periods wil not do the trick. +Alternatively higher temperatures to speed up or actually make possible the precipitation simulation are needed. + {\color{red}Todo: Read again about the accelerated dynamics methods and maybe explain a bit more here.} +Finally explain which methods will be applied in the following. + +\subsection{Constructed minimal 3C-SiC precipitate in crystalline silicon} + +\subsection{Increased temperature simulations} + \subsection{Simulations at temperatures exceeding the silicon melting point} LL Cool J is hot as hell!