From: hackbard Date: Mon, 26 Apr 2010 14:23:18 +0000 (+0200) Subject: start and nearly eand of high conc sim X-Git-Url: https://hackdaworld.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=004b2ada91b8fdcd91f352cded7ec18ceaf16483;p=lectures%2Flatex.git start and nearly eand of high conc sim --- diff --git a/posic/thesis/md.tex b/posic/thesis/md.tex index c267178..e114a3d 100644 --- a/posic/thesis/md.tex +++ b/posic/thesis/md.tex @@ -339,13 +339,37 @@ The continuous dashed line corresponds to the distance of a substitutional C wit By comparison with the radial distribution it becomes evident that the shift accompanies the advancing transformation of \hkl<1 0 0> dumbbells into substitutional C. Next to combinations of two substitutional C atoms and two \hkl<1 0 0> dumbbells respectively also combinations of \hkl<1 0 0> dumbbells with a substitutional C atom arise. In addition, structures form that result in distances residing inbetween the ones obtained from combinations of mixed defect types and the ones obtained by substitutional C configurations, as can be seen by quite high g(r) values to the right of the continuous dashed line and to the left of the first arrow with a solid line. -For the most part these structures can be identified as configurations of one substitutional C atom with either another C atom that basically occupies a Si lattice with a Si interstitial residing in the very next surrounding or a C atom that nearly occupies a Si lattice site forming a defect other than the \hkl<1 0 0>-type with the Si atom. -Again, this is a quite promising result since the ... -Both cases ... -Might be due to other defects compensatig strain by pushing them together. -Actually promising result, since the structure is right and even the lengthes begin to compare. -Structures with 3 C which are right in place are observable. -Hmm ... foo. +For the most part these structures can be identified as configurations of one substitutional C atom with either another C atom that practically occupies a Si lattice site but with a Si interstitial residing in the very next surrounding or a C atom that nearly occupies a Si lattice site forming a defect other than the \hkl<1 0 0>-type with the Si atom. +Again, this is a quite promising result, since the C atoms are taking the appropriate coordination as expected in 3C-SiC. +However, this is contrary to the initial precipitation model proposed in section \ref{section:assumed_prec}, which assumes that the transformation into 3C-SiC takes place in a very last step once enough C-Si dumbbells agglomerated. + +\begin{figure}[!ht] +\begin{center} +\includegraphics[width=12cm]{12_pc_thesis.ps}\\ +\includegraphics[width=12cm]{12_pc_c_thesis.ps} +\end{center} +\caption[Si-C and C-C radial distribution for the high concentration simulations at different elevated temperatures.]{Si-C (top) and C-C (bottom) radial distribution for the high concentration simulations at different elevated temperatures. All structures are cooled down to $20\,^{\circ}\mathrm{C}$.} +\label{fig:md:12_pc} +\end{figure} +Figure \ref{fig:md:12_pc} displays the radial distribution for Si-C and C-C pairs obtained from high C concentration simulations at different elevated temperatures. +Again, in both cases, the cut-off artifact decreases with increasing temperature. +Peaks that already exist for the low temperature simulations get slightly more distinct for elevated temperatures. +This is also true for peaks located past distances of next neighbours indicating an increase for the long range order. +However this change is rather small and no significant structural change is observeable. +As for low temperatures order in the short range exist decreasing with increasing distance. +The increase of the amount of Si-C pairs at 0.186 nm could pe positively interpreted since this type of bond also exists in 3C-SiC. +On the other hand the amount of next neighboured C atoms with a distance of approximately 0.15 nm, which is the distance of C in graphite or diamond, is likewise increased. +Thus, higher temperatures seem to additionally enhance a conflictive process, that is the formation of C agglomerates, instead of the desired process of 3C-SiC formation. +This is supported by the C-C peak at 0.252 nm, which corresponds to the second next neighbour distance in the diamond structure of elemental C. +Investigating the atomic data indeed reveals two C atoms which are bound to and interconnect by a third C atom to be responsible for this distance. +The C-C peak at about 0.31 nm, wich is slightly shifted to higher distances (0.317 nm) with increasing temperature corresponds quite well to the next neighbour distance of C in 3C-SiC as well as a-SiC and indeed results from C-Si-C bonds. +The Si-C peak at 0.282 nm, which is pronounced with increasing temperature is constructed out of a Si atom and a C atom, which are both bound to another central C atom. + +This said, there is clear evidence that this is amorphous SiC +However there is no significant change in structure. +But there is a decrease in the artifacts of the potential. +So, first limitations might be condiered as +Now, more temperature to increase infrequent events ... \subsection{Constructed 3C-SiC precipitate in crystalline silicon}