From: hackbard Date: Tue, 16 Mar 2010 11:39:48 +0000 (+0100) Subject: vac, c sub and si int + c int + vac in head words .. X-Git-Url: https://hackdaworld.org/gitweb/?a=commitdiff_plain;h=8a062fc323352dab284951ad6dd31c674cae5ada;p=lectures%2Flatex.git vac, c sub and si int + c int + vac in head words .. --- diff --git a/posic/thesis/defects.tex b/posic/thesis/defects.tex index d5afa44..3292808 100644 --- a/posic/thesis/defects.tex +++ b/posic/thesis/defects.tex @@ -898,12 +898,51 @@ Type & \hkl<-1 0 0> & \hkl<1 0 0> & \hkl<1 0 0> & \hkl<1 0 0> & \hkl<1 0 0> & \h Figure \ref{fig:defects:comb_db110} shows the corresponding plot of the data including a cubic spline interplation and a suitable fitting curve. The funtion found most suitable for curve fitting is $f(x)=a/x^3$ comprising the single fit parameter $a$. Thus, far-off located dumbbells show an interaction proportional to the reciprocal cube of the distance and the amount of bonds along \hkl<1 1 0> respectively. -This behavior is no longer valid for the immediate vicinity revealed by the saturating binding energy of a second dumbbell at position 1, which was ignored in the fitting procedure. - +This behavior is no longer valid for the immediate vicinity revealed by the saturating binding energy of a second dumbbell at position 1, which is ignored in the fitting procedure. {\color{red}Todo: DB mig along 110?} +The second part of table \ref{tab:defects:e_of_comb} lists the energetic results of substitutional carbon and vacancy combinations with the initial \hkl<0 0 -1> dumbbell. + +Figure ... +c-sub: +position 5: the sub and the db both pull the the bottom si atoms in concerning \hkl<1 1 0> direction. +Tensile strain which explains the binding energy. +lowest energy observed at position 3. +sub is located in top of the initial db. +in contrast to the latter case, strain compensation occurs. +position 2 and 4 the sub is (zwar) located (unter) db but due to the configuration not that much strain arises, since ... +at position 1, c-c bond is formed, like in graphit or diamond. +both c atoms are pushed towards each other resulting in high displacements and high strain energy in the near surrounding of the si crystal, which perfectly explains the high energy of ... eV. + +The creation of the vacancy at position 1 ... c interstitital moves to acancy position ending up in a configuration of a substitutional carbon which explains the highbinding energy. +At position 3 a great amount of strain energy is reduced, since the the vacancy replaces a silicon atom usually bond to and thus starined by the silicon dumbbell atom. +db moves towards the vacancy in \hkl<1 -1 0> direction. +Vac at position 2 and 4 have similar results. +Less strain is reduced, since the displacement of the bottom silicon atom, whcih would be directly bond to the silicon atom replaced by the vacancy, is less. +In the second case, there is even less strain reduction since the second next neighbour is replaced by the vacancy. +A symmetric configuration is expected, but it is not! +jahn-Teller distortion ... check this! +In both cases the db is tilted in such a way, that the carbon atom moves towards the vacancy. +At position 5 the silicon dumbbell atom moves in \hkl<1 1 0> direction, the same direction where the vacancy is located. +Strain reducde by this is partialy absorbed by strain originating from the fact that si atom bound to and pulled by the carbon atom is also pulled by the vacancy. + +CHECK C-C DIST AND SI-C DIST !!! of all!!! + +{\color{red}Todo: Jahn-Teller distortion (vacancy) $\rightarrow$ actually three possibilities? Due to the initial defect symmetries are broken. It should have relaxed into the minumum energy configuration!?} +Once a vacancy exists the minimal e conf is the c sub conf and ofcourse necessary for formation of SiC. +The question is whether the migration into this conf is possible. +Fig shows the migration of the 2 and 3 conf into the c sub conf. +Low migration barriers, which means that SiC will modt probably form ... and so on ... + {\color{red}Todo: Si int and C sub ...} +The existance of a vacancy is most often accompanied by an interstitial. +The silicon interstitital might diffuse to the surface or recombine with other vacancy defects and tus is out of the interested simulation region. +However, investigation of near by vacancy, Si and C interstititla is necessary, too. +As for the ground state of the single Si self-int a 110 this is also assumed as the lowest possibility in combination with other defects, which is a cruel assumption!!! {\color{red}Todo: Model of kick-out and kick-in mechnism?} -{\color{red}Todo: Jahn-Teller distortion (vacancy) $\rightarrow$ actually three possibilities! :(} + +\section{Summary} +... +