discussion almost finished

diff --git a/posic/publications/defect_combos.tex b/posic/publications/defect_combos.tex
index 3d0cb68b2f53488a833c55229b38e9279a31cdd9..8226e0c04cfb492053816e4369239ec380d4c5d2 100644 (file)
--- a/posic/publications/defect_combos.tex
+++ b/posic/publications/defect_combos.tex
@@ -509,16 +509,60 @@ $t=\unit[2900]{fs}$
 \r
 \section{Discussion}\r
 \r
-The ground state configuration of a C atom in otherwise perfect c-Si is the C$_{\text{i}}$ \hkl<1 0 0> DB.\r
+Obtained results for separated point defects in Si are in good agreement to previous theoretical work on this subject, both for intrinsic defects\cite{leung99,al-mushadani03} as well as for C point defects\cite{dal_pino93,capaz94}.\r
+The ground state configurations of these defects, i.e. the Si$_{\text{i}}$ \hkl<1 1 0> and C$_{\text{i}}$ \hkl<1 0 0> DB, have been reproduced and compare well to previous findings of theoretical investigations on Si$_{\text{i}}$\cite{leung99,al-mushadani03} as well as theoretical\cite{dal_pino93,capaz94,burnard93,leary97,jones04} and experimental\cite{watkins76,song90} studies on C$_{\text{i}}$.\r
+A quantitatively improved activation energy of \unit[0.9]{eV} for a qualitatively equal migration path based on studies by Capaz et.~al.\cite{capaz94} to experimental values\cite{song90,lindner06,tipping87} ranging from \unit[0.70-0.87]{eV} reinforce their derived mechanism of diffusion for C$_{\text{i}}$ in Si.\r
+\r
+The investigation of defect pairs indicates a general trend of defect agglomeration mainly driven by the potential of strain reduction.\r
+Obtained results for the most part compare well with results gained in previous studies\cite{leary97,capaz98,mattoni2002,liu02} and show an astnishingly good agreement with experiment\cite{song90}.\r
+Configurations involving two C impurities indeed exhibit the ground state for structures consisting of C-C bonds, which are responsible for the vast gain in energy.\r
+However, based on investigations of possible migration pathways, these structures are less likely to arise than structures, in which both C atoms are interconnected by another Si atom, which is due to high activation energies of the respective pathways or alternative pathways with less high activation energies, which, however, involve intermediate unfavorable configurations.\r
+Thus, agglomeration of C$_{\text{i}}$ is expected while the formation of C-C bonds is assumed to fail to appear by thermally activated diffusion processes.\r
+\r
+In contrast, C$_{\text{i}}$ and V were found to efficiently react with each other exhibiting activation energies as low as \unit[0.1]{eV} and \unit[0.6]{eV} resulting in C$_{\text{s}}$ configurations.\r
+In addition, a highly attractive interaction exhibiting a large capture radius was observed, effective independent of the orientation and the direction of separation of the defects.\r
+Thus, the formation of C$_{\text{s}}$ is very likely to occur.\r
+Comparatively high energies necessary for the reverse process reveal this configuration to be extremely stable.\r
+\r
+Investigating configurations of C$_{\text{s}}$ and Si$_{\text{i}}$ formation energies higher than that of the C$_{\text{i}}$ \hkl<1 0 0> DB were obtained keeping up previously derived assumptions concerning the ground state of C$_{\text{i}}$ in otherwise perfect Si.\r
+However, a small capture radius was identified for the respective interaction that might prevent the recombination of defects exceeding a separation of \unit[0.6]{nm} into the ground state configuration.\r
+In addition, a rather small activation energy of \unit[0.77]{eV} allows for the formation of a C$_{\text{s}}$-Si$_{\text{i}}$ pair originating from the C$_{\text{i}}$ \hkl<1 0 0> DB structure by thermally activated processes.\r
+Thus, elevated temperatures might lead to configurations of C$_{\text{s}}$ and a remaining Si atom in the near interstitial lattice, which is supported by the result of the molecular dynamics run.\r
+\r
+These findings allow to draw conclusions on the mechanisms involved in the process of SiC conversion in Si.\r
+Agglomeration of C$_{\text{i}}$ is energetically favored and enabled by a low activation energy for migration.\r
+Although ion implantation is a process far from thermodynamic equlibrium, which might result in phases not described by the Si/C phase diagram, i.e. a C phase in Si, high activation energies are believed to be responsible for a low probability of the formation of C clusters.\r
+\r
+Unrolling these findings on the initially stated controversy present in the precipitation model, an increased participation of C$_{\text{s}}$ already in the initial stage must be assumed.\r
+Thermally activated C$_{\text{i}}$ might turn into C$_{\text{s}}$.\r
+The associated emission of Si$_{\text{i}}$ serves two needs, as a vehicle for other C$_{\text{s}}$ and as a supply of Si atoms needed elsewhere to form the SiC structure.\r
+As for the vehicle, Si$_{\text{i}}$ is believed to react with C$_{\text{s}}$ turning it into a highly mobile C$_{\text{i}}$ again, allowing for the rearrangement of the C atom.\r
+The rearrangement is crucial to end up in a configuration of C atoms only occupying substitutionally the lattice sites of one of the fcc lattices that build up the diamond lattice as expected in 3C-SiC.\r
+On the other hand the conversion of some region of Si into SiC by substitutional C is accompanied by a reduction of the volume since SiC exhibits a \unit[20]{\%} smaller lattice constant than Si.\r
+The reduction in volume is compensated by excess Si$_{\text{i}}$ serving as building blocks for the surrounding Si host or a further formation of SiC.\r
+\r
+It is, thus, concluded that precipitation occurs by a successive agglomeration of C$_{\text{s}}$.\r
+However, the process is governed by both, C$_{\text{s}}$ accompanied by Si$_{\text{i}}$ as well as C$_{\text{i}}$.\r
+... HIER WEITER ...\r
+By this,  explains the alignment of the \hkl(h k l) lattice planes of the precipitate and the substrate.\r
+No contradiction to ... has Si int ... nice to explain cloudy TEM images indicating atoms in interstitial lattice.\r
+\r
 Our calculations show that point defects which unavoidably are present after ion implantation significantly influence the mobility of implanted carbon \r
 in the silicon crystal.\r
 A large capture radius has been found  for...   \r
 Especially vacancies....  \r
 \r
 \r
+C$_{\text{s}}$ must be attributed an important role in SiC formation ...\r
+\r
+Spin polarized ... Si or C-C show qualitatively other defect structure than C-Si , in which the C forms almot colinear bond and Si remains 120 ... COOL!\r
+\r
 \section{Summary}\r
 In summary, we have shown that ...\r
 \r
+Interactions ... improved by migration paths and acivation energies ... probability ...\r
+\r
+\r
 % ----------------------------------------------------\r
 \section*{Acknowledgment}\r
 We gratefully acknowledge financial support by the Bayerische Forschungsstiftung (DPA-61/05) and the Deutsche Forschungsgemeinschaft (DFG SCHM 1361/11).\r