very first alpha of paper 3

diff --git a/posic/publications/sic_prec.tex b/posic/publications/sic_prec.tex
index 614be92..33e0708 100644 (file)
--- a/posic/publications/sic_prec.tex
+++ b/posic/publications/sic_prec.tex
@@ -109,9 +109,7 @@ Integration of equations of motion is realized by the velocity Verlet algorithm\
 For structural relaxation of defect structures the same algorith is used with the temperature set to 0 K.
 
 The formation energy $E-N_{\text{Si}}\mu_{\text{Si}}-N_{\text{C}}\mu_{\text{C}}$ of a defect configuration is defined by chosing SiC as a particle reservoir for the C impurity, i.e. the chemical potentials are determined by the cohesive energies of a perfect Si and SiC supercell after ionic relaxation.
 For structural relaxation of defect structures the same algorith is used with the temperature set to 0 K.
 
 The formation energy $E-N_{\text{Si}}\mu_{\text{Si}}-N_{\text{C}}\mu_{\text{C}}$ of a defect configuration is defined by chosing SiC as a particle reservoir for the C impurity, i.e. the chemical potentials are determined by the cohesive energies of a perfect Si and SiC supercell after ionic relaxation.

-Migration and recombination pathways have been investigated utilizing the constraint conjugate gradient relaxation technique (CRT)\cite{kaukonen98}.
-The binding energy of a defect pair is given by the difference of the formation energy of the complex and the sum of the two separated defect configurations.
-Accordingly, energetically favorable configurations show binding energies below zero while non-interacting isolated defects result in a binding energy of zero.
+Migration and recombination pathways have been investigated utilizing the constraint conjugate gradient relaxation technique\cite{kaukonen98}.

 
 \section{Results}
 
 
 \section{Results}
 


@@ -337,7 +335,7 @@ For both structures the C atom appears to reside on a substitutional rather than
 However, huge amount of damage hampers identification.
 The alignment of the investigated structures to the c-Si host is lost in many cases, which suggests the necissity of much more time for structural evolution to maintain the topotaptic orientation of the precipitate.
 
 However, huge amount of damage hampers identification.
 The alignment of the investigated structures to the c-Si host is lost in many cases, which suggests the necissity of much more time for structural evolution to maintain the topotaptic orientation of the precipitate.
 

-\section{Discussion}
+\section{Summary and discussion}

 
 Investigations are targeted on the initially stated controversy of SiC precipitation, i.e. whether precipitation occurs abrubtly after ehough C$_{\text{i}}$ agglomerated or a successive agglomeration of C$_{\text{s}}$ on usual Si lattice sites (and Si$_{\text{i}}$) followed by a contraction into incoherent SiC.
 Results of a previous ab initio study on defects and defect combinations in C implanted Si\cite{zirkelbach10b} sugeest C$_{\text{s}}$ to play a decisive role in the precipitation of SiC in Si.
 
 Investigations are targeted on the initially stated controversy of SiC precipitation, i.e. whether precipitation occurs abrubtly after ehough C$_{\text{i}}$ agglomerated or a successive agglomeration of C$_{\text{s}}$ on usual Si lattice sites (and Si$_{\text{i}}$) followed by a contraction into incoherent SiC.
 Results of a previous ab initio study on defects and defect combinations in C implanted Si\cite{zirkelbach10b} sugeest C$_{\text{s}}$ to play a decisive role in the precipitation of SiC in Si.


@@ -362,11 +360,17 @@ However, we observed a phase tranisiton of the C$_{\text{i}}$-dominated into a c
 The amount of substitutionally occupied C atoms increases with increasing temperature.
 Entropic contributions are assumed to be responsible for these structures at eleveated temperatures that deviate from the ground state at 0 K.
 Indeed, in a previous ab initio MD simulation\cite{zirkelbach10b} performed at \unit[900]{$^{\circ}$C} we observed the departing of a Si$_{\text{i}}$ \hkl<1 1 0> DB located next to a C$_{\text{s}}$ atom instead of a recombination into the ground state configuration, i.e. a C$_{\text{i}}$ \hkl<1 0 0> DB.
 The amount of substitutionally occupied C atoms increases with increasing temperature.
 Entropic contributions are assumed to be responsible for these structures at eleveated temperatures that deviate from the ground state at 0 K.
 Indeed, in a previous ab initio MD simulation\cite{zirkelbach10b} performed at \unit[900]{$^{\circ}$C} we observed the departing of a Si$_{\text{i}}$ \hkl<1 1 0> DB located next to a C$_{\text{s}}$ atom instead of a recombination into the ground state configuration, i.e. a C$_{\text{i}}$ \hkl<1 0 0> DB.

-Ci to Cs by increased temperatures ...\cite{eichhorn99}
-Increased temperatures during implantation more efficient than postannealing methods, which reflects the present problems of low temperature and low time strcutural evolution ...\cite{eichhorn02}
-C-C for low temperatures, postannealing no that efficient as for high C implantations ...\cite{deguchi92}

 
 

-Thus, we propose an increased participation of C$_{\text{s}}$ already in the initial stages of the precipitation process.
+% postannealing less efficient than hot implantation
+Experimental studies revealed increased implantation temperatures to be more efficient than postannealing methods for the formation of topotactically aligned precipitates\cite{eichhorn02}.
+In particular restructuring of strong C-C bonds is affected\cite{deguchi92}, which preferentially arise if additional kinetic energy provided by an increase of the implantation temperature is missing to accelerate or even enable atomic rearrangements.
+We assume this to be related to the problem of slow structural evolution encountered in the high C concentration simulations due to the insertion of high amounts of C into a small volume within a short period of time resulting in essentially no time for the system to rearrange.
+% rt implantation + annealing
+Implantations of an understoichiometric dose at room temperature followed by thermal annealing results in small spherical sized C$_{\text{i}}$ agglomerates at temperatures below \unit[700]{$^{\circ}$C} and SiC precipitates of the same size at temperatures above \unit[700]{$^{\circ}$C}\cite{werner96}.
+Since, however, the implantation temperature is considered more efficient than the postannealing temperature, SiC precipitates are expected -- and indeed are observed for as-implanted samples\cite{lindner99,lindner01} -- in implantations performed at \unit[450]{$^{\circ}$C}.
+Implanted C is therefor expected to occupy substitutionally usual Si lattice sites right from the start.
+
+Thus, we propose an increased participation of C$_{\text{s}}$ already in the initial stages of the implantation process at temperatures above \unit[450]{$^{\circ}$C}, the temperature most aplicable for the formation of SiC layers of high crystalline quality and topotactical alignment\cite{lindner99}.

 Thermally activated, C$_{\text{i}}$ is enabled to turn into C$_{\text{s}}$ accompanied by Si$_{\text{i}}$.
 The associated emission of Si$_{\text{i}}$ is needed for several reasons.
 For the agglomeration and rearrangement of C Si$_{\text{i}}$ is needed to turn C$_{\text{s}}$ into highly mobile C$_{\text{i}}$ again.
 Thermally activated, C$_{\text{i}}$ is enabled to turn into C$_{\text{s}}$ accompanied by Si$_{\text{i}}$.
 The associated emission of Si$_{\text{i}}$ is needed for several reasons.
 For the agglomeration and rearrangement of C Si$_{\text{i}}$ is needed to turn C$_{\text{s}}$ into highly mobile C$_{\text{i}}$ again.


@@ -380,18 +384,6 @@ However, agglomeration and rearrangement is enabled by mobile C$_{\text{i}}$, wh
 In contrast to assumptions of an abrupt precipitation of an agglomerate of C$_{\text{i}}$\cite{werner96,werner97,eichhorn99,lindner99_2,koegler03}, however, structural evolution is believed to occur by a successive occupation of usual Si lattice sites with substitutional C.
 This mechanism satisfies the experimentally observed alignment of the \hkl(h k l) planes of the precipitate and the substrate, whereas there is no obvious reason for the topotactic orientation of an agglomerate consisting exclusively of C-Si dimers, which would necessarily involve a much more profound change in structure for the transition into SiC.
 
 In contrast to assumptions of an abrupt precipitation of an agglomerate of C$_{\text{i}}$\cite{werner96,werner97,eichhorn99,lindner99_2,koegler03}, however, structural evolution is believed to occur by a successive occupation of usual Si lattice sites with substitutional C.
 This mechanism satisfies the experimentally observed alignment of the \hkl(h k l) planes of the precipitate and the substrate, whereas there is no obvious reason for the topotactic orientation of an agglomerate consisting exclusively of C-Si dimers, which would necessarily involve a much more profound change in structure for the transition into SiC.
 

-\section{Summary}
-
-To conclude, we have shown that ab initio calculations on interstitial carbon in silicon are very close to the results expected from experimental data.
-The calculations presented in this work agree well with other theoretical results.
-So far, the best quantitative agreement with experimental findings has been achieved concerning the interstitial carbon mobility.
-For the first time, we have shown that the bond-centered configuration indeed constitutes a real local minimum configuration resulting in a net magnetization if spin polarized calculations are performed.
-Classical potentials, however, fail to describe the selected processes.
-This has been shown to have two reasons, i.e. the overestimated barrier of migration due to the artificial interaction cut-off on the one hand, and on the other hand the lack of quantum-mechanical effects which are crucial in the problem under study. 
-% ref mod: language - being investigated
-%In order to get more insight on the SiC precipitation mechanism, further ab initio calculations are currently investigated.
-In order to get more insight on the SiC precipitation mechanism, further ab initio calculations are currently being performed.
-

 % ----------------------------------------------------
 \section*{Acknowledgment}
 We gratefully acknowledge financial support by the Bayerische Forschungsstiftung (DPA-61/05) and the Deutsche Forschungsgemeinschaft (DFG SCHM 1361/11).
 % ----------------------------------------------------
 \section*{Acknowledgment}
 We gratefully acknowledge financial support by the Bayerische Forschungsstiftung (DPA-61/05) and the Deutsche Forschungsgemeinschaft (DFG SCHM 1361/11).