From 06b5a10c4be0574aa9b45f7068ac8157dcb1815c Mon Sep 17 00:00:00 2001 From: hackbard Date: Thu, 28 Jul 2011 12:02:53 +0200 Subject: [PATCH] beta version before spell check --- posic/thesis/basics.tex | 2 +- posic/thesis/defects.tex | 4 +-- posic/thesis/md.tex | 12 ++++++-- posic/thesis/thesis.tex | 3 ++ posic/thesis/vasp_patch.tex | 61 +++++++++++++++++++++++-------------- 5 files changed, 54 insertions(+), 28 deletions(-) diff --git a/posic/thesis/basics.tex b/posic/thesis/basics.tex index ba62d82..4568141 100644 --- a/posic/thesis/basics.tex +++ b/posic/thesis/basics.tex @@ -669,7 +669,7 @@ In the modified version respective energies could be higher than the real ones d Structures of maximum configurational energy do not necessarily constitute saddle point configurations, i .e. the method does not guarantee to find the true minimum energy path. Whether a saddle point configuration and, thus, the minimum energy path is obtained by the CRT method, needs to be verified by caculating the respective vibrational modes. -Modifications used to add the CRT feature to the VASP code and a short instruction on how to use it can be found in appendix \ref{app:patch_vasp}. +Modifications used to add the CRT feature to the {\textsc vasp} code and a short instruction on how to use it can be found in appendix \ref{app:patch_vasp}. % todo - advantages of pw basis concenring hf forces diff --git a/posic/thesis/defects.tex b/posic/thesis/defects.tex index 381dab5..cdc95a8 100644 --- a/posic/thesis/defects.tex +++ b/posic/thesis/defects.tex @@ -1659,7 +1659,7 @@ Thus, elevated temperatures might lead to thermodynamically unstable configurati % todo - sync with conclusion chapter -These findings allow to draw conclusions on the mechanisms involved in the process of SiC conversion in Si. +These findings allow to draw conclusions on the mechanisms involved in the process of SiC conversion in Si, which is elaborated in more detail within the comprehensive description in chapter~\ref{chapter:summary}. Agglomeration of C$_{\text{i}}$ is energetically favored and enabled by a low activation energy for migration. Although ion implantation is a process far from thermodynamic equilibrium, 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-C clusters. @@ -1671,7 +1671,7 @@ The rearrangement is crucial to end up in a configuration of C atoms only occupy On the other hand, the conversion of some region of Si into SiC by \cs{} is accompanied by a reduction of the volume since SiC exhibits a \unit[20]{\%} smaller lattice constant than Si. 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. -To conclude, precipitation occurs by successive agglomeration of C$_{\text{s}}$. +To conclude, the available results suggest precipitation by successive agglomeration of C$_{\text{s}}$. However, the agglomeration and rearrangement of C$_{\text{s}}$ is only possible by mobile C$_{\text{i}}$, which has to be present at the same time. Accordingly, the process is governed by both, C$_{\text{s}}$ accompanied by Si$_{\text{i}}$ as well as C$_{\text{i}}$. It is worth to mention that there is no contradiction to results of the HREM studies \cite{werner96,werner97,eichhorn99,lindner99_2,koegler03}. diff --git a/posic/thesis/md.tex b/posic/thesis/md.tex index 3253d2b..43565f2 100644 --- a/posic/thesis/md.tex +++ b/posic/thesis/md.tex @@ -499,12 +499,20 @@ The insertion of high amounts of C into a small volume within a short period of % rt implantation + annealing Furthermore, C implanted at room temperature was found to be able to migrate towards the surface and form C-rich clusters in contrast to implantations at elevated temperatures, which form stable epitaxially aligned 3C-SiC precipitates \cite{serre95}. In simulation, low temperatures result in configurations of highly mobile \ci{} \hkl<1 0 0> DBs whereas elevated temperatures show configurations of \cs{}, which constitute an extremely stable configuration that is unlikely to migrate. +% +% added +This likewise agrees to results of IBS experiments utilizing implantation temperatures of \degc{550}, which require annealing temperatures as high as \degc{1405} for C segregation due to the stability of \cs{} \cite{reeson87}. +% Indeed, in the optimized recipe to form 3C-SiC by IBS \cite{lindner99}, elevated temperatures are used to improve the epitaxial orientation together with a low temperature implant to destroy stable SiC nanocrystals at the interface, which are unable to migrate during thermal annealing resulting in a rough surface. Furthermore, the improvement of the epitaxial orientation of the precipitate with increasing temperature in experiment perfectly conforms to the increasing occurrence of \cs{} in simulation. % -% todo add sync here starting from werner96 (Similar, implan ...) +% todo add sync here starting from strane93, werner96 ... +Moreover, implantations of an understoichiometric dose into preamorphized Si followed by an annealing step at \degc{700} result in Si$_{1-x}$C$_x$ layers with C residing on substitutional Si lattice sites \cite{strane93}. +For implantations of an understoichiometric dose into c-Si at room temperature followed by thermal annealing below and above \degc{700}, the formation of small C$_{\text{i}}$ agglomerates and SiC precipitates was observed respectively \cite{werner96}. +However, increased implantation temperatures were found to be more efficient than postannealing methods resulting in the formation of SiC precipitates for implantations at \unit[450]{$^{\circ}$C} \cite{lindner99,lindner01}. % -At elevated temperatures, implanted C is therefore expected to occupy substitutionally usual Si lattice sites right from the start. +Thus, at elevated temperatures, implanted C is expected to occupy substitutionally usual Si lattice sites right from the start. +These findings, which are outlined in more detail within the comprehensive description in chapter~\ref{chapter:summary}, are in perfect agreement with previous results of the quantum-mechanical investigations. Thus, elevated temperatures are considered to constitute a necessary condition to deviate the system from equilibrium, as it is the case in IBS. It is concluded that precipitation occurs by successive agglomeration of C$_{\text{s}}$ as already proposed by Nejim et~al.~\cite{nejim95}. diff --git a/posic/thesis/thesis.tex b/posic/thesis/thesis.tex index acfcdb8..dd3eacc 100644 --- a/posic/thesis/thesis.tex +++ b/posic/thesis/thesis.tex @@ -28,6 +28,9 @@ %\usepackage[resetlabels]{multibib} \newcites{pub}{List of publications} +% box around verbatim text +\usepackage{fancyvrb} + % miller \usepackage{miller} diff --git a/posic/thesis/vasp_patch.tex b/posic/thesis/vasp_patch.tex index 500ec42..e495e8d 100644 --- a/posic/thesis/vasp_patch.tex +++ b/posic/thesis/vasp_patch.tex @@ -2,33 +2,48 @@ \label{app:patch_vasp} \section{Description} -The modifications to the VASP code allow to rotate all atom coordinates individually in the particle position evaluation routine of VASP. -In that way constraints for every atom can be applied independently of the chosen basis. -A patch against version 4.6 of the VASP code containing these modifications is available for download\footnote{http://www.physik.uni-augsburg.de/\~{}zirkelfr/download/posic/sd\_rot\_all-atoms.patch}. +In the {\textsc vasp} code, the {\em selective dynamics} mode provides a feature to allow or constrain the change of each of the three coordinates for every single atom. +By this, however, applied constraints are restricted to the chosen basis. +For the investigation of migration pathways utilizing the constrained relaxation technique as detailed in section~\ref{section:basics:migration}, the required constraint not necessarily corresponds to one of the coordinate axes as defined by the basis, which, in turn, is determined to enable a construction within the supercell approach. -\section{Usage} +Thus, the functionality of the {\em selective dynamics} mode had to be extended by modifications in the particle position evaluation routine of {\textsc vasp}. +These modifications allow for a rotation of all atom coordinates individually before respective constraints are applied and a following, final inverse transformation. +In that way, constraints for every single atom can be applied independently of the chosen basis. +A patch against version 4.6 of the {\textsc vasp} code containing these modifications is available for download\footnote{http://www.physik.uni-augsburg.de/\~{}zirkelfr/download/posic/sd\_rot\_all-atoms.patch}. -Since this feature only makes sense in selective dynamics mode, it can be switched on by adding the word {\em Transformed} in front of the {\em selective dynamics} switch. -This feature only works in direct mode. +\section{Mode of operation} + +The extended capabilities can only be used within the {\em selective dynamics} mode. +It is enabled by adding the word {\em transformed} in front of the {\em selective dynamics} switch. +This feature only works in {\em direct} mode. Two values of angles need to be added after the extra flags of each atom. The first angle corresponds to the rotation of the basis about the $z$-axis. The second angle determines the rotation about the transformed $x$-axis, $x'$. All values have to be supplied in degrees. -All these information is given in the POSCAR file as can be seen in the follwing example: -\begin{verbatim} -cubic diamond - 5.48000000000000 - 2.9909698580839312 0.0039546630279804 -0.0039658085666586 - 0.0039548953566878 2.9909698596656376 -0.0039660323646892 - -0.0039680658132861 -0.0039674231313905 2.9909994291263242 - 216 1 -Transformed selective dynamics -Direct - 0.994174 0.994174 -0.000408732 T F T 45 36.5145 - 0.182792 0.182792 0.981597 T F T -135 -5.95043 - ... - 0.119896 0.119896 0.0385525 T F T -135 21.8036 -\end{verbatim} -In case of the first atom the basis is transformed by a rotation of $45^{\circ}$ and $36.5145^{\circ}$ about the $z$ and $x'$ axis. -Relaxation of this atom is constrained to the $y''$-axis. +The entire information is given in the POSCAR file as can be seen in the example displayed in Fig.~\ref{fig:vasp_input}. +\begin{figure}[t] +\begin{Verbatim}[frame=single] +cubic diamond + 5.429 + 1.00000 0.00000 0.00000 + 0.00000 1.00000 0.00000 + 0.00000 0.00000 1.00000 + 8 +transformed selective dynamics +direct + 0.00000 0.00000 0.00000 T F T 45.0 30.0 + 0.50000 0.50000 0.00000 T T T 0.0 0.0 + 0.50000 0.00000 0.50000 T T T 0.0 0.0 + 0.00000 0.50000 0.50000 T T T 0.0 0.0 + 0.25000 0.25000 0.25000 T F T 135.0 -10.0 + 0.75000 0.75000 0.25000 T T T 0.0 0.0 + 0.75000 0.25000 0.75000 T T T 0.0 0.0 + 0.25000 0.75000 0.75000 T T T 0.0 0.0 +\end{Verbatim} +\caption{Example {\textsc vasp} input file utilizing the {\em transformed selective dynamics} mode of operation.} +\label{fig:vasp_input} +\end{figure} +In case of the first atom, the basis is transformed by a rotation of $45^{\circ}$ and $30^{\circ}$ about the $z$ and $x'$ axis. +The basis of the fifth atom is likewise rotated by $135^{\circ}$ and $-10^{\circ}$ respectively. +Relaxation of both atoms is only allowed within the plane perpendicular to the $y''$-axis. -- 2.39.2