X-Git-Url: https://hackdaworld.org/gitweb/?a=blobdiff_plain;f=posic%2Fthesis%2Fdefects.tex;h=92d08484a6a1a0ca368614b43450a3b082ddd3a7;hb=0e66d3c664ff4a68a8000bd4ee9ae9350fbe69ed;hp=32ff82429980a51e651bf6a092223fbc3ad64524;hpb=1de6d05da5be8de10b91e221d1de6580742e93f9;p=lectures%2Flatex.git diff --git a/posic/thesis/defects.tex b/posic/thesis/defects.tex index 32ff824..92d0848 100644 --- a/posic/thesis/defects.tex +++ b/posic/thesis/defects.tex @@ -115,7 +115,7 @@ In Fig.~\ref{fig:defects:kin_si_hex} the relaxation process is shown on the basi \caption{Kinetic energy plot of the relaxation process of the hexagonal silicon self-interstitial defect simulation using the EA potential.} \label{fig:defects:kin_si_hex} \end{figure} -To exclude failures in the implementation of the potential or the MD code itself the hexagonal defect structure was double-checked with the \textsc{parcas} MD code~\cite{parcas_md}. +To exclude failures in the implementation of the potential or the MD code itself, the hexagonal defect structure was double-checked with the \textsc{parcas} MD code~\cite{parcas_md}. The respective relaxation energetics are likewise plotted and look similar to the energetics obtained by \textsc{posic}. In fact, the same type of interstitial arises using random insertions. In addition, variations exist, in which the displacement is only along two \hkl<1 0 0> axes ($E_\text{f}=3.8\,\text{eV}$) or along a single \hkl<1 0 0> axes ($E_\text{f}=3.6\,\text{eV}$) successively approximating the tetrahedral configuration and formation energy. @@ -388,7 +388,7 @@ On the other hand, the C atom forms an almost collinear bond ($\theta_3$) with t This is supported by the image of the charge density isosurface in Fig.~\ref{img:defects:charge_den_and_ksl}. The two lower Si atoms are $sp^3$ hybridized and form $\sigma$ bonds to the Si DB atom. The same is true for the upper two Si atoms and the C DB atom. -In addition the DB atoms form $\pi$ bonds. +In addition, the DB atoms form $\pi$ bonds. However, due to the increased electronegativity of the C atom the electron density is attracted by and, thus, localized around the C atom. In the same figure the Kohn-Sham levels are shown. There is no magnetization density. @@ -479,7 +479,7 @@ This is in agreement with results of the EA potential simulations, which reveal However, this fact could not be reproduced by spin polarized \textsc{vasp} calculations performed in this work. Present results suggest this configuration to correspond to a real local minimum. In fact, an additional barrier has to be passed to reach this configuration starting from the \ci{} \hkl<1 0 0> interstitial configuration, which is investigated in section~\ref{subsection:100mig}. -After slightly displacing the C atom along the \hkl[1 0 0] (equivalent to a displacement along \hkl[0 1 0]), \hkl[0 0 1], \hkl[0 0 -1] and \hkl[1 -1 0] direction the distorted structures relax back into the BC configuration. +After slightly displacing the C atom along the \hkl[1 0 0] (equivalent to a displacement along \hkl[0 1 0]), \hkl[0 0 1], \hkl[0 0 -1] and \hkl[1 -1 0] direction, the distorted structures relax back into the BC configuration. As will be shown in subsequent migration simulations, the same would happen to structures where the C atom is displaced along the migration direction, which approximately is the \hkl[1 1 0] direction. These relaxations indicate that the BC configuration is a real local minimum instead of an assumed saddle point configuration. Fig.~\ref{img:defects:bc_conf} shows the structure, charge density isosurface and Kohn-Sham levels of the BC configuration. @@ -1317,7 +1317,7 @@ The migration pathways of configuration~\ref{fig:defects:314} and~\ref{fig:defec \label{fig:059-539} \end{figure} Activation energies as low as \unit[0.1]{eV} and \unit[0.6]{eV} are observed. -In the first case the Si and C atom of the DB move towards the vacant and initial DB lattice site respectively. +In the first case, the Si and C atom of the DB move towards the vacant and initial DB lattice site respectively. In total three Si-Si and one more Si-C bond is formed during transition. The activation energy of \unit[0.1]{eV} is needed to tilt the DB structure. Once this barrier is overcome, the C atom forms a bond to the top left Si atom and the \si{} atom capturing the vacant site is forming new tetrahedral bonds to its neighbored Si atoms. @@ -1327,7 +1327,7 @@ In the second case the lowest barrier is found for the migration of Si number 1, A net amount of five Si-Si and one Si-C bond are additionally formed during transition. An activation energy of \unit[0.6]{eV} necessary to overcome the migration barrier is found. This energy is low enough to constitute a feasible mechanism in SiC precipitation. -To reverse this process \unit[5.4]{eV} are needed, which make this mechanism very improbable. +To reverse this process, \unit[5.4]{eV} are needed, which make this mechanism very improbable. % The migration path is best described by the reverse process. Starting at \unit[100]{\%}, energy is needed to break the bonds of Si atom 1 to its neighbored Si atoms as well as the bond of the C atom to Si atom number 5.