slide 15
-in addition, it is instructive to look at combinations of Cs and Si_i,
-again, a situation which is very likely to arise in ibs.
-Cs located right next to the 110 Si db within the 110 chain
-constitutes the energetically most favirable configuration,
-which, however, is still less favorable than the Ci 100 ground state.
+in addition, it is instructive to look at combinations of Cs and Si_i.
+the most favorable configuration is obtained for
+Cs located right next to the 110 Si db within the 110 chain.
+this configuration is still less favorable than the Ci 100 ground state.
however, the interaction of C_s and Si_i drops quickly to zero
indicating a low capture radius.
in ibs, configurations exceedinig this separation distance are easily produced.
as a last task, reproducing the SiC precipitation is attempted
by successive insertion of 6000 C atoms,
-the number necessary to form a precipitate with a radius of approximately 3 nm,
+the number necessary to form a minimal precipitate,
into a supercell consisting of 31 Si unit cells in each direction.
insertion is realized at constant temperature.
due to the high amount of particles,
-the classical potential is exclusively used.
+the classical potential must be used.
since low carbon diffusion due to the overestimated barriers is expected,
insertion volumes v2 and v3 next to the total volume v1 are considered.
v2 corresponds to the minimal precipiatte size.
to summarize, the formation of cubic SiC fails to appear.
neither agglomeration of C interstitials
-nor a transition into crystalline SiC can be identified.
+nor a transition into SiC can be identified.
slide 20
however, in addition, the overestimated diffusion barriers,
due to the short range character of the potential,
-intensify this problem, which I called:
+intensify this problem, which I termed:
potential enhanced slow phase space propagation.
the approach used in this study is to simply increase the temperature, however,
along a 110 direction.
the C-C next neighbor pairs are reduced,
-which is mandatory for cubic SiC formation.
-the peak at roughly 0.3 nm gets slightly shifter to higher distances,
+which is mandatory for SiC formation.
+the peak at roughly 0.3 nm gets slightly shifted to higher distances,
due to a decrease of interstitial carbon combinations accompanied by an
increase in interstitial and substitutional as well as pure substitutional
combinations.
increasing values in this range
-correpsond to bonds of Cs and another Cs with a nearby Si_i atom.
+correspond to bonds of Cs and another Cs with a nearby Si_i atom.
slide 22
-to conclude, stretched coherent structures of SiC embedded in the Si host
-are directly observed.
-therefore, it is concluded that Cs is extensively involved
+to conclude, stretched coherent structures are directly observed.
+therefore, it is expected that Cs is extensively involved
in the precipitation process for implantations at elevated temperatures.
the emission of Si_i serves several needs:
as a vehicle to rearrange stable Cs,
-furthermore, it serves as a building block for the surrounding Si host
-or further SiC formation.
-finally, it may compensate stress at the Si/SiC interface
+as a building block for the surrounding Si host or further SiC formation.
+and for strain compensation either at the Si/SiC interface
or in the stretched SiC structure, which, again,
was diretly observed in simulation.
this perfectly explains the results of the annealing experiments
stated in the beginning of this talk.
-at low temperatures highly mobile Ci whereas at high temperatures stable Cs
-configurations are formed.
+at low temperatures highly mobile Ci
+whereas at high temperatures stable Cs configurations are formed.
-it is further concluded that high temperatures are necessary to model
+thus, it is further concluded that high temperatures are necessary to model
ibs conditions, which are far from equilibrium.
the high temperatures deviate the system from thermodynamic equilibrium
enabling Ci to turn into Cs.
slide 23
to summarize and conclude ...
-defect structures were described by both methods.
+point defects were investigated by both methods.
the interstitial carbon mmigration path was identified.
-it turned out that the the diffusion barrier is drastically overestimated
+it turned out that the diffusion barrier is drastically overestimated
within the ea description.
combinations of defects were investigated by first principles methods.
however, substitutional carbon arises in all probability.
even transitions from the ground state are very likely to occur.
-concerning the precipitation simulations, the problem of the potential
-enhanced slow phase space propagation was discussed.
-by comparing with experiment it is concluded
-that high temperatures are necessary to model simultae ibs conditions.
-at elevated temperatures stretched structures of SiC were directly observed
-in simulation.
+concerning the precipitation simulations, the problem of
+potential enhanced slow phase space propagation was discussed.
+high temperatures are assumed necessary to simulate ibs conditions.
+at low temperatures a dumbbell dominated structure is obatined
+whereas
+it is expected that
+Stretched structures of SiC were observed at elevated temperatures.
it is thus concluded that
substitutional carbon is heavily involved in the precipitation process.
-the role of the Si_i was outlined and in one case also directly observed
-in simulation.
+the role of the Si_i was outlined.
-in total, it is my feeling, that cubic SiC precipitation occurs by successive
-agglomeration of substitutional C.
+in total, these results suggest,
+that cubic SiC precipitation occurs by successive agglomeration of Cs.
slide 24
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