Page 381 - Fiber Fracture

ATOMIC TRANSFORMATIONS 363
z
Y
h
;
S
w 0.0 --
S
0
-= -2.0
Q
E -4.0
0 0 2 4 6 8 10
LL
strain (%)
Fig. 4. Formation energy of the (5-7-7-5) defect in the (5,5) tube at different strains.

I I
Q- - a Classical MD
-ab initio -

-

--=.
- =. -
3.0 -.
W a-
‘8- q
1 .o I t I I

We have investigated the energetics of further bond rotations in the presence of a
pre-existing (5-7-7-5) defect at various strains, mostly in the (10,lO) tube. The choice
of this particular tube structure is due to the fact that (10,lO) tubes are the most abundant
product in the laser ablation apparatus (Thess et al., 1997). However, the results are
qualitatively valid for all armchair tubes. Fig. 7 shows the formation energies of (1) an
octagonal defect at the preexisting (5-7-7-5) defect as produced by a further rotation
of a strictly azimuthal bond; (2) the initial stage of separation of the two dislocation
cores (5-7) and (7-3, as produced by the rotation of the ‘shoulder’ bond in the (5-7)
core. These results show that the separation of the dislocation cores is energetically
favored over the formation of a larger open ring structure for strains up to -6%. The