Abstract
We study the pressure induced collapse of single-, double- and
triple-wall carbon nanotubes. Theoretical simulations were performed
using density-functional tight-binding theory. For tube walls separated
by the graphitic distance, we show that the radial collapse pressure,
P-c, is mainly determined by the diameter of the innermost tube, d(in)
and that its value significantly deviates from the usual P-c
proportional to d(in)(-3) Levy-Carrier law. A modified expression, P-c d(in)(-3) = alpha(1-beta(2) / d(in)(2)) with alpha and beta numerical
parameters, which reduces the collapse pressure for low diameters is
proposed. For d(in) greater than or similar to 1.5 nm an enhanced
stability is found which may be assigned as due to the bundle intertube
geometry-induced interactions. If the inner and outer tubes are
separated by larger distances, the collapse process is found to be more
complex. High-pressure resonant Raman experiments were performed in
double-wall carbon nanotubes having inner and outer diameters averaging
1.5 nm and 2.0 nm, respectively. A modification in the response of the
G-band and the disappearance of the radial breathing modes between 2 GPa
and 5 GPa indicate the beginning and the end of the radial collapse
process. Experimental results are in good agreement with our theoretical
predictions, but do not allow to discriminate from those corresponding
to a continuum mechanics model. (C) 2017 Elsevier Ltd. All rights
reserved.
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