  Transistors made up of carbon nanotubes CNT have demonstrated excellent
current-voltage characteristics which outperform some high-grade silicon-based
transistors. A continuously tunable energy barrier across semiconductor
interfaces is desired to make the CNT-based transistors more robust. Despite
the direct band gap of carbyne inside a CNT can be widely tuned by strain, the
size of carbyne cannot be controlled easily. The production of a monoatomic
chain with more than 6000 carbon atoms is an enormous technological challenge.
To predict the optimal chain length of a carbyne in different molecular
environments, we have developed a Monte Carlo model in which a finite-length
carbyne with a size of 4000-15000 atoms is encapsulated by a CNT at finite
temperatures. Our simulation shows that the stability of the carbyne@nanotube
is strongly influenced by the nature and porosity of the CNT, the external
pressure, the temperature and the chain length. We have observed an initiation
of chain-breaking process in a compressed carbyne@nanotube. Our work provides
much needed input for optimising the carbyne length to produce carbon chains
much longer than 6000 atoms at ~300K. Design rules are proposed for
synthesizing ~1% strained carbyne@(6,5)CNT as a component in CNT-based
transistors to tune the energy barriers continuously.
