Strong chemical activity and extreme instability in ambient conditions characterize carbyne, an infinite sp1 hybridized carbon chain. As a result, much less has been explored about carbyne as compared to other carbon allotropes such as fullerenes, nanotubes and graphene. Although end-capping groups can be used to stabilize carbon chains, length limitations are still a barrier for production, and even more so for application. An international team of researchers, led by Dr. Thomas Pichler from the University of Vienna report a method for the bulk production of long acetylenic linear carbon chains protected by thin double-walled carbon nanotubes. The synthesis of very long arrangements is confirmed by a combination of transmission electron microscopy, X-ray diffraction and (near-field) resonance Raman spectroscopy. Our results establish a route for the bulk production of exceptionally long and stable chains composed of more than 6,000 carbon atoms, representing an elegant forerunner towards the final goal of carbyne’s bulk production.
Calculations by Yakobson and his group at Rice University:
* Carbyne’s tensile strength – the ability to withstand stretching – surpasses “that of any other known material” and is double that of graphene. (Scientists had already calculated it would take an elephant on a pencil to break through a sheet of graphene.)
* It has twice the tensile stiffness of graphene and carbon nanotubes and nearly three times that of diamond.
* Stretching carbyne as little as 10 percent alters its electronic band gap significantly.
Viennese researchers have developed a new route for the first truly bulk production of LLCCs, i.e. carbyne, confined inside DWCNTs. From our Raman and TEM studies with contemporary ab-initio calculations we prove that stability, growth conditions as well as the length and yield of the LLCCs crucially depend on the size confinement. By analyzing the growth temperature dependence, we unambiguously revealed that there is a coupling between the LLCCs and the inner tubes as strongly supported by a model of coupled Raman modes. This allows us to directly correlate the LLCCs length to the diameter of the inner tubes and determine the optimal diameter for the high yield growth of carbyne (about 0.71 nm). Our approach of HV high temperature annealing has a great advantage over filling SWCNT/DWCNT by polyynes and converting them to carbyne because of the superior yield achieving real bulk samples, This is proven by an extremely huge Raman mode with the intensity of more than 900 % of the G-band at 38 K in-keeping with a bulk lattice constant of the confined LLCCs chains of d=0.252 nm. Our longest LLCCs can be correlated to a chain length of more than 10000 carbon atoms, which can be seen as the closest realization of carbyne so far
It is possible to control the electronic properties (tunable band gap) of the hybrid system by different filling yield of LLCCs. Furthermore, quantum spin transport in LLCC can also be a promising application according to the theoretical predictions. Consequently, as true 1D nanocarbon, this novel LLCC@DWCNT system would be, beside the basic interest in chemistry, also a fascinating candidate for the next generation of nanoelectronic devices. As a last point the LLCCs might also be further extracted from the DWCNTs and stabilized in liquid environment later on.
Arxiv – Confined linear carbon chains: a route to bulk carbyne
Nature – confined linear carbon chain as a route to carbyne
33 pages of supplemental material from Nature
SOURCES- Vienna University, Nature, Rice university
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