Sculpting carbon bonds for allotropic transformation through solid-state re-engineering of –sp2 carbon

Abstract

Carbon forms one of nature's strongest chemical bonds; its allotropes having provided some of the most exciting scientific discoveries in recent times. The possibility of inter-allotropic transformations/hybridization of carbon is hence a topic of immense fundamental and technological interest. Such modifications usually require extreme conditions (high temperature, pressure and/or high-energy irradiations), and are usually not well controlled. Here we demonstrate inter-allotropic transformations/hybridizations of specific types that appear uniformly across large-area carbon networks, using moderate alternating voltage pulses. By controlling the pulse magnitude, small-diameter single-walled carbon nanotubes can be transformed predominantly into larger-diameter single-walled carbon nanotubes, multi-walled carbon nanotubes of different morphologies, multi-layered graphene nanoribbons or structures with sp 3 bonds. This re-engineering of carbon bonds evolves via a coalescence-induced reconfiguration of sp 2 hybridization, terminates with negligible introduction of defects and demonstrates remarkable reproducibility. This reflects a potential step forward for large-scale engineering of nanocarbon allotropes and their junctions.

Mechanical properties of fused carbon nanotube networks

“…This is consistent with previous findings of voltage as a dominant parameter in the fusion of micro-scale CNT networks [Jung, 2014]. In this chapter, voltages between 1 V and 12…”

“…However, it is reasonable to ask whether the alignment could be responsible for the improvement in mechanical properties seen here. SWCNTs organized into microstructures were observed to become aligned during the fusion process of [Jung, 2014], even under the influence of relatively low voltages (40% of the breakdown voltage) that did not improve the measured electrical properties. Since no improvement in mechanical properties is seen under similar conditions in the present experiments, alignment is unlikely to be responsible for the changes in mechanical properties seen here.…”

“…Recent research has demonstrated the possibility of inter-allotropic transformations that create strong covalent bonds in place of weaker van der Waals interactions. These transformations may be driven by electron irradiation [Ajayan,1998;Terrones, 2000;Kis, 2004;Yoon, 2004;Peng, 2008;Filleter, 2011], high-temperature heat treatment [Gutierrez, 2005], or high temperature electro-migration [Jin, 2008;Jia, 2009;Chuvllin, 2011;Jung, 2014;Zhang, 2016]. The transformations enable a "zipper mechanism" in which adjacent CNTs form larger graphitic structures.…”

“…The increased linear properties suggest a higher collective strength and work done by the filaments up to the linear strength point. These changes after higher-current fusion correlate with the increased prevalence of larger graphitic structures [Jung, 2014] (MWCNTs, GNRs) and with increased covalently-bonded "linkages" [Kis, 2004] whereas the average range of strains over which significant slip occurs (the slip strain is the difference between failure strain and linear strain) first increases and then decreases (Figure 4.10b). In the tension to failure tests, fused CNT yarns also show abrupt failure, indicating that the filaments are mostly broken rather than slipping out of yarn's the failure area.…”

“…Single-walled CNTs (SWCNT) transform into larger multi-walled CNTs (MWCNT) and finally collapse into flat multilayered graphene nano-ribbons (GNRs) as the applied voltage increases. The sketch is adapted from[Jung, 2014] 1.6 Contribution of this workA major part of the research focuses on investigating the outputs of different fusion conditions. To operate CNT fusion, an alternative square wave current is applied to CNT yarns; controllable input parameters include applied voltage, time, frequency, and duty cycle of the signal.…”