Real-Time Imaging of Self-Organization and Mechanical Competition in Carbon Nanotube Forest Growth

Abstract

The properties of carbon nanotube (CNT) networks and analogous materials comprising filamentary nanostructures are governed by the intrinsic filament properties and their hierarchical organization and interconnection. As a result, direct knowledge of the collective dynamics of CNT synthesis and self-organization is essential to engineering improved CNT materials for applications such as membranes and thermal interfaces. Here, we use real-time environmental transmission electron microscopy (E-TEM) to observe nucleation and self-organization of CNTs into vertically aligned forests. Upon introduction of the carbon source, we observe a large scatter in the onset of nucleation of individual CNTs and the ensuing growth rates. Experiments performed at different temperatures and catalyst particle densities show the critical role of CNT density on the dynamics of self-organization; low-density CNT nucleation results in the CNTs becoming pinned to the substrate and forming random networks, whereas higher density CNT nucleation results in self-organization of the CNTs into bundles that are oriented perpendicular to the substrate. We also find that mechanical coupling between growing CNTs alters their growth trajectory and shape, causing significant deformations, buckling, and defects in the CNT walls. Therefore, it appears that CNT-CNT coupling not only is critical for self-organization but also directly influences CNT quality and likely the resulting properties of the forest. Our findings show that control of the time-distributed kinetics of CNT nucleation and bundle formation are critical to manufacturing well-organized CNT assemblies and that E-TEM can be a powerful tool to investigate the mesoscale dynamics of CNT networks.

Process-morphology scaling relations quantify self-organization in capillary densified nanofiber arrays

“…O nc E 0.60 AE 0.04 and O c E 0.58 AE 0.02), which indicates crack initiation and propagation in the CNT arrays, and leads to formation of anisotropic cells with aspect ratios B3.5 AE 0.3 (see Section S2 in the ESI † for details), that is likely dependent on spatial variations in number density and tortuosity of the CNTs that originate from the CNT growth process. [63][64][65][66] These results indicate that although the onedimensional simplifications used here can capture the underlying physical mechanisms that govern cell formation, and thereby yield predictions that agree well with the experimental data presented in Fig. 3, further work that quantifies and simulates topological inhomogeneities present within the CNT arrays is needed to better model CNT cellular network formation in two-dimensions.…”

Low‐Temperature Growth of Carbon Nanotubes Catalyzed by Sodium‐Based Ingredients

“…Na catalyzes high‐yield CNT growth on flat substrates as well, including but not limited to Si wafer chips and Ti sheets. CNT areal yields were estimated to be ≈95 tubes/μm 2 for silicon nitride TEM grid substrates, which is on the same order as previous high‐yield results on the same substrate …”

Use of carbon nanotubes for passive radio-frequency devices

“…In this case, the atoms diffused from the surface are predominant for the growth speed of the VLS mechanism. This also implies that the nucleation phase and growths are faster the larger the size of the particles, which is experimentally verified for CNT growth in [35].…”

“…Raman spectrum Figure 2-7 also show the quality (crystallinity) of the CNTs dropping with this method. According to [35] and [39] this is due to the diameter of the CNTs influencing on the mechanical constraints on the CNTs during the growth, introducing defects. Since we are here more interested on the equivalent conductivity of the bulk of the forest, this effect is compensated by the multi- shows well in accordance with [35] and [39] that the CNTs have many buckles.…”