Parameters Affecting Interfacial Assembly and Alignment of Nanotubes

Abstract

Tangential flow interfacial self-assembly (TaFISA) is a promising scalable technique enabling uniformly aligned carbon nanotubes for high-performance semiconductor electronics. In this process, flow is utilized to induce global alignment in two-dimensional nematic carbon nanotube assemblies trapped at a liquid/liquid interface, and these assemblies are subsequently deposited on target substrates. Here, we present an observational study of experimental parameters that affect the interfacial assembly and subsequent aligned nanotube deposition. We specifically study the water contact angle (WCA) of the substrate, nanotube ink composition, and water subphase and examine their effects on liquid crystal defects, overall and local alignment, and nanotube bunching or crowding. By varying the substrate chemical functionalization, we determine that highly aligned, densely packed, individualized nanotubes deposit only at relatively small WCA between 35 and 65°. At WCA (< 10°), high nanotube bunching or crowding occurs, and the film is nonuniform, while aligned deposition ceases to occur at higher WCA (>65°). We find that the best alignment, with minimal liquid crystal defects, occurs when the polymer-wrapped nanotubes are dispersed in chloroform at a low (0.6:1) wrapper polymer to nanotube ratio. We also demonstrate that modifying the water subphase through the addition of glycerol not only improves overall alignment and reduces liquid crystal defects but also increases local nanotube bunching. These observations provide important guidance for the implementation of TaFISA and its use toward creating technologies based on aligned semiconducting carbon nanotubes.

Assembly and Alignment of High Packing Density Carbon Nanotube Arrays Using Lithographically Defined Microscopic Water Features

“…All of the films are made using the previously published TaFISA style ink delivery and substrate motion process, , but the chemical patterning of the substrate determines the type of array deposited. A sample substrate and a sacrificial substrate are inserted in a water bath at 45° with their surfaces facing each other to form a 3 mm wide channel.…”

“…Maximizing the performance of CNT-based transistors requires that the CNTs in the transistors are aligned and arranged into densely packed arrays . Approaches being investigated for creating such arrays include shear, , vacuum filtration, , flow-directed evaporation, , evaporation and shear on patterned substrates, − dielectrophoresis, , evaporative self-assembly, , blown-bubble assembly, gas flow self-assembly, spin-coating, contact-printing, elastomeric release, dimension-limited self-alignment (DLSA), , DNA-directed assembly, floating evaporative self-assembly (FESA), , tangential flow interfacial self-assembly (TaFISA), , and Langmuir–Blodgett (LB) , and −Schaefer (LS) , methods, among others. Techniques that collect polymer-wrapped CNTs at liquid–liquid or liquid–air interfaces are particularly promising (e.g., FESA, TaFISA, DSLA, and LB/LS).…”

Aligned Arrays of Semiconducting HiPCO SWCNTs Prepared by Liquid–Liquid Interface Confinement Self-Assembly for Optic–Electronic Applications

“…Zhang et al further introduced the binary liquid interface-confined self-assembly (BLIS) technique, which effectively reduced the consumption of SWCNT solution . The continuous advancement of these techniques has led to a constant improvement in the quality of aligned arrays based on arc-discharge SWCNTs, and the device performance has successively broken new records. ,− …”

“…Moreover, researchers have continuously focused on studying SWCNT alignment to make use of their unique anisotropy. − In particular, uniformly aligned arrays of SWCNTs with controlled nanotube densities are desired core components for various electronic and photoelectric devices. However, wafer-scale fabrication of monolayer SWCNT arrays is currently challenging, especially for small-diameter SWCNTs …”

Small Molecule Additives to Suppress Bundling in Dimensional‐Limited Self‐Alignment Method for High‐Density Aligned Carbon Nanotube Array

“…[22] The adaptability of LLI-based assembly methods is noteworthy, allowing for the deposition of dense CNT arrays on various surfaces, including silicon wafers with SiO 2 [22] coatings, quartz substrates, [23] and surfaces of self-assembled monolayer. [24] This versatility, influenced by the properties of the LLI and less dependent on substrate nature, suggests that LLI-based methods may offer advantages for diverse electronic applications, such as radio frequency transistors. [23] However, despite there has been abundant assembly progress reported by multiple groups, achieving the individualization of CNT, where each CNT exists in a separated and unbundled state within dense arrays, remains elusive for meeting the stringent demands of logic transistor technology.…”