Parameters Affecting Interfacial Assembly and Alignment of Nanotubes

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

Boundary-directed epitaxy of block copolymers

Directing the position, orientation, and long-range lateral order of block copolymer domains to produce technologically-useful, sublithographic patterns is a challenge. Here, the authors present a promising approach to overcome the challenge by directing assembly using spatial boundaries between planar, low-resolution regions on a surface with different composition

Nanotube Alignment Mechanism in Floating Evaporative Self-Assembly

The challenge of assembling semiconducting single-wall carbon nanotubes (s-SWCNTs) into densely packed, aligned arrays has limited the scalability and practicality of high-performance nanotube-based electronics technologies. The aligned deposition of s-SWCNTs via floating evaporative self-assembly (FESA) has promise for overcoming this challenge; however, the mechanisms behind FESA need to be elucidated before the technique can be improved and scaled. Here, we gain a deeper understanding of the FESA process by studying a stationary analogue of FESA and optically tracking the dynamics of the organic ink/water/substrate and ink/air/substrate interfaces during the typical FESA process. We observe that the ink/water interface serves to collect and confine the s-SWCNTs before alignment and that the deposition of aligned bands of s-SWCNTs occurs at the ink/water/substrate contact line during the depinning of both the ink/air/substrate and ink/water/substrate contact lines. We also demonstrate improved control over the interband spacing, bandwidth, and packing density of FESA-aligned s-SWCNT arrays. The substrate lift rate (5–15 mm min^–1) is used to tailor the interband spacing from 90 to 280 μm while maintaining a constant aligned s-SWCNT bandwidth of 50 μm. Varying the s-SWCNT ink concentration (0.75–10 μg mL^–1) allows the control of the bandwidth from 2.5 to 45 μm. A steep increase in packing density is observed from 11 s-SWCNTs μm^–1 at 0.75 μg mL^–1 to 20 s-SWCNTs μm^–1 at 2 μg mL^–1, with a saturated packing density of ∼24 s-SWCNTs μm^–1. We also demonstrate the scaling of FESA to align s-SWCNTs on a 2.5 × 2.5 cm² scale while preserving high-quality alignment on the nanometer scale. These findings help realize the scalable fabrication of well-aligned s-SWCNT arrays to serve as large-area platforms for next-generation semiconductor electronics