Design of Surfactant–Substrate Interactions for Roll-to-Roll Assembly of Carbon Nanotubes for Thin-Film Transistors

Abstract

Controlled assembly of single-walled carbon nanotube (SWCNT) networks with high density and deposition rate is critical for many practical applications, including large-area electronics. In this regard, surfactant chemistry plays a critical role as it facilitates the substrate− nanotube interactions. Despite its importance, detailed understanding of the subject up until now has been lacking, especially toward tuning the controllability of SWCNT assembly for thin-film transistors. Here, we explore SWCNT assembly with steroid-and alkyl-based surfactants. While steroid-based surfactants yield highly dense nanotube thin films, alkyl surfactants are found to prohibit nanotube assembly. The latter is attributed to the formation of packed alkyl layers of residual surfactants on the substrate surface, which subsequently repel surfactant encapsulated SWCNTs. In addition, temperature is found to enhance the nanotube deposition rate and density. Using this knowledge, we demonstrate highly dense and rapid assembly with an effective SWCNT surface coverage of ∼99% as characterized by capacitance−voltage measurements. The scalability of the process is demonstrated through a roll-to-roll assembly of SWCNTs on plastic substrates for large-area thin-film transistors. The work presents an important process scheme for nanomanufacturing of SWCNT-based electronics. 37 printed TFTs based on SWCNT networks have also been reported, demonstrating excellent performances, surpassing that of printed organic devices by a large margin. The performance of SWCNT TFTs is largely dependent on the properties of the assembled random networks. ■ INTRODUCTION38 Specifically, high nanotube density yields high ON-state current, while bundling during assembly increases the OFF-state current. 39,40 Thus, understanding and controlling the nanotube−substrate binding as facilitated through the surfactant−surface interactions is of profound interest, with strong emphasis on enhancing density and reducing bundling. Furthermore, fast nanotube assembly on substrates is essential for practical applications as it determines the process throughput, eventually allowing roll-to-roll (R2R) assembly and processing of SWCNTs over large-areas.Significant research has focused on dispersion of SWCNTs in liquids over the past decade, 41−60 with one promising method involving the use of aqueous solutions with organic surfactants that show long-term stability over several months. 52,54,55 Thin and thick films of SWCNTs from nanotube suspensions have also been widely explored for various applications. 9,15,33,34,36,61 However, the details of the assembly process of SWCNTs for "TFT-grade" random networks have not been fully explored, which is a critical step for optimizing the deposition quality and rate. In addition, most work in literature has focused on the use of commercially available solutions of semiconductor-enriched SWCNTs for TFT fabrication. The surfactants used for these commercial solutions are often not publically known, and a change in the surfactant ...

Ultrasonic-assisted synthesis of Pd–Pt/carbon nanotubes nanocomposites for enhanced electro-oxidation of ethanol and methanol in alkaline medium

“…Moreover, the supporting materials can prevent NPs aggregate, and reduce the usage of noble metals to some content. Carbon nanotubes (CNTs) have received significant attentions due to their unique chemical and physical properties [16][17][18]. They have been widely investigated in the fields of electronics, biomedicines and sensors [19][20][21][22] for their fast electron transfer, large active surface area, and high stability.…”

Surface effects on network formation of conjugated polymer wrapped semiconducting single walled carbon nanotubes and thin film transistor performance

“…A substantive body of work has been accomplished thus far in which aqueous dispersions of enriched sc-SWCNTs, typically obtained via chromatography [9,10] or density gradient ultracentrifugation [11], are used to fabricate TFTs and their adhesion to SiO 2 or PET has been drastically improved by using an adhesion promoter having free amine groups such as (3-aminopropyl)trime thoxysilane (APTMS) or poly-L-lysine (PLL) [12][13][14][15]. The binding mechanism largely involves an interaction between the amine groups in the adhesion layer and the acid groups of the surfactants used to disperse the tubes, but also direct interactions between the charged adhesion layer and the hydrophobic regions of the SWCNTs should not be discounted [16,17].…”

Raman microscopy mapping for the purity assessment of chirality enriched carbon nanotube networks in thin-film transistors

“…The advantage of using networks of sc-SWCNTs over aligned nanotubes [52][53][54][55] for the active channel in TFTs is the favorable trade-off between targeted performance and ease of fabrication [56][57][58]. Such TFTs will be useful in low-cost display drivers and logic-circuit elements fabricated using scalable deposition techniques such as dip-coating and ink-jet or gravure printing [59][60][61][62][63][64][65][66]. This work bridges the gap between separation methods that yield high-purity sc-SWCNTs and the available characterization tools for purity assessment, thus providing a framework for device design that considers TFT channel scaling with SWCNT density and purity.…”