Separation of Semiconducting Carbon Nanotubes Using Conjugated Polymer Wrapping

Size Matters in Conjugated Polymer Chirality-Selective SWCNT Extraction

Carbon-based nanomaterials have catalyzed breakthroughs across various scientific and engineering disciplines. The key to unlocking a new generation of tailor-made nanomaterials based on single-walled carbon nanotubes (SWCNTs) lies in the precise sorting of raw material into individual chiralities, each possessing unique properties. This can be achieved using conjugated polymer extraction (CPE), but to a very limited extent since the process generates only a few chirality-enriched suspensions. Therefore, it is imperative to comprehend the mechanism of the wrapping of SWCNTs by polymers to unleash CPE's full potential. However, the lack of a diverse palette of chirality-selective polymers with varying macromolecular parameters has hindered a comprehensive understanding of how the nature of the polymer affects the performance and selectivity of SWCNT isolation. To address this gap, multiple batches of such polymers are synthesized to elucidate the impact of molecular weight and dispersity on the purity and concentrations of the generated SWCNT suspensions. The obtained results explain the inconsistent outcomes reported in the literature, greatly improving the application potential of this promising SWCNT sorting approach. Concomitantly, the discovered significant influence of the macromolecular characteristics of conjugated polymers on the SWCNT isolation efficacy sheds considerable insight into the unresolved mechanism of this sorting technique.

High-yield and chirality-selective isolation of single-walled carbon nanotubes using conjugated polymers and small molecular chaperones

Single-walled carbon nanotubes (SWCNTs) have potential for a wide range of applications in diverse fields, but the heterogeneous properties of the synthesized mixtures of SWCNT types hinder the realization of these aspirations. Recent developments in extractive purification methods of polychiral SWCNT mixtures have somewhat gradually alleviated this problem, but either the yield or purity of the obtained fractions remains unsatisfactory. In this work, we showed the possibility of simultaneously achieving both the aforementioned goals, commonly considered mutually exclusive, via the enhancement of the capabilities of the conjugated polymer extraction (CPE) technique. We found that combining small molecular species, which alone are unwanted in the system, with a selective poly(9,9'-dioctylfluorenyl-2,7-diyl-alt-6,6'-(2,2'-bipyridine)) polymer increased the concentration of the harvested SWCNTs by an order of magnitude while maintaining near-monochiral purity of the materials. The conducted modeling revealed that the presence of these additives facilitated the folding of conjugated polymers around (6,5) SWCNTs, leading to a substantial increase in the concentration and quality of the SWCNT suspension. The obtained results lay the foundation for the widescale implementation of the CPE of usually scarcely available chirality-defined SWCNTs owing to the molecular chaperones expediting the folding of the conjugated polymers.

Mixed-Solvent Engineering as a Way around the Trade-Off between Yield and Purity of (7,3) Single-Walled Carbon Nanotubes Obtained Using Conjugated Polymer Extraction

The inability to purify nanomaterials such as single-walled carbon nanotubes (SWCNTs) to the desired extent hampers the progress in nanoscience. Various SWCNT types can be purified by extraction, but it is challenging to establish conditions giving rise to the isolation of high-purity fractions. The problem stems from the fact that common organic solvents or water cannot provide an optimal environment for purification. Consequently, one must often decide between the separation yield and purity of the product. This article reports how through the self-synthesis of poly(9,9-dioctylfluorene-alt-benzothiadiazole) with tailored characteristics, in-depth elucidation of the extraction process, and mixed-solvent engineering, a high-yield isolation of monochiral (7,3) SWCNTs is developed. The combination of toluene and tetralin affords a separation medium of unique properties, wherein both high yield and exceptional purity can be attained simultaneously. The reported results pave the way for further research on this rare chirality, which, as illustrated herein, is much more reactive than any of the previously separated SWCNTs.

Enrichment of Large-Diameter Semiconducting Single-Walled Carbon Nanotubes by Conjugated Polymer-Assisted Separation

Semiconducting single-walled carbon nanotubes (s-SWCNTs) with large diameters are highly desired in the construction of high performance optoelectronic devices. However, it is difficult to selectively prepare large-diameter s-SWCNTs since their structure and chemical stability are quite similar with their metallic counterparts. In this work, we use SWCNTs with large diameter as a raw material, conjugated polymer of regioregular poly-(3-dodecylthiophene) (rr-P3DDT) with long side chain as a wrapping agent to selectively separate large-diameter s-SWCNTs. It is found that s-SWCNTs with a diameter of ~1.9 nm are effectively enriched, which shows a clean surface. By using the sorted s-SWCNTs as a channel material, we constructed thin-film transistors showing charge-carrier mobilities higher than 10 cm² V^-1 s^-1 and on/off ratios higher than 10³.

Efficient Selective Sorting of Semiconducting Carbon Nanotubes Using Ultra-Narrow-Band-Gap Polymers

Conjugated polymers with narrow band gaps are particularly useful for sorting and discriminating semiconducting single-walled carbon nanotubes (s-SWCNT) due to the low charge carrier injection barrier for transport. In this paper, we report two newly synthesized narrow-band-gap conjugated polymers (PNDITEG-TVT and PNDIC8TEG-TVT) based on naphthalene diimide (NDI) and thienylennevinylene (TVT) building blocks, decorated with different polar side chains that can be used for dispersing and discriminating s-SWCNT. Compared with the mid-band-gap conjugated polymer PNDITEG-AH, which is composed of naphthalene diimide (NDI) and head-to-head bithiophene building blocks, the addition of a vinylene linker eliminates the steric congestion present in head-to-head bithiophene, which promotes backbone planarity, extending the π-conjugation length and narrowing the band gap. Cyclic voltammetry (CV) and density functional theory (DFT) calculations suggest that inserting a vinylene group in a head-to-head bithiophene efficiently lifts the highest occupied molecular orbital (HOMO) level (-5.60 eV for PNDITEG-AH, -5.02 eV for PNDITEG-TVT, and -5.09 eV for PNDIC8TEG-TVT). All three polymers are able to select for s-SWCNT, as evidenced by the sharp transitions in the absorption spectra. Field-effect transistors (FETs) fabricated with the polymer:SWCNT inks display p-dominant properties, with higher hole mobilities when using the NDI-TVT polymers as compared with PNDITEG-AH (0.6 cm² V^-1 s^-1 for HiPCO:PNDITEG-AH, 1.5 cm² V^-1 s^-1 for HiPCO:PNDITEG-TVT, and 2.3 cm² V^-1 s^-1 for HiPCO:PNDIC8TEG-TVT). This improvement is due to the better alignment of the HOMO level of PNDITEG-TVT and PNDIC8TEG-TVT with that of the dominant SWCNT specie.

Interlocking of Single-Walled Carbon Nanotubes with Metal-Tethered Tetragonal Nanobrackets to Enrich a Few Hundredths of a Nanometer Range in Their Diameters

We have separated carbon nanotubes through host-guest complexation using host molecules named "nanotweezers" and "nanocalipers". In this work, a host molecule named tetragonal "M-nanobrackets", consisting of a pair of dipyrrin nanocalipers corresponding to two brackets "[" and "]" tethered by two metals (M), is designed, synthesized, and employed to separate single-walled carbon nanotubes (SWNTs). A facile three-step process including one-pot Suzuki coupling is developed to synthesize M-nanobrackets in a 37% total yield (M = Cu). Upon extraction of SWNTs with a square nanobracket and Cu(II), in situ formed tetragonal M-nanobrackets are found to interlock SWNTs to disperse them in 2-propanol. The interlocking is confirmed by absorption and Raman spectroscopy as well as transmission electron and atomic force microscopy. Especially, Raman spectroscopy is utilized to prove the interlocking of SWNTs; Cu-nanobrackets are found to show inherent resonance Raman signals and affect the SWNT signals, or a radial breathing vibration, due to the rigid rectangular structure of Cu-nanobrackets. The interlocking is facilely and thoroughly released through demetalation to recover the pristine SWNTs as well as the square nanobracket. Such chemically controlled locking and unlocking for SWNTs are one of the characteristics of our separation process. This enables a precise evaluation by Raman, photoluminescence, and absorption spectroscopy of the diameter selectivity to SWNTs, revealing the diameter enrichment of only three kinds of SWNTs, (7,6), (9,4), and (8,5), in the 0.02 nm diameter range from 0.90 to 0.92 nm among ∼20 kinds of SWNTs from 0.76 to 1.17 nm in their diameter range.

Printable inks and deformable electronic array devices

Deformable printed electronic array devices are expected to revolutionize next-generation electronics. However, although remarkable technological advances in printable inks and deformable electronic array devices have recently been achieved, technical challenges remain to commercialize these technologies. In this review article a brief introduction to printing methods highlighting significant research studies on ink formation for conductors, semiconductors, and insulators is provided, and the structural design and successful printing strategies of deformable electronic array devices are described. Successful device demonstrations are presented in the applications of passive- and active-matrix array devices. Finally, perspectives and technological challenges to be achieved are pointed out to print practically available deformable devices.

Recent Advances in Structure Separation of Single-Wall Carbon Nanotubes and Their Application in Optics, Electronics, and Optoelectronics

Structural control of single-wall carbon nanotubes (SWCNTs) with uniform properties is critical not only for their property modulation and functional design but also for applications in electronics, optics, and optoelectronics. To achieve this goal, various separation techniques have been developed in the past 20 years through which separation of high-purity semiconducting/metallic SWCNTs, single-chirality species, and even their enantiomers have been achieved. This progress has promoted the property modulation of SWCNTs and the development of SWCNT-based optoelectronic devices. Here, the recent advances in the structure separation of SWCNTs are reviewed, from metallic/semiconducting SWCNTs, to single-chirality species, and to enantiomers by several typical separation techniques and the application of the corresponding sorted SWCNTs. Based on the separation procedure, efficiency, and scalability, as well as, the separable SWCNT species, purity, and quantity, the advantages and disadvantages of various separation techniques are compared. Combined with the requirements of SWCNT application, the challenges, prospects, and development direction of structure separation are further discussed.

Enrichment of high-purity large-diameter semiconducting single-walled carbon nanotubes

Semiconducting single-walled carbon nanotubes SWCNTs (s-SWCNTs) are considered one of the most promising alternatives to traditional silicon-based semiconductors. In particular, large-diameter s-SWCNTs (>1.2 nm) exhibit more advantages over small-diameter ones in high-performance electronic applications because of their higher charge carrier mobility and reduced Schottky barrier height. Great efforts have been made to enriching large-diameter s-SWCNTs from mass-produced raw CNTs that contain both metallic SWCNTs and s-SWCNTs. Among separation technologies, the effective and scalable ones are conjugated polymer wrapping (CPW), gel permeation chromatography (GC), aqueous two-phase extraction (ATPE), and density gradient ultracentrifugation (DGU). In this review, we survey recent progress on enriching large-diameter s-SWCNTs using those methods and outline the strategies and challenges in the separation according to the electronic type and chirality of SWCNTs. Finally, we highlight some applications of the enriched large-diameter s-SWCNTs and outlook for the future of SWCNT-based electronic devices.

Advances and Frontiers in Single-Walled Carbon Nanotube Electronics

Single-walled carbon nanotubes (SWCNTs) have been considered as one of the most promising electronic materials for the next-generation electronics in the more Moore era. Sub-10 nm SWCNT-field effect transistors (FETs) have been realized with several performances exceeding those of Si-based FETs at the same feature size. Several industrial initiatives have attempted to implement SWCNT electronics in integrated circuit (IC) chips. Here, the recent advances in SWCNT electronics are reviewed from in-depth understanding of the fundamental electronic structures, the carrier transport mechanisms, and the metal/SWCNT contact properties. In particular, the subthreshold switching properties are highlighted for low-power, energy-efficient device operations. State-of-the-art low-power SWCNT-based electronics and the key strategies to realize low-voltage and low-power operations are outlined. Finally, the essential challenges and prospects from the material preparation, device fabrication, and large-scale ICs integration for future SWCNT-based electronics are foregrounded.

The Impacts of Polyisoprene Physical Interactions on Sorting of Single-Wall Carbon Nanotubes

Conjugated polymer sorting is currently the best method to select large-diameter single-walled carbon nanotubes (SWCNTs) with tunable narrow chirality in the adaption of highly desired electronics applications. The acceleration on conjugated polymers-SWCNTs interaction with long-term stability through different molecular designs; for example, longer alkyl side-chains or conjugation moieties have been extensively developed in recent years. However, the importance of the macromolecules with abundant van der Waals (VDW) interaction in the conjugated-based block copolymer system acting during SWCNTs sorting is not clearly demonstrated. In this work, a conjugated diblock copolymer involving polyisoprene (PI) and highly dense π-interaction of poly (9,9-dioctylfluorene) (PFO) is utilized to investigate the impact of natural rubber PI physical interaction on sorting effectiveness and stability. Through the rational design of diblock copolymer, PFO with ≈1200 isoprene units can remarkably enhance SWCNTs sorting ability and selected few chiralities with a diameter of ≈0.83-1.1 nm and highly stable solution for more than 1 year. The introduction of long-chain PI system is attributed not only to form weak VDW force with SWCNTs and strengthen the wrapping of PFO around the semiconducting SWCNTs but also to act as a barrier among nanotubes to prevent reaggregation of sorted SWCNTs.

Host-Guest Molecular Interaction Enabled Separation of Large-Diameter Semiconducting Single-Walled Carbon Nanotubes

Semiconducting single-walled carbon nanotubes (s-SWCNTs) with a diameter of around 1.0-1.5 nm, which present bandgaps comparable to silicon, are highly desired for electronic applications. Therefore, the preparation of s-SWCNTs of such diameters has been attracting great attention. The inner surface of SWCNTs has a suitable curvature and large contacting area, which is attractive in host-guest chemistry triggered by electron transfer. Here we reported a strategy of host-guest molecular interaction between SWCNTs and inner clusters with designed size, thus selectively separating s-SWCNTs of expected diameters. When polyoxometalate clusters of ∼1 nm in size were filled in the inner cavities of SWCNTs, s-SWCNTs with diameters concentrated at ∼1.3-1.4 nm were selectively extracted with the purity of ∼98% by a commercially available polyfluorene derivative. The field-effect transistors built from the sorted s-SWCNTs showed a typical behavior of semiconductors. The sorting mechanisms associated with size-dependent electron transfer from nanotubes to inner polyoxometalate were revealed by the spectroscopic and in situ electron microscopic evidence as well as the theoretical calculation. The polyoxometalates with designable size and redox property enable the flexible regulation of interaction between the nanotubes and the clusters, thus tuning the diameter of sorted s-SWCNTs. The present sorting strategy is simple and should be generally feasible in other SWCNT sorting techniques, bringing both great easiness in dispersant design and improved selectivity.

Conformally Gated Surface Conducting Behaviors of Single-Walled Carbon Nanotube Thin-Film-Transistors

Semiconducting single-walled carbon nanotubes (s-SWCNTs) have gathered significant interest in various emerging electronics due to their outstanding electrical and mechanical properties. Although large-area and low-cost fabrication of s-SWCNT field effect transistors (FETs) can be easily achieved via solution processing, the electrical performance of the solution-based s-SWCNT FETs is often limited by the charge transport in the s-SWCNT networks and interface between the s-SWCNT and the dielectrics depending on both s-SWCNT solution synthesis and device architecture. Here, we investigate the surface and interfacial electro-chemical behaviors of s-SWCNTs. In addition, we propose a cost-effective and straightforward process capable of minimizing polymers bound to s-SWCNT surfaces acting as an interfering element for the charge carrier transport via a heat-assisted purification (HAP). With the HAP treated s-SWCNTs, we introduced conformal dielectric configuration for s-SWCNT FETs, which are explored by a carefully designed wide array of electrical and chemical characterizations with finite-element analysis (FEA) computer simulation. For more favorable gate-field-induced surface and interfacial behaviors of s-SWCNT, we implemented conformally gated highly capacitive s-SWCNT FETs with ion-gel dielectrics, demonstrating field-effect mobility of ~8.19 cm2/V⋅s and on/off current ratio of ~105 along with negligible hysteresis.