On‐Chip Chemical Self‐Assembly of Semiconducting Single‐Walled Carbon Nanotubes (SWNTs): Toward Robust and Scale Invariant SWNTs Transistors

In this paper, the fabrication of carbon nanotubes field effect transistors by chemical self‐assembly of semiconducting single walled carbon nanotubes (s‐SWNTs) on prepatterned substrates is demonstrated. Polyfluorenes derivatives have been demonstrated to be effective in selecting s‐SWNTs from raw mixtures. In this work the authors functionalized the polymer with side chains containing thiols, to obtain chemical self‐assembly of the selected s‐SWNTs on substrates with prepatterned gold electrodes. The authors show that the full side functionalization of the conjugated polymer with thiol groups partially disrupts the s‐SWNTs selection, with the presence of metallic tubes in the dispersion. However, the authors determine that the selectivity can be recovered either by tuning the number of thiol groups in the polymer, or by modulating the polymer/SWNTs proportions. As demonstrated by optical and electrical measurements, the polymer containing 2.5% of thiol groups gives the best s‐SWNT purity. Field‐effect transistors with various channel lengths, using networks of SWNTs and individual tubes, are fabricated by direct chemical self‐assembly of the SWNTs/thiolated‐polyfluorenes on substrates with lithographically defined electrodes. The network devices show superior performance (mobility up to 24 cm² V^?1 s^?1), while SWNTs devices based on individual tubes show an unprecedented (100%) yield for working devices. Importantly, the SWNTs assembled by mean of the thiol groups are stably anchored to the substrate and are resistant to external perturbation as sonication in organic solvents.     

Single‐Molecule Electrical Biosensors Based on Single‐Walled Carbon Nanotubes

Interactions between biological molecules are fundamental to biology. Probing the complex behaviors of biological systems at the molecular level provides new opportunities to uncover the wealth of molecular information that is usually hidden in conventional ensemble experiments and address the “unanswerable” questions in the physical, chemical and biological sciences. Nanometer‐scale materials are particularly well matched with biomolecular interactions due to their biocompatibility, size comparability, and remarkable electrical properties, thus setting the basis for biological sensing with ultrahigh sensitivity. This brief review aims to highlight the recent progress of the burgeoning field of single‐molecule electrical biosensors based on nanomaterials, with a particular focus on single‐walled carbon nanotubes (SWNTs), for better understanding of the molecular structure, interacting dynamics, and molecular functions. The perspectives and key issues that will be critical to the success of next‐generation single‐molecule biosensors toward practical applications are also discussed, such as the device reproducibility, system integration, and theoretical simulation.     

Selective Dispersion of Large‐Diameter Semiconducting Single‐Walled Carbon Nanotubes with Pyridine‐Containing Copolymers

The purity of single‐walled carbon nanotubes (SWNTs) is a key parameter for their integration in electronic, optoelectronic and photonic devices. Samples of pristine SWNTs are inhomogeneous in terms of electric behavior and diameter and contain a variety of amorphous carbon and catalyst residues. To obtain high performance devices, purification of SWNTs is required. Conjugated polymers have emerged as efficient solubilizing and sorting agents for small diameter SWNTs (HiPco tubes, 0.7 nm<Ø<1.1 nm). Nevertheless, reports on polymers able to efficiently sort large diameter SWNTs with Ø>1.1 nm are lacking. Several pyridine‐containing copolymers were synthesized for this purpose and showed efficient and selective extraction of semiconducting large diameter SWNTs (PLV tubes, Ø>1.1 nm). High concentration and high purity suspensions are obtained without the use of ultracentrifugation, which gives an up‐scaling potential of the method. The emission wavelength is in near infrared region around 1550 nm and fits with broadly used telecommunication wavelength window. The processes taking place at the interface were simulated by a newly designed hybrid coarse‐grain model combining density functional theory and geometrical calculation to yield insights into the wrapping processes with an unprecedented level of details for such large diameter SWNTs.     

High‐Performance Partially Aligned Semiconductive Single‐Walled Carbon Nanotube Transistors Achieved with a Parallel Technique

Single‐walled carbon nanotubes (SWNTs) are widely thought to be a strong contender for next‐generation printed electronic transistor materials. However, large‐scale solution‐based parallel assembly of SWNTs to obtain high‐performance transistor devices is challenging. SWNTs have anisotropic properties and, although partial alignment of the nanotubes has been theoretically predicted to achieve optimum transistor device performance, thus far no parallel solution‐based technique can achieve this. Herein a novel solution‐based technique, the immersion‐cum‐shake method, is reported to achieve partially aligned SWNT networks using semiconductive (99% enriched) SWNTs (s‐SWNTs). By immersing an aminosilane‐treated wafer into a solution of nanotubes placed on a rotary shaker, the repetitive flow of the nanotube solution over the wafer surface during the deposition process orients the nanotubes toward the fluid flow direction. By adjusting the nanotube concentration in the solution, the nanotube density of the partially aligned network can be controlled; linear densities ranging from 5 to 45 SWNTs/μm are observed. Through control of the linear SWNT density and channel length, the optimum SWNT‐based field‐effect transistor devices achieve outstanding performance metrics (with an on/off ratio of ~3.2 × 10⁴ and mobility 46.5 cm²/Vs). Atomic force microscopy shows that the partial alignment is uniform over an area of 20 × 20 mm² and confirms that the orientation of the nanotubes is mostly along the fluid flow direction, with a narrow orientation scatter characterized by a full width at half maximum (FWHM) of <15° for all but the densest film, which is 35°. This parallel process is large‐scale applicable and exploits the anisotropic properties of the SWNTs, presenting a viable path forward for industrial adoption of SWNTs in printed, flexible, and large‐area electronics.