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.

Real-Time Monitoring of Cellular Cultures with Electrolyte-Gated Carbon Nanotube Transistors.

Cell-based biosensors constitute a fundamental tool in biotechnology, and their relevance has greatly increased in recent years as a result of a surging demand for reduced animal testing and for high-throughput and cost-effective in vitro screening platforms dedicated to environmental and biomedical diagnostics, drug development, and toxicology. In this context, electrochemical/electronic cell-based biosensors represent a promising class of devices that enable long-term and real-time monitoring of cell physiology in a noninvasive and label-free fashion, with a remarkable potential for process automation and parallelization. Common limitations of this class of devices at large include the need for substrate surface modification strategies to ensure cell adhesion and immobilization, limited compatibility with complementary optical cell-probing techniques, and the need for frequency-dependent measurements, which rely on elaborated equivalent electrical circuit models for data analysis and interpretation. We hereby demonstrate the monitoring of cell adhesion and detachment through the time-dependent variations in the quasi-static characteristic current curves of a highly stable electrolyte-gated transistor, based on an optically transparent network of printable polymer-wrapped semiconducting carbon-nanotubes.

Inducing ferromagnetism and Kondo effect in platinum by paramagnetic ionic gating.

Electrically controllable magnetism, which requires the field-effect manipulation of both charge and spin degrees of freedom, has attracted growing interest since the emergence of spintronics. We report the reversible electrical switching of ferromagnetic (FM) states in platinum (Pt) thin films by introducing paramagnetic ionic liquid (PIL) as the gating media. The paramagnetic ionic gating controls the movement of ions with magnetic moments, which induces itinerant ferromagnetism on the surface of Pt films, with large coercivity and perpendicular anisotropy mimicking the ideal two-dimensional Ising-type FM state. The electrical transport of the induced FM state shows Kondo effect at low temperature, suggesting spatially separated coexistence of Kondo scattering beneath the FM interface. The tunable FM state indicates that paramagnetic ionic gating could serve as a versatile method to induce rich transport phenomena combining field effect and magnetism at PIL-gated interfaces.

Enhancing Molecular n-Type Doping of Donor-Acceptor Copolymers by Tailoring Side Chains.

In this contribution, for the first time, the molecular n-doping of a donor-acceptor (D-A) copolymer achieving 200-fold enhancement of electrical conductivity by rationally tailoring the side chains without changing its D-A backbone is successfully improved. Instead of the traditional alkyl side chains for poly{[N,N'-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl](NDI)-alt-5,5'-(2,2'-bithiophene)} (N2200), polar triethylene glycol type side chains is utilized and a high electrical conductivity of 0.17 S cm-1 after doping with (4-(1,3-dimethyl-2,3-dihydro-1H-benzoimidazol-2-yl)phenyl)dimethylamine is achieved, which is the highest reported value for n-type D-A copolymers. Coarse-grained molecular dynamics simulations indicate that the polar side chains can significantly reduce the clustering of dopant molecules and favor the dispersion of the dopant in the host matrix as compared to the traditional alkyl side chains. Accordingly, intimate contact between the host and dopant molecules in the NDI-based copolymer with polar side chains facilitates molecular doping with increased doping efficiency and electrical conductivity. For the first time, a heterogeneous thermoelectric transport model for such a material is proposed, that is the percolation of charge carriers from conducting ordered regions through poorly conductive disordered regions, which provides pointers for further increase in the themoelectric properties of n-type D-A copolymers.

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.