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The availability of purely semiconducting single-walled carbon nanotube (s-SWCNT) dispersions has prompted their widespread application in solution-processed thin-film transistors with excellent device performance but has also raised the question of how their precise composition influences charge transport properties in random networks. Here, we compare hole and electron transport in three different polymer-sorted s-SWCNT networks from nearly monochiral (6,5) nanotubes (diameter 0.76 nm) to mixed networks of s-SWCNTs with medium (0.8–1.3 nm) and large (1.2–1.6 nm) diameters. Temperature-dependent field-effect mobilities are extracted from gated four-point probe measurements that exclude any contributions by contact resistance and indicate thermally activated transport. The mobility data can be fitted to the fluctuation-induced tunneling model, although with significant differences between the network compositions. The network with the broadest diameter and thus bandgap range results in the strongest tempe...

Dense layers of semiconducting single-walled carbon nanotubes (SWNTs) serve as electrochromic (EC) materials in the near-infrared with high optical density and high conductivity. EC cells with tunable notch filter properties instead of broadband absorption are created via highly selective dispersion of specific semiconducting SWNTs through polymer-wrapping followed by deposition of thick films by aerosol-jet printing. A simple planar geometry with spray-coated mixed SWNTs as the counter electrode renders transparent metal oxides redundant and facilitates complete bleaching within a few seconds through iongel electrolytes with high ionic conductivities. Monochiral (6,5) SWNT films as working electrodes exhibit a narrow absorption band at 997 nm (full width at half-maximum of 55–73 nm) with voltage-dependent optical densities between 0.2 and 4.5 and a modulation depth of up to 43 dB. These (6,5) SWNT notch filters can retain more than 95% of maximum bleaching for several hours under open-circuit conditions. In addition, different levels of transmission can be set by applying constant low voltage (1.5 V) pulses with modulated width or by a given number of fixed short pulses.

Nanomaterial-based field-effect transistors (FETs) have been proposed for real-time, label-free detection of various biological species. However, two major challenges have limited their use in physiological samples: screening of the analyte charge by electrolyte ions (Debye screening) and non-specific adsorption. Here, these challenges are overcome by combining highly stable FETs based on single-walled semiconducting carbon nanotube (SWCNTs) networks with a novel surface functionalization comprising: 1) short nanobody (VHH) receptors, and 2) a polyethylene glycol (PEG) layer. Nanobodies are stable, easy-to-produce biological receptors that are very small (∼2–4 nm), thus enabling analyte binding closer to the sensor surface. Despite their unique properties, nanobodies have not been used yet as receptors in FET based biosensors. The addition of PEG strongly enhances the signal in high ionic strength environment. Using green fluorescent protein (GFP) as a model antigen, high selectivity and sub-picomolar detection limit with a dynamic range exceeding 5 orders of magnitude is demonstrated in physiological solutions. In addition, long-term stability measurements reveal a low drift of SWCNTs of 0.05 mV/h. The presented immunoassay is fast, label-free, does not require any sample pretreatment or washing steps.

We investigate the impact of electrochemical doping on the frequency of the G + -mode of a selection of polymer-sorted, nearly monochiral and semiconducting single-walled carbon nanotubes (SWCNTs) via in-situ Raman spectroscopy of ambipolar electrolyte-gated SWCNT network transistors. The purified semiconducting nanotubes have small diameters from 0.76 nm to 1.39 nm. In contrast to previous experimental data on large diameter nanotubes and current electron-phonon coupling theories, we find a pronounced red-shift (phonon softening) of the G + -mode at low to medium hole concentrations before an upshift is observed for larger hole concentrations. The effect is largest for those nanotubes with the smallest diameters. The pronounced dependence of these frequency shifts on the diameter of the semiconducting SWCNTs suggests that curvature effects start to play a significant role and should not be neglected.

The ability to select and enrich semiconducting single-walled carbon nanotubes (SWNT) with high purity has led to a fast rise of solution-processed nanotube network field-effect transistors (FETs) with high carrier mobilities and on/off current ratios. However, it remains an open question whether it is best to use a network of only one nanotube species (monochiral) or whether a mix of purely semiconducting nanotubes but with different bandgaps is sufficient for high performance FETs. For a range of different polymer-sorted semiconducting SWNT networks, we demonstrate that a very small amount of narrow bandgap nanotubes within a dense network of large bandgap nanotubes can dominate the transport and thus severely limit on-currents and effective carrier mobility. Using gate-voltage-dependent electroluminescence, we spatially and spectrally reveal preferential charge transport that does not depend on nominal network density but on the energy level distribution within the network and carrier density. On the basis of these results, we outline rational guidelines for the use of mixed SWNT networks to obtain high performance FETs while reducing the cost for purification.

Efficient, stable, and solution-based n-doping of semiconducting single-walled carbon nanotubes (SWCNTs) is highly desired for complementary circuits but remains a significant challenge. Here, we present 1,2,4,5-tetrakis(tetramethylguanidino)benzene (ttmgb) as a strong two-electron donor that enables the fabrication of purely n-type SWCNT field-effect transistors (FETs). We apply ttmgb to networks of monochiral, semiconducting (6,5) SWCNTs that show intrinsic ambipolar behavior in bottom-contact/top-gate FETs and obtain unipolar n-type transport with 3–5-fold enhancement of electron mobilities (approximately 10 cm2 V–1 s–1), while completely suppressing hole currents, even at high drain voltages. These n-type FETs show excellent on/off current ratios of up to 108, steep subthreshold swings (80–100 mV/dec), and almost no hysteresis. Their excellent device characteristics stem from the reduction of the work function of the gold electrodes via contact doping, blocking of hole injection by ttmgb2+ on the elec...

For all-printed circuits, the critical device dimensions, in particular, the channel length in lateral field-effect transistors (FETs), are limited by the printing resolution and alignment accuracy. In contrast, the channel length in vertical electrolyte-gated transistors (VEGTs) is mainly defined by the film thickness and can be easily scaled down to less than 100 nm to achieve high current densities. For practical VEGTs, the printed semiconductor must be highly porous to enable efficient electrolyte-gating by ion penetration. Here, we use aerosol-jet (AJ)-printed layers of polymer-sorted (6,5) single-walled carbon nanotubes with film thicknesses from less than 50 nm to several hundred nanometers as the semiconducting layer sandwiched between evaporated (gold) or printed (silver nanoparticle) metal electrodes and gated by an ionic-liquid-based ion gel. Vertical charge transport in the obtained three-dimensional nanotube networks is confirmed via conductive AFM measurements. The nanotube network VEGTs exh...

Nanomaterial-based field-effect transistors (FETs) have been proposed for real-time, label-free detection of various biological species. However, screening of the analyte charge by electrolyte ions (Debye screening) has so far limited their use in physiological samples. Here, this challenge is overcome by combining FETs based on single-walled semiconducting carbon nanotube networks (SWCNTs) with a novel surface functionalization comprising: (1) short nanobody receptors, and (2) a polyethylene glycol layer (PEG). Nanobodies are stable, easy-to-produce, short biological receptors (~2–4 nm) that enable analyte binding closer to the sensor surface. The addition of PEG enhances the signal in high ionic strength environment. Using green fluorescent protein (GFP) as a model antigen, high selectivity and sub-picomolar detection limit with a dynamic range exceeding 4 orders of magnitude is demonstrated in physiological solutions. The presented immunoassay is fast, label-free, does not require any sample pre-treatment or washing steps.

The field-effect mobility is an important figure of merit for semiconductors such as random networks of single-walled carbon nanotubes (SWNTs). However, owing to their network properties and quantum capacitance, the standard models for field-effect transistors cannot be applied without modifications. Several different methods are used to determine the mobility with often very different results. We fabricated and characterized field-effect transistors with different polymer-sorted, semiconducting SWNT network densities ranging from low (≈6 μm−1) to densely packed quasi-monolayers (≈26 μm−1) with a maximum on-conductance of 0.24 μS μm−1 and compared four different techniques to evaluate the field-effect mobility. We demonstrate the limits and requirements for each method with regard to device layout and carrier accumulation. We find that techniques that take into account the measured capacitance on the active device give the most reliable mobility values. Finally, we compare our experimental results to a ra...

Single-walled carbon nanotubes (SWNTs) are a promising material for flexible and printed electronics. Efficient dispersion and sorting methods facilitate the production of large quantities of high-quality semiconducting SWNT inks for direct printing. Here, the suitability of aerosol-jet printing of polymer-sorted (6,5) SWNTs for top-gate field-effect transistors is investigated. Despite the sonication involved in the printing process, almost no impact on the quality of the SWNTs in terms of defects and length is found. Printed network transistors show reproducible device performance over extended printing periods and for different ink batches with constant printing parameters. Deposition of multiple SWNT layers to obtain thicker and optically dense films increases the effective mobility and on-conductance, while also decreasing hysteresis. Aerosol-jet printing of SWNTs is thus suitable for the fabrication of integrated circuits based on nanotube transistors.

Charge transport in a network of only semiconducting single-walled carbon nanotubes is modeled as a random-resistor network of tube-tube junctions. Solving Kirchhoff's current law with a numerical solver and taking into account the one-dimensional density of states of the nanotubes enables the evaluation of carrier density dependent charge transport properties such as network mobility, local power dissipation, and current distribution. The model allows us to simulate and investigate mixed networks that contain semiconducting nanotubes with different diameters, and thus different band gaps and conduction band edge energies. The obtained results are in good agreement with available experimental data.