Semiconducting Single-walled Carbon Nanotubes Research Articles

Resistive Analysis of Scattering-Dependent Electrical Transport in Single-Wall Carbon-Nanotube Networks

With the development of separation and sorting techniques, highly enriched semiconducting single-walled carbon nanotubes (SWNTs) have become widely accessible, which has led to the rapid growth of high-performance solution-processed SWNT-based thin-film field-effect transistors (TFTs) showing capabilities comparable to the ideal single-SWNT FETs. With such improvements, theoretical studies and detailed analyses of these networks have become necessary. In this work, a model justifying the near-ideal electrical transport in SWNT networks is presented. The field-dependent resistive properties of the networks are calculated using a numerical solver based on the derived individual resistances of SWNTs and the intertube couplings. The model is capable of simulating mixed SWNT networks consisting of both metallic and semiconducting nanotubes of varying chiralities. Our analysis reveals that the high electrical currents in networks could be largely attributed to the suppression of phonon scattering and strong intertube couplings in highly dense SWNT networks (>30-40 SWNTs/μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ). Comparisons between the simulated and experimental results indicate good agreement thereby demonstrating the accuracy of the proposed model.

A nanoscale paper-based near-infrared optical nose (NIRON)

Electronic noses (e-nose) and optical noses (o-nose) are two emerging approaches for the development of artificial olfactory systems for flavor and smell evaluation. The current work leverages the unique optical properties of semiconducting single-wall carbon nanotubes (SWCNTs) to develop a prototype of a novel paper-based near-infrared optical nose (NIRON). We have drop-dried an array of SWCNTs encapsulated with a wide variety of peptides on a paper substrate and continuously imaged the emitted SWCNTs fluorescence using a CMOS camera. Odors and different volatile molecules were passed above the array in a flow chamber, resulting in unique modulation patterns of the SWCNT photoluminescence (PL). Quartz crystal microbalance (QCM) measurements performed in parallel confirmed the direct binding between the vapor molecules and the peptide-SWCNTs. PL levels measured before and during exposure demonstrate distinct responses to the four tested alcoholic vapors (ethanol, methanol, propanol, and isopropanol). In addition, machine learning tools directly applied to the fluorescence images allow us to distinguish between the aromas of red wine, beer, and vodka. Further, we show that the developed sensor can detect limonene, undecanal, and geraniol vapors, and differentiate between their smells utilizing the PL response pattern. This novel paper-based optical biosensor provides data in real-time, and is recoverable and suitable for working at room temperature and in a wide range of humidity levels. This platform opens new avenues for real-time sensing of volatile chemical compounds, odors, and flavors.

Glutathione-S-transferase Fusion Protein Nanosensor.

Fusion protein tags are widely used to capture and track proteins in research and industrial bioreactor processes. Quantifying fusion-tagged proteins normally requires several purification steps coupled with classical protein assays. Here, we developed a broadly applicable nanosensor platform that quantifies glutathione-S-transferase (GST) fusion proteins in real-time. We synthesized a glutathione-DNA-carbon nanotube system to investigate glutathione-GST interactions via semiconducting single-walled carbon nanotube (SWCNT) photoluminescence. We found that SWCNT fluorescence wavelength and intensity modulation occurred specifically in response to GST and GST-fusions. The sensor response was dependent on SWCNT structure, wherein mod(n - m, 3) = 1 nanotube wavelength and intensity responses correlated with nanotube diameter distinctly from mod(n - m, 3) = 2 SWCNT responses. We also found broad functionality of this sensor to diverse GST-tagged proteins. This work comprises the first label-free optical sensor for GST and has implications for the assessment of protein expression in situ, including in imaging and industrial bioreactor settings.

Site-Specific Protein Conjugation onto Fluorescent Single-Walled Carbon Nanotubes

Semiconducting single-walled carbon nanotubes (SWCNTs) are among the few photostable optical emitters that are ideal for sensing, imaging, drug delivery, and monitoring of protein activity. These a...

Frequency dependence of dielectrophoretic fabrication of single-walled carbon nanotube field-effect transistors

A new theoretical model for the dielectrophoretic (DEP) fabrication of single-walled carbon nanotubes (SWCNTs) is presented. A different frequency interval for the alignment of wide-energy-gap semiconductor SWCNTs is obtained, exhibiting a considerable difference from the prevalent model. Two specific models are study, namely the spherical model and the ellipsoid model, to estimate the frequency interval. Then, the DEP process is performed and the obtained frequencies (from the spherical and ellipsoid models) are used to align the SWCNTs. These empirical results confirm the theoretical predictions, representing a crucial step towards the realization of carbon nanotube field-effect transistors (CNT-FETs) via the DEP process based on the ellipsoid model.

Multidipping Technique for Fabrication Time Reduction and Performance Improvement of Solution‐Processed Single‐Walled Carbon Nanotube Thin‐Film Transistors

A newly-designed multi-dipping technique of semiconducting single-walled carbon nanotubes (SWCNTs) enables easy implementation of flexible/stretchable solution-processed SWCNT thin-film transistors (TFTs) in a very short time. Using commercialized aqueous SWCNT ink, repetition of deionized (DI) water rinsing during multi-dipping process makes possible the rapid deposition of a dense and high quality SWCNT network formation, thus leading to significant reduction in total fabrication time but improved electrical performances for SWCNT TFTs. The image shows deposition mechanisms for conventional one-time dipping (left) and multi-dipping techniques (right). Further details can be found in the article number 1901413 by Taehoon Kim, Yongtaek Hong and co-workers.

Control of High-Harmonic Generation by Tuning the Electronic Structure and Carrier Injection.

High-harmonic generation (HHG), which is the generation of light with multiple optical harmonics, is an unconventional nonlinear optical phenomenon beyond the perturbation regime. HHG, which was initially observed in gaseous media, has recently been demonstrated in solid-state materials. Determining how to control such extreme nonlinear optical phenomena is a challenging subject. Here, we demonstrate the control of HHG through tuning the electronic structure and carrier injection using single-walled carbon nanotubes (SWCNTs). We reveal systematic changes in the high-harmonic spectra of SWCNTs with a series of electronic structures ranging from a metal structure to a semiconductor structure. We demonstrate enhancement or reduction of harmonic generation by more than 1 order of magnitude by tuning the electron and hole injection into the semiconductor SWCNTs through electrolyte gating. These results open a path toward the control of HHG in the context of field-effect transistor devices.

Effects of Water and Different Solutes on Carbon-Nanotube Low-Voltage Field-Effect Transistors.

Semiconducting single-walled carbon nanotubes (swCNTs) are a promising class of materials for emerging applications. In particular, they are demonstrated to possess excellent biosensing capabilities, and are poised to address existing challenges in sensor reliability, sensitivity, and selectivity. This work focuses on swCNT field-effect transistors (FETs) employing rubbery double-layer capacitive dielectric poly(vinylidene fluoride-co-hexafluoropropylene). These devices exhibit small device-to-device variation as well as high current output at low voltages (<0.5 V), making them compatible with most physiological liquids. Using this platform, the swCNT devices are directly exposed to aqueous solutions containing different solutes to characterize their effects on FET current-voltage (FET I-V) characteristics. Clear deviation from ideal characteristics is observed when swCNTs are directly contacted by water. Such changes are attributed to strong interactions between water molecules and sp2 -hybridized carbon structures. Selective response to Hg2+ is discussed along with reversible pH effect using two distinct device geometries. Additionally, the influence of aqueous ammonium/ammonia in direct contact with the swCNTs is investigated. Understanding the FET I-V characteristics of low-voltage swCNT FETs may provide insights for future development of stable, reliable, and selective biosensor systems.

LCAO-TDDFT-k-ω: spectroscopy in the optical limit

Understanding, optimizing, and controlling the optical absorption process, exciton gemination, and electron–hole separation and conduction in low dimensional systems is a fundamental problem in materials science. However, robust and efficient methods capable of modelling the optical absorbance of low dimensional macromolecular systems and providing physical insight into the processes involved have remained elusive. We employ a highly efficient linear combination of atomic orbitals (LCAOs) representation of the Kohn–Sham (KS) orbitals within time dependent density functional theory (TDDFT) in the reciprocal space (k) and frequency (ω) domains, as implemented within our LCAO-TDDFT-k-ω code, applying either a priori or a posteriori the derivative discontinuity correction of the exchange functional Δx to the KS eigenenergies as a scissors operator. In so doing we are able to provide a semi-quantitative description of the photoabsorption cross section, conductivity, and dielectric function for prototypical 0D, 1D, 2D, and 3D systems within the optical limit (‖q‖ → 0+) as compared to both available measurements and from solving the Bethe–Salpeter equation with quasiparticle G0W0 eigenvalues (G0W0-BSE). Specifically, we consider 0D fullerene (C60), 1D metallic (10, 0) and semiconducting (10, 10) single-walled carbon nanotubes, 2D graphene (Gr) and phosphorene (Pn), and 3D rutile (R-TiO2) and anatase (A-TiO2). For each system, we also employ the spatially and energetically resolved electron–hole spectral density to provide direct physical insight into the nature of their optical excitations. These results demonstrate the reliability, applicability, efficiency, and robustness of our LCAO-TDDFT-k-ω code, and open the pathway to the computational design of macromolecular systems for optoelectronic, photovoltaic, and photocatalytic applications in silico.

Ultrafast saturable absorption of large-diameter single-walled carbon nanotubes for passive mode locking in the mid-infrared.

We study the saturable absorption properties of single-walled carbon nanotubes (SWCNTs) with a large diameter of 2.2 nm and the corresponding exciton resonance at a wavelength of 2.4 µm. At resonant excitation, a large modulation depth of approximately 30 % and a small saturation fluence of a few tens of µJ/cm2 are evaluated. The temporal response is characterized by an instantaneous rise and a subpicosecond recovery. We also utilize the SWCNTs to realize sub-50 fs, self-start mode locking in a Cr:ZnS laser, revealing that the film thickness is an important parameter that affects the possible pulse energy and duration. The results prove that semiconductor SWCNTs with tailored diameters exceeding 2 nm are useful for passive mode locking in the mid-infrared range.

Effect of sorted, homogeneous electronic grade single-walled carbon nanotube on the electromagnetic shielding effectiveness

Enhancing the electromagnetic interference (EMI) shielding effectiveness (SH EF) with lightweight materials is a significant challenge. Herein, we introduce the fabrication of a heterogeneous metallic and semiconducting single-walled carbon nanotube (SWCNT) from the current synthetic method into films to optimize EMI SH EF. Because EMI SH EF can be affected by absorption and reflectance attenuation, optimizing the ratio of the metallic or semiconducting nature of SWCNT as a homogeneous electronic grade is critical. We optimized the SWCNT thin film as a homogeneous electronic grade and compared the EMI SH EF performance between them, with mechanistic insights. Specifically, we tuned the ratio of the metallic (m-) and semiconducting (s-) SWCNT in thin film and determined the EMI SH EF. Electronically pure m-SWCNT thin films showed the higher EMI SH EF than s-SWCNT thin film with the comparable tube length. Furthermore, a 1.2 μm thick film of sorted SWCNT exhibited a maximum EMI SH EF of approximately 35 dB with 3 mg of the lightweight film, and the highest normalized specific EMI SH EF (ESE/t), which is the EMI SH EF normalized by the density and thickness of the film, obtained herein was 153,333 dB cm2 g−1 in the frequency range of 12–19 GHz. Our findings demonstrate a substantial material design paradigm for the creation of next-generation material for high-performance EMI SH EF.

Guiding Charge Transport in Semiconducting Carbon Nanotube Networks by Local Optical Switching.

Photoswitchable, ambipolar field-effect transistors (FETs) are fabricated with dense networks of polymer-sorted, semiconducting single-walled carbon nanotubes (SWCNTs) in top-gate geometry with photochromic molecules mixed in the polymer matrix of the gate dielectric. Both hole and electron transport are strongly affected by the presence of spiropyran and its photoisomer merocyanine. A strong and persistent reduction of charge carrier mobilities and thus drain currents upon UV illumination (photoisomerization) and its recovery by annealing give these SWCNT transistors the basic properties of optical memory devices. Temperature-dependent mobility measurements and density functional theory calculations indicate scattering of charge carriers by the large dipoles of the merocyanine molecules and electron trapping by protonated merocyanine as the underlying mechanism. The direct dependence of carrier mobility on UV exposure is employed to pattern high- and low-resistance areas within the FET channel and thus to guide charge transport through the nanotube network along predefined paths with micrometer resolution. Near-infrared electroluminescence imaging enables the direct visualization of such patterned current pathways with good contrast. Elaborate mobility and thus current density patterns can be created by local optical switching, visualized and erased again by reverse isomerization through heating.

Chemiresistive sensor arrays for detection of air pollutants based on carbon nanotubes functionalized with porphyrin and phthalocyanine derivatives

Air pollution is a serious environmental and health issue that necessitates accurate and timely air-quality monitoring to provide timely health warnings to affected demographics and as a regulatory tool for reduction of emission. Thus, a high-density sensor array was developed for detection and quantification of NO2, SO2, and O3—three contributing air pollutants used for monitoring Air Quality Index (AQI). The gas sensor array operates on the principle of chemiresistive gas sensing with light-tunable selectivity and sensitivity which was achieved by combining the chemical selectivity and photoactive property of macrocyclic compounds with the chemical and electrical sensitivity of semiconducting single-walled carbon nanotubes (SWNTs). More specifically, sensing materials comprising hybrid nanostructures of SWNTs functionalized with either a metallophthalocyanine (MPc) derivative or a metalloporphyrin (MPor) derivative were formulated into printable inks. Each sensor in the array was fabricated by ink-jet printing of sensing materials onto interdigitated platinum electrodes. The sensor array demonstrated tunable sensitivity (in the range of sub-ppm to tens of ppm) to NO2, SO2, and O3 under different combinations of illumination conditions and specific sensing materials.

High-Temperature-Annealed Flexible Carbon Nanotube Network Transistors for High-Frequency Wearable Wireless Electronics.

Semiconducting single-walled carbon nanotubes (SWNTs) are potential active materials for fast-growing flexible/wearable applications with low-power dissipation, especially suitable for increasingly important radio-frequency (RF) wireless biosensor systems. However, the operation frequency of the existing flexible carbon nanotube field-effect transistors (CNT-FETs) is far below the current state-of-the-art GSM spectrum frequency band (typical 850 MHz) for near-field wireless communication applications. In this paper, we successfully conduct a 900 °C annealing process for the flexible CNT-FETs and hence significantly improve their operation frequency up to 2.1 gigahertz (GHz), making it possible to cover the current GSM spectra for integrated wireless sensor systems. The high-temperature annealing process significantly improves the electrical characteristic of the flexible CNT-FETs by removing the surfactant impurities of the SWNT materials. The obtained flexible CNT-FETs exhibit record transconductance (gm) as high as 48 μS/μm. Despite an applied strain level of 2%, a characteristic frequency of over 1 GHz is observed. Further demonstration of GHz performance is also exhibited for flexible RF integrated circuits (ICs) such as frequency multipliers and mixers, which are the fundamental components for wireless applications. This work offers a new pathway for realizing SWNT-based wearable wireless GHz sensor systems with power efficiency.

Exploring the Impact of Counterion Chemistry on Carrier Doping of Carbon Nanotubes

Semiconducting single-walled carbon nanotubes (s-SWCNT) are viewed as a promising candidate for optical, electronic, and energy conversion applications. Often the performance of carbon nanotubes in these applications is dependent on being able to control the interplay between their optical and electronic properties. One strategy toward achieving this control is tuning the position of the Fermi level through chemical doping to inject charge carriers into the electronic density of states.We have previously demonstrated that p-type doping using the one-electron oxidant, triethyloxonium hexachloroantimonate (OA) results in very efficient injection of free carriers into near-monochiral s-SWCNT networks. Here we build on our previous work by employing a series of charge-transfer dopants based on boron clusters appended with various organic moieties that control the redox properties of the dopant. These dopants are unique, since their chemical structure means that the electron that is extracted from the nanotube is localized on the boron cluster and spatially separated from hole density injected into the carbon nanotube. We explore the charge-transfer doping process using these boron-cluster dopants, the resulting charge-carrier transport properties of the doped s-SWCNT networks, and make a comparison to networks doped using either OA or 2,3,5,6-Tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ). We will present spectroscopic and bulk conductivity measurements of charge-transport in high-mobility s-SWCNT networks and will discuss the impact that the chemistry and structure of the dopant counterion has on charge transport and the implications for electronic devices comprised of these tailored s-SWCNT networks.

(Invited) Challenges in Quantifying the Purity of Semiconducting Single-Walled Carbon Nanotubes

Semiconducting carbon nanotubes (sc-SWCNT) sit amongst the most promising nanomaterials for a new generation of electronic devices. Progress towards commercial applications is combined with challenges related to materials development and characterization, fabrication methods as well as device modeling. This talk will focus primarily on the enrichment process and the related ink formulation for printed electronics and integrated circuits. [1] The quality of carbon nanotube ink solutions is closely tied with the rapid feedback provided by optical spectroscopy methods: UV-vis, Raman and fluorescence. [2] I will describe our efforts on improving the material’s assessment when purity exceeds well beyond 99%. [3] [1] Ding, J.; Li, Z.; Lefebvre, J.; Cheng, F.; Dubey, G.; Zou, S.; Finnie, P.; Hrdina, A.; Scoles, L.; Lopinski, G. P.; Kingston, C. T.; Simard, B.; Malenfant, P. R. L. Enrichment of Large-Diameter Semiconducting SWCNTs by Polyfluorene Extraction for High Network Density Thin Film Transistors. Nanoscale 2014, 6, 2328-2339.[2] J. Lefebvre, J.; Finnie, P.; Fagan, J.; Zheng, M.; Hight Walker, A. R. Metrological Assessment of Single-Wall Carbon Nanotube Materials by Optical Methods. Handbook of Carbon Nanomaterials 2019, 9, R. B. Weisman and J. Kono editors (World Scientific) ISBN 978-981-3235-45-8.[3] Lefebvre, J.; Ding, J.; Li, Z.; Finnie, P.; Lopinski, G.; Malenfant, P. R. L. High-Purity Semiconducting Single-Walled Carbon Nanotubes: A Key Enabling Material in Emerging Electronics. Acc. Chem. Res. 2017, 50 (10), 2479-2486. Figure 1

Deciphering Plant Signaling Pathway with Semiconducting Single-Walled Carbon Nanotubes

As a consequence of their sessile nature, plants have developed complex signaling mechanisms to cope with the highly dynamic environment that they live in. In response to external stimuli, plants can utilize various signaling pathways for intercellular communication to engage different metabolic and genetic machineries involved in the plant defense system. Among the many signaling molecules recently uncovered, hydrogen peroxide (H2O2) represents one of the most versatile signaling molecule in plants in response to environmental stresses such as mechanical wounding. Here, we develop an optical nanosensor platform using DNA-wrapped semiconducting single-walled carbon nanotubes (SWNT) to monitor the wound-induced H2O2 signaling pathway in plants. This approach enables non-destructive, real-time detection of changes in endogenous H2O2 level in plants at a remote distance with portable and inexpensive electronics. We demonstrate the versatility of this method to investigate the dynamics between H2O2 and electric signalling pathways in different vegetable crops and plant species. The reversibility of the sensor in vivo and its use to monitor insect feeding for agricultural applications are also demonstrated. In addition, we also developed an auto-propagating wave model to explain the propagation dynamics of H2O2 post-wounding. This newly developed tool offers new opportunities to understand plant defense responses as well as to monitor crop health in real time.

Strategies for Chemical Sensing Using High Purity Semiconducting Single-Walled Carbon Nanotube Electronic Devices

Semiconducting single-walled carbon nanotubes (sc-SWCNTs) are attractive in chemical sensing [1] because of their peculiarities: As they present a single atom-thick wall and a quasi 1D form factor, sc-SWCNTs are especially sensitive to their surroundings’ electrostatics. Moreover, their band gap of approximately 1 eV is much greater than room-temperature thermal energy while being in a convenient range for electronic applications. Also, their electronic structure exhibits van Hove singularities (sharp spikes in the density of states) that drastically alters their conductivity and optical properties when charge carriers are injected. Although sc-SWCNT electronic devices are very sensitive, they lack in selectivity and they usually need to be functionalized to implement a lock-and-key detection mechanism.In this talk, we will present various strategies for chemical sensing using enriched sc-SWCNTs. We will discuss the advantages and disadvantages of using sc-SWCNTs in electronic chemical sensing devices. Sub-ppm ammonia sensing will be demonstrated using a sc-SWCNT material wrapped with a decomposable polymer in a chemiresistor configuration. [2] Also using chemiresistors, CO2 detection has been achieved by designing a SWCNT-wrapping polymer with specific interactions. Finally, we will present a strategy to differentiate the response of sensor elements to a variety of volatile analytes by changing the polymer gate dielectrics in a three-terminal bottom gate chemitransistor configuration. [3] This methodology opens the way to the implementation of sc-SWCNT-based chemitransistors in a printed cross-reactive sensor array.

(Invited) Progress in Using Carbon Nanotube Spectra for Mechanical Strain Sensing

A characteristic property of semiconducting single-wall carbon nanotubes (SWCNTs) is distinct near-infrared photoluminescence following excitation by visible light. Theory and experiment show that these optical emission peaks shift predictably in wavelength as nanotubes are compressed or stretched along their axis. We are exploiting this effect in a powerful new method intended for measuring mechanical strain in critical infrastructure components such as airframes, pressurized vessels, pipelines, support beams, etc. The method involves applying a dilute dispersion of nanotubes in a polymeric host onto the surface of the specimen to form a sub-micron thick film in which SWCNTs act as strain sensors. This layer is overcoated with a transparent protective top coat such as a polyurethane varnish. Subsequent strains in the substrate are transmitted to the nanotubes by load transfer. The substrate strain magnitude and direction are then measured by illuminating the surface at any point of interest with a small visible laser beam and spectrally analyzing the resulting near-IR nanotube emission. Single-point measurements currently provide strain magnitude resolution of ca. 100 microstrain, strain angle resolution of ca. 5 degrees, and spatial resolution of ca. 50 mm. Each reading takes less than one second, allowing compilation of strain maps from scanned data. In contrast to digital image correlation, which is currently the only commercial non-contact strain technology, the new method can measure strains induced when the specimen is not under observation. It thus has the potential for routine use in industrial structural health monitoring as well as in testing and development laboratories. We will also describe recent progress in adapting the technology to camera-based measurements using spectrally resolved fluorescence imaging.

(Invited) Alteration of the Electrical Transport in Carbon Nanotube Network Field-Effect Transistors Using Polymer Encapsulants and Gate Dielectrics

Enriched semiconducting single-walled carbon nanotubes (SWCNTs) inks of high purity opens a wealth of possibilities for device fabrication using printing techniques and solution processes. [1] Logics, displays, sensors and large-scale integrated circuits [2] appear to be within reach. For those promises to concretize, a better control over parameters such as carrier type and mobility, operation power and device-to-device variability is needed. Beside the ambient effect (notably water and oxygen) on the transport of carbon nanotube network field-effect transistors (CNN-FETs), the nature of the surrounding materials (as a passivation layer or as a gate dielectric) appears to play a crucial role in determining the device’s characteristics.Firstly, we have tested a large number of polymeric materials as the bottom gate in three-terminal CNN-FETs. We have found that the transport characteristics parameters such as the threshold voltage and the hysteresis are affected by the chemical nature of the polymer. [3] Subjecting those CNN-FETs with various gate dielectrics to a series of volatile analytes, we observed drastically different responses which suggests the usefulness of polymer gate dielectric variations in cross-reactive sensors arrays.Secondly, polymeric materials were used as an encapsulant over bottom gate CNN-FETs. [4] A smooth and continuous variation of the threshold voltage has been achieved by using a series of poly(styrene–co–2-vinyl pyridine) copolymers with different monomer ratios. A surface charge density measurement methodology has been developed to rationalize the threshold voltage variations upon encapsulation with various polymers. Finally, we explored the use of n-doping molecules blended with polymer encapsulants as an efficient way to obtain n-type transport characteristics. This strategy is further used in the implementation of simple p-n junctions showing a modest rectification.