Single-walled Carbon Nanotube Networks Research Articles

Controllable Hysteresis and Threshold Voltage of Single-Walled Carbon Nano-tube Transistors with Ferroelectric Polymer Top-Gate Insulators.

Double-gated field effect transistors have been fabricated using the SWCNT networks as channel layer and the organic ferroelectric P(VDF-TrFE) film spin-coated as top gate insulators. Standard photolithography process has been adopted to achieve the patterning of organic P(VDF-TrFE) films and top-gate electrodes, which is compatible with conventional CMOS process technology. An effective way for modulating the threshold voltage in the channel of P(VDF-TrFE) top-gate transistors under polarization has been reported. The introduction of functional P(VDF-TrFE) gate dielectric also provides us an alternative method to suppress the initial hysteresis of SWCNT networks and obtain a controllable ferroelectric hysteresis behavior. Applied bottom gate voltage has been found to be another effective way to highly control the threshold voltage of the networked SWCNTs based FETs by electrostatic doping effect.

Thermal conductivity of chirality-sorted carbon nanotube networks

The thermal properties of single-walled carbon nanotubes (SWNTs) are of significant interest, yet their dependence on SWNT chirality has been, until now, not explored experimentally. Here, we used electrical heating and infrared thermal imaging to simultaneously study thermal and electrical transport in chirality-sorted SWNT networks. We examined solution processed 90% semiconducting, 90% metallic, purified unsorted (66% semiconducting), and as-grown HiPco SWNT films. The thermal conductivities of these films range from 80 to 370 W m−1 K−1 but are not controlled by chirality, instead being dependent on the morphology (i.e., mass and junction density, quasi-alignment) of the networks. The upper range of the thermal conductivities measured is comparable to that of the best metals (Cu and Ag), but with over an order of magnitude lower mass density. This study reveals important factors controlling the thermal properties of light-weight chirality-sorted SWNT films, for potential thermal and thermoelectric applications.

Electric Characteristics of the Carbon Nanotube Network Transistor with Directly Grown ZnO Nanoparticles

We report on the electrical characteristics of field effect transistors fabricated with random networks of single-walled carbon nanotubes with surfaces modified by ZnO nanoparticles. ZnO nanoparticles are directly grown on single-walled carbon nanotubes by atomic layer deposition using diethylzinc (DEZ) and water. Electrical observations show that ZnO nanoparticles act as charge transfer sources that provide electrons to the nanotube channel. The valley position in ambipolar transport of nanotube transistors is negatively shifted for 3V due to the electronic n-typed property of ZnO nanoparticles. However, the Raman resonance remains invariant despite the charge transfer effect produced by ZnO nanoparticles.

An Organocobalt-Carbon Nanotube Chemiresistive Carbon Monoxide Detector.

A chemiresistive detector for carbon monoxide was created from single-walled carbon nanotubes (SWCNTs) by noncovalent modification with diiodo(η5: η1-1-[2-(N,N-dimethylamino)ethyl]-2,3,4,5-tetramethylcyclopentadienyl)-cobalt(III) ([Cp^CoI2]), an organocobalt complex with an intramolecular amino ligand coordinated to the metal center that is displaced upon CO binding. The unbound amino group can subsequently be transduced chemiresistively by the SWCNT network. The resulting device was shown to have a ppm-level limit of detection and unprecedented selectivity for CO gas among CNT-based chemiresistors. This work, the first molecular-level mechanistic elucidation for a CNT-based chemiresistive detector for CO, demonstrates the efficacy of using an analyte's reactivity to produce another chemical moiety that is readily transduced as a strategy for the rational design of chemiresistive CNT-based detectors.

SnO2 nanospheres among GO and SWNTs networks as anode for enhanced lithium storage performances

Conducting supporters of purified single-walled carbon nanotubes (SWNTs) and graphene oxide (GO) were used to confine pomegranate-structured SnO2 nanospheres for forming SnO2-GO-SWNT composites. As anode material for lithium ion batteries (LIBs), this composite exhibits a stable and large reversible capacity together with an excellent rate capability. In addition, an analysis of the AC impedance spectroscopy has been used to confirm the enhanced mechanism for LIB performance. The improved electrochemical performance should be ascribed greatly to the reinforced synergistic effects between GO and SWNT networks, and their enhanced contribution of the conductivity. These results indicate that this composite has potential for utilization in high-rate and durable LIBs.

Accelerating Gas Adsorption on 3D Percolating Carbon Nanotubes.

In the field of electronic gas sensing, low-dimensional semiconductors such as single-walled carbon nanotubes (SWCNTs) can offer high detection sensitivity owing to their unprecedentedly large surface-to-volume ratio. The sensitivity and responsivity can further improve by increasing their areal density. Here, an accelerated gas adsorption is demonstrated by exploiting volumetric effects via dispersion of SWCNTs into a percolating three-dimensional (3D) network in a semiconducting polymer. The resultant semiconducting composite film is evaluated as a sensing membrane in field effect transistor (FET) sensors. In order to attain reproducible characteristics of the FET sensors, a pulsed-gate-bias measurement technique is adopted to eliminate current hysteresis and drift of sensing baseline. The rate of gas adsorption follows the Langmuir-type isotherm as a function of gas concentration and scales with film thickness. This rate is up to 5 times higher in the composite than only with an SWCNT network in the transistor channel, which in turn results in a 7-fold shorter time constant of adsorption with the composite. The description of gas adsorption developed in the present work is generic for all semiconductors and the demonstrated composite with 3D percolating SWCNTs dispersed in functional polymer represents a promising new type of material for advanced gas sensors.

Effect of Tunnel Junctions and Coulomb Blockade on Semiconducting Property of Networks of Single-Wall Carbon Nanotubes

The optical and electrical characterization techniques were employed to demonstrate both experimentally and theoretically (parallel nonlinear resistor model) that the existence of tunnel junctions between semiconducting single-wall carbon nanotubes implies that the Coulomb blockade effect dominates their semiconducting property. Multiwall carbon nanotubes were added to a network of single-wall carbon nanotubes, and Raman spectroscopy and UV–vis–NIR spectroscopy enabled us to observe the semiconducting property of individual single-wall carbon nanotubes in a network with a high concentration of multiwall carbon nanotubes. However, the field effect measurement at 300 K on the network of single-wall carbon nanotubes and the electrical tunnel current measurements over a wide temperature range (4–300 K) at different bias voltages (0.001–10 V) on all of the networks revealed that the networks can be treated as networks of disordered metallic nanoparticles and the semiconducting property of single-wall carbon nanotubes is significantly diminished. Furthermore, we demonstrate that the electron tunneling in networks of carbon nanotubes cannot be fully described by models such as Efros–Shklovskii, Mott variable range hopping, electron cotunneling, or fluctuation-induced tunneling because of the diameter and length distributions in the networks. The effect of tunnel junctions on the performance of such networks for sensing applications and field effect transistors is discussed.

Metal-free SWNT/carbon/MnO2 hybrid electrode for high performance coplanar micro-supercapacitors

In this work, we report on superior coplanar micro-supercapacitors (MSCs) where single-wall carbon nanotube (SWNT)/carbon and SWNT/carbon/MnO2 are employed as the current collectors and hybrid electrodes, respectively. A composite of high dense SWNT network and photoresist is firstly patterned on the substrate and a followed carbonization process converts the photoresist into amorphous carbon to form the SWNT/carbon current collectors which demonstrates good conductivity and superior electrochemical performance. In addition, MnO2 nanostructures are uniformly grown on the carbon collectors to significantly increase the specific capacitance of the MSCs. It is found that the MSCs with SWNT/carbon/MnO2 hybrid electrodes show an excellent electrochemical performance with a high stack capacitance of 20.4Fcm−3 and an outstanding cycling performance, i.e., 92.4% of the initial capacitance after 5000 cycles. In addition, the as-prepared hybrid electrodes could be transferred to a soft substrate so that the designed coplanar MSCs can serve as a power source to be integrated with flexible microelectronic devices.

Intrinsic current–voltage characteristics of metal-carbon nanotube networks: A first-principles study

The interconnections involving metal atoms in single-walled carbon nanotube (SWNT) networks are crucial for building nanoscaled devices. The influence of the metal-(η6-SWNT) interconnects in the electrical conductivity of SWNT film have been reported in recent experiments [X. Tian et al. Nano lett. 2014,14,3930]. Using non-equilibrium Green's function with density function theory, we performed theoretical calculations on the electron transport properties of (Cr, Li, Au)-SWNT systems. We revealed the roles of transition metal Cr, alkalis metal Li and inert metal Au in improving the electrical conductance of metal-SWNT systems. Our calculated results show that transport properties along the inter-tube direction are strongly dependent on the connecting metal atoms varying over many orders of magnitudes. Gold atoms fail to enhance the electrical conductance of SWNT systems. Meanwhile, negative differential resistances are demonstrated in semiconducting inter-tube models, which would have potential applications in the electronic device. Our results provide a promising way to optimize the performance of SWNT based networks.

Three-Dimensional Flexible Complementary Metal-Oxide-Semiconductor Logic Circuits Based On Two-Layer Stacks of Single-Walled Carbon Nanotube Networks.

We have proposed and fabricated stable and repeatable, flexible, single-walled carbon nanotube (SWCNT) thin film transistor (TFT) complementary metal-oxide-semiconductor (CMOS) integrated circuits based on a three-dimensional (3D) structure. Two layers of SWCNT-TFT devices were stacked, where one layer served as n-type devices and the other one served as p-type devices. On the basis of this method, it is able to save at least half of the area required to construct an inverter and make large-scale and high-density integrated CMOS circuits easier to design and manufacture. The 3D flexible CMOS inverter gain can be as high as 40, and the total noise margin is more than 95%. Moreover, the input and output voltage of the inverter are exactly matched for cascading. 3D flexible CMOS NOR, NAND logic gates, and 15-stage ring oscillators were fabricated on PI substrates with high performance as well. Stable electrical properties of these circuits can be obtained with bending radii as small as 3.16 mm, which shows that such a 3D structure is a reliable architecture and suitable for carbon nanotube electrical applications in complex flexible and wearable electronic devices.

Conjugated fluorene-moiety-containing pendant polymers for the dispersion of single-wall carbon nanotubes: polymer wrapping abilities and electrical properties

We report a new strategy to disperse single-wall carbon nanotubes (SWNTs) via conjugated moiety-containing pendant polymers, poly(2-vinylpyridine)-co-poly(9,9-dihexyl-2-(4-vinylphenyl)-9H-fluorene) (P2VP-co-P(StFl)). The polymer composition ratio and molecular weight were varied to control the SWNT dispersion. The P(St-Fl) segments were adsorbed to the surface of the de-bundled SWNTs through π–π interaction, while the P2VP segments surrounded the outer surfaces of the SWNTs to enhance their solubility and stability. A low-voltage field-effect transistor (FET) was fabricated using a P(St-Fl)-wrapped SWNT network, SWNTs wrapped with P2VP79-co-P(St-Fl)347, and hafnium oxide as the active layer, gate electrode, and dielectric, respectively. The field-effect mobility of the fabricated device was as high as 0.82 cm2 V−1 s−1 on average, with an ON/OFF ratio over 104 under a −5 V bias. This study highlights the tailored wrapping power of pendant polymers, as well as the tunable electrical conducting/semiconducting properties of SWNTs for FET device applications. The wrapping abilities of comb-like polymers with pendant conjugated fluorine moieties and their tunable electrical properties of SWNTs were discussed. It is found that longer side-chain-conjugated fluorene segments in homopolymer (P(St-Fl)300, 7) can strongly bind to the SWNTs surfaces through π–π interaction and its copolymer (P2VP79-co-P(St-Fl)347, 5a) lead to predominant dispersion of SWNTs due to the flexibility of P2VP for further increasing the solubility. Thus, SWNTs wrapped by 5a after thermal annealing can be selected as a gate electrode, whereas the spin-coated SWNTs wrapped by 7 can be as a semiconductor for the FET channel, resulting in a mobility of 0.82 cm2 V−1s−1, a threshold voltage of 0.35 V and an ON/OFF ratio of 2.8 × 104.

Preparation and enhanced conducting properties of open networks of poly(3-hexylthiophene)/carbon nanotube hybrids

The preparation of new high conductivity nanohybrid open networks of poly(3-hexylthiophene) and single-walled carbon nanotubes (P3HT/SWNTs) by spin coating deposition is reported.

Selective synthesis of large diameter, highly conductive and high density single-walled carbon nanotubes by a thiophene-assisted chemical vapor deposition method on transparent substrates

Selective synthesis of single-walled carbon nanotubes (SWNTs) with controlled properties is an important research topic for SWNT studies. Here we report a thiophene-assisted chemical vapor deposition (CVD) method to directly grow highly conductive SWNT thin films on substrates, including transparent ones. By adding low concentration thiophene into the carbon feedstock (ethanol), the as-prepared carbon nanotubes demonstrate an obvious up-shift in the diameter distribution while the single-walled structure is still retained. In the proposed mechanism, the change in the diameter is sourced from the increase in the carbon yield induced by the sulfur-containing compound. Such SWNTs are found to possess high conductivity with 95% SWNTs demonstrating on/off ratios lower than 100 in transistors. More importantly, it is further demonstrated that this method can be used to directly synthesize dense SWNT networks on transparent substrates which can be utilized as transparent conductive films (TCFs) with very high transparency. Such TCFs can be applied to fabricate a light modulating window as a proof-of-concept. The present work provides important insights into the growth mechanism of SWNTs and great potential for the preparation of TCFs with high scalability, easy operation and low cost.

Synthesis of single-walled carbon nanotube networks using monodisperse metallic nanocatalysts encapsulated in reverse micelles

We report on a method of synthesis of single-walled carbon nanotubes percolated networks on silicon dioxide substrates using monodisperse Co and Ni catalyst. The catalytic nanoparticles were obtained by modified method of reverse micelles of bis-(2-ethylhexyl) sulfosuccinate sodium in isooctane solution that provides the nanoparticle size control in range of 1 to 5 nm. The metallic nanoparticles of Ni and Co were characterized using transmission electron microscopy (TEM) and atomic-force microscopy (AFM). Carbon nanotubes were synthesized by chemical vapor deposition of CH4/H2 composition at temperature 1000 ?? on catalysts pre-deposited on silicon dioxide substrate. Before temperature treatment during the carbon nanotube synthesis most of the catalyst material agglomerates due to magnetic forces while during the nanotube growth disintegrates into the separate nanoparticles with narrow diameter distribution. The formed nanotube networks were characterized using AFM, scanning electron microscopy (SEM) and Raman spectroscopy. We find that the nanotubes are mainly single-walled carbon nanotubes with high structural perfection up to 200 ?m long with diameters from 1.3 to 1.7 nm consistent with catalyst nanoparticles diameter distribution and independent of its material.

Damage of single-wall carbon nanotube network structure under electric current loading

Damage of single-wall carbon nanotube network structure under electric current loading

Toward the Limits of Uniformity of Mixed Metallicity SWCNT TFT Arrays with Spark-Synthesized and Surface-Density-Controlled Nanotube Networks.

We report the fabrication of thin film transistors (TFTs) from networks of nonbundled single-walled carbon nanotubes with controlled surface densities. Individual nanotubes were synthesized by using a spark generator-based floating catalyst CVD process. High uniformity and the control of SWCNT surface density were realized by mixing of the SWCNT aerosol in a turbulent flow mixer and monitoring the online number concentration with a condensation particle counter at the reactor outlet in real time. The networks consist of predominantly nonbundled SWCNTs with diameters of 1.0-1.3 nm, mean length of 3.97 μm, and metallic to semiconducting tube ratio of 1:2. The ON/OFF ratio and charge carrier mobility of SWCNT TFTs were simultaneously optimized through fabrication of devices with SWCNT surface densities ranging from 0.36 to 1.8 μm(-2) and channel lengths and widths from 5 to 100 μm and from 100 to 500 μm, respectively. The density optimized TFTs exhibited excellent performance figures with charge carrier mobilities up to 100 cm(2) V(-1) s(-1) and ON/OFF current ratios exceeding 1 × 10(6), combined with high uniformity and more than 99% of devices working as theoretically expected.

Characterisation of SU‐8 n ‐doping carbon nanotube‐based electronic devices

Triarylium–solphonium salt, the chemical component of the SU-8 photo resist, has been proved as an effective n-doping source for graphene. In this reported work, a study has been made of the effects of SU-8 on single walled carbon nanotube networks. The results indicate that SU-8 behaves as an electrons donor and causes an upward shift in the Fermi level. The cross-linking property of the SU-8 resembles an efficient isolator from the oxygen of the ambient. This leads to ambient-stability of this doping technique. In addition, the doping technique shows negligible defects on the CNT surface and then higher transconductance is expected to be achieved. The temperature dependence of the Raman spectra of the CNT network observed a downshift in the G-band with increasing temperature. Finally, since SU-8 is an e-beam sensitive resist as well as a photo resist, it was used to selectively dope CNTs within the substrate area.

Fabrication of single walled carbon nanotubes/poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) layers under enhanced gravity drying

In this contribution, we explore the use of enhanced gravity in order to achieve composite films of single walled carbon nanotubes (SWCNTs)/poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) with improved properties. The samples were characterized by atomic force microscopy, scanning electron microscopy, and electrochemical impedance spectroscopy, in order to determine the differences caused by the enhanced gravity. Impedance spectroscopy results show that there is an improvement of the electrical properties of the SWCNT/PEDOT:PSS junction, manifested as lower contact resistance, modified chemical capacitance, and induced p-type doping. A force-induced interpenetration of the polymer into the SWCNT network and the efficient removal of water and PSS are proposed to explain the results. The transparency and electrical properties of these films forecast their application as a buffer layer in organic solar cell heterojunctions, or as hole transporting materials in perovskite-based solar cells.

Investigation of optimal hydrogen sensing performance in semiconducting carbon nanotube network transistors with palladium electrodes

The work function of palladium (Pd) is known to be sensitive to hydrogen (H2) via the formation of a surface dipole layer or Pd hydride. One approach to detect such a change in the work function is based on the formation of a Schottky barrier between Pd and a semiconductor. Here, we demonstrate a H2 sensor operable at room temperature by assembling solution-processed, pre-separated semiconducting single-walled carbon nanotube (SWNT) network bridged by Pd source/drain (S/D) electrodes in a configuration of field-effect transistors (FETs) with a local back-gate electrode. To begin with, we observed that the H2 response of the fabricated SWNT FETs can be enhanced in the linear operating regime, where the change in the work function of the Pd S/D electrodes by H2 can be effectively detected. We also explore the H2 responses in various SWNT FETs with different physical dimensions to optimize the sensing performance.

Photo-induced refractive index and topographical surface gratings in functionalized nanocarbon solid film

We demonstrate that a single-walled carbon nanotube network noncovalently coupled with a pyrene-modified azo-benzene chromophore functions as a host matrix for a broad range of photo-orientation and photomechanical effects. The chromophore could be efficiently reoriented through repeated trans-cis-trans isomerization under linearly polarized 480 nm light, with Δn of 0.012 at 650 nm and fast characteristic rise-times of 0.12 s. Erasable phase diffraction gratings could also be written, with permanent surface relief gratings forming at sufficiently long irradiation times. In addition to demonstrating a mechanism for photo-manipulation of single-walled carbon nanotubes, these results show photo-orientation of chromophores in azo-functionalized single-walled carbon nanotube networks as a path towards the photosensitive tuning of the electrostatic environment of the nanotube.