Single-walled Carbon Nanotube Electrodes Research Articles

Electrochemical characterization of single-walled carbon nanotubes for electrochemical double layer capacitors using non-aqueous electrolyte

Single-walled carbon nanotubes (SWCNTs) were investigated by cyclic voltammetry and electrochemical impedance spectroscopy in a non-aqueous electrolyte, 1 M Et 4NBF 4 in acetonitrile, suitable for supercapacitors. Further, in situ dilatometry and in situ conductance measurements were performed on single electrodes and the results compared to an activated carbon, YP17. Both materials show capacitive behavior characteristic of high surface area electrodes for supercapacitors, with the maximum full cell gravimetric capacitance being 34 F/g for YP17 and 20 F/g for SWCNTs at 2.5 V with respect to the total active electrode mass. The electronic resistance of SWCNTs and activated carbon decreases significantly during charging, showing similarities of the two materials during electrochemical doping. The SWCNT electrode expands irreversibly during the first electrochemical potential sweep as verified by in situ dilatometry, indicative of at least partial debundling of the SWCNTs. A reversible periodic swelling and shrinking during cycling is observed for both materials, with the magnitude of expansion depending on the type of ions forming the double layer.

Organic molecule assembled between carbon nanotubes: A highly efficient switch device

We report a highly efficient switch built from an organic molecule assembled between single-wall carbon nanotube electrodes. We theoretically show that changes in the distance between the electrodes alter the molecular conformation within the gap, affecting in a dramatic way the electronic and charge transport properties, with an on/off ratio larger than 300. This opens up the perspective of combining molecular electronics with carbon nanotubes, bringing great possibilities for the design of nanodevices.

Direct measurement of charge transport through helical poly(ethyl propiolate) nanorodswired into gaps in single walled carbon nanotubes

We report the direct measurement of electrical transport through rod-like polymer molecules,of poly(ethyl propiolate) (PEP), utilizing single walled carbon nanotubes (SWNTs) aselectrodes. The electrical properties of the devices were measured (i) before cutting aSWNT, (ii) when a SWNT was cut and (iii) after PEP deposition into the nanoscale gap ina cut SWNT. The gate-dependent electrical properties showed a reduction in current fromIon = 2.4 × 10−7 A for SWNTdevices to Ion = 3.6 × 10−9 A for PEP bridge devices, both with the ON/OFF ratio of104. Similarly, metallic SWNT devices showed a reduction in current from a few hundreds ofµA fora SWNT device to a few nA for a PEP–SWNT structure. The current density of a single PEP moleculeis 105–106 A cm−2, which is relatively high, indicating that the PEP molecule can carry significant current.Use of SWNT electrodes was seen to be an effective method of contacting PEP nanorods tofacilitate electrical measurements.

Carbon Nanotube Electrodes for Hot‐Wire Electrochemistry

The use and preparation of single-walled carbon nanotubes (SWCNTs) at thin metallic wire electrodes for hot-wire electrochemical studies is described. The nanotubes were deposited on metal substrates such as gold by electrophoresis from a dispersion containing sodium dodecyl sulphate as an anionic surfactant. The formation of a layer of pure SWCNTs is achieved by thermal treatment at 350 degrees C. When heated in situ by a strong ac current, the electrodes can be used for electrochemical studies of nanotubes at increased temperatures. The state and functionality of the electrodes were characterized by Raman spectroscopy, scanning electron microscopy, and cyclic voltammetry with both anionic and cationic redox systems (dopamine, ferrocene carboxylic acid). First time experiments at the heated SWCNT electrodes demonstrated an excellent suitability of these as-prepared electrodes for thermoelectrochemical studies.

First-principles study of the switching characteristics of the 15,16-dinitrile DDP/CPD-based optical molecular switch with carbon nanotube electrodes

We have studied the switching characteristics of an optical molecular switch based on the 15,16-dinitrile dihydropyrene/cyclophanediene (DDP/CPD) molecule with two single-walled carbon nanotube (SWCNT) electrodes using first-principles transport calculations. It is shown that the DDP shows an overall higher conductance than the CPD at low bias which is independently of the SWCNT chirality. Meantime, the conductance of the molecular switch can be tuned by the chirality of the SWCNT.

Photoresponsive nanoscale columnar transistors.

This study reports a general methodology for making stable high-performance photosensitive field effect transistors (FET) from self-assembled columns of polycyclic aromatic hydrocarbons by using single-walled carbon nanotubes (SWNTs) as point contacts. In particular, the molecules used in this work are liquid crystalline materials of tetra(dodecyloxy)hexabenzocoronenes (HBCs) that are able to self-organize into columnar nanostructures with a diameter similar to that of SWNTs and then form nanoscale columnar transistors. To rule out potential artifacts, 2 different structural approaches were used to construct devices. One approach is to coat thin films of HBCs onto the devices with the SWNT-metal junctions protected by hydrogensilsesquioxane resin (HSQ), and the other is to place a droplet of HBC exactly on the nanogaps of SWNT electrodes. Both types of devices showed typical FET behaviors, indicating that SWNT-molecule-SWNT nanojunctions are responsible for the electrical characteristics of the devices. After thermally annealing the devices, HBC molecules assembled into columnar structures and formed more efficacious transistors with increased current modulation and higher gate efficiency. More interestingly, when the devices were exposed to visible light, photocurrents with an on/off ratio of >3 orders of magnitude were observed. This study demonstrates that stimuli-responsive nanoscale transistors have the potential applications in ultrasensitive devices for environmental sensing and solar energy harvesting.

Specific contact resistance at metal/carbon nanotube interfaces

In this report, the specific contact resistance between a thin film single wall carbon nanotube electrode and a deposited silver contact was measured. The specific contact resistance was found to be 20 mΩ cm2, which is an order of magnitude higher than typically observed in standard Si photovoltaic technology. We demonstrate that when utilized as the transparent anode in organic photovoltaics, the specific contact resistance has the potential to induce non-negligible resistive power losses. Thus, specific contact resistance will adversely affect the performance of these systems and should therefore be addressed.

Formation of a solid electrolyte interface on single wall carbon nanotube electrodes in lithium ion batteries

Formation of a solid electrolyte interface on single wall carbon nanotube electrodes in lithium ion batteries

Flexible and Transparent SWCNT Electrodes for Alternating Current Electroluminescence (ACEL) Devices

AbstractThe application of transparent single-walled carbon nanotube (SWCNT) electrodes in rigid and flexible alternating current electroluminescence (ACEL) devices is demonstrated. SWCNT thin film electrodes (50 – 160 nm) were made using a spray-coating process suitable for adjusting transparency and sheet resistance. The emission intensity was as high as for indium tin oxide (ITO) based ACEL devices with transparencies comparable to ITO coated polymer slides.

All‐organic actuator fabricated with single wall carbon nanotube electrodes

AbstractCompliant electrodes to replace conventional metal electrodes have been required for many actuators to relieve the constraint on the electroactive layer. Many conducting polymers have been proposed for the alternative electrodes, but they still have a problem of poor thermal stability. This article reports a novel all‐ organic actuator with single wall carbon nanotube (SWCNT) films as an alternative electrode. The SWCNT film was obtained by filtering a SWCNT solution through an anodized alumina membrane. The conductivity of the SWCNT film was about 280 S/cm. The performance of the SWCNT film electrode was characterized by measuring the dielectric properties of NASA Langley Research Center – Electroactive Polymer (LaRC‐EAP) sandwiched by the SWCNT electrodes over a broad range of temperature (from 25 to 280 °C) and frequency (from 1 kHz to 1 MHz). The all‐organic actuator with the SWCNT electrodes showed a larger electric field‐induced strain than that with metal electrodes, under identical measurement conditions. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2532–2538, 2008

First-principles study of the switching characteristics of the phenoxynaphthacenequinone-based optical molecular switch with carbon nanotube electrodes

We have studied the switching characteristics of an optical molecular switch based on the phenoxynaphthacenequinone (PNQN) molecule with two armchair single-walled carbon nanotube (SWCNT) electrodes using the first-principles density functional-based non-equilibrium Green's function (DFT-NEGF) method. It is shown that a maximum on–off ratio (about 120) can be obtained at 0.9 V. Our result shows that the PNQN molecule is one of the good candidates for optical molecular switches and the SWCNTs are promising electrode materials and will be useful in the near future.

Molecular Electronic Devices Based on Single-Walled Carbon Nanotube Electrodes

As the top-down fabrication techniques for silicon-based electronic materials have reached the scale of molecular lengths, researchers have been investigating nanostructured materials to build electronics from individual molecules. Researchers have directed extensive experimental and theoretical efforts toward building functional optoelectronic devices using individual organic molecules and fabricating metal-molecule junctions. Although this method has many advantages, its limitations lead to large disagreement between experimental and theoretical results. This Account describes a new method to create molecular electronic devices, covalently bridging a gap in a single-walled carbon nanotube (SWNT) with an electrically functional molecule. First, we introduce a molecular-scale gap into a nanotube by precise oxidative cutting through a lithographic mask. Now functionalized with carboxylic acids, the ends of the cleaved carbon nanotubes are reconnected with conjugated diamines to give robust diamides. The molecular electronic devices prepared in this fashion can withstand and respond to large environmental changes based on the functional groups in the molecules. For example, with oligoanilines as the molecular bridge, the conductance of the device is sensitive to pH. Similarly, using diarylethylenes as the bridge provides devices that can reversibly switch between conjugated and nonconjugated states. The molecular bridge can perform the dual task of carrying electrical current and sensing/recognition through biological events such as protein/substrate binding and DNA hybridization. The devices based on DNA can measure the difference in electrical properties of complementary and mismatched strands. A well-matched duplex DNA 15-mer in the gap exhibits a 300-fold lower resistance than a duplex with a GT or CA mismatch. This system provides an ultrasensitive way to detect single-nucleotide polymorphisms at the individual molecule level. Restriction enzymes can cleave certain cDNA strands assembled between the SWNT electrodes; therefore, these strands maintain their native conformation when bridging the ends of the SWNTs. This methodology for creating novel molecular circuits forges both literal and figurative connections between chemistry, physics, materials science, and biology and promises a new generation of integrated multifunctional sensors and devices.

Electrochemical doping of single-walled carbon nanotubes in double layer capacitors studied by in situ Raman spectroscopy

The electrochemical doping of single-walled carbon nanotubes (SWCNTs) in 1 M Et 4NBF 4 in acetonitrile was investigated by in situ Raman spectroscopy. The capacitance was determined to be 82 F/g for the positive and 71 F/g for the negative SWCNT electrode, respectively, which approaches the typical values for microporous activated carbons used in supercapacitors. The changes in the Raman intensities and shifts of the D and G + bands as well as of the radial breathing modes (RBMs) during electron and hole injection were studied as a function of the electrode potential. For the D and G + bands, hole doping leads to strong upshifts which can be attributed to a stiffening of C–C bonds and the corresponding phonon modes. Electron doping results in much less pronounced changes in the band positions. The intensity attenuation of the RBM bands was found to be markedly different for semi-conducting and metallic SWCNTs, whereby sufficiently high doping leads to a loss of Raman intensity due to bleaching of electronic transitions. The main RBM bands upshift upon both electron and hole doping, which is attributed to changes in the chemical environment of individual SWCNTs upon charging and discharging of the electrochemical double layer within SWCNT bundles.

The role of electrical and thermal contact resistance for Joule breakdown of single-wallcarbon nanotubes

Several data sets for the electrical breakdown in air of single-wall carbon nanotubes(SWNTs) on insulating substrates are collected and analyzed. A universal scaling of theJoule breakdown power with nanotube length is found, which appears to be independent ofthe substrate thermal properties of their thickness. This suggests that the thermalresistances at SWNT–insulator and at SWNT–electrode interfaces govern heatsinking from the nanotube. Analytical models for the breakdown power scalingare presented, providing an intuitive, physical understanding of the breakdownprocess. The electrical and thermal resistances at the electrode contacts limit thebreakdown behavior for sub-micron SWNTs; the breakdown power scales linearlywith length for tubes that are microns long, and a minimum breakdown power(∼0.05 mW) is observed forthe intermediate (∼0.5 µm) length range.

Polymyxin-Coated Au and Carbon Nanotube Electrodes for Stable [NiFe]-Hydrogenase Film Voltammetry

We report on the use of polymyxin (PM), a cyclic cationic lipodecapeptide, as an electrode modifier for studying protein film voltammetry (PFV) on Au and single-walled carbon nanotube (SWNT) electrodes. Pretreating the electrodes with PM allows for the subsequent immobilization of an active submonolayer of [NiFe]-hydrogenase from Allochromatium vinosum ( Av H2ase). Probed by cyclic voltammetry (CV), the adsorbed enzyme exhibits characteristic electrocatalytic behavior that is stable for several hours under continuous potential cycling. An unexpected feature of the immobilization procedure is that the presence of chloride ions is a prerequisite for obtaining electrocatalytic activity. Atomic force microscopy (AFM) relates the observed catalytic activity to enzymatic adsorption at the PM/Au(111) surface, and a combination of concentration-dependent CV and AFM is used to investigate the interaction between the enzyme and the PM layer.

Lithium Ion Capacity of Single Wall Carbon Nanotube Paper Electrodes

The electrochemical cycling performance of high purity single wall carbon nanotube (SWCNT) paper electrodes has been measured vs lithium metal for a series of electrolyte solvent compositions. The addition of propylene carbonate (PC) into the conventional ethylene carbonate (EC):dimethyl carbonate (DMC) cosolvent mixture enabled a reversible lithium ion capacity of 520 mAh/g for high purity SWCNTs. The free-standing SWCNT electrode (absent of polymer binder or metal substrate support) with this electrolyte combination demonstrates enhanced cycleability, retaining >95% of the initial capacity after 10 cycles. The first cycle hysteresis, common in these materials, is shown to vary dramatically with solvent selection and illustrates the importance of the solid−electrolyte−interface (SEI) formation on SWCNT capacity. The effect of galvanostatic charge rate (i.e., C-rate) on lithium ion capacity shows a 2× improvement [in capacity per current] over reported values for conventional graphite anode materials. The...

Modification of single-walled carbon nanotube electrodes by layer-by-layer assembly for electrochromic devices

We have studied the morphological properties and electrochromic (EC) performance of polythiophene multilayer films on single wall carbon nanotube (SWCNT) conductive electrodes. The morphology for different numbers of layer-by-layer (LbL) bilayer on the SWCNT electrode has been characterized with atomic force microscopy and scanning electron microscope, and it was found that the LbL multilayers significantly decrease the surface roughness of the nanoporous nanotube films. The controlled surface roughness of transparent nanotube electrodes could be beneficial for their device applications. We have also fabricated EC devices with LbL films of poly[2-(3-thienyl) ethoxy-4-butylsulfonate∕poly(allylamine hydrochloride) on SWCNT electrodes, which not only have high EC contrast but also sustain higher applied voltage without showing any degradation for more than 20000cycles, which is not possible in the case of indium tin oxide electrodes. Cyclic voltammetry of the LbL films formed on SWCNT shows higher current at low potential, revealing the feasibility of SWCNT electrode as a good host for electrolyte ion insertion.

Conductivity of a single DNA duplex bridging a carbon nanotube gap

We describe a general method to integrate DNA strands between single-walled carbon nanotube electrodes and to measure their electrical properties. We modified DNA sequences with amines on either the 5' terminus or both the 3' and 5' termini and coupled these to the single-walled carbon nanotube electrodes through amide linkages, enabling the electrical properties of complementary and mismatched strands to be measured. Well-matched duplex DNA in the gap between the electrodes exhibits a resistance on the order of 1 M(Omega). A single GT or CA mismatch in a DNA 15-mer increases the resistance of the duplex approximately 300-fold relative to a well-matched one. Certain DNA sequences oriented within this gap are substrates for Alu I, a blunt end restriction enzyme. This enzyme cuts the DNA and eliminates the conductive path, supporting the supposition that the DNA is in its native conformation when bridging the ends of the single-walled carbon nanotubes.

Lithium Ions Intercalated into Pyrene-Functionalized Carbon Nanotubes and Their Mass Transport: A Chemical Route to Carbon Nanotube Schottky Diode

We developed a facile chemical route by which single-walled carbon nanotube (SWNT) Schottky diodes are realized. When a bias voltage was applied to a lithium ion intercalated SWNT field effect transistor (FET) device, lithium ions intercalated between 1-pyrenmethylamine (1-PMA), and SWNTs are migrated to the drain (−) electrode to be reduced at the junction of SWNT and drain metal electrode. As a result, asymmetric work function energy levels are formed between both junctions of SWNT−drain and SWNT−source, resulting in a Schottky diode. Using scanning photoelectron microscopy (SPEM) and space-resolved X-ray photoelectron spectroscopy (XPS), the mass transport of the lithium ion was qualitatively confirmed by monitoring the population distribution of lithium along the nanotube axis from the source to drain electrodes. The highest population of lithium was observed near the drain electrode. This approach is a simple and versatile process that can be further applied for the modifications of various nanomaterial-based electronic devices.

Fault‐Tolerant Dielectric Elastomer Actuators using Single‐Walled Carbon Nanotube Electrodes

Certain dielectric elastomers such as the 3M VHB 4910 acrylic adhesive films have exhibited electrically induced strains as high as 380 % in area expansion. The calculated maximum specific energy density of 3.4 J g and maximum stress of 8 MPa are attractive for a wide range of applications including robotics, prosthetic devices, medical implants, pumps, and valves. However, the performance of actuators based on the VHB films is substantially lower than the calculated values which reflect the maximum intrinsic material properties. Defects in the soft dielectric films, such as gel particles, uneven thickness, non-uniform crosslinking, and stress concentration, are possible causes for the reduced actuator performance. They also reduce the actuator reliability, hindering technology commercialization. We introduce self-clearable compliant electrode materials that could enhance the fault-tolerance of the dielectric elastomers actuators. Thin metallic layers (10–100 nm) are being used for polypropylene thin-film capacitors for fault-tolerance. The electrode materials locally evaporate, or self-clear, around defects during highvoltage breakdown. Metallic films are not sufficiently compliant for the dielectric elastomers. To enhance the compliancy of metallic electrodes, zig-zag shaped metallic lines were used to obtain 80 % area strains. Uniform metallic coatings on corrugated silicone elastomer surfaces supported linear strains up to 33 %. The commonly used compliant electrode materials for the VHB elastomers are powdered carbon graphite, carbon black, or carbon fibrils dispersed in grease or silicon oil, and electrolyte solutions. No self-clearing has been reported for these electrode materials. Our experiments showed that single-walled carbon nanotubes (SWNTs) can overcome this morass. The SWNT electrodes have exhibited flexibility as transparent electrodes in lightemitting diodes, solar cells, and thin-film transistors. With thin SWNT electrodes, the dielectric elastomer can not only be strained larger than 200 % in area expansion, but can achieve fault-tolerance through localized degradation of SWNTs. Figure 1 shows a 300 % biaxially prestrained VHB 4910 film (62 lm thick after prestrain) with the SWNT electrodes at rest (Fig. 1a) and during actuation at 5 kV (Fig. 1b). The calculated strain is 200 %. This value is comparable with the same film using conventional carbon grease electrodes. The observed strain for 300 % biaxially prestrained VHB 4905 films (31 lm thick after prestrain) was 190 % at 3.5 kV.