Showing papers on "Carbon nanotube published in 2003"
TL;DR: It is shown that contacting semiconducting single-walled nanotubes by palladium, a noble metal with high work function and good wetting interactions with nanotube, greatly reduces or eliminates the barriers for transport through the valence band of nanot tubes.
Abstract: A common feature of the single-walled carbon-nanotube field-effect transistors fabricated to date has been the presence of a Schottky barrier at the nanotube–metal junctions1,2,3. These energy barriers severely limit transistor conductance in the ‘ON’ state, and reduce the current delivery capability—a key determinant of device performance. Here we show that contacting semiconducting single-walled nanotubes by palladium, a noble metal with high work function and good wetting interactions with nanotubes, greatly reduces or eliminates the barriers for transport through the valence band of nanotubes. In situ modification of the electrode work function by hydrogen is carried out to shed light on the nature of the contacts. With Pd contacts, the ‘ON’ states of semiconducting nanotubes can behave like ohmically contacted ballistic metallic tubes, exhibiting room-temperature conductance near the ballistic transport limit of 4e2/h (refs 4–6), high current-carrying capability (∼25 µA per tube), and Fabry–Perot interferences5 at low temperatures. Under high voltage operation, the current saturation appears to be set by backscattering of the charge carriers by optical phonons. High-performance ballistic nanotube field-effect transistors with zero or slightly negative Schottky barriers are thus realized.
3,126 citations
TL;DR: A review of the literature on thermal transport in nanoscale devices can be found in this article, where the authors highlight the recent developments in experiment, theory and computation that have occurred in the past ten years and summarizes the present status of the field.
Abstract: Rapid progress in the synthesis and processing of materials with structure on nanometer length scales has created a demand for greater scientific understanding of thermal transport in nanoscale devices, individual nanostructures, and nanostructured materials. This review emphasizes developments in experiment, theory, and computation that have occurred in the past ten years and summarizes the present status of the field. Interfaces between materials become increasingly important on small length scales. The thermal conductance of many solid–solid interfaces have been studied experimentally but the range of observed interface properties is much smaller than predicted by simple theory. Classical molecular dynamics simulations are emerging as a powerful tool for calculations of thermal conductance and phonon scattering, and may provide for a lively interplay of experiment and theory in the near term. Fundamental issues remain concerning the correct definitions of temperature in nonequilibrium nanoscale systems. Modern Si microelectronics are now firmly in the nanoscale regime—experiments have demonstrated that the close proximity of interfaces and the extremely small volume of heat dissipation strongly modifies thermal transport, thereby aggravating problems of thermal management. Microelectronic devices are too large to yield to atomic-level simulation in the foreseeable future and, therefore, calculations of thermal transport must rely on solutions of the Boltzmann transport equation; microscopic phonon scattering rates needed for predictive models are, even for Si, poorly known. Low-dimensional nanostructures, such as carbon nanotubes, are predicted to have novel transport properties; the first quantitative experiments of the thermal conductivity of nanotubes have recently been achieved using microfabricated measurement systems. Nanoscale porosity decreases the permittivity of amorphous dielectrics but porosity also strongly decreases the thermal conductivity. The promise of improved thermoelectric materials and problems of thermal management of optoelectronic devices have stimulated extensive studies of semiconductor superlattices; agreement between experiment and theory is generally poor. Advances in measurement methods, e.g., the 3ω method, time-domain thermoreflectance, sources of coherent phonons, microfabricated test structures, and the scanning thermal microscope, are enabling new capabilities for nanoscale thermal metrology.
2,933 citations
TL;DR: It is demonstrated that DNA-coated carbon nanotubes can be separated into fractions with different electronic structures by ion-exchange chromatography, and opens the door to carbon-nanotube-based applications in biotechnology.
Abstract: Carbon nanotubes are man-made one-dimensional carbon crystals with different diameters and chiralities. Owing to their superb mechanical and electrical properties, many potential applications have been proposed for them. However, polydispersity and poor solubility in both aqueous and non-aqueous solution impose a considerable challenge for their separation and assembly, which is required for many applications. Here we report our finding of DNA-assisted dispersion and separation of carbon nanotubes. Bundled single-walled carbon nanotubes are effectively dispersed in water by their sonication in the presence of single-stranded DNA (ssDNA). Optical absorption and fluorescence spectroscopy and atomic force microscopy measurements provide evidence for individually dispersed carbon nanotubes. Molecular modelling suggests that ssDNA can bind to carbon nanotubes through pi-stacking, resulting in helical wrapping to the surface. The binding free energy of ssDNA to carbon nanotubes rivals that of two nanotubes for each other. We also demonstrate that DNA-coated carbon nanotubes can be separated into fractions with different electronic structures by ion-exchange chromatography. This finding links one of the central molecules in biology to a technologically very important nanomaterial, and opens the door to carbon-nanotube-based applications in biotechnology.
2,620 citations
TL;DR: Results show that, for the test conditions described here and on an equal-weight basis, if carbon nanotubes reach the lungs, they are much more toxic than carbon black and can be more Toxic than quartz, which is considered a serious occupational health hazard in chronic inhalation exposures.
1,954 citations
TL;DR: In this article, a simple process to solubilize high weight fraction single-wall carbon nanotubes in water by nonspecific physical adsorption of sodium dodecylbenzene sulfonate was reported.
Abstract: We report a simple process to solubilize high weight fraction single-wall carbon nanotubes in water by the nonspecific physical adsorption of sodium dodecylbenzene sulfonate. The diameter distribution of nanotubes in the dispersion, measured by atomic force microscopy, showed that even at 20 mg/mL ∼63 ± 5% of single-wall carbon nanotube bundles exfoliated into single tubes. A measure of the length distribution of the nanotubes showed that our dispersion technique reduced nanotube fragmentation.
1,829 citations
TL;DR: In this article, the use of carbon nanotubes (CNT) and nanofibers as catalysts and catalysts supports has been analyzed from the early 1990s until the beginning of 2003.
Abstract: This review analyses the literature from the early 1990s until the beginning of 2003 and covers the use of carbon nanotubes (CNT) and nanofibers as catalysts and catalysts supports. The article is composed of three sections, the first one explains why these materials can be suitable for these applications, the second describes the different preparation methods for supporting metallic catalysts on these supports, and the last one details the catalytic results obtained with nanotubes or nanofibers based catalysts. When possible, the results were compared to those obtained on classical carbonaceous supports and explanations are proposed to clarify the different behaviors observed.
1,742 citations
TL;DR: In this article, individual single-walled carbon nanotubes (SWNTs) have been suspended in aqueous media using various anionic, cationic, nonionic surfactants and polymers.
Abstract: Individual single-walled carbon nanotubes (SWNTs) have been suspended in aqueous media using various anionic, cationic, nonionic surfactants and polymers. The surfactants are compared with respect to their ability to suspend individual SWNTs and the quality of the absorption and fluorescence spectra. For the ionic surfactants, sodium dodecylbenzene sulfonate (SDBS) gives the most well resolved spectral features. For the nonionic systems, surfactants with higher molecular weight suspend more SWNT material and have more pronounced spectral features.
1,682 citations
TL;DR: A gas sensor fabricated by the simple casting of single-walled carbon nanotubes (SWNTs) on an interdigitated electrode (IDE) is presented for gas and organic vapor detection at room temperature.
Abstract: A gas sensor, fabricated by the simple casting of single-walled carbon nanotubes (SWNTs) on an interdigitated electrode (IDE), is presented for gas and organic vapor detection at room temperature. The sensor responses are linear for concentrations of sub ppm to hundreds of ppm with detection limits of 44 ppb for NO2 and 262 ppb for nitrotoluene. The time is on the order of seconds for the detection response and minutes for the recovery. The variation of the sensitivity is less than 6% for all of the tested devices, comparable with commercial metal oxide or polymer microfilm sensors while retaining the room-temperature high sensitivity of the SWNT transistor sensors and manufacturability of the commercial sensors. The extended detection capability from gas to organic vapors is attributed to direct charge transfer on individual semiconducting SWNT conductivity with additional electron hopping effects on intertube conductivity through physically adsorbed molecules between SWNTs.
1,648 citations
TL;DR: The experimental percolation threshold for the aligned carbon nanotubes used in this paper represents the lowest threshold observed for carbon-nanotube-based polymer composites yet reported.
1,646 citations
TL;DR: This work has developed a method to separate metallic from semiconducting single-walled carbon nanotubes from suspension using alternating current dielectrophoresis, taking advantage of the difference of the relative dielectric constants of the two species with respect to the solvent.
Abstract: We have developed a method to separate metallic from semiconducting single-walled carbon nanotubes from suspension using alternating current dielectrophoresis. Our method takes advantage of the difference of the relative dielectric constants of the two species with respect to the solvent, resulting in an opposite movement of metallic and semiconducting tubes along the electric field gradient. Metallic tubes are attracted toward a microelectrode array, leaving semiconducting tubes in the solvent. Proof of the effectiveness of separation is given by a comparative Raman spectroscopy study on the dielectrophoretically deposited tubes and on a reference sample.
1,592 citations
TL;DR: In this paper, the creation of a stable, superhydrophobic surface using the nanoscale roughness inherent in a vertically aligned carbon nanotube forest together with a thin conformal hydrophobic poly(tetrafluoroethylene) (PTFE) coating on the surface of the nanotubes was demonstrated.
Abstract: The present study demonstrates the creation of a stable, superhydrophobic surface using the nanoscale roughness inherent in a vertically aligned carbon nanotube forest together with a thin, conformal hydrophobic poly(tetrafluoroethylene) (PTFE) coating on the surface of the nanotubes. Superhydrophobicity is achieved down to the microscopic level where essentially spherical, micrometer-sized water droplets can be suspended on top of the nanotube forest.
TL;DR: A systematic search of the ssDNA library selected a sequence d(GT)n, n = 10 to 45 that self-assembles into a helical structure around individual nanotubes in such a way that the electrostatics of the DNA-CNT hybrid depends on tube diameter and electronic properties, enabling nanotube separation by anion exchange chromatography.
Abstract: Wrapping of carbon nanotubes (CNTs) by single-stranded DNA (ssDNA) was found to be sequence-dependent. A systematic search of the ssDNA library selected a sequence d(GT)n, n = 10 to 45 that self-assembles into a helical structure around individual nanotubes in such a way that the electrostatics of the DNA-CNT hybrid depends on tube diameter and electronic properties, enabling nanotube separation by anion exchange chromatography. Optical absorption and Raman spectroscopy show that early fractions are enriched in the smaller diameter and metallic tubes, whereas late fractions are enriched in the larger diameter and semiconducting tubes.
TL;DR: An exploration of single-walled carbon nanotubes is presented as a platform for investigating surface–protein and protein–protein binding and developing highly specific electronic biomolecule detectors for detecting clinically important biomolecules such as antibodies associated with human autoimmune diseases.
Abstract: Novel nanomaterials for bioassay applications represent a rapidly progressing field of nanotechnology and nanobiotechnology. Here, we present an exploration of single-walled carbon nanotubes as a platform for investigating surface-protein and protein-protein binding and developing highly specific electronic biomolecule detectors. Nonspecific binding on nanotubes, a phenomenon found with a wide range of proteins, is overcome by immobilization of polyethylene oxide chains. A general approach is then advanced to enable the selective recognition and binding of target proteins by conjugation of their specific receptors to polyethylene oxide-functionalized nanotubes. This scheme, combined with the sensitivity of nanotube electronic devices, enables highly specific electronic sensors for detecting clinically important biomolecules such as antibodies associated with human autoimmune diseases.
TL;DR: Diazonium reagents functionalize single-walled carbon nanotubes suspended in aqueous solution with high selectivity and enable manipulation according to electronic structure to reverse the chemistry by using a thermal treatment that restores the pristine electronic structure of the nanotube.
Abstract: Diazonium reagents functionalize single-walled carbon nanotubes suspended in aqueous solution with high selectivity and enable manipulation according to electronic structure. For example, metallic species are shown to react to the near exclusion of semiconducting nanotubes under controlled conditions. Selectivity is dictated by the availability of electrons near the Fermi level to stabilize a charge-transfer transition state preceding bond formation. The chemistry can be reversed by using a thermal treatment that restores the pristine electronic structure of the nanotube.
TL;DR: In this article, a new synthesis route to high-quality large mesoporous cubic Ia3d silica is reported, utilizing a triblock copolymer (EO20PO70EO20) mixture for the structure direction in aqueous solution.
TL;DR: In this article, a structural mechanics approach to modeling the deformation of carbon nanotubes is presented, where the primary bonds between two nearest-neighboring atoms act like loadbearing beam members, whereas an individual atom acts as the joint of the related beam members.
TL;DR: The use of a polymerizable ionic liquid as the gelling medium allows for the fabrication of a highly electroconductive polymer/nanotube composite material, which showed a substantial enhancement in dynamic hardness.
Abstract: When mixed with imidazolium ion-based room-temperature ionic liquid, pristine single-walled carbon nanotubes formed gels after being ground. The heavily entangled nanotube bundles were found to untangle within the gel to form much finer bundles. Phase transition and rheological properties suggest that the gels are formed by physical cross-linking of the nanotube bundles, mediated by local molecular ordering of the ionic liquids rather than by entanglement of the nanotubes. The gels were thermally stable and did not shrivel, even under reduced pressure resulting from the nonvolatility of the ionic liquids, but they would readily undergo a gel-to-solid transition on absorbent materials. The use of a polymerizable ionic liquid as the gelling medium allows for the fabrication of a highly electroconductive polymer/nanotube composite material, which showed a substantial enhancement in dynamic hardness.
TL;DR: This first demonstration of nanotube-based biosensors provides a new tool for enzymatic studies and opens the way to biomolecular diagnostics.
Abstract: We demonstrate the use of individual semiconducting single-wall carbon nanotubes as versatile biosensors. Controlled attachment of the redox enzyme glucose oxidase (GOx) to the nanotube sidewall is achieved through a linking molecule and is found to induce a clear change of the conductance. The enzyme-coated tube is found to act as a pH sensor with large and reversible changes in conductance upon changes in pH. Upon addition of glucose, the substrate of GOx, a steplike response can be monitored in real time, indicating that our sensor is also capable of measuring enzymatic activity at the level of a single nanotube. This first demonstration of nanotube-based biosensors provides a new tool for enzymatic studies and opens the way to biomolecular diagnostics.
TL;DR: Investigation of adverse effects of single-wall carbon nanotubes using a cell culture of immortalized human epidermal keratinocytes indicates that dermal exposure to unrefined SWCNT may lead to dermal toxicity due to accelerated oxidative stress in the skin of exposed workers.
Abstract: Carbon nanotubes are new members of carbon allotropes similar to fullerenes and graphite. Because of their unique electrical, mechanical, and thermal properties, carbon nanotubes are important for novel applications in the electronics, aerospace, and computer industries. Exposure to graphite and carbon materials has been associated with increased incidence of skin diseases, such as carbon fiber dermatitis, hyperkeratosis, and naevi. We investigated adverse effects of single-wall carbon nanotubes (SWCNT) using a cell culture of immortalized human epidermal keratinocytes (HaCaT). After 18 h of exposure of HaCaT to SWCNT, oxidative stress and cellular toxicity were indicated by formation of free radicals, accumulation of peroxidative products, antioxidant depletion, and loss of cell viability. Exposure to SWCNT also resulted in ultrastructural and morphological changes in cultured skin cells. These data indicate that dermal exposure to unrefined SWCNT may lead to dermal toxicity due to accelerated oxidative stress in the skin of exposed workers.
TL;DR: An ‘epitaxial casting’ approach for the synthesis of single-crystal GaN nanotubes with inner diameters of 30–200 nm and wall thicknesses of 5–50nm is reported, applicable to many other semiconductor systems.
Abstract: Since the discovery of carbon nanotubes in 1991 (ref. 1), there have been significant research efforts to synthesize nanometre-scale tubular forms of various solids. The formation of tubular nanostructure generally requires a layered or anisotropic crystal structure. There are reports of nanotubes made from silica, alumina, silicon and metals that do not have a layered crystal structure; they are synthesized by using carbon nanotubes and porous membranes as templates, or by thin-film rolling. These nanotubes, however, are either amorphous, polycrystalline or exist only in ultrahigh vacuum. The growth of single-crystal semiconductor hollow nanotubes would be advantageous in potential nanoscale electronics, optoelectronics and biochemical-sensing applications. Here we report an 'epitaxial casting' approach for the synthesis of single-crystal GaN nanotubes with inner diameters of 30-200 nm and wall thicknesses of 5-50 nm. Hexagonal ZnO nanowires were used as templates for the epitaxial overgrowth of thin GaN layers in a chemical vapour deposition system. The ZnO nanowire templates were subsequently removed by thermal reduction and evaporation, resulting in ordered arrays of GaN nanotubes on the substrates. This templating process should be applicable to many other semiconductor systems.
TL;DR: In this paper, a linear relationship between the contact angle and the water monomer binding energy on graphite was established and a new route to calibrate interaction potential parameters was presented, which was obtained by applying a carbon−oxygen Lennard-Jones potential with parameters eCO = 0.392 kJ mol-1 and σCO = 3.19 A.
Abstract: A systematic molecular dynamics study shows that the contact angle of a water droplet on graphite changes significantly as a function of the water−carbon interaction energy. Together with the observation that a linear relationship can be established between the contact angle and the water monomer binding energy on graphite, a new route to calibrate interaction potential parameters is presented. Through a variation of the droplet size in the range from 1000 to 17 500 water molecules, we determine the line tension to be positive and on the order of 2 × 10-10 J/m. To recover a macroscopic contact angle of 86°, a water monomer binding energy of −6.33 kJ mol-1 is required, which is obtained by applying a carbon−oxygen Lennard-Jones potential with the parameters eCO = 0.392 kJ mol-1 and σCO = 3.19 A. For this new water−carbon interaction potential, we present density profiles and hydrogen bond distributions for a water droplet on graphite.
TL;DR: In this article, the effect of chemical oxidation on the structure of single-walled carbon nanotubes (SWNTs) by using different oxidants was investigated using infrared spectroscopy and transmission electron microscopy (TEM).
Abstract: In the present study, we report the systematic investigation of the effect of chemical oxidation on the structure of single-walled carbon nanotubes (SWNTs) by using different oxidants. The oxidation procedure was characterized by using infrared spectroscopy and transmission electron microscopy (TEM). The SWNTs were produced by chemical vapor deposition (CVD) and oxidized with three kinds of oxidants: (1) nitric acid (2.6 M), (2) a mixture of concentrated sulfuric acid (98 wt %) and concentrated nitric acid (16 M) (v/v = 3/1) and (3) KMnO4. The results reveal that the different functional groups can be introduced when the SWNTs are treated with different oxidants. Refluxing in dilute nitric acid can be considered as a mild oxidation for SWNTs, introducing the carboxylic acid groups only at those initial defects that already exist. The abundance of the carboxylic acid groups generated with this oxidant remained constant along with the treating time. In contrast, sonication of SWNTs in H2SO4/HNO3 increased ...
TL;DR: In this article, the first model-independent prediction of first and second van Hove optical transitions as a function of structure for a wide range of semiconducting nanotubes is presented in equation, graphical and tabular forms.
Abstract: Spectrofluorimetric data for identified single-walled carbon nanotubes in aqueous SDS suspension have been accurately fit to empirical expressions. These are used to obtain the first model-independent prediction of first and second van Hove optical transitions as a function of structure for a wide range of semiconducting nanotubes. To allow for convenient use in support of spectral studies, the results are presented in equation, graphical, and tabular forms. These empirical findings differ significantly from Kataura plots computed using a simple tight-binding model. It is suggested that the empirically based results should be used in preference to conventional model-based predictions in spectroscopic nanotube research.
TL;DR: These findings indicate that heat transport in a nanotube composite material will be limited by the exceptionally small interface thermal conductance and that the thermal conductivity of the composite will be much lower than the value estimated from the intrinsic thermal conductivities of the nanotubes and their volume fraction.
Abstract: The enormous amount of basic research into carbon nanotubes has sparked interest in the potential applications of these novel materials. One promising use of carbon nanotubes is as fillers in a composite material to improve mechanical behaviour, electrical transport and thermal transport. For composite materials with high thermal conductivity, the thermal conductance across the nanotube-matrix interface is of particular interest. Here we use picosecond transient absorption to measure the interface thermal conductance (G) of carbon nanotubes suspended in surfactant micelles in water. Classical molecular dynamics simulations of heat transfer from a carbon nanotube to a model hydrocarbon liquid are in agreement with experiment. Our findings indicate that heat transport in a nanotube composite material will be limited by the exceptionally small interface thermal conductance (G approximately 12 MW m(-2) K(-1)) and that the thermal conductivity of the composite will be much lower than the value estimated from the intrinsic thermal conductivity of the nanotubes and their volume fraction.
TL;DR: In this paper, a polyethyleneimine coating is applied to nanotubes for detecting NO2 at less than 1 ppb (parts-per-billion) concentrations while being insensitive to NH3.
Abstract: Arrays of electrical devices with each comprising multiple single-walled carbon nanotubes (SWNT) bridging metal electrodes are obtained by chemical vapor deposition (CVD) of nanotubes across prefabricated electrode arrays. The ensemble of nanotubes in such a device collectively exhibits large electrical conductance changes under electrostatic gating, owing to the high percentage of semiconducting nanotubes. This leads to the fabrication of large arrays of low-noise electrical nanotube sensors with 100% yield for detecting gas molecules. Polymer functionalization is used to impart high sensitivity and selectivity to the sensors. Polyethyleneimine coating affords n-type nanotube devices capable of detecting NO2 at less than 1 ppb (parts-per-billion) concentrations while being insensitive to NH3. Coating Nafion (a polymeric perfluorinated sulfonic acid ionomer) on nanotubes blocks NO2 and allows for selective sensing of NH3. Multiplex functionalization of a nanotube sensor array is carried out by microspotti...
TL;DR: In this paper, the basic concepts and characteristics of Raman spectra from carbon nanotubes (both isolated and bundled) are presented, with the focus directed toward their use for carbon Nanotube characterization.
Abstract: The basic concepts and characteristics of Raman spectra from carbon nanotubes (both isolated and bundled) are presented. The general characteristics of the radial breathing mode, tangential mode (G band), disorder-induced mode (D-band) and other Raman features are presented, with the focus directed toward their use for carbon nanotube characterization. Polarization analysis, surface enhanced Raman spectroscopy and complementary optical techniques are also discussed in terms of their advantages and limitations.
TL;DR: In this paper, it was shown that the transistors exhibit hysteresis in their electrical characteristics because of charge trapping by water molecules around the nanotubes, including SiO2 surface-bound water proximal to the nanotsubes.
Abstract: Carbon nanotube field-effect transistors commonly comprise nanotubes lying on SiO2 surfaces exposed to the ambient environment. It is shown here that the transistors exhibit hysteresis in their electrical characteristics because of charge trapping by water molecules around the nanotubes, including SiO2 surface-bound water proximal to the nanotubes. Hysteresis persists for the transistors in vacuum since the SiO2-bound water does not completely desorb in vacuum at room temperature, a known phenomenon in SiO2 surface chemistry. Heating under dry conditions significantly removes water and reduces hysteresis in the transistors. Nearly hysteresis-free transistors are obtainable by passivating the devices with polymers that hydrogen bond with silanol groups on SiO2 (e.g., with poly(methyl methacrylate) (PMMA)). However, nanotube humidity sensors could be explored with suitable water-sensitive coatings. The results may have implications to field-effect transistors made from other chemically derived materials.
TL;DR: This work fabricated fully dense nanocomposites of single-wall carbon nanotubes with nanocrystalline alumina (Al2O3) matrix at sintering temperatures as low as 1,150 °C by spark-plasma sintered, demonstrating their potential use in reinforcing nanocrystaline ceramics.
Abstract: The extraordinary mechanical, thermal and electrical properties of carbon nanotubes have prompted intense research into a wide range of applications in structural materials, electronics, chemical processing and energy management. Attempts have been made to develop advanced engineering materials with improved or novel properties through the incorporation of carbon nanotubes in selected matrices (polymers, metals and ceramics). But the use of carbon nanotubes to reinforce ceramic composites has not been very successful; for example, in alumina-based systems only a 24% increase in toughness has been obtained so far. Here we demonstrate their potential use in reinforcing nanocrystalline ceramics. We have fabricated fully dense nanocomposites of single-wall carbon nanotubes with nanocrystalline alumina (Al2O3) matrix at sintering temperatures as low as 1,150 degrees C by spark-plasma sintering. A fracture toughness of 9.7 MPa m 1/2, nearly three times that of pure nanocrystalline alumina, can be achieved.
IBM1
TL;DR: Electrical measurements show that the observed optical emission originates from radiative recombination of electrons and holes that are simultaneously injected into the undoped nanotubes, consistent with a nanotube FET model in which thin Schottky barriers form at the source and drain contacts.
Abstract: Polarized infrared optical emission was observed from a carbon nanotube ambipolar field-effect transistor (FET). An effective forward-biased p-n junction, without chemical dopants, was created in the nanotube by appropriately biasing the nanotube device. Electrical measurements show that the observed optical emission originates from radiative recombination of electrons and holes that are simultaneously injected into the undoped nanotube. These observations are consistent with a nanotube FET model in which thin Schottky barriers form at the source and drain contacts. This arrangement is a novel optical recombination radiation source in which the electrons and holes are injected into a nearly field-free region. Sucha source may form the basis for ultrasmall integrated photonic devices.
TL;DR: The fabrication and successful testing of ionization microsensors featuring the electrical breakdown of a range of gases and gas mixtures at carbon nanotube tips are reported, enabling compact, battery-powered and safe operation of such sensors.
Abstract: Gas sensors operate by a variety of fundamentally different mechanisms1,2,3,4,5,6,7,8,9,10,11,12,13,14. Ionization sensors13,14 work by fingerprinting the ionization characteristics of distinct gases, but they are limited by their huge, bulky architecture, high power consumption and risky high-voltage operation. Here we report the fabrication and successful testing of ionization microsensors featuring the electrical breakdown of a range of gases and gas mixtures at carbon nanotube tips. The sharp tips of nanotubes generate very high electric fields at relatively low voltages, lowering breakdown voltages several-fold in comparison to traditional electrodes, and thereby enabling compact, battery-powered and safe operation of such sensors. The sensors show good sensitivity and selectivity, and are unaffected by extraneous factors such as temperature, humidity, and gas flow. As such, the devices offer several practical advantages over previously reported nanotube sensor systems15,16,17. The simple, low-cost, sensors described here could be deployed for a variety of applications, such as environmental monitoring, sensing in chemical processing plants, and gas detection for counter-terrorism.