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Journal ArticleDOI

Carbon Nanotubes--the Route Toward Applications

02 Aug 2002-Science (American Association for the Advancement of Science)-Vol. 297, Iss: 5582, pp 787-792
TL;DR: Many potential applications have been proposed for carbon nanotubes, including conductive and high-strength composites; energy storage and energy conversion devices; sensors; field emission displays and radiation sources; hydrogen storage media; and nanometer-sized semiconductor devices, probes, and interconnects.
Abstract: Many potential applications have been proposed for carbon nanotubes, including conductive and high-strength composites; energy storage and energy conversion devices; sensors; field emission displays and radiation sources; hydrogen storage media; and nanometer-sized semiconductor devices, probes, and interconnects. Some of these applications are now realized in products. Others are demonstrated in early to advanced devices, and one, hydrogen storage, is clouded by controversy. Nanotube cost, polydispersity in nanotube type, and limitations in processing and assembly methods are important barriers for some applications of single-walled nanotubes.
Citations
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Journal ArticleDOI
15 Sep 2011-ACS Nano
TL;DR: This new synthetic methodology promises to be an effective approach to fabricating hybrid CNF/inorganic nanostructures for future sensing technologies.
Abstract: Ultrafine metal-oxide-decorated hybrid carbon nanofibers (CNFs) were fabricated by a single-nozzle co-electrospinning process using a phase-separated mixed polymer composite solution and heat treatment. To decorate metal oxides on the CNF surface, core (PAN) and shell (PVP) structured nanofibers (NFs) were fabricated as starting materials. The core-shell NF structure was prepared by single-nozzle co-electrospinning because of the incompatibility of the two polymers. Ultrafine hybrid CNFs were then formed by decomposing the PVP phase, converting the metal precursors to metal oxide nanonodules, and transforming the PAN to CNFs of ca. 40 nm diameter during heat treatment. The decoration morphology of the metal oxide nanonodules could be controlled by precursor concentration in the PVP solution. These ultrafine hybrid CNFs were applied to a dimethyl methylphosphonate (DMMP) chemical sensor at room temperature with excellent sensitivity. The minimum detectable level (MDL) of hybrid CNFs was as low as 0.1 ppb, which is 10-100 times higher than for a chemical sensor based on carbon nanotubes. This is because the metal oxide nanonodules of hybrid CNFs increase the surface area and affinity to DMMP vapor. Our new synthetic methodology promises to be an effective approach to fabricating hybrid CNF/inorganic nanostructures for future sensing technologies.

189 citations

Journal ArticleDOI
TL;DR: In this article, the authors demonstrate that pristine graphene can detect gas molecules at extremely low concentrations with detection limits as low as 158 parts-per-quadrillion (ppq) for a range of gases at room temperature.
Abstract: Graphene is widely regarded as one of the most promising materials for sensor applications. Here, we demonstrate that a pristine graphene can detect gas molecules at extremely low concentrations with detection limits as low as 158 parts-per-quadrillion (ppq) for a range of gas molecules at room temperature. The unprecedented sensitivity was achieved by applying our recently developed concept of continuous in situ cleaning of the sensing material with ultraviolet light. The simplicity of the concept, together with graphene’s flexibility to be used on various platforms, is expected to intrigue more investigations to develop ever more sensitive sensors.

189 citations

Journal ArticleDOI
TL;DR: In this paper, the authors used a hydrothermal method to synthesize an enamel prism-like structure, consisting of fluorapatite (FA) crystals, which are similar to those seen in human enamel.
Abstract: Dental enamel is the outermost layer of teeth and the hardest mineralized tissue in the human body. It consists of nanorod-like hydroxyapatite (HA) crystals arranged into a highly organized micro-architectural unit called an enamel prism. These special units play an important role in determining the unique physicochemical properties of dental enamel. Cells (ameloblasts) and enamel proteins are thought to be intimately involved in vivo in producing this unique structure. The aim of this research was to create a similar structure directly by crystal growth without using cells and/or enamel proteins. Using a hydrothermal method we have been able to synthesize these prism-like structures, consisting of fluorapatite (FA) crystals, which are similar to the dimensions of those seen in human enamel. Dental pulp stem cells (DPSCs) were cultured on these crystals and showed the excellent biocompatibility of the FA crystals. The growth mechanism of this structure is outlined and its use in tissue repair is discussed. Ninety-five percent (by volume) of human enamel is comprised of nanorod-like calcium hydroxyapatite crystals, which have an approximate cross section of 25–100 nm and an undetermined length of 100 nm to 100 lm or longer along the c-axis. The typical human enamel prism structure is approximately 5 lm in cross section, and can span the entire enamel thickness, that is, approximately 1–2 mm in length. The prevailing theory is that the ameloblasts secrete amelogenin, a major enamel protein constituting approximately 90 % of all organic matrix material in developing enamel, and this protein plays a vital role in enabling crystallites to form a well-organized prism pattern. These prisms project from the dentino–enamel junction to the enamel surface. The prisms are aligned parallel to each other and separated by an interprismatic structure to form a densely compacted enamel layer. Unlike other calcified tissues, such as dentin and bone, there are no living cells in the mature enamel. The ameloblast cells die after the enamel is formed. Thus, when the enamel is damaged, the body has no ability to regenerate it. The approach to create artificial bone and tooth structures has attracted the interest of many researchers. Kniep and co-workers have described a fluorapatite–gelatine system that resembles the biosystem hydroxyapatite–collagen in both bone and dentine. Recently, Yamagishi et al. have reported a paste of fluoridated hydroxyapatite that could be used to repair a small carious lesion. Although the interface between the precipitated layer from the paste and the tooth surface contains elongated crystals some of which are orientated towards the tooth surface, the unique enamel prism structure is not visible from the transmission electron microscopy (TEM) images. In our previous paper, we reported a way to mimic the natural biomineralization process to create these special structures by modifying synthetic hydroxyapatite nanorods with surfactants that allow the nanorods to self-assemble into an enamel prismlike structure at a water/air interface. However, those self-assembled enamel prism-like structures are small, only about 400 nm in length and 100 nm in cross section, and dispersed randomly. Very recently, Fowler et al. reported that they were able to synthesize an HA bundle structure directly from a solution containing the surfactant bis(2-ethylhexyl)sulfosuccinate sodium salt (AOT), water, and oil. These bundles were only 750 nm to 1 lm in length, 250–350 nm wide and they were dispersed randomly. These unique structures, therefore, have limited applications, and the introduction of other chemicals, for example AOT may cause unnecessary biological effects. The development of nanotechnology has created many ways to grow 1D nanostructures. Among them, the hydrothermal method is a widely adopted technique to create nanorods, nanowires, and whiskers and has already been shown to be an effective way to create long hydroxyapatite nanorods and whiskers. In this study, we demonstrate a direct growth method to produce fluorapatite dental enamel prismlike structures using a hydrothermal technique. A film of compacted well-aligned FA crystals, which was grown on metal plates, had a structure C O M M U N IC A TI O N S

188 citations

Journal ArticleDOI
TL;DR: In this paper, ZnO nanoflowers were synthesized by a simple process (ammonia-evaporation-induced synthetic method) and were applied to the hydrazine electrochemical sensor.

188 citations

References
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Journal ArticleDOI
28 Jan 2000-Science
TL;DR: The nanotubes sensors exhibit a fast response and a substantially higher sensitivity than that of existing solid-state sensors at room temperature and the mechanisms of molecular sensing with nanotube molecular wires are investigated.
Abstract: Chemical sensors based on individual single-walled carbon nanotubes (SWNTs) are demonstrated. Upon exposure to gaseous molecules such as NO 2 or NH 3 , the electrical resistance of a semiconducting SWNT is found to dramatically increase or decrease. This serves as the basis for nanotube molecular sensors. The nanotube sensors exhibit a fast response and a substantially higher sensitivity than that of existing solid-state sensors at room temperature. Sensor reversibility is achieved by slow recovery under ambient conditions or by heating to high temperatures. The interactions between molecular species and SWNTs and the mechanisms of molecular sensing with nanotube molecular wires are investigated.

5,908 citations

Journal ArticleDOI
01 May 1998-Nature
TL;DR: In this paper, the fabrication of a three-terminal switching device at the level of a single molecule represents an important step towards molecular electronics and has attracted much interest, particularly because it could lead to new miniaturization strategies in the electronics and computer industry.
Abstract: The use of individual molecules as functional electronic devices was first proposed in the 1970s (ref 1) Since then, molecular electronics2,3 has attracted much interest, particularly because it could lead to conceptually new miniaturization strategies in the electronics and computer industry The realization of single-molecule devices has remained challenging, largely owing to difficulties in achieving electrical contact to individual molecules Recent advances in nanotechnology, however, have resulted in electrical measurements on single molecules4,5,6,7 Here we report the fabrication of a field-effect transistor—a three-terminal switching device—that consists of one semiconducting8,9,10 single-wall carbon nanotube11,12 connected to two metal electrodes By applying a voltage to a gate electrode, the nanotube can be switched from a conducting to an insulating state We have previously reported5 similar behaviour for a metallic single-wall carbon nanotube operated at extremely low temperatures The present device, in contrast, operates at room temperature, thereby meeting an important requirement for potential practical applications Electrical measurements on the nanotube transistor indicate that its operation characteristics can be qualitatively described by the semiclassical band-bending models currently used for traditional semiconductor devices The fabrication of the three-terminal switching device at the level of a single molecule represents an important step towards molecular electronics

5,258 citations

Journal ArticleDOI
26 Jul 1996-Science
TL;DR: X-ray diffraction and electron microscopy showed that fullerene single-wall nanotubes (SWNTs) are nearly uniform in diameter and that they self-organize into “ropes,” which consist of 100 to 500 SWNTs in a two-dimensional triangular lattice with a lattice constant of 17 angstroms.
Abstract: The major part of this chapter has already appeared in [1], but because of the length restrictions (in Science), the discussion on why we think this form is given in only brief detail. This chapter goes into more depth to try to answer the questions of why the fullerenes form themselves. This is another example of the very special behavior of carbon. From a chemist’s standpoint, it is carbon’s ability to form multiple bonds that allows it to make these low dimensional forms rather than to produce tetrahedral forms. Carbon can readily accomplish this and it is in the mathematics and physics of the way this universe was put together, that carbon is given this property. One of the consequences of this property is that, if left to its own devices as carbon condenses from the vapor and if the temperature range is just right, above 1000°C, but lower than 1400°C, there is an efficient self-assembly process whose endpoint is C60.

5,215 citations

Journal ArticleDOI
26 Sep 1997-Science
TL;DR: In this paper, the Young's modulus, strength, and toughness of nanostructures are evaluated using an atomic force microscopy (AFM) approach. And the results showed that the strength of the SiC NRs were substantially greater than those found previously for larger SiC structures, and they approach theoretical values.
Abstract: The Young's modulus, strength, and toughness of nanostructures are important to proposed applications ranging from nanocomposites to probe microscopy, yet there is little direct knowledge of these key mechanical properties. Atomic force microscopy was used to determine the mechanical properties of individual, structurally isolated silicon carbide (SiC) nanorods (NRs) and multiwall carbon nanotubes (MWNTs) that were pinned at one end to molybdenum disulfide surfaces. The bending force was measured versus displacement along the unpinned lengths. The MWNTs were about two times as stiff as the SiC NRs. Continued bending of the SiC NRs ultimately led to fracture, whereas the MWNTs exhibited an interesting elastic buckling process. The strengths of the SiC NRs were substantially greater than those found previously for larger SiC structures, and they approach theoretical values. Because of buckling, the ultimate strengths of the stiffer MWNTs were less than those of the SiC NRs, although the MWNTs represent a uniquely tough, energy-absorbing material.

4,627 citations

Journal ArticleDOI
TL;DR: The thermal conductivity and thermoelectric power of a single carbon nanotube were measured using a microfabricated suspended device and shows linear temperature dependence with a value of 80 microV/K at room temperature.
Abstract: The thermal conductivity and thermoelectric power of a single carbon nanotube were measured using a microfabricated suspended device. The observed thermal conductivity is more than 3000 W/K m at room temperature, which is 2 orders of magnitude higher than the estimation from previous experiments that used macroscopic mat samples. The temperature dependence of the thermal conductivity of nanotubes exhibits a peak at 320 K due to the onset of umklapp phonon scattering. The measured thermoelectric power shows linear temperature dependence with a value of 80 microV/K at room temperature.

3,166 citations