301
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Masmanidis SC, Karabalin RB, De Vlaminck I, Borghs G, Freeman MR, Roukes ML. Multifunctional Nanomechanical Systems via Tunably Coupled Piezoelectric Actuation. Science 2007; 317:780-3. [PMID: 17690289 DOI: 10.1126/science.1144793] [Citation(s) in RCA: 82] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Efficient actuation is crucial to obtaining optimal performance from nanoelectromechanical systems (NEMS). We employed epitaxial piezoelectric semiconductors to obtain efficient and fully integrated NEMS actuation, which is based on exploitation of the interaction between piezoelectric strain and built-in charge depletion. The underlying actuation mechanism in these depletion-mediated NEMS becomes important only for devices with dimensions approaching semiconductor depletion lengths. The induced actuation forces are controlled electrically, and resonant excitation approaching single-electron efficiency is demonstrated. The fundamental electromechanical coupling itself can be programmed by heterostructure band engineering, externally controllable charge depletion, and crystallographic orientation. These attributes are combined to realize a prototype, mechanically based, exclusive-or logic element.
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Affiliation(s)
- Sotiris C Masmanidis
- Kavli Nanoscience Institute, California Institute of Technology, Pasadena, CA 91125, USA
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302
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Lepró X, Vega-Cantú Y, Rodríguez-Macías FJ, Bando Y, Golberg D, Terrones M. Production and characterization of coaxial nanotube junctions and networks of CNx/CNT. NANO LETTERS 2007; 7:2220-6. [PMID: 17658866 DOI: 10.1021/nl0706502] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/16/2023]
Abstract
Novel coaxial structures consisting of nitrogen-doped carbon nanotube (MWNTs-CNx) cores with external concentric shells of pure carbon were produced by the pyrolysis of toluene over Fe-coated MWNTs-CNx. These materials were thoroughly characterized by SEM, HRTEM, X-ray diffraction, and TGA; a possible growth scenario for their formation is also proposed. In addition, these coaxial structures were able to form 2D and 3D covalent networks that mainly exhibited T-, Y-, and on-type morphologies. The two-step technique presented here could be further developed to fully control the growth of these new coaxial structures, study of individual junctions, and it could be used to create periodic nanotube networks, in which the heterocable structure could find applications in nanoelectronics.
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Affiliation(s)
- X Lepró
- Advanced Materials Department, IPICYT, Camino a la Presa San José 2055, Col. Lomas 4a sección, San Luis Potosí, 78216, México
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303
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Cava CE, Possagno R, Schnitzler MC, Roman PC, Oliveira MM, Lepiensky CM, Zarbin AJ, Roman LS. Iron- and iron oxide-filled multi-walled carbon nanotubes: Electrical properties and memory devices. Chem Phys Lett 2007. [DOI: 10.1016/j.cplett.2007.07.029] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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304
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Tarakanov YA, Kinaret JM. A carbon nanotube field effect transistor with a suspended nanotube gate. NANO LETTERS 2007; 7:2291-4. [PMID: 17604404 DOI: 10.1021/nl070891+] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/16/2023]
Abstract
We investigate theoretically field effect transistors based on single-walled carbon nanotubes (CNTFET) and explore two device geometries with suspended multiwalled carbon nanotubes (MWNT) functioning as gate electrodes. In the two geometries, a doubly or singly clamped MWNT is electrostatically deflected toward the transistor channel, allowing for a variable gate coupling and leading to, for instance, a superior subthreshold slope. We suggest that the proposed designs can be used as nanoelectromechanical switches and as detectors of mechanical motion on the nanoscale.
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Affiliation(s)
- Yury A Tarakanov
- Department of Applied Physics, Chalmers University of Technology, SE-412 96 Gothenburg, Sweden.
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305
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Gui Z, Liu J, Wang Z, Song L, Hu Y, Fan W, Chen D. From Multicomponent precursor to nanoparticle nanoribbons of ZnO. J Phys Chem B 2007; 109:1113-7. [PMID: 16851068 DOI: 10.1021/jp047088d] [Citation(s) in RCA: 94] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
A simple mild solution method is developed to synthesize a novel nanoribbon multicomponent precursor. A new 1-D nanostructure, porous structured nanoribbons which are self-assembled by textured ZnO nanoparticles, was found upon removal of ligand molecules from the ribbonlike precursor. The structure combines 1-dimensional geometry with nanoparticle morphology and displays porous structure because there are gaps/pores between the particles. The orientation textured structure of the ZnO nanoparticles can be formed by controlling the annealing time. The ZnO nanoparticle nanoribbons exhibit a long geometrical shape, uniformity, a high aspect ratio, and different optical activities with different nanostuctures. These findings demonstrate a convenient, simple technique for production of the novel one-dimensional semiconductor nanostructure suitable for subsequent processing into nanostructures, materials, and devices.
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Affiliation(s)
- Zhou Gui
- State Key Lab of Fire Science and Department of Chemistry, University of Science and Technology of China, Hefei, 230027, P. R. China.
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306
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Choi HC, Park J, Kim B. Distribution and structure of N atoms in multiwalled carbon nanotubes using variable-energy X-ray photoelectron spectroscopy. J Phys Chem B 2007; 109:4333-40. [PMID: 16851499 DOI: 10.1021/jp0453109] [Citation(s) in RCA: 138] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We investigated the inhomogeneous distribution of concentration and electronic structure of the nitrogen (N) atoms doped in the multiwalled carbon nanotubes (CNTs) by variable-energy X-ray photoelectron spectroscopy (XPS), X-ray absorption near-edge structure, and electron energy-loss spectroscopy. The vertically aligned N-doped CNTs on the substrates were grown via pyrolysis of iron phthalocyanine (FePc), cobalt phthalocyanine (CoPc), and nickel phthalocyanine (NiPc) in the temperature range 750-1000 degrees C. They usually have a bamboo-like structure, and the diameter is in the range of 15-80 nm. As the photon energy of XPS increases from 475 to 1265 eV, the N content increases up to 8 atomic %, indicating a higher N concentration at the inside of nanotubes. We identified three typed N structures: graphite-like, pyridine-like, and molecular N(2). The pyridine-like N structure becomes significant at the inner walls. Molecular N(2) would exist as intercalated forms in the vicinity of hollow inside. The XPS valence band analysis reveals that the pyridine-like N structure induces the metallic behaviors. The CNTs grown using NiPc contain the higher content of pyridine-like structure compared to those grown using FePc and CoPc, so they exhibit more metallic properties.
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Affiliation(s)
- Hyun Chul Choi
- Department of Chemistry, Korea University, Jochiwon 339-700, Korea
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307
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Gu F, Li C, Wang S. Solution−Chemical Synthesis of Carbon Nanotube/ZnS Nanoparticle Core/Shell Heterostructures. Inorg Chem 2007; 46:5343-8. [PMID: 17523634 DOI: 10.1021/ic7004858] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
A facile solution-chemical method has been developed to be capable of encapsulating a multiwalled carbon nanotube (MWCNT) with ZnS nanocrystals without using any bridging species. The thickness of the ZnS shell can be tuned easily by controlling the experimental conditions. The optical properties of the MWCNT/ZnS heterostructures were investigated using UV-vis absorption and photoluminescence spectroscopy. The optical absorption spectrum indicates that the band gap of ZnS nanocrystallites is 4.2 eV. On the basis of the photoluminescence spectrum, charge transfer is thought to proceed from ZnS nanocrystals to the nanotube in the ZnS-carbon nanotube system. These special heterostructures are very easily encapsulated within a uniform silica layer by a modified-Stöber process and still show better stability even after heat treatment at 400 degrees C, which makes them appealing for practical applications in biochemistry and biodiagnostics.
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Affiliation(s)
- Feng Gu
- Key Laboratory for Ultrafine Materials of Ministry of Education, School of Materials Science and Engineering, East China University of Science and Technology, Shanghai 200237, PR China.
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308
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Hu X, Wang T, Wang L, Guo S, Dong S. A general route to prepare one- and three-dimensional carbon nanotube/metal nanoparticle composite nanostructures. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2007; 23:6352-7. [PMID: 17408292 DOI: 10.1021/la063246b] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/14/2023]
Abstract
Adsorption of polyethyleneimine (PEI)-metal ion complexes onto the surfaces of carbon nanotubes (CNTs) and subsequent reduction of the metal ion leads to the fabrication of one-dimensional CNT/metal nanoparticle (CNT/M NP) heterogeneous nanostructures. Alternating adsorption of PEI-metal ion complexes and CNTs on substrates results in the formation of multilayered CNT films. After exposing the films to NaBH4, three-dimensional CNT composite films embedded with metal nanoparticles (NPs) are obtained. UV-visible spectroscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy are used to characterize the film assembly. The resulting (CNT/M NP)n films inherit the properties from both the metal NPs and CNTs that exhibit unique performance in surface-enhanced Raman scattering (SERS) and electrocatalytic activities to the reduction of O2; as a result, they are more attractive compared to (CNT/polyelectrolyte)n and (NP/polyelectrolyte)n films because of their multifunctionality.
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Affiliation(s)
- Xiaoge Hu
- State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin 130022, People's Republic of China
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309
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Cui G, Zhi L, Thomas A, Kolb U, Lieberwirth I, Müllen K. One-Dimensional Porous Carbon/Platinum Composites for Nanoscale Electrodes. Angew Chem Int Ed Engl 2007; 46:3464-7. [PMID: 17394275 DOI: 10.1002/anie.200700077] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Guanglei Cui
- Max-Planck-Institut für Polymerforschung, Ackermannweg 10, 55128 Mainz, Germany
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310
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Cui G, Zhi L, Thomas A, Kolb U, Lieberwirth I, Müllen K. One-Dimensional Porous Carbon/Platinum Composites for Nanoscale Electrodes. Angew Chem Int Ed Engl 2007. [DOI: 10.1002/ange.200700077] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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311
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Tahir MN, Zink N, Eberhardt M, Therese HA, Faiss S, Janshoff A, Kolb U, Theato P, Tremel W. Hierarchical assembly of TiO2 nanoparticles on WS2 nanotubes achieved through multifunctional polymeric ligands. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2007; 3:829-34. [PMID: 17407103 DOI: 10.1002/smll.200600663] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/14/2023]
Affiliation(s)
- Muhammad Nawaz Tahir
- Anorganische Chemie und Analytische Chemie, Johannes Gutenberg-Universität Mainz, Mainz, Germany
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312
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Huang J, Momenzadeh M, Lombardi F. An Overview of Nanoscale Devices and Circuits. ACTA ACUST UNITED AC 2007. [DOI: 10.1109/mdt.2007.121] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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313
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Ramanathan K, Bangar M, Yun M, Chen W, Mulchandani A, Myung N. In Situ Fabrication of Single Poly(methyl pyrrole) Nanowire. ELECTROANAL 2007. [DOI: 10.1002/elan.200603773] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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314
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Wang XF, Xu ZJ, Zhu ZY. Reversible mechanical bistability of carbon nanotubes under radial compression. Chem Phys 2007. [DOI: 10.1016/j.chemphys.2007.02.020] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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315
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Anticipating technological breakthroughs: Using bibliographic coupling to explore the nanotubes paradigm. Scientometrics 2007. [DOI: 10.1007/s11192-007-0311-5] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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316
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Meunier V, Kalinin SV, Sumpter BG. Nonvolatile memory elements based on the intercalation of organic molecules inside carbon nanotubes. PHYSICAL REVIEW LETTERS 2007; 98:056401. [PMID: 17358877 DOI: 10.1103/physrevlett.98.056401] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/23/2006] [Indexed: 05/14/2023]
Abstract
We propose a novel class of nonvolatile memory elements based on the modification of the transport properties of a conducting carbon nanotube by the presence of an encapsulated molecule. The guest molecule has two stable orientational positions relative to the nanotube that correspond to conducting and nonconducting states. The mechanism, governed by a local gating effect of the molecule on the electronic properties of the nanotube host, is studied using density functional theory. The mechanisms of reversible reading and writing of information are illustrated with a F4TCNQ molecule encapsulated inside a metallic carbon nanotube. Our results suggest that this new type of nonvolatile memory element is robust, fatigue-free, and can operate at room temperature.
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Affiliation(s)
- Vincent Meunier
- Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
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317
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Yan Y, Chan-Park MB, Zhang Q. Advances in carbon-nanotube assembly. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2007; 3:24-42. [PMID: 17294465 DOI: 10.1002/smll.200600354] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
Iijima's observation in 1991 of fullerene-like materials by high-resolution transmission electron microscopy heralded the beginning of the carbon nanotube (CNT) era. A wealth of theoretical predictions and experimental verifications about CNTs have disclosed remarkable size- and structure-dependent properties that are attractive for various potential applications, ranging from conducting wires in molecular devices to fillers in nanocomposites. Many of these applications require assembly (alignment and/or patterning) of CNTs into hierarchical arrays over large-scale areas with controllable shape, location, orientation, and density of the nanotubes. Efforts from both the scientific and engineering points of view have been made to address this issue, beginning shortly after the discovery of CNTs. We review here the development of CNT-assembly techniques under the two rubrics of synthetic assembly and post-synthetic assembly, with emphasis given to the post-synthetic approach. Preliminary to the survey of assembly techniques, we also discuss the characterization techniques that have been widely used for the challenging tasks of visualizing and quantifying CNT assembly.
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Affiliation(s)
- Yehai Yan
- Key Laboratory of Rubber-Plastics (Ministry of Education), Department of Polymer Science and Engineering, Qingdao University of Science and Technology, 266042 Qingdao, China
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318
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Hyung H, Fortner JD, Hughes JB, Kim JH. Natural organic matter stabilizes carbon nanotubes in the aqueous phase. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2007; 41:179-84. [PMID: 17265945 DOI: 10.1021/es061817g] [Citation(s) in RCA: 490] [Impact Index Per Article: 28.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
This study investigates the aqueous stability of multi-walled carbon nanotubes (MWNTs) in the presence of natural organic matter (NOM). MWNTs were readily dispersed as an aqueous suspension in both model NOM (Suwannee River NOM (SR-NOM)) solutions and natural surface water (actual Suwannee River water with unaltered NOM background), which remained stable for over 1 month. Microscopic analyses suggested that the suspension consisted primarily of individually dispersed MWNTs. Concentrations of MWNTs suspended in the aqueous phase, quantified using thermal optical transmittance analysis (TOT), ranged from 0.6 to 6.9 mg/L as initial concentrations of MWNT and SR-NOM were varied from 50 to 500 mg/L and 10 to 100 mg/L, respectively. Suwannee River water showed a similar MWNT stabilizing capacity as compared to the model SR-NOM solutions. For the same initial MWNT concentrations, the concentrations of suspended MWNT in SR-NOM solutions and Suwannee River water were considerably higher than that in a solution of 1% sodium dodecyl sulfate, a commonly used surfactant to stabilize CNTs in the aqueous phase. These findings suggest that dispersal of carbon-based nanomaterials in the natural, aqueous environment might occur to an unexpected extent following a mechanism that has not been previously considered in environmental fate and transport studies.
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Affiliation(s)
- Hoon Hyung
- School of Civil and Environmental Engineering, Georgia Institute of Technology, 200 Bobby Dodd Way, Atlanta, Georgia 30332, USA
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319
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320
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Huang L, Jia Z, O'Brien S. Orientated assembly of single-walled carbon nanotubes and applications. ACTA ACUST UNITED AC 2007. [DOI: 10.1039/b702080e] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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321
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Deak DS, Porfyrakis K, Castell MR. C70 ordering on nanostructured SrTiO3(001). Chem Commun (Camb) 2007:2941-3. [PMID: 17622438 DOI: 10.1039/b703081a] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The nanostructured (7 x 4) surface of SrTiO(3)(001) is used as a template to order C(70) into single-molecule-wide chains and linear islands.
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Affiliation(s)
- David S Deak
- Department of Materials, University of Oxford, Parks Road, Oxford, UK OX1 3PH
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322
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Salgueiriño-Maceira V, Hoppe CE, Correa-Duarte MA. Formation of Fractal-Like Structures Driven by Carbon Nanotubes-Based Collapsed Hollow Capsules. J Phys Chem B 2006; 111:331-4. [PMID: 17214481 DOI: 10.1021/jp0669963] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Carbon nanotubes (CNTs) based hollow capsules were obtained by degradation under acidic conditions of core-shell nanocomposites build up upon adsorption of multilayers of CNTs (shell) onto melamine-formaldehyde (MF) spheres (core). By evaporation of the dispersions obtained, polymeric fractal patterns from the degradation products of the MF core were formed onto silicon wafers. The proposed mechanism for the formation of these structures is based on the role of the capsules as arrangements of heterogeneities that facilitate the dewetting of the liquid polymeric films.
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323
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Templeton RC, Ferguson PL, Washburn KM, Scrivens WA, Chandler GT. Life-cycle effects of single-walled carbon nanotubes (SWNTs) on an estuarine meiobenthic copepod. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2006; 40:7387-93. [PMID: 17180993 DOI: 10.1021/es060407p] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
Single-walled carbon nanotubes (SWNT) are finding increasing use in consumer electronics and structural composites. These nanomaterials and their manufacturing byproducts may eventually reach estuarine systems through wastewater discharge. The acute and chronic toxicity of SWNTs were evaluated using full life-cycle bioassays with the estuarine copepod Amphiascus tenuiremis (ASTM method E-2317-04). A synchronous cohort of naupliar larvae was assayed by culturing individual larvae to adulthood in individual 96-well microplate wells amended with SWNTs in seawater. Copepods were exposed to "as prepared" (AP) SWNTs, electrophoretically purified SWNTs, or a fluorescent fraction of nanocarbon synthetic byproducts. Copepods ingesting purified SWNTs showed no significant effects on mortality, development, and reproduction across exposures (p < 0.05). In contrast, exposure to the more complex AP-SWNT mixture significantly increased life-cycle mortality, reduced fertilization rates, and reduced molting success in the highest exposure (10 mg x L(-1)) (p < 0.05). Exposure to small fluorescent nanocarbon byproducts caused significantly increased life-cycle mortality at 10 mg x L(-1) (p < 0.05). The fluorescent nanocarbon fraction also caused significant reduction in life-cycle molting success for all exposures (p < 0.05). These results suggest size-dependent toxicity of SWNT-based nanomaterials, with the smallest synthetic byproduct fractions causing increased mortality and delayed copepod development over the concentration ranges tested.
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Affiliation(s)
- Ryan C Templeton
- Marine Science Program, Department of Chemistry and Biochemistry, University of South Carolina, Columbia, South Carolina 29208, USA
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324
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Lin Y, Cai W, Shao X. Fullerenes connected nanotubes: An approach to build multidimensional carbon nanocomposites. Chem Phys 2006. [DOI: 10.1016/j.chemphys.2006.09.031] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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325
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Ke C, Espinosa HD. In situ electron microscopy electromechanical characterization of a bistable NEMS device. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2006; 2:1484-9. [PMID: 17193010 DOI: 10.1002/smll.200600271] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
A previously proposed two-terminal carbon-nanotube-based device with closed-loop feedback is demonstrated through in situ scanning electron microscopy (SEM) experiments. The pull-in/pull-out tests were carried out using a multi-walled carbon nanotube (MWCNT) welded to a conductive probe attached to a nanomanipulator. The MWCNTs were cantilevered over a gold electrode and electrostatically actuated. The measured current-voltage curves exhibited the theoretically predicted hysteretic loop between the pull-in and pull-out processes. Both experiments and theoretical modeling demonstrated the bistability of the device confirming its utility in applications such as memory elements, NEMS switches, and logic devices. Failure mechanisms observed during the pull-in/pull-out event are also reported and discussed.
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Affiliation(s)
- Changhong Ke
- Department of Mechanical Engineering, Northwestern University, Evanston, IL 60208-3111, USA
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326
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Prociuk A, Van Kuiken B, Dunietz BD. Benchmarking the performance of density functional theory based Green’s function formalism utilizing different self-energy models in calculating electronic transmission through molecular systems. J Chem Phys 2006; 125:204717. [PMID: 17144733 DOI: 10.1063/1.2397676] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Electronic transmission through a metal-molecule-metal system is calculated by employing a Green's function formalism in the scattering based scheme. Self-energy models representing the bulk and the potential bias are used to describe electron transport through the molecular system. Different self-energies can be defined by varying the partition between device and bulk regions of the metal-molecule-metal model system. In addition, the self-energies are calculated with different representations of the bulk through its Green's function. In this work, the dependence of the calculated transmission on varying the self-energy subspaces is benchmarked. The calculated transmission is monitored with respect to the different choices defining the self-energy model. In this report, we focus on one-dimensional model systems with electronic structures calculated at the density functional level of theory.
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Affiliation(s)
- Alexander Prociuk
- Department of Chemistry, University of Michigan, Ann Arbor, MI 48109, USA
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327
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328
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Chen Z, Wu Z, Tong L, Pan H, Liu Z. Simultaneous Dielectrophoretic Separation and Assembly of Single-Walled Carbon Nanotubes on Multigap Nanoelectrodes and Their Thermal Sensing Properties. Anal Chem 2006; 78:8069-75. [PMID: 17134141 DOI: 10.1021/ac0614487] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
By using the specifically designed multigap nanoelectrodes, we demonstrated an effective approach for the simultaneous dielectrophoretic separation and assembly of metallic and semiconducting single-walled carbon nanotubes (SWNTs). An approximate metallic-semiconducting-metallic multiarray structure was created by an inward-propagative sequential assembly of SWNTs under ac electric field. Such kinds of SWNT multiarray structures exhibited ultra-low-power consumption and excellent thermal sensing performances with the sensitivity being dependent on the number of gaps: the more gaps, the higher sensitivity. The effective separation of metallic and semiconducting tubes in different gaps is believed to be responsible for the improved sensitivity to temperature.
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Affiliation(s)
- Zhuo Chen
- CNST/Beijing National Laboratory for Molecular Sciences, State Key Laboratory for Structural Chemistry of Unstable and Stable Species, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, P. R. China
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329
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Cohen-Karni T, Segev L, Srur-Lavi O, Cohen SR, Joselevich E. Torsional electromechanical quantum oscillations in carbon nanotubes. NATURE NANOTECHNOLOGY 2006; 1:36-41. [PMID: 18654139 DOI: 10.1038/nnano.2006.57] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/27/2006] [Accepted: 08/30/2006] [Indexed: 05/20/2023]
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330
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Li CY, Chou TW. Charge-induced strains in single-walled carbon nanotubes. NANOTECHNOLOGY 2006; 17:4624-4628. [PMID: 21727586 DOI: 10.1088/0957-4484/17/18/015] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
This paper investigates the electromechanical coupling in single-walled carbon nanotubes. In the model system, the extra electric charge of the nanotube is assumed to be uniformly distributed on carbon atoms. The electrostatic interactions between charged carbon atoms are calculated using the Coulomb law. The deformation of the charged nanotube is obtained by using the molecular structural mechanics method and considering the electrostatic interactions as an external loading acting on carbon atoms. The axial strain is found to be a symmetric function of applied charge, and our predictions are in very good agreement with those from ab initio calculations. The present results indicate that the nanotube aspect ratio has a strong effect on the axial strain when the ratio is less than 10 and the general trend is that the strain increases with the aspect ratio. The peak axial and radial strains occur at nanotube diameters of around 1.2-1.5 nm.
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Affiliation(s)
- Chun-Yu Li
- Department of Mechanical Engineering, University of Delaware, Newark, DE 19716, USA
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331
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Khomutov GB, Koksharov YA. Effects of organic ligands, electrostatic and magnetic interactions in formation of colloidal and interfacial inorganic nanostructures. Adv Colloid Interface Sci 2006; 122:119-47. [PMID: 16887093 DOI: 10.1016/j.cis.2006.06.011] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
This paper discusses effects of organic ligands, electrostatic and magnetic interactions involved in morphological control of chemically synthesized inorganic nanostructures including colloid and planar systems. The special attention was concentrated on noble metal (gold and palladium) nanoparticles and nanostructures formed at the gas-liquid interface. The analysis of experimental data showed that electrostatic and ligand-related interactions influence very strongly on the metal nanostructure morphology. The hydrophobicity of ligand, charge and binding affinity to inorganic phase are important factors influencing the morphology of inorganic nanostructures formed in a layer at the gas/liquid interface by the interfacial synthesis method. The important point of this method is the quasi two-dimensional character of reaction area and possibilities to realize ultimately thin and anisotropic dynamic monomolecular reaction system with two-dimensional diffusion and interactions of precursors, intermediates and ligands resulting in planar growth and organization of inorganic nanoparticles and nanostructures in the plain of Langmuir monolayer. The morphology of resulting inorganic nanostructures can be controlled efficiently by variations of growth conditions via changes in state and composition of interfacial planar reaction media with the same precursor, and by variations of composition of adjacent bulk phases. The extreme anisotropy and heterogeneity of two-dimensional interfacial reaction system allows creating conditions when growing inorganic particles floating on the aqueous phase surface interact selectively with hydrophobic water-insoluble ligands in interfacial monolayer or with hydrophilic bulk-phase ligands, or at the same time with ligands of different nature present in monolayer and in aqueous phase. The spatial anisotropy of interfacial reaction system and non-homogeneity of ligand binding to inorganic phase gives possibilities for growth of integrated anisotropic nanostructures with unique morphologies, in particularly those characterized by very high surface/volume ratio, high effective perimeter, and labyrinth-like structure. In a case of magnetic nanoparticles dispersed in colloids specific magnetic dipolar interactions can result in formation of chains, rings and more complex nanoparticulate structures or separated highly anisotropic nanoparticles. Theoretical considerations indicate to the importance of system dimensionality in relation to the energy balance which determines specific features of structure organization in planar charged metallic and magnetic nanostructures. For example, a requirement of Coulomb energy minimum, the possibility of free electron redistribution and strengthened attractive interactions between particles in metallic nanostructures can explain formation of very branchy systems with extremely high "effective perimeter". The obtained experimental and literature data show that system dimensionality, organic ligand nature along with electrostatic and magnetic interactions are most important factors of morphological control of chemically synthesized inorganic nanomaterials. The understanding and appropriate exploitation of these factors can be useful for further developments of efficient nanofabrication techniques based on colloidal and interfacial synthetic methods.
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Affiliation(s)
- G B Khomutov
- Faculty of Physics, Moscow State University, 119992 Moscow, Russia.
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332
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Liu H, Zhai J, Jiang L. Wetting and anti-wetting on aligned carbon nanotube films. SOFT MATTER 2006; 2:811-821. [PMID: 32680273 DOI: 10.1039/b606654b] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
This review covers recent advances in the wettability of aligned carbon nanotubes (ACNT). Carbon nanotubes (CNT) are inherently somewhat hydrophilic, with a water contact angle of less than 86°. When they are arranged in a textured manner on substrates having different surface topographies, different wettabilities are exhibited. These range from hydrophilic to hydrophobic, and even superhydrophobic, and with isotropic to anisotropic contact angle (CA) hysteresis. If chemical modification is involved, the wettability can be adjusted from superhydrophobic to superhydrophilic on a certain structured ACNTs. Here, we first examine the structural influence of isotropic roughness on this effect (including nano-structures and hierarchical structures), where isotropic wetting (including wetting and anti-wetting) is observed. Water can wet the nano-structured CNT alignment, resulting in self-assembly; on the other hand, superhydrophobicity is durable on hierarchical and chemically-modified nano-structured alignments. Secondly, the effects of anisotropic roughness on wetting behavior are discussed. Finally, we suggest the remaining challenges in the field, and several practical applications of ACNT possessing special wettability.
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Affiliation(s)
- Huan Liu
- Center for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing, 100080. and National Center for Nanoscience and Technology, Beijing, 100080, China
| | - Jin Zhai
- Center for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing, 100080.
| | - Lei Jiang
- Center for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing, 100080. and National Center for Nanoscience and Technology, Beijing, 100080, China
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333
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334
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Ismach A, Joselevich E. Orthogonal self-assembly of carbon nanotube crossbar architectures by simultaneous graphoepitaxy and field-directed growth. NANO LETTERS 2006; 6:1706-10. [PMID: 16895360 DOI: 10.1021/nl0610026] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
Crossbar arrays of single-wall carbon nanotubes are produced spontaneously in a single step of chemical vapor deposition by simultaneous graphoepitaxy along faceted nanosteps and field-directed growth, perpendicular to each other. The two alignment mechanisms take place selectively on miscut C-plane sapphire and patterned amorphous SiO2 islands, respectively, without mutual interference, producing dense nanotube grids, with up to 12 junctions per square micrometer. This one-step method of orthogonal self-assembly may open up new possibilities for nanotube circuit integration.
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Affiliation(s)
- Ariel Ismach
- Department of Materials and Interfaces, Weizmann Institute of Science, Rehovot 76100, Israel
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335
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Im J, Lee M, Myung S, Huang L, Rao SG, Lee DJ, Koh J, Hong S. Directed-assembly of single-walled carbon nanotubes using self-assembled monolayer patterns comprising conjugated molecular wires. NANOTECHNOLOGY 2006; 17:3569-3573. [PMID: 19661606 DOI: 10.1088/0957-4484/17/14/035] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Self-assembled monolayer (SAM) patterns on electrodes are often utilized to guide the assembly of single-walled carbon nanotubes (SWCNTs) onto the electrodes to form desired device structures. In this case, the SWCNTs are in contact with the electrodes through the SAM which comprises molecular wires. Presumably, it is desirable to use conjugated molecular wires for a low contact resistance because they have been reported as a better electric conductor than non-conjugated ones. However, until now, the directed-assembly of SWCNTs has been driven mostly via molecular wires with alkane backbones which are known to be relatively poor conductors. Herein, we report large-scale directed-assembly of SWCNTs utilizing SAM patterns comprising conjugated molecular wires. We achieved highly selective adsorption and precision alignment of SWCNTs utilizing polar SAM patterns comprising conjugated molecular wires, while SAM patterns with non-polar terminal groups efficiently prevented adsorption of SWCNTs. Furthermore, we developed a process for assembling a SWCNT across two electrodes coated with conjugated molecular wires, and the electrical conduction through the SWCNT was measured via a conducting atomic force microscope. This result could be an important guideline for large-scale directed-assembly of SWCNT-based devices in the future.
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Affiliation(s)
- Jiwoon Im
- School of Physics and NANO Systems Institute, Seoul National University, Seoul 151-747, Korea
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336
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Mannik J, Goldsmith BR, Kane A, Collins PG. Chemically induced conductance switching in carbon nanotube circuits. PHYSICAL REVIEW LETTERS 2006; 97:016601. [PMID: 16907392 DOI: 10.1103/physrevlett.97.016601] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/31/2006] [Indexed: 05/11/2023]
Abstract
The chemical reactivity of carbon nanotubes in H2SO4 is investigated using individual, single-walled carbon nanotubes (SWNTs) incorporated into electronic devices. Exploiting the device conductance as a sensitive indicator of chemical reactions, discrete oxidation and reduction events can be clearly observed. During oxidation, a SWNT opens circuits to a nanometer-scale tunnel junction with residual conduction similar to Frenkel-Poole charge emission. When electrochemically reduced, a SWNT returns to its original conductance. This redox cycle can be repeated many times, suggesting a novel chemical method of reversibly switching SWNT conductivity.
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Affiliation(s)
- Jaan Mannik
- Department of Physics and Astronomy, University of California at Irvine, Irvine, California 92697, USA
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337
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Bonifazi D, Nacci C, Marega R, Campidelli S, Ceballos G, Modesti S, Meneghetti M, Prato M. Microscopic and spectroscopic characterization of paintbrush-like single-walled carbon nanotubes. NANO LETTERS 2006; 6:1408-14. [PMID: 16834420 DOI: 10.1021/nl060394d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Abstract
Understanding and controlling the chemical reactivity of carbon nanotubes (CNTs) is a fundamental requisite to prepare novel nanoscopic structures with practical uses in materials applications. Here, we present a comprehensive microscopic and spectroscopic characterization of carbon nanotubes which have been chemically modified. Specifically, scanning tunneling microscopy (STM) investigations of short-oxidized single-walled carbon nanotubes (SWNTs) functionalized with aliphatic chains via amide reaction reveal the presence of bright lumps both on the sidewalls and at the tips. The functionalization pattern is consistent with the oxidation reaction which mainly occurs at the nanotube tips. Thermogravimetric analysis (TGA), steady-state electronic absorption (UV-vis-NIR), and Raman spectroscopic studies confirm the STM observations.
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Affiliation(s)
- Davide Bonifazi
- Dipartimento di Scienze Farmaceutiche and INSTM UdR Trieste, Università degli Studi di Trieste, Italy
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338
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Urita K, Seki S, Utsumi S, Noguchi D, Kanoh H, Tanaka H, Hattori Y, Ochiai Y, Aoki N, Yudasaka M, Iijima S, Kaneko K. Effects of gas adsorption on the electrical conductivity of single-wall carbon nanohorns. NANO LETTERS 2006; 6:1325-8. [PMID: 16834404 DOI: 10.1021/nl060120q] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Abstract
We present significant electrical conductivity responses of the pelletized as-prepared and oxidized (ox-) single-wall carbon nanohorns (SWNHs) on adsorption of CO(2) and O(2). The morphological and pore structures of both pelletized SWNHs were examined by transmission electron microscopy (TEM) and nitrogen adsorption isotherm, leading to explicit evidences of the formation of nanoscale windows on the wall by oxidation. The SWNH and ox-SWNH induced a semiconducting behavior, strongly responded to CO(2) and O(2) adsorptions, and each exhibited n-type- and p-type-like conductivities. The electrical conductivity increase and decrease for CO(2) and O(2) adsorption, respectively, were observed for SWNH, whereas ox-SWNH showed a marked electrical conductivity drop on CO(2) adsorption and almost no change on O(2) adsorption. The dramatically different electrical conductivity response of ox-SWNH is presumed to be ascribed to the annihilation of pentagons in the single graphene wall by oxidation.
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Affiliation(s)
- Koki Urita
- Graduate School of Science and Technology, Chiba University, Japan
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339
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Zhu W, Kaxiras E. The nature of contact between Pd leads and semiconducting carbon nanotubes. NANO LETTERS 2006; 6:1415-9. [PMID: 16834421 DOI: 10.1021/nl0604311] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Abstract
The contact between semiconducting single-wall carbon nanotubes (SWCNTs) and metallic leads is of central importance to potential electronic device applications. We investigate the nature of the contact of SWCNTs with Pd leads in a fully covered geometry that closely resembles experimental setups. We employ first-principles calculations within density functional theory to obtain the equilibrium structure for representative semiconducting SWCNTs embedded in Pd and analyze their electronic structure features, charge-transfer effects, electrostatic potentials, and Fermi level alignment at the interfaces with the metal contact. We find that there is no electrostatic or Schottky-type barrier to electron transfer between the metal and the nanotube.
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Affiliation(s)
- Wenguang Zhu
- Department of Physics and Division of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, USA
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340
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Gu F, Guo G, Wang Z, Guo H. Synthesis and bundle-like assemblies of LaPO4 nanofibers in reverse micelles system. Colloids Surf A Physicochem Eng Asp 2006. [DOI: 10.1016/j.colsurfa.2006.01.040] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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341
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Deshpande VV, Chiu HY, Postma HWC, Mikó C, Forró L, Bockrath M. Carbon nanotube linear bearing nanoswitches. NANO LETTERS 2006; 6:1092-5. [PMID: 16771559 DOI: 10.1021/nl052513f] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Abstract
We exploit the remarkable low-friction bearing capabilities of multiwalled carbon nanotubes (MWNTs) to realize nanoelectromechanical switches. Our switches consist of two open-ended MWNT segments separated by a nanometer-scale gap. Switching occurs through electrostatically actuated sliding of the inner nanotube shells to close the gap, producing a conducting ON state. For double-walled nanotubes in particular, a gate voltage can restore the insulating OFF state. Acting as a nonvolatile memory element capable of several switching cycles, our devices are straightforward to implement, self-aligned, and do not require complex fabrication or geometries, allowing for convenient scalability.
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Affiliation(s)
- V V Deshpande
- Department of Applied Physics, California Institute of Technology, Pasadena, California 91125, USA
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342
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Maslov L. Concept of nonvolatile memory based on multiwall carbon nanotubes. NANOTECHNOLOGY 2006; 17:2475-2482. [PMID: 21727492 DOI: 10.1088/0957-4484/17/10/007] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
In this study, a novel concept is proposed for molecular electronics that uses vertically aligned multiwall carbon nanotubes as nonvolatile memory elements. Nanotubes grown on a patterned substrate may be opened by partially deleting the outer molecular layer or layers, so that the inner core is able to move along the vertical tube axis. Mounting another dielectric plate above the nanotube forest at a specific distance from the tube caps can provide two stable van der Waals states of the inner core, providing for nonvolatile data storage. A device built using this architecture can function as a two-dimensional memory array. At each cross point in the array, a multiwall carbon nanotube exists in either the separated off-state or in the contact on-state, and can be switched between these states by applying voltage pulses at the corresponding electrodes. A theoretical memory density as high as 10(13) memory elements per square centimetre is possible, with an operation frequency exceeding 100 GHz. Significant physical characteristics of such a device are bi-stability and reversibility. Such a device can function both as nonvolatile random access memory and as terabit solid-state storage.
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Affiliation(s)
- Leonid Maslov
- Samsung Advanced Institute of Technology (SAIT), San 14-1, Nongseo-Ri, Giheung-Eup, Yongin-Si, Gyeonggi-Do, Korea
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343
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Moran AM, Maddox JB, Hong JW, Kim J, Nome RA, Bazan GC, Mukamel S, Scherer NF. Optical coherence and theoretical study of the excitation dynamics of a highly symmetric cyclophane-linked oligophenylenevinylene dimer. J Chem Phys 2006; 124:194904. [PMID: 16729841 DOI: 10.1063/1.2196041] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
Optoelectronic properties of a polyphenylenevinylene-based oligomer and its paracylophane-linked dimer are studied using a variety of experimental and theoretical techniques. Despite the symmetrical structure and redshifted absorption of the dimer versus the monomer, an exciton picture is not the most appropriate. Electronic structure calculations establish changes in charge density upon optical excitation and show localized excitations that cannot be accounted for by a simple Frenkel exciton model. Visible frequency pump-probe anisotropy measurements suggest that the dimer should be considered as a three-level system with a fast, approximately 130 fs, internal conversion from the higher to lower energy excited electronic state. Signatures of nuclear relaxation processes are compared for electric field-resolved transient grating and two-dimensional photon echo spectra. These measurements reveal that nuclear relaxation occurs on similar time scales for the monomer and dimer. The connection between the spectral phase of four-wave mixing signals and the time dependent width of a nuclear wave packet is discussed. Semiempirical electronic structure and metropolis Monte Carlo calculations show that the dominant line broadening mechanisms for the monomer and dimer are associated with inter-ring torsional coordinates. Together, the theoretical calculations and electric field-resolved four-wave mixing experiments suggest that while the structure of dimer is more rigid than that of monomer, the difference in their rigidities is not sufficient to slow down excited state relaxation of dimer with respect to the monomer.
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Affiliation(s)
- Andrew M Moran
- Department of Chemistry, The University of Chicago, Chicago, IL 60637, USA
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344
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Huang L, White B, Sfeir MY, Huang M, Huang HX, Wind S, Hone J, O'Brien S. Cobalt Ultrathin Film Catalyzed Ethanol Chemical Vapor Deposition of Single-Walled Carbon Nanotubes. J Phys Chem B 2006; 110:11103-9. [PMID: 16771372 DOI: 10.1021/jp060693r] [Citation(s) in RCA: 76] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We report a simple and efficient chemical vapor deposition (CVD) process that can grow oriented and long single-walled carbon nanotubes (SWNTs) using a cobalt ultrathin film ( approximately 1 nm) as the catalyst and ethanol as carbon feedstock. In the process, millimeter- to centimeter-long, oriented and high-quality SWNTs can grow horizontally on various flat substrate surfaces, traverse slits as large as hundreds of micrometers wide, or grow over vertical barriers as high as 20 microm. Such observations demonstrate that the carbon nanotubes are suspended in the gas flow during the growth. The trace amount of self-contained water (0.2-5 wt %) in ethanol may act as a mild oxidizer to clean the nanotubes and to elongate the lifetime of the catalysts, but no yield improvement was observed at the CVD temperature of 850 degrees C. We found that tilting the substrates supporting the Co ultrathin film catalysts can grow more, longer carbon nanotubes. A mechanism is discussed for the growth of long SWNTs.
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Affiliation(s)
- Limin Huang
- Department of Applied Physics, Columbia University, New York, New York 10027, USA.
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345
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Lu J, Kopley T, Dutton D, Liu J, Qian C, Son H, Dresselhaus M, Kong J. Generating Suspended Single-Walled Carbon Nanotubes Across a Large Surface Area via Patterning Self-Assembled Catalyst-Containing Block Copolymer Thin Films. J Phys Chem B 2006; 110:10585-9. [PMID: 16771301 DOI: 10.1021/jp061422j] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Using self-assembled block copolymers as templates, catalytically active nanostructures with controlled size and space have been produced. A self-assembled polystyrene-b-polyferrocenylsilane thin film and monolayer of surface micelles of cobalt-complexed polystyrene-b-poly(2-vinylpyridine) are fully compatible with novolac-based conventional photoresists. Combining bottom-up self-assembly of catalyst-containing block copolymers with top-down microfabrication processing, plateaus covered with arrays of catalytically active nanostructures have been generated. Spatially selective growth of suspended single-walled carbon nanotubes over a large surface area has been achieved. Greatly enhanced Raman signals have been detected from the suspended tubes. This facile method of creating highly ordered catalyst nanostructures on top of posts enables the rational synthesis of suspended carbon nanotubes, thus facilitating the study of CNT properties by optical methods and enabling the fabrication of devices based on suspended CNTs.
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346
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Myung S, Im J, Huang L, Rao SG, Kim T, Lee DJ, Hong S. “Lens” Effect in Directed Assembly of Nanowires on Gradient Molecular Patterns. J Phys Chem B 2006; 110:10217-9. [PMID: 16722718 DOI: 10.1021/jp062108s] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We report a new phenomenon, named here as the "lens" effect, in the directed-assembly process of nanowires (NWs) on self-assembled monolayer (SAM) patterns. In this process, the adsorption of NWs is focused in the nanoscale regions at the center of microscale SAM patterns with gradient surface molecular density just like an optical lens focuses light. As a proof of concepts, we successfully demonstrated the massive assembly of V2O5 NWs and single-walled carbon nanotubes (swCNTs) with a nanoscale resolution using only microscale molecular patterning methods. This work provides us with important insights about the directed-assembly process, and from a practical point of view, it allows us to generate nanoscale patterns of NWs over a large area for mass fabrication of NW-based devices.
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347
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Li J, Grennberg H. Microwave-Assisted Covalent Sidewall Functionalization of Multiwalled Carbon Nanotubes. Chemistry 2006; 12:3869-75. [PMID: 16502454 DOI: 10.1002/chem.200501314] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Thermal cycloaddition of 1,3-dipolar azomethine ylides to the sidewalls of multiwalled carbon nanotubes (MWNTs) has been used to prepare MWNTs that contain 2-methylenethiol-4-(4-octadecyloxyphenyl) (4), N-octyl-2-(4-octadecyloxyphenyl) (5) or 2-(4-octadecyloxyphenyl)pyrrolidine (6) units. All these contain the 4-octadecyloxyphenyl substituent that acts as a solubilizing group. Microwave (MiW)-assisted heating was found to be highly efficient for soluble MWNTs, for which the amount of added groups after only 2 h of MiW heating at 200 degrees C, determined by using thermogravimetric analysis, was found to be in the same range as that obtained after 100-120 h of conventional heating of soluble and insoluble MWNTs. Solubility is a key feature for a successful MiW-heated reaction; MWNTs insoluble in the reaction medium yielded considerably less addends in the MiW-heated reactions than in the conventionally heated reaction. The location and even distribution of the pyrrolidine units over the outermost layer of the MWNTs was verified by transmission electron microscopy analysis of 4 that had been treated with gold nanoparticles and thoroughly washed to remove gold particles adsorbed on nonfunctionalized parts of the MWNTs.
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Affiliation(s)
- Junxin Li
- Department of Organic Chemistry, Uppsala University, PO Box 599, 75124 Uppsala, Sweden
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348
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Kaul AB, Wong EW, Epp L, Hunt BD. Electromechanical carbon nanotube switches for high-frequency applications. NANO LETTERS 2006; 6:942-7. [PMID: 16683830 DOI: 10.1021/nl052552r] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
We describe the fabrication and characterization of a nanoelectromechanical (NEM) switch based on carbon nanotubes. Our NEM structure consists of single-walled nanotubes (SWNTs) suspended over shallow trenches in a SiO(2) layer, with a Nb pull electrode beneath. The nanotube growth is done on-chip using a patterned Fe catalyst and a methane chemical vapor deposition (CVD) process at 850 degrees C. Electrical measurements of these devices show well-defined ON and OFF states as a dc bias up to a few volts is applied between the CNT and the Nb pull electrode. The CNT switches were measured to have speeds that are 3 orders of magnitude higher than MEMS-based electrostatically driven switches, with switching times down to a few nanoseconds, while at the same time requiring pull voltages less than 5 V.
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Affiliation(s)
- Anupama B Kaul
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109, USA.
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349
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Shimazaki T, Xue Y, Ratner MA, Yamashita K. A theoretical study of molecular conduction. III. A nonequilibrium-Green’s-function-based Hartree-Fock approach. J Chem Phys 2006; 124:114708. [PMID: 16555911 DOI: 10.1063/1.2177652] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Many recent experimental and theoretical studies have paid attention to the conductivity of single molecule transport junctions, both because it is fundamentally important and because of its significance in the development of molecular-based electronics. In this paper, we discuss a nonequilibrium Green's function (NEGF)-based Hartree-Fock (HF) approach; the NEGF method can appropriately accommodate charge distributions in molecules connected to electrodes. In addition, we show that a NEGF-based density matrix can reduce to an ordinary HF density matrix for an isolated molecule if the molecule does not interact with electrodes. This feature of the NEGF-based density matrix also means that NEGF-based Mulliken charges can be reduced to ordinary Mulliken charges in those cases. Therefore, the NEGF-based HF approach can directly compare molecules that are connected to electrodes with isolated ones, and is useful in investigating complicated features of molecular conduction. We also calculated the transmission probability and conduction for benzenedithiol under finite electrode biases. The coupling between the electrodes and molecule causes electron transfer from the molecule to the electrodes, and the applied bias modifies this electron transfer. In addition, we found that the molecule responds capacitively to the applied bias, by shifting the molecular orbital energies.
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Affiliation(s)
- Tomomi Shimazaki
- Department of Chemical System Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-8656, Japan
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350
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Berber S, Oshiyama A. Atomic and electronic structures of carbon nanotubes on Si(001) stepped surfaces. PHYSICAL REVIEW LETTERS 2006; 96:105505. [PMID: 16605759 DOI: 10.1103/physrevlett.96.105505] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/19/2005] [Indexed: 05/08/2023]
Abstract
We report first-principles total-energy calculations that provide energetics and electronic structures of adsorbed carbon nanotubes (CNTs) on stepped Si(001) surfaces. We find that adsorption energies strongly depend on the directions of CNTs, and that there are several metastable adsorption sites both on terraces and near step edges. We also find that the electronic structure of adsorbed metallic CNTs becomes semiconducting or remains metallic, depending on the adsorption site. Charge redistribution upon adsorption is prominent mainly at the CNT-surface interface.
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Affiliation(s)
- Savas Berber
- Institute of Physics, University of Tsukuba, Tsukuba 305-8571, Japan.
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