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Showing papers by "Zhifeng Ren published in 2005"


Journal ArticleDOI
TL;DR: A highly efficient molecular delivery technique, named nanotube spearing, based on the penetration of nickel-embedded nanotubes into cell membranes by magnetic field driving is reported, achieving an unprecedented high transduction efficiency in Bal17 B-lymphoma, ex vivo B cells and primary neurons with high viability after transduction.
Abstract: Introduction of exogenous DNA into mammalian cells represents a powerful approach for manipulating signal transduction. The available techniques, however, are limited by low transduction efficiency and low cell viability after transduction. Here we report a highly efficient molecular delivery technique, named nanotube spearing, based on the penetration of nickel-embedded nanotubes into cell membranes by magnetic field driving. DNA plasmids containing the enhanced green fluorescent protein (EGFP) sequence were immobilized onto the nanotubes, and subsequently speared into targeted cells. We have achieved an unprecedented high transduction efficiency in Bal17 B-lymphoma, ex vivo B cells and primary neurons with high viability after transduction. This technique may provide a powerful tool for highly efficient gene transfer into a variety of cells, especially the hard-to-transfect cells.

534 citations


Journal ArticleDOI
TL;DR: Atomic-scale imaging with concurrent transport measurements of the breakdown of individual multiwall carbon nanotubes inside a transmission electron microscope equipped with a piezomanipulator finds three distinct breakdown sequences, proving unambiguously that every wall is conducting.
Abstract: We report the atomic-scale imaging with concurrent transport measurements of the breakdown of individual multiwall carbon nanotubes inside a transmission electron microscope equipped with a piezomanipulator. We found unexpectedly three distinct breakdown sequences: namely, from the outermost wall inward, from the innermost wall outward, and alternatively between the innermost and the outmost walls. Remarkably, a significant amount of current drop was observed when an innermost wall is broken, proving unambiguously that every wall is conducting. Moreover, the breakdown of each wall in any sequence initiates in the middle of the nanotube, not at the contact, proving that the transport is not ballistic.

221 citations


Journal ArticleDOI
16 Jun 2005-Analyst
TL;DR: The attractive behavior of the new carbon NEA sensing platform holds great promise for onsite environmental monitoring and biomonitoring of toxic metals.
Abstract: We describe an ultrasensitive voltammetric detection of trace heavy metal ions using nanoelectrode arrays (NEAs) that are based on low-site density carbon nanotubes (CNTs). The NEAs were prepared by sealing the side-walls of CNTs with an epoxy passive layer that reduces the current leakage and eliminates the electrode capacitance, leading to a low background current. This provides a high signal-to-noise ratio. The CNTs-NEAs coated with a bismuth film were used successfully for voltammetric detection of trace cadmium(II) and lead(II) at the sub-ppb level. The detection limit of 0.04 μg L−1 was obtained under optimum experimental conditions. The attractive behavior of the new carbon NEA sensing platform holds great promise for onsite environmental monitoring and biomonitoring of toxic metals.

125 citations



Patent
31 Oct 2005
TL;DR: In this paper, the authors proposed a nanocomposite thermoelectric materials that exhibit enhanced thermolectric properties, where two or more components are chosen such that thermal conductivity of the composite is decreased without substantially diminishing the composite's electrical conductivity.
Abstract: The present invention is generally directed to nanocomposite thermoelectric materials that exhibit enhanced thermoelectric properties. The nanocomposite materials include two or more components, with at least one of the components forming nanosized structures within the composite material. The components are chosen such that thermal conductivity of the composite is decreased without substantially diminishing the composite’s electrical conductivity. Suitable component materials exhibit similar electronic band structures. For example, a band-edge gap between at least one of a conduction band or a valence band of one component material and a corresponding band of the other component material at interfaces between the components can be less than about 5kBT, wherein kB is the Boltzman constant and T is an average temperature of said nanocomposite composition.

117 citations


Journal ArticleDOI
TL;DR: In this paper, spin-coating of an epoxy resin provides a new way to create the electrode passivation layer effectively reducing electrode capacitance and current leakage, and the CNTs-NEAs were used successfully for voltammetric detection of trace concentrations of lead(II) at ppb level at first-time.
Abstract: Fabrication, electrochemical characterization, and applications of low-site density carbon nanotubes based nanoelectrode arrays (CNTs-NEAs) are reported in this work. Spin-coating of an epoxy resin provides a new way to create the electrode passivation layer effectively reducing electrode capacitance and current leakage. Cyclic voltammetry showed the sigmoidal shape curves with low capacitive current and scan-rate-independent limiting current. Squarewave voltammetry showed well-defined peak shapes in voltammograms of K3Fe(CN)6 and 4-acetamidophenol (acetaminophen) and the peak currents to be proportioned to their concentrations, demonstrating the feasibility for voltammetric analysis of the CNTs-NEAs. The CNTs-NEAs were also used successfully for voltammetric detection of trace concentrations of lead(II) at ppb level at first-time. The CNTs-NEAs provide an excellent platform for ultra sensitive electrochemical sensors for chemical and biological sensing.

101 citations


Journal ArticleDOI
TL;DR: In this paper, the microstructure of the Pt/aligned-CNT electrode was characterized by scanning electron microscopy (SEM), and nano-scale Pt catalysts dispersed highly on CNT arrays by electrodeposition can be obtained.

74 citations


Patent
14 Oct 2005
TL;DR: In this paper, a solar cell comprising a nanostructure array capable of accepting energy and producing electricity is presented, where the optical antenna accepts energy and converts the energy from AC to DC along the rectifier.
Abstract: The present invention discloses a solar cell comprising a nanostructure array capable of accepting energy and producing electricity. In an embodiment, the solar cell comprises an at least one optical antenna having a geometric morphology capable of accepting energy. In addition, the cell comprises a rectifier having the optical antenna at a first end and engaging a substrate at a second end wherein the rectifier comprises the optical antenna engaged to a rectifying material (such as, a semiconductor). In addition, an embodiment of the solar cell comprises a metal layer wherein the metal layer surrounds a length of the rectifier, wherein the optical antenna accepts energy and converts the energy from AC to DC along the rectifier. Further, the invention provides various methods of efficiently and reliably producing such solar cells.

64 citations


Journal ArticleDOI
TL;DR: In this article, double-walled carbon nanotubes (DWCNTs) were synthesized by chemical vapour deposition using Fe-Mo catalyst supported on magnesium oxide particles.
Abstract: Double-walled carbon nanotubes (DWCNTs) were synthesized by chemical vapour deposition using Fe–Mo catalyst supported on magnesium oxide particles A mixture of gases of methane and hydrogen was used for the growth The effect of gas pressure, ratio of methane to hydrogen, and growth temperature on the structure, purity, and yield of DWCNTs has been studied in detail Transmission electron microscope studies revealed that the growth temperature is the crucial factor determining the size of the catalyst particles Scanning electron microscope studies were also carried out to provide information on the purity and diameter of DWCNTs synthesized under various conditions

57 citations


Journal ArticleDOI
18 Jan 2005-Langmuir
TL;DR: A low-temperature inverse micelle solvothermal approach for the synthesis of germanium nanocubes using the surfactant heptaethylene glycol monodododecyl ether as a capping agent is presented.
Abstract: We present a low-temperature inverse micelle solvothermal approach for the synthesis of germanium nanocubes using the surfactant heptaethylene glycol monododecyl ether as a capping agent. X-ray diffraction results indicate that the as-prepared nanocubes are diamond-type pure germanium. Transmission electron microscopy observations show that the as-prepared germanium nanocubes have an edge length of 100 ± 20 nm, highly crystallized.

39 citations


Journal ArticleDOI
TL;DR: In this paper, the field emission of carbon nanotubes (CNTs) grown on carbon cloth under various growth conditions has been studied, and the morphology of CNTs is strongly dependent on the growth conditions: temperature, gas combination, and growth time.
Abstract: Field emission of carbon nanotubes (CNTs) grown on carbon cloth under various growth conditions has been studied. Iron sulfate or stainless steel was used as the catalyst, acetylene (C2H2) or methane (CH4) was used as the carbon source, and argon (Ar), hydrogen (H2), or ammonia (NH3) was used as the carrier gas. It is found that the morphology of CNTs is strongly dependent on the growth conditions: temperature, gas combination, and growth time. In general, higher temperature produces better field emitters than lower temperature, C2H2∕Ar is better than C2H2∕NH3, but CH4∕H2 is the best, and longer growth time normally yields longer CNTs leading to better field emitters. The best sample was made from 0.18mol∕l iron sulfate catalyst with CH4∕H2 at 860 °C for 2 h: an emission current density of 1mA∕cm2 was obtained at 0.4V∕μm corresponding to a field enhancement factor of 3.5×104.

Journal ArticleDOI
TL;DR: In this article, the authors studied the dielectric properties of nanocomposites in the 0-15 GHz frequency regime and found that the properties of these composites depend crucially on the shape and monodispersity of the nanoparticles.
Abstract: We study the dielectric properties of nanocomposites in the 0–15-GHz frequency regime These composites consist of electrically insulated metallic nanoparticles and carbon nanotubes, the elongated nanostructures in this study, uniformly dispersed in a dielectric matrix We find that the properties of these composites depend crucially on the shape and monodispersity of the nanoparticles While at high concentrations the spherical nanoparticles cause only slight modification of the dielectric function of the composite with respect to the matrix, the elongated nanoparticles produce composites with an enhanced real part of the dielectric function and low imaginary part Our theory, which is in excellent agreement with these results, suggests specific ways to further improve the dielectric properties of the composites

Patent
03 May 2005
TL;DR: In this article, a thermoelectric composition comprising a plurality of nanoparticles each of which includes an alloy matrix formed of a Group IV element and Group VI element and a metallic dopant distributed within the matrix.
Abstract: The present invention generally relates to binary or higher order semiconductor nanoparticles doped with a metallic element, and thermoelectric compositions incorporating such nanoparticles. In one aspect, the present invention provides a thermoelectric composition comprising a plurality of nanoparticles each of which includes an alloy matrix formed of a Group IV element and Group VI element and a metallic dopant distributed within the matrix.

Journal ArticleDOI
TL;DR: A review of some of the results obtained to date is presented in this paper, where a review of the recent advances in enhancing the thermoelectric figure of merit are linked to nanoscale phenomena.
Abstract: Many of the recent advances in enhancing the thermoelectric figure of merit are linked to nanoscale phenomena with both bulk samples containing nanoscale constituents and nanoscale materials exhibiting enhanced thermoelectric performance in their own right. Prior theoretical and experimental proof of principle studies on isolated quantum well and quantum wire samples have now evolved into studies on bulk samples containing nanostructured constituents. In this review, nanostructural composites are shown to exhibit nanostructures and properties that show promise for thermoelectric applications. A review of some of the results obtained to date are presented.

Patent
Zhifeng Ren1, Jian Wen1, Jing Lao1, Wenzhi Li1, Shuo Chen1 
24 Mar 2005
TL;DR: In this article, reinforced carbon nanotubes (CNTs) having a plurality of boron carbide nanolumps formed substantially on a surface of the reinforced CNTs to reinforce the CNT, enabling their use as effective reinforcing fillers for matrix materials to give high strength composites.
Abstract: The present invention relates generally to reinforced carbon nanotubes, and more particularly to reinforced carbon nanotubes having a plurality of microparticulate carbide or oxide materials formed substantially on the surface of such reinforced carbon nanotubes composite materials. In particular, the present invention provides reinforced carbon nanotubes (CNTs) having a plurality of boron carbide nanolumps formed substantially on a surface of the reinforced CNTs to reinforce the CNTs, enabling their use as effective reinforcing fillers for matrix materials to give high-strength composites. The present invention also provides methods for producing carbide reinforced CNTs.

Journal ArticleDOI
TL;DR: In this paper, a two-step masking technique was used to prepare triangular lattices of catalytic nanodots at low cost using polystyrene microspheres, and then the triangular lattice of aligned carbon nanotubes on a silicon substrate was achieved by plasma enhanced chemical vapor deposition.
Abstract: Self-assembly of polystyrene microspheres has been utilized in a two-step masking technique to prepare triangular lattices of catalytic nanodots at low cost. Subsequent triangular lattices of aligned carbon nanotubes on a silicon substrate are achieved by plasma-enhanced chemical vapor deposition. Nickel is used both in the nanodots and in the secondary mask. The triangular lattices of carbon nanotube arrays as two-dimensional photonic crystals show higher geometrical symmetry than the hexagonal lattices previously reported, enabling broader applications including negative index of refraction and subwavelength lensing effect.

Journal ArticleDOI
TL;DR: The experimental results indicate that a high concentration of NaOH is essential to the formation of carbon nanotubes, which opens a new route for the synthesis of CNTs and other carbon nanostructured materials.
Abstract: We report the synthesis of highly crystallized multiwalled carbon nanotubes through a modified Wolff−Kishner reduction process at a low temperature of 180 °C without adding the conventional catalysts of Fe/Co/Ni into the reaction vessel The as-synthesized carbon nanotubes are about 10−40 nm in diameter and several tens of micrometers in length The experimental results indicate that a high concentration of NaOH is essential to the formation of carbon nanotubes This technique opens a new route for the synthesis of CNTs and other carbon nanostructured materials

Patent
03 May 2005
TL;DR: In this paper, a method for the synthesis of IV-VI nanostructures and thermoelectric compositions formed of such structures is presented, which includes forming a solution of a Group IV reagent, a Group VI reagent and a surfactant, and a reducing agent can be added to the solution, and the resultant solution can be maintained at an elevated temperature, e.g., in a range of about 20° C to about 360° C.
Abstract: The present invention provides methods for synthesis of IV–VI nanostructures, and thermoelectric compositions formed of such structures. In one aspect, the method includes forming a solution of a Group IV reagent, a Group VI reagent and a surfactant. A reducing agent can be added to the solution, and the resultant solution can be maintained at an elevated temperature, e.g., in a range of about 20° C. to about 360° C., for a duration sufficient for generating nanoparticles as binary alloys of the IV–VI elements.

Journal ArticleDOI
TL;DR: In this article, a thin film of carbonfluorine was deposited on the surfaces of aligned carbon nanotubes using a plasma polymerization treatment, and high-resolution transmission electron microscopy images revealed that the thin film was uniformly deposited.
Abstract: The thin film of carbonfluorine was deposited on the surfaces of aligned carbon nanotubes using a plasma polymerization treatment. High-resolution transmission electron microscopy images revealed that a thin film of the polymer layer (20nm) was uniformly deposited on the surfaces of the aligned carbon nanotubes. Time-of-flight secondary ion mass spectroscopy and Fourier transform infrared experiments identified the carbonfluorine thin films on the carbon nanotubes. The plasma deposition mechanism is discussed.

Patent
06 Apr 2005
TL;DR: In this paper, a method for improving thermoelectric properties of alloys by subjecting them to one or more high temperature annealing steps, performed at temperatures at which the alloys exhibit a mixed solid/liquid phase, followed by cooling steps.
Abstract: The present invention generally provides methods of improving thermoelectric properties of alloys by subjecting them to one or more high temperature annealing steps, performed at temperatures at which the alloys exhibit a mixed solid/liquid phase, followed by cooling steps. For example, in one aspect, such a method of the invention can include subjecting an alloy sample to a temperature that is sufficiently elevated to cause partial melting of at least some of the grains. The sample can then be cooled so as to solidify the melted grain portions such that each solidified grain portion exhibits an average chemical composition, characterized by a relative concentration of elements forming the alloy, that is different than that of the remainder of the grain.

Proceedings ArticleDOI
19 Jun 2005
Abstract: In this study, we developed a nano-composite approach to make bulk materials with nanostructures that have lower thermal conductivity than their bulk alloy counterparts. Room temperature measurement results of Si/Ge composites with nano-particle shows lower thermal conductivity than that of Si/Ge composites made with micro-sized particles. For high density sample, we also observed thermal conductivity reduction without deterioration of electrical conductivity so that higher ZT than bulk alloy is achieved.

Patent
15 Jul 2005
TL;DR: In this paper, a device and method for achieving a high field emission from the application of a low electric field was presented, where a plurality of nanostructures are grown on the substrate.
Abstract: A device and method is presented for achieving a high field emission from the application of a low electric field. More specifically, the device includes a substrate wherein a plurality of nanostructures are grown on the substrate. The relationship of the nanostructures and the substrate (the relationship includes the number of nanostructures on the substrate, the orientation of the nanostructures in relationship to each other and in relationship to the substrate, the geometry of the substrate, the morphology of the nanostructures and the morphology of the substrate, the manner in which nanostructures are grown on the substrate, the composition of nanostructure and composition of substrate, etc) allow for the generation of the high field emission from the application of the low electric field.

Proceedings ArticleDOI
TL;DR: In this article, a comparison of non-periodic arrays and periodic arrays of carbon nanotubes is made, and it is shown that the reflectance signature is only observed when the carbon atoms are oriented in a periodic array.
Abstract: Spectroscopic observations are presented for carbon nanotubes grown on silicon and quartz substrates in a hexagonal honeycomb configuration using self-assembly nanosphere lithography and plasma enhanced chemical vapor deposition method. A white light source is used as an incident beam and light reflected from the surface of the carbon nanotubes results in a distinctive signature in the reflected spectrum. A comparison of non-periodic arrays and periodic arrays of carbon nanotubes show that the reflectance signature is only observed when the carbon nanotubes are oriented in a periodic array. Further observations regarding the light antenna effect observed in nonperiodic arrays are also reported. Theoretical curves show good agreement to experimentally observed phenomena. The unique optical properties of the arrays combined with the excellent mechanical and electrical properties of carbon nanotubes indicate that these materials may find many uses in the field of optoelectronics.


Patent
06 Apr 2005
TL;DR: In this article, a method for improving thermoelectric properties of alloys by subjecting them to one or more high temperature annealing steps, performed at temperatures at which the alloys exhibit a mixed solid/liquid phase, followed by cooling steps.
Abstract: The present invention generally provides methods of improving thermoelectric properties of alloys by subjecting them to one or more high temperature annealing steps, performed at temperatures at which the alloys exhibit a mixed solid/liquid phase, followed by cooling steps. For example, in one aspect, such a method of the invention can include subjecting an alloy sample to a temperature that is sufficiently elevated to cause partial melting of at least some of the grains. The sample can then be cooled so as to solidify the melted grain portions such that each solidified grain portion exhibits an average chemical composition, characterized by a relative concentration of elements forming the alloy, that is different than that of the remainder of the grain.

Proceedings ArticleDOI
23 Nov 2005
TL;DR: In this paper, the growth of carbon nanotubes by chemical vapor deposition and zinc oxide nanowires by physical vapor deposition on carbon cloth with iron sulfate or stainless steel as a catalyst, and various combinations of carbon source and carrier gases.
Abstract: We have studied growth of carbon nanotubes by chemical vapor deposition and zinc oxide nanowires by physical vapor deposition on carbon cloth with iron sulfate or stainless steel as a catalyst, and various combinations of carbon source and carrier gases. The field emission of these nanostructures shows a combined result of field enhancement from carbon nanotubes or Zinc oxide nanowires and carbon cloth. An emission current density of 1 mA/cm 2 was obtained at 0.4 V/μm and 0.7 V/μm for nanotubes and nanowires, respectively. Field enhancement factor of ~4x10 4 has been observed. Moreover, electron transport characteristics and structural studies of carbon nanotubes have been investigated. Microscopic observations of electric wall-by-wall breakdown imply that transport in the nanotubes is not ballistic and that a significant scattering occurs as carriers traverse nanotubes length.