We report the controlled synthesis of multiwalled carbon nanotube−quantum dot (CNT-QD) heterojunctions using the ethylene carbodiimide coupling procedure (EDC). Thiol-stabilized ZnS-capped CdSe quantum dots containing amine terminal groups (QD−NH 2 ) were conjugated with acid-treated multiwalled carbon nanotubes (MWCNT) ranging from 400 nm to 4 µm in length. Scanning and transmission electron microscopy were used to characterize the conjugation process.The unique electrical, mechanical, and chemical properties of carbon nanotubes have made them intensively studied materials in the field of nanotechnology. [1][2][3][4] A number of device applications of these nanoscale materials have been envisioned. [5][6][7][8][9][10] Single-walled carbon nanotubes (SWCNTs) 11 and multiwalled carbon nanotubes (MWCNTs) 12,13 under special conditions have been shown to possess ballistic conduction behavior, which makes them attractive candidates for field-emission devices. 14 SWCNTs indicate either metallic or semiconductor behavior depending on their chirality 15 and radial dimension. 16,17 Although the electronic properties of MWCNTs 18-20 are less well known, they have been shown to exhibit either metallic 19 or semiconducting properties 20 depending on their outermost shell. The intershell interactions in an MWCNT are weak; therefore, electrical transport is confined to the outermost shell. 17 It has been shown recently that it is possible to manipulate the electrical properties of an MWCNT by using current-induced oxidation to break down systematically the outermost shells layer by layer. 21 This opens up the possibility of selecting the tube with the desired electrical property. In addition, doping 8 and the introduction of defects 20 or distortion 22 into the CNTs have also been utilized for manipulating their energy-band structure. The versatile electrical properties of CNTs make them promising candidates for nanoscale electronic devices, 12,14,23,24 especially transistors. 25,26 In most of the previous work on CNT-based nanoscale transistors, control over the electrical
We report the hierarchical self-assembly of ZnO nanoparticles on single-walled carbon nanotubes (SWCNT–ZnO) and multi-walled carbon nanotubes (MWCNT–ZnO) by utilizing an electrostatic coordination approach. The affinity for Zn atoms to the oxygen of the C = O in the carboxyl groups is utilized to decorate oxidized single-walled and multi-walled carbon nanotubes with ZnO nanoparticles. The CNT–ZnO structures are indicative of the carboxyl group distribution along the carbon nanotubes (CNTs). By this technique we have achieved complex design architecture such as T- and Y-junctions that would be useful for device applications. The ZnO conjugation is a reversible process; that is, the ZnO nanoparticles can be washed off from the CNTs by dissolving in NaOH or H2SO4. The conjugation leaves the suspension with carbon nanotubes of smaller lengths compared to the average lengths of the material that we started with. Scanning and transmission electron microscopy along with energy dispersive spectroscopy (EDS) were used to characterize the conjugation.
Recently, semiconducting nanoparticles have been successfully applied in live mammalian cell cultures, as alternative biological labels for multicolour imaging, by verifying known physiological processes. Here, we report the application of semiconducting nanoparticles to live plant cells in culture. Utilizing this technique, we have uncovered new knowledge regarding the localization of a plant pollen tube adhesion protein, stigma/stylar cysteine-rich adhesin (SCA). The potential of these nanoparticles is evident when the results were compared with conventional immunolocalization methods using fluorescently labelled antibodies.
Monte Carlo simulations are performed to investigate the effects of salt concentration, valence and size of small ions, surface charge density, and Bjerrum length on the overcharging of isolated spherical nanoparticles within the framework of a primitive model. It is found that charge inversion is most probable in solutions containing multivalent counterions at high salt concentrations. The maximum strength of overcharging occurs near the nanoparticle surface where counterions and coions have identical local concentrations. The simulation results also suggest that both counterion size and electrostatic correlations play major roles for the occurrence of overcharging.
The possibility of selectively assembling three-dimensional structures along bundles of single-walled carbon nanotubes (SWCNTs) will pave the way to using SWCNTs as nanoconducting templates that can spontaneously integrate into a conductive probe or pathway in a nano device. In the past 2 years, ZnO microcages have attracted interest due to their potential application in the remote coupling of electromagnetic signals into nanoscale machines or devices. We report here, for the first time, highly selective self-assembly of ZnO cages on bundles of conducting SWCNT templates. For the selective Zn nucleation we use electrostatic coordination of carboxyl groups on the SWCNTs to Zn atoms. Bundles of SWCNTs perform a dual function as templates for growth and as scaffolds providing structural integrity to the hollow ZnO spheres (20 nm wall thickness).
The effect of ion size on the mean force between a pair of isolated charged particles in an electrolyte solution is investigated using Monte Carlo simulations within the framework of the primitive model where both colloidal particles and small ions are represented by charged hard spheres and the solvent is treated as a dielectric continuum. It is found that the short-ranged attraction between like-charged macroions diminishes as the diameter of the intermediating divalent counterions and coions increases and the maximum attractive force is approximately a linear function of the counterion diameter. This size effect contradicts the prediction of the Asakura-Oosawa theory suggesting that an increase in the excluded volume of small ions would lead to a stronger depletion between colloidal particles. Interestingly, the simulation results indicate that both the hard-sphere collision and the electrostatic contributions to the mean force are insensitive to the size disparity of colloidal particles with the same average diameter.
We report the fabrication of Prussian blue nanotubes and nanowires via a novel technique wherein a liquid metal surface is nano-patterned with a porous polycarbonate membrane used as a hard mask. Prussian blue as 1D nanowires and nanotubes is an excellent candidate for ultra-low level sensing, optical waveguides and model systems to test the one-dimensional Ising model. One of the most feasible techniques for nanowire fabrication is to use a porous template. However, Prussian blue dissolves in strong acids and decomposes in strong bases. Conventional procedures which use porous alumina blocked with a back side metal contact require strong acid and base treatment in the various steps of the nanowire fabrication. We report a novel technique which will pave a new route for the facile synthesis of nanowires and nanotubes of materials that are sensitive to strong acidic or basic treatment. Hence, nano-patterning of a liquid metal (Hg, which functions as a top-side metal contact) with polycarbonate membrane instead of porous alumina membrane excludes the necessity of both strong acid and base during the fabrication of nanowires. By attempting this innovative technique, we report the synthesis of novel organic Prussian blue nanotubes and nanowires.
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