| 1. |
- Warad, H. C., et al.
(författare)
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Luminescent nanoparticles of Mn doped ZnS passivated with sodium hexametaphosphate
- 2005
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Ingår i: Science and Technology of Advanced Materials. - : Elsevier. - 1468-6996 .- 1878-5514. ; 6:3-4 SPEC. ISS., s. 296-301
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Tidskriftsartikel (refereegranskat)abstract
- We report the synthesis of luminescent nanoparticles of manganese doped zinc sulfide (ZnS:Mn2+) with an emission peak at around 590 nm. Nanoparticles of ZnS:Mn2+ are prepared by a co-precipitation reaction from homogenous solutions of zinc and manganese salts. Based on Ostwald ripening and surface passivation, we discuss a mechanism for the formation of ZnS:Mn2+ nanoparticles. The reaction proceeds with the nucleation of ZnS crystals, which are immediately passivated by the anions in the solution. This in turn attracts cations including zinc and manganese which contribute to the growth of the crystal. These nanoparticles are sterically stabilized using polyphosphates of sodium namely sodium tripolyphosphate (STTP) and sodium hexametaphosphate (SHMP). The nanoparticles consist of particles of 60-80 nm in diameter, each containing primary crystallites that was estimated from the X-ray diffraction patterns to be at around 2.2 nm
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| 2. |
- Hossain, M. K., et al.
(författare)
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Growth of Zinc Oxide nanowires and nanobelts for gas sensing applications
- 2005
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Ingår i: Journal of Metastable and Nanocrystalline Materials. - 1422-6375. ; 23, s. 27-30
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Tidskriftsartikel (refereegranskat)abstract
- Zinc Oxide (ZnO) is a very useful as a solid state gas sensor material. In chemical sensing the surface and interface interactions between the analyte molecules and the sensing material is all but important that is read through the changes in electrical conductance. In that sense, nano-objects with a large surface atom/bulk atom ratio, like nanoparticles and nanowires, are potentially the best chemical sensors. The mechanism envisioned involves the adsorption (and eventually diffusion) of the analyte molecule at the surface that induces a change in the electrical resistance of the nano-object. The most convenient way to measure changes in electrical resistance in such devices is to obtain the specific material as nanowires or as connected nanoparticles. Here, we will discuss about a low-temperature wet-chemical process of synthesizing ZnO nanoparticles, nanowires and nanobelts for application as gas sensors.
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| 3. |
- Baruah, S., et al.
(författare)
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Growth of ZnO nanowires on nonwoven polyethylene fibers
- 2008
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Ingår i: Science and Technology of Advanced Materials. - : Taylor & Francis. - 1468-6996 .- 1878-5514. ; 9:2
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Tidskriftsartikel (refereegranskat)abstract
- We report the growth of ZnO nanowires on nonwoven polyethylene fibers using a simple hydrothermal method at a temperature below the boiling point of water. The ZnO nanowires were grown from seed ZnO nanoparticles affixed onto the fibers. The seed ZnO nanoparticles, with diameters of about 6-7 nm, were synthesized in isopropanol by reducing zinc acetate hydrate with sodium hydroxide. The growth process was carried out in a sealed chemical bath containing an equimolar solution of zinc nitrate hexahydrate and hexamethylene tetramine at a temperature of 95°C over a period of up to 20 h. The thickness and length of the nanowires can be controlled by using different concentrations of the starting reactants and growth durations. A 0.5 mM chemical bath yielded nanowires with an average diameter of around 50 nm, while a 25 mM bath resulted in wires with a thickness of up to about 1 μm. The length of the wires depends both on the concentration of the precursor solution as well as the growth duration, and in 20 h, nanowires as long as 10 μm can be grown. The nonwoven mesh of polyethylene fibers covered with ZnO nanowires can be used for novel applications such as water treatment by degrading pollutants by photocatalysis. Photocatalysis tests carried out on standard test contaminants revealed that the polyethylene fibers with ZnO nanowires grown on them could accelerate the photocatalytic degradation process by a factor of 3.
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| 4. |
- Hemtanon, B., et al.
(författare)
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Diode fabricated by layer by layer deposition of semiconductor nanoparticles
- 2007
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Konferensbidrag (refereegranskat)abstract
- We report the development of a modified polyelectrolyte deposition technique for building multilayer thin films. The quantum dots of zinc sulphide nanoparticles doped with manganese were synthesized by co-precipitation techniques and the nanoparticles were found to consist of crystallites that were estimated to be around 2.2 nm. The modified polyelectrolyte deposition technique has been used for the growth of multifunctional nanoparticulate ZnS thin films and schottky diodes. The Schottky junction device exhibit diode-like behavior and this technique shows promise for large area construction of diodes using wet-chemical synthesis of semiconductor nanoparticles.
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| 5. |
- Jafri, S. H. M., et al.
(författare)
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Directed self-assembly of multilayer thin films of ZnS and gold nanoparticles by modified polyelectrolyte deposition technique
- 2005
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Ingår i: Materials Research Society Symposium Proceedings. - : Materials Research Society. - 1558998551 - 9781558998551 ; , s. 483-494
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Konferensbidrag (refereegranskat)abstract
- Fabrication strategies based on mechanisms of self-assembly are now widely being recognized as inevitable tools in nanotechnology. Self-organized construction of advanced materials and devices may be done starting with tailor made nanoparticles as building blocks. Multilayer thin films of gold, zinc sulphide and manganese doped zinc Sulfide nanoparticles were fabricated by a modified polyelectrolyte deposition process, A prerequisite to utilization of colloids for the fabrication of uniform layers is that they remain in suspension and resist unwanted agglomeration. The stability of colloids is generally achieved either by electrostatic stabilization, involving the creation of an electrical double layers arising from ions intentionally adsorbed on the surface of the particle and associated counter ions that surround the particle, or by steric hindrance that is achieved by the adsorption of macromolecules on the surface of the particles. The inherent necessity to introduce electrostatic or steric hindrance to avoid colloidal agglomeration was utilized to induce self-assembly of multilayers applying similar concept used for the layering of polyelectrolytes. Polyacrylic acid was used as the polyanion and chitosan as the polycation for the deposition process. Upto 100 layers of nanoparticles were constructed and films that wore found to be stable and uniform over the substrate. The layer-by-layer deposition of multilayers of several different structures was prepared and devices showing resistive and capacitive electrical characteristics have been fabricated. The onset of electrical conduction in the resistive devices could be varied by introducing a dielectric interlayer between gold nanoparticles and by introducing a gold overlayer on the zinc sulphide nanoparticle devices.
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| 6. |
- Sugunan, A, et al.
(författare)
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Heavy-metal ion sensors using chitosan-capped gold nanoparticles
- 2005
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Ingår i: Science and Technology of Advanced Materials. - : Informa UK Limited. - 1468-6996 .- 1878-5514. ; 6:3-4, s. 335-340
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Tidskriftsartikel (refereegranskat)abstract
- We report a novel strategy for using gold nanoparticles capped with chitosan for sensing ions of heavy metals. Acidic anions (glutamate ions in our case) are expected to cap the nanoparticle surfaces similar to conventional methods of stabilization of gold nanoparticles by citrate ions. The polycationic nature of chitosan enables attachment of the polymer to the negatively charged gold nanoparticle surfaces through electrostatic interactions. Use of chitosan serves dual purpose of providing sufficient steric hindrance ensuring stability of the colloid and also to functionalize the nanoparticles for use as sensors. The well-documented chelating properties of chitosan and the sensitivity of the optical properties of gold nanoparticles to agglomeration have been employed to detect low concentrations of heavy metals ions (Zn2+ and Cu2+) in water. A comparison of the optical absorption spectra of the colloidal suspension before and after exposure to metal ions is a good indicator of the concentration of the heavy metal ions.
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