| 1. |
- Hornyak, G. L., et al.
(författare)
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Dynamical Maxwell-Garnett optical modeling of nanogold-porous alumina composites : Mie and kappa influence on absorption maxima
- 1997
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Ingår i: Nanostructured materials. - : Elsevier BV. - 0965-9773 .- 1872-9150. ; 9:1-8, s. 575-578
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Tidskriftsartikel (refereegranskat)abstract
- Composites consisting of nanogold in porous alumina host membranes have been fabricated and characterized. Nanocluster size (11 nm to 60 nm radius) and shape (prolate to oblate) were varied experimentally. Two phenomena were responsible for the position of maximum absorption (λmax) of the composites. First, light scattering due to extrinsic electrodynamic effects became important as particle size was increased. This resulted in red shifts in λmax and is known as the Mie effect. Secondly, blue shifts were induced as particle aspect ratio was increased. We have designated shifts due to particle shape and orientation as the "kappa" effect. The two appeared to exert their influence independently. Simulations by means of the dynamical Maxwell-Garnett (DMG) expression resulted in good correlation with experimental λmax. We demonstrate again the versatility of the template method of synthesizing nanostructured materials. © 1997 Acta Metallurgica Inc.
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| 2. |
- Hornyak, G. L., et al.
(författare)
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Effective medium theory characterization of Au/Ag nanoalloy-porous alumina composites
- 1997
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Ingår i: Nanostructured materials. - : Elsevier BV. - 0965-9773 .- 1872-9150. ; 9:1-8, s. 571-574
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Tidskriftsartikel (refereegranskat)abstract
- The optical constants nAl and kAl of a 50/50 volume fraction Au/Ag alloy were derived synthetically by application of a Bruggeman (BG) effective medium expression. The alloy data base was then input into a Maxwell-Garnett (MG) effective medium expression to determine the absorption maximum of the nano- alloy/insulator composite (the volume fraction of the nano-alloy was equal to 5%). The absorption maximum (λmax) of the hypothetical composite was found to be 499 nm for spherical particles and was blue-shifted relative to that of a composite containing pure gold nanospheres (499 vs. 528 nm respectively). The transmission color at this wavelength was a red-orange. λmax in the range 512 to 519 nm (Au/Ag alloy between 60/40 - 70/30 volume fraction respectively) is needed to obtain the scarlet-red exhibited by the famous Lycurgus cup of 4th century Rome (1). © 1997 Acta Metallurgica Inc.
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| 3. |
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| 4. |
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| 5. |
- Dutta, Joydeep, 1964-, et al.
(författare)
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Crystallization of nanosized silicon powder prepared by plasma-induced clustering reactions
- 1997
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Ingår i: AIChE Journal. - 0001-1541 .- 1547-5905. ; 43:11 A, s. 2610-2615
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Tidskriftsartikel (refereegranskat)abstract
- Nanosized silicon powders were prepared by gas-phase cluster agglomeration reactions in a low-pressure silane plasma. The formation and agglomeration of clusters leading to the growth of primary particles of powder were studied by in-situ techniques including mass spectroscopy and laser light-scattering experiments. These powders, generally amorphous and crystallized in a reducing atmosphere, were studied in detail by Raman spectroscopy and high-resolution electron microscopy, which revealed a very rough surface of as-prepared single powder particles with structures of 1 to 2 nm. Upon 1-h annealing at temperatures between 300 and 600 °C, circular contrast features, 1.5 to 2.5 nm in size, are observed in the amorphous particles, which show medium-range order. A distinct onset of crystallization is observed at 700 °C with structures ranging from very small crystalline ordered regions of 2.5-3.5 nm in size to fast-grown multiple-twinned crystallites. The crystallization behavior is influenced by the clusters that form primary particles. Observed sintering behavior cannot be explained by a classical approach; hence, theoretical models need to be adapted to nanosized powders.
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| 6. |
- Vacassy, R., et al.
(författare)
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Synthesis of zirconia-coated gold nanoparticles
- 1998
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Ingår i: Journal of materials science letters. - : Kluwer Academic Publishers. - 0261-8028 .- 1573-4811. ; 17:19, s. 1665-1667
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Tidskriftsartikel (refereegranskat)
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| 7. |
- Valmalette, J. -C, et al.
(författare)
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Optical properties of gold clusters precipitated on zirconia particles
- 1998
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Ingår i: Materials Research Society Symposium - Proceedings. - : MRS, Warrendale, United States. ; , s. 85-88
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Konferensbidrag (refereegranskat)abstract
- We have studied precipitation of noble metals with a view to extending these synthetic processes to other metals. In this paper we discuss the synthesis of gold clusters on the surface of oxide fine particles (in the range 60-100 nm). The influence of pH of the solution, the concentration of metal and the reducing agent are discussed. The size distribution of the precipitated gold clusters, determined by transmission electron microscopy, are around 2-10 nm. The interface between the gold clusters and oxide has been investigated by HRTEM. Optical measurements of the zirconia supported gold clusters shows a significant shift in the plasmon resonance. A model based on effective medium theory is proposed taking into account the high refractive index of zirconia.
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