| 1. |
- Dutta, Joydeep, 1964-, et al.
(författare)
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Cluster-induced crystallization of nano-silicon particles
- 1997
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Ingår i: Nanostructured materials. - : Elsevier BV. - 0965-9773 .- 1872-9150. ; 9:1-8, s. 359-362
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Tidskriftsartikel (refereegranskat)abstract
- The possibility of producing from 20 nm to 100 nm sized silicon powders by plasma-induced reactions of silane including the formation of high-mass hydrogenated silicon anion clusters has been recently demonstrated. Careful HREM imaging showed circular contrast features, 1.5 to 2.5 nm in size, embedded in the amorphous particles which was attributed to the presence of medium range order in these regions. This non-homogeneous atomic distribution with partially ordered regions of a couple of nanometer dimension became more pronounced upon annealing upto the onset of crystallization. This observation and the formation of fivefold crystallites thereafter indicate that the clusters serve as seeds in the amorphous-to-crystalline transition.
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| 2. |
- Hedlund, Jonas, et al.
(författare)
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Synthesis of thin molecular sieve films
- 1999
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Ingår i: Nanostructured materials. - 0965-9773 .- 1872-9150. ; 12:1-4, s. 413-416
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Tidskriftsartikel (refereegranskat)abstract
- A method to synthesize thin films of various molecular sieves on a number of substrates employing pre-seeding has been developed. The substrate is modified to enable adsorption of seed crystals. Substrates with an originally negative surface charge are charge reversed by adsorption of cationic polymer molecules. Nobel metal substrates are first silanized to obtain a negative surface charge. Nano seed crystals are adsorbed on the modified substrates from a sol and induced to grow in a synthesis solution to form a dense film with controlled thickness. The versatility of the method may be of great value in the development of novel applications. Films have been tested in membrane and sensor applications with successful results.
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| 3. |
- 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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| 4. |
- 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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| 5. |
- Schoeman, Brian J., et al.
(författare)
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Nanoparticles of microporous materials
- 1999
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Ingår i: Nanostructured materials. - 0965-9773 .- 1872-9150. ; 12:1, s. 49-54
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Tidskriftsartikel (refereegranskat)abstract
- The hydrolysis and condensation of tetraethoxy silane in the presence of structure directing agents, such as the tetraalkylammonium cations, results in the formation of microporous siliceous particles with average sizes in the range 2 to 5 nm, the size being a function of the hydrolysis conditions and the composition of the mixture. Increased dilution favors larger particles while increased pH results in smaller particles. The option of isomorphous substitution of silicon for either alumina or titania is also shown to result in nano-sized particles were the substituted metals exist in the tetrahedral coordination
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| 6. |
- Wahlberg, Sverker, et al.
(författare)
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Nanostructured hard material composites by molecular engineering .1. Synthesis from soluble tungstate salts
- 1997
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Ingår i: Nanostructured materials. - 0965-9773 .- 1872-9150. ; 9:1-8, s. 105-108
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Tidskriftsartikel (refereegranskat)abstract
- A key issue, in the development of very fine grades, is to produce materials with high uniformity. The aqueous chemistry of tungsten offers several possibilities for the synthesis of homogenous molecular precursors containing W and Co mixed on the atomic scale. Powders containing (NH4)(8)[H2Co2W11O40] have been prepared starting from sodium tungstate or ammonium metatungstate. Nanophase powders of W-Co and WC-Co powders were obtained after reduction at 750 degrees C under H-2 and carburisation at 1000 degrees C under H-2/CH4. Hard materials with submicron microstructures were obtained after sintering at 1410 degrees C.
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| 7. |
- Zhang, Zongyin, et al.
(författare)
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Processing of nanostructured WC-Co powder from precursor obtained by co-precipitation
- 1999
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Ingår i: Nanostructured materials. - 0965-9773 .- 1872-9150. ; 12:1-4, s. 163-166
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Tidskriftsartikel (refereegranskat)abstract
- The paper reports the processing of a homogenous cobalt tungstate salt synthesised by co-precipitation starting from ammonium paratungstate and cobalt hydroxide. Different processing parameters such as temperatures and times of reduction and carburization and the composition of the carburization gas were studied. Powders of W and Co were obtained after the reduction of the precursor at 600 'C, 650 'C and 700 'C. The specific surface area of W-Co powders increased with decreasing reduction temperature. The carburization was carried out at 700 'C for 3 hours in different CO/CO2 - mixtures. The extent of the reaction was found to depend on the CO/CO2 - ratio. A nanophase WC-Co powder agglomerated at the micrometer scale was obtained after carburization in a 90%CO/10%CO2 gas-mixture.
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| 8. |
- Deppert, Knut, et al.
(författare)
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Feasibility study of nanoparticle synthesis from powders of compounds with incongruent sublimation behavior by the evaporation/condensation method
- 1998
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Ingår i: Nanostructured Materials. - 0965-9773. ; 10:4, s. 565-573
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we investigate the feasibility of a fabrication route to produce nanocrystals of compound material with incongruent sublimation behavior via the simple evaporation of the powder of the compound. The generation of stoichiometric particles would only be possible if the particle formation occurs at temperatures below the incongruent sublimation point. Our experiments, done on three different III-V compounds, show that the simple evaporation of the powder of those materials to obtain stoichiometric particles is not possible. Particle formation does not start at temperatures below the incongruent sublimation point. Particles synthesized consisted not of the compound but almost entirely of the more volatile group-Velement, leading to a change in the composition of the source material and thus to irreproducible behavior.
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| 9. |
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| 10. |
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| 11. |
- Elihn, K, et al.
(författare)
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Nanoparticle formation by laser-assisted photolysis of ferrocene.
- 1999
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Ingår i: NANOSTRUCTURED MATERIALS. - 0965-9773. ; 12:1-4, s. 79-82
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Tidskriftsartikel (refereegranskat)abstract
- Laser-assisted formation of iron-containing nanoparticles has been performed by photolytic dissociation of ferrocene vapour by a pulsed ArF excimer laser at 193 nm. The process was carried out at atmospheric pressure, either in an inert atmosphere of argo
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| 12. |
- Hartmann, O, et al.
(författare)
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Positive muons in nanocrystalline transition metals diffusion and magnetic nanostructure
- 1999
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Ingår i: NANOSTRUCTURED MATERIALS. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0965-9773. ; 12:5-8, s. 943-946
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Systematic studies with Muon Spin Rotation (mu SR) on nano-Cu and nano-Ni samples produced by pulsed electrodeposition, demonstrates that the diffusion of mu+ in nanocrystalline metals is influenced by the nanostructure. In nano-Cu the mobility of muons i
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| 13. |
- Keis, K, et al.
(författare)
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Nanostructured ZnO electrodes for photovoltaic applications
- 1999
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Ingår i: NANOSTRUCTURED MATERIALS. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0965-9773. ; 12:1-4, s. 487-490
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Photoelectrochemical properties of nanostructured ZnO (wurtzite) electrodes have been investigated. Studies were carried out on various types of electrodes with controlled morphology, particle size and doping. The monochromatic photon-to-current conversio
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| 14. |
- Kish, LB, et al.
(författare)
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The real origin of lognormal size distributions of nanoparticles in vapor growth processes
- 1999
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Ingår i: NANOSTRUCTURED MATERIALS. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0965-9773. ; 12:1-4, s. 327-332
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Tidskriftsartikel (refereegranskat)abstract
- In modern nanoparticle production methods, such as inert-gas evaporation, a strong effort is made to avoid coagulation of particles. Therefore, the classical coagulation models are not suitable for predicting the particle size distribution. This paper
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| 15. |
- Palmqvist, AEC, et al.
(författare)
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Surfaces of doped nanophase cerium oxide catalysts
- 1999
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Ingår i: NANOSTRUCTURED MATERIALS. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0965-9773. ; 11:8, s. 995-1007
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Tidskriftsartikel (refereegranskat)abstract
- Solid solutions of nanophase cerium oxides have been prepared and the relationship between their bulk crystal structure and surface characteristics has been studied at room temperature with X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS
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| 16. |
- Sotelo, JA, et al.
(författare)
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Optical properties of quasifractal metal nanoparticle aggregates
- 1999
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Ingår i: NANOSTRUCTURED MATERIALS. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0965-9773. ; 12:1-4, s. 135-138
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Tidskriftsartikel (refereegranskat)abstract
- We calculate the optical extinction efficiency of two-dimensional small quasifractal aggregates consisting of metal nanoparticles. Computations were carried out in the octupolar approximation for aggregates of 25 particles. Calculations for gold particles
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| 17. |
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