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- Svechnikov, S., et al.
(författare)
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Spiral antenna nbn hot-electron bolometer mixer at submm requencies
- 1997
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Ingår i: IEEE Transactions on Applied Superconductivity. - : Institute of Electrical and Electronics Engineers (IEEE). - 1558-2515 .- 1051-8223. ; 7:2, s. 3395-3398
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Tidskriftsartikel (refereegranskat)abstract
- We have studied the phonon-cooled hot-electron bolometer (HEB) as a quasioptical mixer based on a spiral antenna designed for the 0.3-1 THz frequency band and fabricated on sapphire and high resistivity silicon substrates. HEB devices were produced from superconducting 3.5-5 nm thick NbN films with a critical temperature 10-12 K and a critical current density of approximately 10/sup 7/ A/cm/sup 2/ at 4.2 K. For these devices we reached a DSB receiver noise temperature below 1500 K, a total conversion loss of L/sub t/=16 dB in the 500-700 GHz frequency range, an IF bandwidth of 3-4 GHz and an optimal LO absorbed power of /spl sime/4 /spl mu/W. We experimentally analyzed various contributions to the conversion loss and obtained an RF coupling factor of about 5 dB, internal mixer loss of 10 dB and IF mismatch of 1 dB.
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| 4. |
- Bossel, C., et al.
(författare)
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Processing of nano-scaled silicon powders to prepare slip cast structural ceramics
- 1995
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Ingår i: Journal of Materials Science and Engineering. - : Elsevier BV. - 2161-6213 .- 0921-5093. ; 204:1-2, s. 107-112
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Tidskriftsartikel (refereegranskat)abstract
- For slip casting of ceramic powders it is necessary to have a well-defined and thus disagglomerated colloidal suspension. Proper selection of the solvent is required in order to achieve separation of the particles to obtain a homogenous mixture of the powders which is necessary for shaping complex geometrical structures, often used in structural ceramics. Here we report a preliminary investigation of the deagglomeration phenomena of nano-scaled silicon powders obtained by plasma induced dissociation of silane and compare it with silicon nitride powders prepared by laser induced condensation reactions and a commercial product (UBE SE E-10). The size dispersion of aggregates in colloidal suspensions, determined by photon correlation spectroscopy and sedimentation particle size analysis techniques, varies from 20 to 500 nm. Variation in the deagglomeration properties of the particles in different solvents depends on the surface property of the powders, and on the inter-particle interactions. These are studied with respect to the variations in the surface property of the powders in different solvents. Ethanol was found to be a suitable solvent for the colloidal suspension as the average aggregate radii of the silicon powders could be reduced to 80 nm.
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| 7. |
- 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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| 8. |
- 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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