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  • 1
    ISSN: 1572-896X
    Keywords: nanoclusters ; powder synthesis ; FTIR spectroscopy ; laser prolysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics , Technology
    Notes: Abstract Pulsed CO2-laser-induced decomposition of different mixtures of SiH4 and C2H2 in a flow reactor has been employed to produce silicon carbide clusters and nanoparticles with varying content of carbon. The as-synthesized species were extracted from the reaction zone by a conical nozzle and expanded into the source chamber of a cluster beam apparatus where, after having traversed a differential chamber, they were analyzed with a time-of-flight mass spectrometer. Thin films of silicon carbide nanoclusters were produced by depositing the clusters at low energy on potassium bromide and sapphire windows mounted into the differential chamber. At the same time, Si and SiC nanoparticles were collected in a filter placed into the exhaust line of the flow reactor. Both beam and powder samples were characterized by FTIR spectroscopy. The close resemblance of the spectra suggests that the composition of the beam and powder particles obtained during the same run is nearly identical. XRD spectroscopy could only be employed for the investigation of the powders. It was found that CO2 laser pyrolysis is ideally suited to produce silicon carbide nanoparticles with a high degree of crystallinity. Nanopowders produced from the pyrolysis of a stoichiometric (2:1) mixture of SiH4/C2H2 were found to contain particles or domains of pure silicon. The characteristic silicon features in the FTIR and XRD spectra, however, disappeared when C2H2 was applied in excess.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 9 (1999), S. 137-140 
    ISSN: 1434-6079
    Keywords: PACS: 61.16.-d Electron, ion, and scanning probe microscopy – 61.46.+w Clusters, nanoparticles, and nanocrystalline materials – 81.05.-t Specific materials: fabrication, treatment, testing and analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. We used laser-induced decomposition of silane for the fabrication of nanosized Si particles and studied in detail their structural characteristics by conventional and high resolution electron microscopy. The silane gas flow reactor incorporated in a molecular beam apparatus was operated without size selection to achieve a broad size distribution. Deposition at low energy on carbon substrates yielded single crystalline, spherical Si particles almost completely free of planar lattice defects. The particles, covered by thin amorphous oxide shells, are not agglomerated into larger aggregates. The lattice of diamond cubic type exhibits deviations from the bulk spacing which vary from distinct contraction to dilatation as with decreasing particle size the oxide shell thickness is reduced. This effect is discussed in terms of the strong Si/oxide interfacial interaction and compressive stresses arising upon oxidation. A negative interface stress, as determined from the size dependence of the lattice spacing, limits the curvature of the interface, i.e., at small sizes Si oxidation must be considered as a self-limiting process.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1434-6079
    Keywords: PACS: 61.46.+w Clusters and nanoparticles – 81.15.Gh Chemical vapor deposition – 82.50.Fv Photolysis – 82.80.Ms Mass spectrometry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. Laser-induced decomposition of iron pentacarbonyl in a flow reactor has been used to produce iron clusters and nanoparticles. The as-synthesized species are extracted from the reaction zone by a conical nozzle and expanded into the source chamber of a cluster beam apparatus where, after having traversed a differential chamber, they are analyzed in situ with a time-of-flight mass spectrometer. Three different lasers have been employed to accomplish decarbonylation of the Fe(CO)5 molecules. A pulsed CO2 laser (λ=10.6 μm) was used to excite a mixture of SF6 and Fe(CO)5 and to pyrolyze the iron pentacarbonyl. Laser photolysis was performed by directly dissociating the Fe(CO)5 molecules with UV radiation. For this purpose, we used the tripled (λ=355 nm) and quadrupled (λ=266 nm) Nd:YAG laser as well as an ArF excimer laser (λ=193 nm). The mass spectrometric analysis showed that only the Nd:YAG laser produced high purity iron clusters which were essentially free of contamination.
    Type of Medium: Electronic Resource
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