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  • 1
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 1000-1007 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The effects of reaction and transport kinetics on deposition resulting from laser-induced gas-phase photodissociation were investigated using numerical and analytical models. Deposition rates and deposit profiles for a laser beam focused onto a substrate in a chamber were determined assuming production of metal atoms in the gas phase by a single-photon dissociation mechanism and free-molecular and diffusive transport to chamber surfaces. The predictions of the model computations were compared to experimental and theoretical results from the literature. The effect of total pressure on deposition rates and profiles depends strongly on the sticking coefficient. With a sticking coefficient of unity, deposition rates and profiles do not depend strongly on the total pressure or transport regime. However, when the sticking coefficient is 0.01, the deposit profile flattens dramatically at pressures below about 1 atm. The conditions and consequences of gas-phase reactant depletion due to diffusional limitations were also demonstrated. The extent of gas-phase reactant depletion can be predicted by a single dimensionless group; however, transport of the reaction product must also be considered to predict deposition rates. At high laser power or total pressure, reactant depletion leads to reduced deposition rates and flatter deposit profiles, and severe depletion can produce volcano-shaped deposits.
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 221-226 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Time-resolved reflectance measurements have been used to study the time evolution of the surface reflectance during deposition of gold from dimethylgold hexafluoroacetylacetonate with both modulated and unmodulated laser light. The observed change in reflectivity found during deposition with a modulated laser source is due to surface melting or sintering of the gold deposit. The change in reflectance observed upon undergoing a transition from a rough to a smooth surface is theoretically calculated for a surface with a random distribution of facet shapes and sizes. The observed changes in reflectance are consistent with the rough polycrystalline surface layer becoming smooth in a transient molten state. An impulsive temperature rise due to a rapid exothermic reaction taking place at the leading edge of the laser pulse has been estimated theoretically and is consistent with the observed time-dependent data.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
    ISSN: 1551-2916
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Maschinenbau , Physik
    Notizen: The influence of precursor characteristics and synthesis conditions on the formation of yttrium aluminum garnet, Y3Al5O12 (YAG), was investigated using “single-source” precursors (cohydrolyzed yttrium and aluminum alkoxides and yttrium aluminum glycolates) and “multiple-source” precursors (mixtures of metal nitrates and mixtures of separately hydrolyzed yttrium and aluminum alkoxides). Phase-pure YAG was formed only in the solid-state thermal decomposition experiments. The lack of formation of YAG in all the spray-pyrolysis experiments was ascribed to the short heating times and fast heating rates, which resulted in the formation of kinetic products. In the case of the metal nitrates, an additional factor that influenced product formation was the difference in thermal reactivity of the precursors. It was concluded that the formation of complex metal oxide materials by conventional or aerosol routes is not necessarily achieved by the use of a chemically homogeneous precursor, such as a single-source precursor. It also was necessary to ensure that the precursors and intermediates have similar thermal decomposition temperatures to avoid phase segregation in the initial stages of thermal decomposition.
    Materialart: Digitale Medien
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  • 4
    ISSN: 1520-510X
    Quelle: ACS Legacy Archives
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 56 (1990), S. 2693-2695 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Thermal laser-induced chemical vapor deposition of gold crystals on alumina substrates has been studied using a modulated Ar+ laser. Deposition of gold from dimethylgold hexafluoroacetylacetonate is accompanied by surface melting of the deposit when the laser source is modulated. Time-resolved reflectance measurements have been used to study the time evolution of the surface reflectance during growth with both modulated and unmodulated laser light. These experiments suggest that the surface melting observed with a modulated laser source is primarily due to the heat released by the exothermic decomposition of reactant adsorbed on the surface during the time that the laser intensity is off.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 6
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 51 (1987), S. 2059-2061 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The surface chemical reactions occurring during the laser-assisted deposition of gold from dimethyl gold hexafluoroacetylacetonate were studied using a photothermal modulation technique. A modulated argon ion laser was used to heat an area roughly 1 mm in diameter on an alumina substrate. Products of the photothermal reaction along with reactants were sampled through a 150×150 μm orifice located at the center of the deposit and were then introduced directly into a quadrupole mass filter. An inert buffer gas was required to confine changes in the reactant and product concentrations to the region surrounding the sampling orifice. Since the reactant concentration at the surface decreased when the laser was turned on while the product concentration at the surface increased when the laser was turned on, modulating the surface reaction rate by modulating the argon ion laser beam and employing phase-sensitive detection allowed the identification of reaction products. The behavior of the system was described qualitatively using a theory for coupled reactant transport to the deposit surface and surface chemical reaction.
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 2513-2522 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A diffusive transport relaxation technique has been developed to study the chemical processes occurring during laser-induced chemical vapor deposition. The technique is based on modulation of the laser light intensity which results in a modulation of the surface reaction rate. This perturbation of the reaction rate produces transients in the gas-phase reactant and product concentrations for the case of gas-phase transport-limited deposition. Product species can be differentiated from species formed from the reactant during ionization and fragmentation due to the phase-sensitive nature of the detection scheme. The system response is examined theoretically by describing the response of the surface reaction rate to the modulated laser light and then examining the response of the gas-phase reactant and product concentrations to the modulated surface reaction. The technique was used to identify the gaseous products formed during laser-induced deposition of gold using dimethyl gold hexafluoroacetylacetonate.
    Materialart: Digitale Medien
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  • 8
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 61 (1987), S. 2749-2753 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Surface temperatures of a laser-heated structure consisting of intersecting gold and nickel lines on a Si substrate with a SiO2 surface layer were determined experimentally and theoretically. Temperatures were measured with micron-sized thin-film thermocouples formed from intersecting gold and nickel lines. Temperature profiles were calculated using a finite difference method which took into account the optical and physical properties of the thermocouple metal lines, the silicon dioxide layer, and the silicon substrate. For a 0.2-μm SiO2 layer, maximum surface temperatures were much higher with the metal lines than without because of the lower reflectivity of the gold relative to the silicon and the limited ability of the thin metal lines to conduct heat away from the irradiated region. Calculated maximum temperatures on the metal lines depended strongly on the thicknesses of the insulating SiO2 layer and the metal lines. Application of these results to the dynamics of laser-induced chemical vapor deposition is discussed.
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 2149-2151 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Single-crystal YBa2Cu3O7 particles have been formed in a carbon-free gaseous flow system by thermally decomposing droplets containing the nitrate salts of Y, Ba, and Cu in water followed by calcining and annealing in the gas phase. The electron diffraction pattern for particles ranging in size from 0.1 to 1.5 μm corresponded to single crystals of orthorhombic YBa2Cu3O7 while the powder x-ray diffraction pattern confirmed the presence of single-phase material. Energy dispersive spectroscopy showed a similar composition for all particles examined. Iodometric titration showed that the particles were fully oxygenated. Two types of single-crystal particles were observed, equiaxed and elongated. Formation of solid single-crystal particles is favored by operation near the melting point of the material and by long reactor-residence times.
    Materialart: Digitale Medien
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  • 10
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 62 (1987), S. 2280-2285 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: An optical method for the measurement of rates of laser induced chemical vapor deposition processes is described. Vertical growth rates are obtained from measurements of the power attenuation by a growing deposit of a probe beam of known diameter directed parallel to the substrate and intersecting the axis of the deposit. A theoretical analysis is presented that relates the growth rate of deposits with various geometries to the attenuation of the probe beam as a function of time and the probe laser beam diameter. The method can be used to obtain growth rates for deposits as small as a few μm in height, as long as the surface of the deposit is smooth relative to the diameter of the probe beam. The method is used to determine rates of photothermal gold deposition as a function of gold precursor partial pressure. Measured deposition rates ranged from 0.2 to 5.5 μm/s for dimethyl gold hexafluoroacetylacetonate partial pressures from 0.03 to 0.62 Torr.
    Materialart: Digitale Medien
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