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  • 1
    Electronic Resource
    Electronic Resource
    Hydriding kinetics of Pd capped YHx switchable mirrors (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 6107-6119 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The kinetics of the metal–insulator transition in polycrystalline, Pd-capped YHx switchable mirrors upon hydrogenation is investigated. Using the accompanying optical transition, we study switching of matrix-like samples with many (∼200) combinations of Pd and Y layer thicknesses. We find that: (i) With increasing Y thickness dY, the switching time τ increases for any constant Pd thickness dPd. (ii) With increasing dPd, there are three regimes. In regime I, it is impossible to switch a device. This can mainly be related to Pd–Y compound formation consuming all Pd within the UHV system, followed by surface oxidation in air. In regimes II and III switching is possible, but only in regime III does Pd form a closed cap layer. The Pd thickness needed for a closed cap layer depends on dY. (iii) An oxide buffer layer hinders Pd–Y interdiffusion, so that a thinner Pd cap layer is needed for switching than in the case without buffer layer. This is interesting for potential applications since it yields a higher optical transmission in the open state of the device. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371660
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  • 2
    Electronic Resource
    Electronic Resource
    Microtorquemeter for magnetization measurements on small superconducting samples (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 5726-5732 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A torquemeter with a noise level of ∼10−12 N m was developed and used for magnetization measurements (due to the Meissner–Ochsenfeld effect) on superconducting samples with a mass typically smaller than 10μg. The torquemeter consists of a very soft, thin metal beam, symmetrically placed between two capacitor plates, which are used for position measurement. Due to the symmetric setup electrostatic forces on the beam are largely compensated. A cheap but accurate electronic device replaces the conventional capacitance bridge and lock-in amplifier. Calibration of this kind of apparatus is discussed in some detail. Experiments are reported on a 6 μg lead disk and on small crystals of YBa2Cu3O7 and Nd2−xCexCuO4−δ.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143355
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  • 3
    Electronic Resource
    Electronic Resource
    Preparation, patterning, and properties of thin YBa2Cu3O7−δ films (1988)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 52 (1988), S. 1904-1906 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High TC superconducting thin films were prepared on (100) SrTiO3 substrates by dc triode sputtering and subsequent annealing. In these films Hall-bar structures having a width down to 5 μm were patterned using a reactive ion etching technique. Superconductivity above 77 K was observed. When compared with the original film there is only a small reduction in TC. The critical current density determined by electrical measurements is substantially reduced. On the other hand, the critical current density in the bulk of the grains as measured by the torque on a film is not reduced by the patterning process. It is suggested that superconductor-normal metal-superconductor junctions between the grains account for this difference.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.99739
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  • 4
    Electronic Resource
    Electronic Resource
    High-quality off-stoichiometric YBa2Cu3O7−δ films produced by diffusion-assisted preferential laser ablation (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 6528-6537 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The fluence dependence of the composition of pulsed-laser deposited YBa2Cu3O7−δ films is investigated and interpreted in terms of laser-induced target modification. Both target degradation (at fluence J〈1.0 J/cm2) and diffusion-assisted preferential ablation (1.0〈J〈1.3 J/cm2) are found to be responsible for nonstoichiometric transfer. A one-dimensional, moving-boundary diffusion model is developed to describe diffusion-assisted preferential ablation. This model predicts stoichiometric transfer at large ablation rates. Indeed, for J(very-much-greater-than)1.3 J/cm2 stoichiometric deposition is found, resulting in precipitate-free films. However, slightly off-stoichiometric films, deposited in the diffusion-assisted preferential ablation regime, exhibit the best superconducting properties (Tc=91.0 K, ΔTc=0.4 K) and can be produced with a remarkably high reproducibility. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371619
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  • 5
    Electronic Resource
    Electronic Resource
    Synthesis of metal hydrides and in situ resistance measurements in a high-pressure diamond anvil cell (1989)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 60 (1989), S. 474-480 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We have constructed a diamond anvil cell and a cryogenic system for high-pressure experiments at temperatures down to 1.5 K. A new mechanism is used to apply the force, and the body of the cell contains a heat-exchanger for use with liquid helium or liquid nitrogen. With the press, a maximum force of 30 000 N can be applied to the diamonds. The force can be changed at any temperature from outside the cryostat. We describe a technique to load metal samples with hydrogen at high pressures and do in situ resistance measurements. With this technique, we have synthesized stoichiometric PdH and PdD at a pressure of ∼4 GPa. We also have measured the pressure dependence of their superconducting transition temperatures. For PdH we find Tc=8.8 K and ∂ ln Tc/∂P=−6.8×10−2 GPa−1, and for PdD we find Tc=11.05 K and ∂ ln Tc/∂P=−5.0×10−2 GPa−1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1140402
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  • 6
    Electronic Resource
    Electronic Resource
    Laser ablation threshold of YBa2Cu3O6+x (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 65 (1994), S. 1581-1583 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using projection optics we made a detailed study of the interaction of a spatially uniform 248 nm excimer laser beam and a 99% dense YBa2Cu3O6+x target. Below a threshold fluence of 1 J/cm2 the roughness of the irradiated target increases dramatically due to non-stoichiometric ablation. The overall target surface composition becomes increasingly Y rich and Cu poor, while the opposite is found for the corresponding ablated thin films. Above the threshold fluence the composition of the ablated target surface is conserved. As a result of the energy homogeneity of the laser beam obtained by means of projection optics, the optimization of the deposition parameters has been improved leading to the reproducible fabrication of flat, stoichiometric YBa2Cu3O7 films with Tc0's over 91 K.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.112921
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  • 7
    Electronic Resource
    Electronic Resource
    Roughness in Nb/Cu multilayers determined by x-ray diffraction and atomic force microscopy (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 3429-3431 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Nb/Cu multilayers grown by molecular beam epitaxy have been studied by x-ray diffraction and atomic force microscopy. X-ray diffraction provides the average interface roughness while atomic force microscopy shows the roughness and topology of the upper surface. Comparison of both methods shows that high-angle diffraction averages over a lateral length which is in good agreement with the typical grain size. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.115269
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  • 8
    Electronic Resource
    Electronic Resource
    Contrast enhancement of rare-earth switchable mirrors through microscopic shutter effect (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 2050-2052 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In contrast to the binary switchable mirror films (YHx, LaHx, REHx with RE:rare earth) which have a weak red transparency window in their metallic dihydride phase, rare-earth alloys containing magnesium are remarkable for the large contrast between their metallic dihydride and transparent trihydride phase. By means of structural, optical transmittance, and electrical resistivity measurements on a series of Y1−yMgyHx, films we show that this is due to a disproportionation of the alloy. While the yttrium dihydride phase is formed, Mg separates out, remaining in its metallic state. Upon further loading, insulating MgH2 is formed together with cubic YH3−δ. In this way Mg acts essentially as a microscopic optical shutter, enhancing the reflectivity of these switchable mirrors in the metallic state and increasing the optical gap in the transparent state. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.124912
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  • 9
    Electronic Resource
    Electronic Resource
    Epitaxial switchable yttrium-hydride mirrors (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 1724-1726 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: By means of x-ray scattering and scanning probe microscopy it is shown that high-quality epitaxial Y films can be deposited on (111)-CaF2 substrates. The films can reversibly be switched from metallic YH2 to transparent insulating YH3−δ. Although hydrogen absorption involves an expansion of the lattice and a symmetry change from hcp to fcc, the epitaxiality of the film remains intact during the switching process. The transparency and the insulating nature of the substrate opens unique possibilities to investigate electrically and optically these switchable mirror films in the single crystalline state. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.124800
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  • 10
    Electronic Resource
    Electronic Resource
    Performance enhancement of metal-hydride switchable mirrors using Pd/AlOx composite cap layers (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 815-817 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A drastic improvement of the optical properties and lifetime of switchable mirrors is obtained by placing a thin AlOx buffer layer between the Pd cap layer and the optically active, rare earth layer. The buffer layer lowers the minimum necessary Pd thickness to ∼1 nm, resulting in a (approximate)20% increase of the maximum transmittance. The optimal Pd and Al layer thicknesses are determined for the YHx and LaHx system using a powerful combination of optical and matrix film techniques. The AlOx buffer is shown to be superior to the native oxide layers YOx and LaOx. The buffer layer is essential for lanthanum, which is a particularly vulnerable, but fundamentally very important material. Using this composite cap layer, we have been able to switch LaHx films several times. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1306643
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