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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 84 (1998), S. 6623-6627 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Mirage technique is proved to be powerful in measurements of thermal diffusivity. Its contactless nature makes it suitable for delicate samples such as thin films and single crystals. However, as the damping of the thermal wave profile increases progressively upon the decrease in thermal diffusivity of the medium, mirage technique becomes more difficult to be applied to low thermal diffusivity measurements. Moreover influences from substrate signals make analysis difficult when the samples are thermally thin. Recently a thermal-wave-coupling method for mirage signal analysis [P. K. Wong, P. C. W. Fung, H. L. Tam, and J. Gao, Phys. Rev. B 51, 523 (1995)] was reported for thermal diffusivity measurements of thin film down to 60 nm thick. In this article we apply the thermal-wave-coupling method to thin films of low thermal diffusivity, especially polymer films. A new lower limit of thermal diffusivity measurable by mirage technique has been reached. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 1564-1569 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The two-beam photoacoustic phase measurement was applied to measure quantitatively the thermal diffusivity (αs) of a ceramic bulk high-Tc superconductor. Neglecting the effects of thermal dilation, and thermoelastic bending was proved valid in accordance with our composite piston model for the chosen experimental conditions. It was found that αs shows different features at the onset and offset temperatures corresponding to the normal–superconducting (NS) transition. A dip was seen at the resistivity transition onset temperature and a cusp at the offset temperature where the electrical resistance disappears. The presence of the cusp at the offset temperature is proposed to be related to weak coupling between superconducting grains. Our studies indicate that the two-beam phase measurement is a very sensitive method for superconductor characterization and NS transition detection. The experimental results also confirm the presence of a large energy gap and strong electron–phonon coupling mechanism in the YBCO superconductor. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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