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  • 1
    Electronic Resource
    Electronic Resource
    Positron-lifetime studies of hydrogenated amorphous silicon (1987)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 62 (1987), S. 108-116 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Positron-lifetime studies have been carried out on hydrogenated amorphous silicon (a-Si:H) films prepared by the glow-discharge method. Films deposited and thermally annealed at different temperatures have been investigated for determination of microstructural aspects such as hydrogen content, microvoids, vacancies, etc. The appearance of a long-lifetime component (τ3〉3 ns) in the lifetime spectrum together with a narrow peak in the two-dimensional angular correlation of positron-annihilation radiation confirms existence of large microvoids in the films. The systematics of the variation of the intensity of the long-lifetime component (I3) as a function of the deposition and annealing temperature is studied in detail. This study clearly shows that molecular hydrogen exists at high pressure in the microvoids and it effuses out at elevated temperature, leaving behind empty microvoids in the film. Two stages of effusion of hydrogen at 275 and 600 °C have been clearly identified in films deposited at 25 °C. Interestingly, the films deposited at 300 °C exhibit only the high-temperature effusion stage, establishing thereby that the low-temperature stage relates to trapped molecular hydrogen, while the one corresponding to high temperature (600 °C) relates to bonded hydrogen. The positronium lifetime (τ3) shows an increase with annealing temperature, representing growth of microvoid dimensions, presumably due to ensuance of an agglomeration process concurrent with hydrogen effusion. Information concerning the presence of quadrivacancies and pentavacancies in the films and their response to thermal treatment is also obtained from the study of the intensity (I2) and lifetime (τ2) corresponding to the trapped positron state. An attempt has been made to correlate the positronium component with electron-spin-resonance results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.339167
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    An integrated PC-based characterization system for optical waveguides (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 2690-2694 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: This paper reports an automatic instrument developed for characterization of optical waveguides. A specially designed waveguide excitation unit offers a flexible platform for measurement of optical waveguide characteristics like number of propagating modes, mode field intensity distribution, the refractive index profiles, waveguide geometry, attenuation, and dispersion. Further, the availability of attachments like filters, polarizers, chopper, intensity profiler, and CCD camera make the instrument flexible enough for a variety of other experiments also. The instrument is PC controlled and assisted by user friendly menu-driven software. A large number of waveguides have been analyzed using the setup. These results are also presented in the paper. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1145611
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    Paper (German National Licenses)
    Fulltext
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