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Subject: Hexagonal

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    Article
    Citation - WoS: 7
    Citation - Scopus: 7
    In situ monitoring of the permanent crystallization, phase transformations and the associated optical and electrical enhancements upon heating of Se thin films
    (Elsevier Science Bv, 2019) Qasrawi, A. F.; Aloushi, Hadil D.
    In this work, the in situ structural transformations from amorphous to polycrystalline upon heating and the associated enhancements in the structural parameters of selenium thin films are studied by means of X-ray diffraction technique. The Se thin films which are grown onto ultrasonically cleaned glass substrate by the thermal evaporation technique under vacuum pressure of 10(-5) mbar exhibits structural transformation from amorphous to polycrystalline near 353 K. The films completed the formation of the structure which includes both of the hexagonal and monoclinic phases at 363 K. It is observed that the hexagonal phase dominates over the monoclinic as temperature is raised. Consistently, the thermally assisted crystallization process is accompanied with increase in the crystallite size, decrease in the microstrain, decrease in defect density and decrease in the percentage of stacking faults. The scanning electron microscopy measurements also confirmed the crystallinity of selenium after heating. The time dependent reputations of the crystallization test has shown that the achieved phase transitions and enhancements in structural parameters are permanent in selenium. Optically, the crystallization process is observed to be associated with redshift in the absorption spectra and in the value of the energy band gap. Electrically, the in situ monitoring of the electrical conductivity during the heating cycle has shown that the electrical conductivity stabilizes and exhibit a decrease in the acceptor levels from 566 to 321 meV after the crystallization was achieved.
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    Article
    Citation - WoS: 8
    Citation - Scopus: 7
    Negative Capacitance Effect in Ag/-in2< Dual Band Stop Filters
    (Springer, 2019) Khanfar, Hazem K.; Qasrawi, A. F.; Shehada, Sufyan R.
    In the current study, a 1.5m thick three channel microwave band filter is designed and characterized. The thin film device which was constructed from the indium selenide, cadmium sulfide and cadmium selenide stacked dielectric materials sandwiched between silver and carbon films is studied by means of x-ray diffraction, energy dispersive x-ray analysis and impedance spectroscopy techniques. It was observed that the Ag thin film substrate induced the formation of the hexagonal -In2Se3 phase of indium selenide. The x-ray analysis has also shown that the deposition of hexagonal CdS over Ag/-In2Se3 and that of hexagonal CdSe over -In2Se3/CdS under vacuum pressure of 10(-8) bar is of a highly strained and mismatched physical nature. The impedance spectroscopy analysis in the frequency domain of 0.10-1.80GHz has shown that; while the Ag/-In2Se3/C channel exhibit negative capacitance (NC) effects in the frequency domain of 0.10-1.40GHz, the Ag/-In2Se3/CdS/C and the Ag/-In2Se3/CdS/CdSe/C channels displayed a NC feature in the domains of 1.24-1.40GHz and 1.10-1.56GHz, respectively. The fitting of the capacitance spectra in accordance with the modified Ershov model allowed determining the NC and band filtering parameters. It was also observed that, although the Ag/-In2Se3/C channel behaves as a high frequency low pass filter, the second and third channels displayed band stop filter features with notch frequencies of 1.38GHz and 1.49GHz, respectively. The features of the device nominate it for use as a parasitic capacitance canceller and as a three channels microwave filter.