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    Au nanosheets-assisted structural phase transitions, in situ monitoring of the enhanced crystallinity, and their effect on the optical and dielectric properties of CuSe/Au/CuSe thin films
    (Wiley, 2022) Qasrawi, Atef Fayez; Baniowdah, Tahani S.; Samen, Lara O. Abu
    Herein, stacked layers of copper selenide thin films comprising Au nanosheets in its structure are fabricated and characterized. The CuSe/Au/CuSe (CAC) thin films are prepared by the thermal evaporation technique under a vacuum pressure of 10?5 mbar. It is shown that Au nanosheets improve the stoichiometric growth of the CuSe thin films and induce the structural phase transitions from cubic to hexagonal. In addition, the in situ monitoring of the structural modifications in the CAC in the temperature range of 293–473 K proves the permanent enhanced crystallinity of the films. Optically, while the Au nanosheets increase the light absorbability and redshifts the energy band gap of CuSe, the in situ heating blueshifts the energy band gap. Moreover, insertion of Au nanosheets between layers of CuSe and heating them at 473 K significantly increase the dielectric constant and the optical conductivity by more than five times. Moreover, the drift mobility of charged carriers, the scattering time at femtosecond level, and the plasmon frequency are remarkably enhanced. Values of plasmon frequency exceed 6.0 GHz nominating the CAC films as signal receivers suitable for 5G technology.
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    Properties of (Glass, Pb)/MgSe interfaces designed as terahertz band filters
    (Springer, 2023) Qasrawi, Atef Fayez; Samen, Lara O. Abu; Atari, Samah S.
    Herein, thin films of MgSe (300 nm) are deposited onto glass and semitransparent Pb (150 nm) substrates by the thermal evaporation technique under a vacuum pressure of 10?5 mbar. The films are structurally, morphologically, compositionally, and optically characterized. It is found that Pb substrates induced the formation of single phase of MgSe against a mixture of MgSe and MgSe2. Lead substrates improved the light absorbability in the infrared (IR) range of light. Pb substrates also red-shifted and blue-shifted the direct and indirect band gap of MgSe by 0.62 eV and 0.10 eV, respectively. The dielectric dispersion analyses have shown that Pb substrates are more effective in the visible and IR ranges of light. When Pb/MgSe films are treated as band filters, they showed wide range of tunability of the terahertz cutoff frequency. The Pb/MgSe interfaces are found good candidates as terahertz band filters sensitive to IR-850 nm lasers which are used in communication technology. Optical oscillators of this wavelength performed within scattering time of 0.50 fs and exhibited drift mobility of 4.69 cm2/Vs. In addition, Drude-Lorentz analyses which targeted finding optoelectronic information about Pb/MgSe have shown the ability of using Pb/MgSe interfaces in thin film transistors, ultraviolet photo-detection, and terahertz technologies.