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    Growth and characterization of lanthanum germanide thin films by the thermal evaporation technique
    (Wiley, 2023) Alkhamisi, Manal M.; Qasrawi, Atef Fayez; Khanfar, Hazem K.
    Lanthanum germanide (La6Ge) thin films are successfully fabricated using the thermal evaporation technique under a vacuum pressure of 10?5 mbar. The resulting films display an orthorhombic structure, characterized by lattice parameters of a = 8.725 ?, b = 8.063 ?, and c = 5.569 ?. Optical analysis of the La6Ge thin films reveal their high transparency, with an energy bandgap of 3.75±0.04 eV. The bandgap exhibits indirect allowed transitions and featured energy band tails with widths measuring (1.64±0.14) eV. In addition, dielectric dispersion analyses indicate the presence of two dominant dielectric resonance peaks centered at 3.15 and 2.08 eV. Moreover, the La6Ge films demonstrate a terahertz (THz) cutoff frequency of 1.0 THz when illuminated with infrared and visible light. This cutoff frequency increases to 45.6 THz in the ultraviolet range. Furthermore, by utilizing the Drude–Lorentz method, the investigation of optical conductivity parameters reveals that the lanthanum germanide optical filters can achieve free hole density and drift mobility values of 14.44 cm2 V?1 s?1 and 2.8×1018 cm?3, respectively, under infrared light irradiation. The outstanding optical and dielectric properties exhibited by the La6Ge thin films make them excellent candidates for highly transparent optical filters suitable for terahertz technology.
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    Growth and characterization of PbSe microcrystals via the pulsed laser welding technique
    (SPRINGER HEIDELBERG, 2022) Alkhamisi, Manal M.; Khanfar, Hazem K.; Algarni, Sabah E.; Qasrawi, Atef Fayez
    Herein lead selenide crystals are fabricated by the pulsed laser welding (PLW) technique within 2 min. The effect of the pulse width on the crystallinity, surface morphology, structural parameters, compositional stoichiometry, electric resistivity and dielectric constant is considered. It is observed that the PLW technique allowed the growth of the crystals in a short period of time. The grown PbSe crystals are mostly cubic containing tetragonal SeO2 as a minor phase. Selenium oxide presented due to the surface oxidation of PbSe after exposing the crystals to air. Remarkable decreases in the electrical resistivity and increase in the dielectric constant by more than two orders of magnitude are achieved as the pulse width increases from 10 to 50 ms. It is observed that the optimum pulse width revealing the highest dielectric constant value is 30 ms. For these samples, a negative capacitance effect is observed for ac signals of frequencies larger than 700 MHz. In addition, analyzing the microwave cut-off frequency spectra for an imposed signal of low amplitude displayed cut-off frequency values larger than 100 GHz at the point where negative capacitance dominates and ac conductance shows a maxima. The features of the PbSe crystals which are prepared in 2 min nominate them for use as negative capacitance sources and band filters suitable for 6G technologies.
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    La/Ge stacked nanosheets designed as optical resonators, microwave oscillators and 5 G/6 G gigahertz receivers
    (Optik, 2023) Alkhamisi, Manal M.; Qasrawi, Atef Fayez; Khanfar, Hazem K.
    Glass/Ge and La/Ge stacked layers, 100 nm thick, were prepared via thermal evaporation under a vacuum pressure of 10-5 mbar. Structural analysis confirmed amorphous growth of Ge nanosheets. Optically coating Ge onto La improved light absorption, energy band gap, and dielectric responses. In addition, dielectric spectra fitting using Lorentz approach showed increased free electron density, plasmon frequency, and drift mobility (up to 1153 cm2/Vs) in Ge due to lanthanum presence. Moreover, LGA Schottky barrier devices (La/Ge/Au) exhibited tunneling-type current conduction with 0.815 eV barrier height and 40 nm width. Resistance spectra of these Schottky barriers displayed negative resistance near 0.40 GHz, while capacitance spectra showed resonance-antiresonance behavior. La/Ge and LGA interface can be utilized for optical receivers and microwave resonators in 5 G/6 G technologies.
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    Lead selenide microcrystals fabricated by the pulsed laser welding technique employed as 6G technology microwave resonators and as MOS capacitors
    (Elsevier, 2023) Alkhamisi, Manal M.; Khanfar, Hazem K.; Qasrawi, Atef Fayez
    value larger than 100 GHz nominating the devices for 6G technology applications. Moreover, investigations on the current conduction mechanism have shown the preferred current conduction by quantum mechanical tunneling accompanied with correlated barrier hopping. On the other hand, measurements of the capacitance-voltage characteristics in the frequency domain of 1.0–100 MHz showed performance of the Ag/PbSe/Ag structures as a metal-oxide- semiconductors (MOS) devices suitable for energy storage at ultrashort times.
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    Lead-tungsten oxide interfaces designed as gigahertz/terahertz filters
    (IOP Science, 2023) Alkhamisi, Manal M.; Qasrawi, Atef Fayez; Khanfar, Hazem K.
    Herein amorphous tungsten oxide thin films of thicknesses of 300 nmare coated onto semitransparent Pb films (100 nm) by the thermal evaporation technique under a vacuum pressure of 10?5 mbar. Optical investigations in these films have shown that Pb nanosheets enhances the light absorbability in the visible and infrared ranges of light without significant change in the energy band gap value. In addition deep analyses of the optical conductivity and terahertz cutoff frequency spectra of the Pb/WO3 optical filters revealed that the cutoff frequency value in the visible range of light is invariant with light signal energy indicating the possibly of filtering none-monochromatic light signals. Onthe other hand imposing an ac signal between the terminals of Pb/WO3/Au devices has proofed the ability of the device to perform as low pass and as band stop filters workable in the microwave frequency domain. The microwave cutoff frequency for this device reached?9 GHz nominating it for use in 5 Gmobile technology. The current study showed that coating of tungsten oxide onto semitransparent Pb substrate and coverage small area of the top contact with Au can all