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    Barium oxide thin films designed as electro-optical gigahertz/terahertz filters
    (John wiley and sons inc, 2025) Alharbi, Seham R.; Qasrawi, Atef Fayez; Gaabour, Laila H.
    Herein barium oxide thin films are studied as a promising electro-optical system. The deposited films exhibited a polycrystalline tetragonal structure and are composed of a mixture of BaO and BaO2. The p-type films are highly transparent (80%) with an energy band gap of 3.55 eV containing exponential band tails of widths of 1.22 eV. Analyses using the Drude-Lorentz model demonstrated the films suitability for nonlinear optical applications, with optical conductivity parameters revealing a scattering time constant in the range of 0.4-1.8 fs, a free hole concentration of 1018-1019 cm-3 and drift mobility values of 0.70-3.16 cm2 Vs-1. Terahertz cutoff frequency spectra calculations indicated the films capability as efficient terahertz band filters with a cutoff frequency range of 3.2-193.0 THz. Additionally, the nonlinear third-order optical susceptibility increased with decreasing incident photon energy. Applying an AC signal with a driving frequency of 0.01-1.40 GHz across the terminals of Yb/BaO/Ag devices revealed a high cutoff frequency (approximate to 9 GHz) in the microwave frequency domain. These properties highlight the potential of BaO films as nonlinear optical filters and microwave waveguides, positioning them as candidates for gigahertz/terahertz technology applications.
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    Enhanced electro-optical performance of barium oxide stacked layers via platinum nanosheets designed for wide band light absorption and terahertz technology
    (IOP Publishing Ltd., 2025) Gaabour, Laila H.; Qasrawi, Atef Fayez; Alharbi, Seham R
    In this study, stacked films of barium oxide (BaO) comprising platinum nanosheets in its structure are designed as electro-optical filters applicable in terahertz technology. The layers were fabricated by the thermal evaporation technique. It was shown that insertion of 50 nm and 100 nm thick Pt nanosheets between stacked layers of BaO improves the crystallinity of the layers by reducing the strains and defect concentrations. In addition, the light absorption and optical conduction is enhanced by more than 300%, 900% and 100% in the ultraviolet (3.5-4.10 eV), visible (1.80-3.10 eV) and infrared (1.10-1.75 eV) ranges of light, respectively. The insertion of Pt nanosheets led to an increase in the dielectric constant epsilon r values by over 104%. Specifically, epsilon r values were initially 1.2-1.5, 1.6-1.8, and 1.8-2.0 in the ultraviolet, visible, and infrared light ranges, respectively. Upon incorporating Pt nanosheets with a thickness of 200 nm, these epsilon r values increased to 1.4-1.7 in the ultraviolet, 1.8-3.6 in the visible, and 3.7-3.9 in the infrared ranges. Significant increase in the terahertz cutoff frequency from similar to 2.5 THz to similar to 15.35 THz was achieved in the infrared range of light. Moreover, the optical conductivity parameters which were obtained with the help of Drude-Lorentz electro-optical analysis showed remarkable enhancement in the free carrier concentration and in the drift mobility of the BaO optical filters from 5 x1018 cm-3 and 0.47 cm2 Vs-1 to 7 x1018 cm-3 and 2.03 cm2 Vs-1 to 9 x1018 cm-3 and 2.03 cm2 Vs-1 upon insertion of Pt nanosheets of thicknesses of 100 nm and 200 nm, respectively. Furthermore, the temperature dependent electrical conductivity measurements has shown that Pt nanosheets increased the electrical conductivity of BaO by eight orders of magnitude. The features of BaO stacked layers comprising Pt nanosheets are promising for terahertz technology applications as waveguides and wideband optical filters.
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    In situ monitoring of crystallinity of FeSe2 thin films during thermal annealing and the annealing effects on the structural, optical and dielectric properties
    (Wiley, 2024) Gaabour, Laila H.; Qasrawi, Atef Fayez
    Herein stacked layers of iron selenide (FeSe2) thin films are deposited by the physical evaporation technique and thermally annealed. An in situ monitoring of the crystallinity during the annealing process has shown that the crystallinity is reached at 100 degrees C. The crystallinity of the films that preferred the orthorhombic phase is enhanced with increasing annealing temperature. Evidences about the improved crystallinity are presented by the increased crystallite and grain sizes, decreased microstrain values, decreased stacking faults, and decreased defect densities with increasing annealing temperature. Optical investigations have shown impressive effect of the annealing process on the optical reflectance, optical contrast, and light absorbability. Namely, respective improvement percentages exceeding 170%, 64%, and 140% is achieved near E approximate to 2 eV for samples annealed at 200 degrees C for 20 min. Both direct and indirect optical transitions are dominant in the film. In addition the annealing increased the dielectric constant in the spectral range of 1.17-4.20 eV. Maximum dielectric enhancement by 214% is reached near approximate to 2.10 eV. Moreover, the annealing process increases the optical conductivity and drift mobility of the FeSe2 films. The improvement in the crystallinity that resulted in enhanced optical properties makes the thermally annealed FeSe2 films promising for optoelectronic technology applications.
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    Stacked layers of Nb2O5/Pt/Nb2O5 designed as conducting oxides, terahertz band filters, and semitransparent light absorbers
    (Springer, 2024) Gaabour, Laila H.; Qasrawi, Atef Fayez; Alharbi, Seham R.
    Herein, stacked layers of Nb2O5 structured with platinum nanosheets were fabricated to handle multifunctional electro-optic operations. The stacked layers of Nb2O5/Pt/Nb2O5 (NPN) were prepared by the ion coating technique and exhibited an amorphous structure. A remarkable increase in light absorption by more than 480% was achieved via the insertion of Pt nanosheets between layers of Nb2O5. Pt nanosheets with thicknesses of 50 nm and 100 nm successfully increased the electrical conductivity of the NPN layers by five and eight orders of magnitude, respectively, without losing transparency. This feature makes the NPN stacks suitable for transparent conducting oxide applications. The insertion of Pt nanosheets between layers of Nb2O5 also converted the conductivity from p- to n-type. In addition, NPN stacked layers exhibited highly enhanced dielectric properties, demonstrating an increase in the dielectric constant by 190%, making the NPN stacked layers suitable for use in the design of high-kappa gate dielectric devices. Moreover, when treated as optical filters, Drude-Lorentz fittings of the dielectric spectra showed that Pt nanosheets increased the free carrier density and the plasmon frequency. The terahertz cutoff frequency of the NPN devices steadily increased with increasing Pt nanosheet thickness. The terahertz cutoff frequency for NPN optical filters comprising a 100-nm-thick layer of Pt displayed values of 7.5 THz and 5.0 THz in the infrared and visible light ranges. The NPN stacks have potential for use in terahertz applications.