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    Barium Oxide Thin Films Designed as Electro-OpticalGigahertz/Terahertz Filters
    (Crystal Research and Technology, Wiley, 23.02.2025) QAsrawi Atef Fayez; Alharbi Seham; Laila H. Gaabour
    Herein barium oxide thin films are studied as a promising electro-opticalsystem. The deposited films exhibited a polycrystalline tetragonalstructure and are composed of a mixture of BaO and BaO2 . The p-type filmsare highly transparent (80%) with an energy band gap of 3.55 eV containingexponential band tails of widths of 1.22 eV. Analyses using the Drude-Lorentzmodel demonstrated the films suitability for nonlinear optical applications,with optical conductivity parameters revealing a scattering time constantin the range of 0.4–1.8 fs, a free hole concentration of 10 18−10 19 cm−3 anddrift mobility values of 0.70–3.16 cm 2 Vs−1 . Terahertz cutoff frequency spectra calculations indicated the films capability as efficient terahertz band filterswith a cutoff frequency range of 3.2–193.0 THz. Additionally, the nonlinear third-order optical susceptibility increased with decreasing incident photonenergy. 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 (≈9 GHz)in the microwave frequency domain. These properties highlight the potential ofBaO films as nonlinear optical filters and microwave waveguides, positioningthem as candidates for gigahertz/terahertz technology applications
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    Bi2O3 nanosheets- based photodetectors designed for visible light communication technology
    (Physica Scripta (IOP), 17.03.2025) QAsrawi Atef Fayez; Zanoon Tateq; Alawneh Isam; Khanfar Hazem
    In this work, n-type bismuth oxide nanosheets deposited onto n-type silicon substrates by a vacuum evaporation technique under a vacuum pressure of 10−5 mbar is fabricated to perform as a daylight photodetectors suitable for visible light and infrared communication technology. The n-Si/n-Bi2O3 heterojunction devices exhibited conduction and valence band offsets of 0.89 eV 0.73 eV, respectively. Two Schottky barriers Pt/n-Si and Pt/Bi2O3 of respective barrier heights of 1.65 eV and 0.76 eV are formed on the sides of the heterojunction devices. Dark electrical characterization on the Pt/n-Si/n-Bi2O3/Pt hybrid structure showed a maximum current rectification ratio of 166. The current transport mechanism in the devices was dominated by the Richardson –Schottky thermionic conduction type and by electric field assisted charge carrier tunneling within a barrier of width and height of 60 nmand 0.83 eV, respectively. On the other hand, electrical measurements handled under the illumination of a daylight mini-lamp have shown that the photodetectors under focus exhibit maximum current responsivity, external quantum efficiency percentage, specific detectivity and linear dynamic range of 30 AW−1, 3000%, 1.7´1012 Jones and 36.4 dB under illumination power of 82 μW, respectively. The features of the bismuth oxide based photodetectors nominate them for visible and infrared lights illumination technology.
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    Design and Characterization of Se/Nb2 O5 Interfaces asHigh Infrared- Absorbers and High Frequency Band Filters
    (Crystal Research and Technology, Wiley, 07/12/2024) QAsrawi Atef Fayez; Daragme B. Rana
    Herein a new class of optoelectronic devices beneficial for infrared light absorption and high-frequency application in the terahertz frequency domain are designed and fabricated. The devices are formed by coating a highly transparent thin layer of Nb2 O5 onto a selenium-thin film to form Se/Nb 2 O5(SNO) optical interfaces. Although coating of Nb 2 O5 nanosheets decreased the crystallite sizes and increased the strain and defect concentration in the hexagonal structured Se films, they successfully increased the light absorption by ≈148% in the infrared range of light. A blueshift in the energy band gap of Se from 2.02 to 2.30 eV is observed. The coating of the Nb2 O5onto Se suppressed the free carrier absorption in Se and Nb 2 O5 . As dielectric active layers, SNO interfaces showed a major resonance dielectric peak centered at 1.67 eV. The optical conductivity and terahertz cutoff frequency analyses which are handled using the Drude-Lorentz approach revealed the highest drift mobility and free carrier concentration of 17.17 cm 2 Vs−1 and5.0 × 1017 cm−3 when an oscillator of energy of 1.75 eV is activated. In addition, the terahertz cutoff frequency spectra which varied in the range of4.0–131 THz showed the suitability of the SNO devices for terahertz technology and other optoelectronics
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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
    (Physica Scripta, 18.12.2024) QAsrawi Atef Fayez; Gaabour Laila H.; 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 (ε_r) values by over 104%. Specifically, ε_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 ε_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 ~2.5 THz 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×〖10〗^18 cm-3 and 0.47 cm2/Vs to 7×〖10〗^18 cm-3 and 2.03 cm2/Vs to 9×〖10〗^18 cm-3 and 2.03 cm2/Vs 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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    Enhanced Performance of Al/Nb2O5/Pt/Nb2O5/Ag Microwave Resonators Designed as Bandstop Filters and Negative Capacitance Sources
    (Materials Research, 09.11.2024) QAsrawi Atef Fayez; Amjad Salamah Mohammad Aljaloud; Latifah Hamad Khalid Alfhaid
    Herein stacked layers of Nb2O5 coated onto Al substrates are fabricated as microwave resonators. Structural and morphological analyses on these stacked layers have shown the amorphous nature of growth of the stacked layers. Electrically, the resonators showed negative capacitance effect accompanied with series and parallel resonance at three well -distinguished notch frequencies. Additionally, the resonators exhibited bandstop filter characteristics with notch frequency (nf) centered at 1.05 GHz, return loss (LR) value of 9.0 dB and voltage standing wave ratios (VSWR) of 2.12. To enhance the performance of the Nb2O5 microwave resonators, platinum nanosheets of thicknesses of 50 nm were inserted between layers of Nb2O5. Platinum nanosheets successfully decreased the surface roughness and increase the electrical conductivity by five orders of magnitude. Pt nanosheets additionally improved the values of nf, 11S, LR and VSWR to 1.16 GHz, 0.039, 30.3 dB and 1.12, respectively. The features of the microwave resonators comprising Pt nanosheets in its structure are promising for using them in communication technology.
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    Enhanced Quad-Band WO3 Antennas with 1.46 THz Cutoff Frequency via Indium Nanosheets between Stacked Layers
    (Physica Status Solidi a (Wiley), 12.12.2024) QAsrawi Atef Fayez; Mashael M. Altaiary; Seham R. Alharbi
    Herein, stacked films of WO3 separated by indium nanosheets are fabricated as quad-band antennas suitable for high-frequency applications. The amorphous WO3 films and indium nanosheets are coated onto each other using the thermal evaporation technique under a high vacuum pressure of 10−5 mbar. The stacked layers of Pt/WO3/In/WO3/Pt are structurally and electrically characterized. The tunneling-type quad-band antennas are tested in the driving frequency domain of 0.01–1.80 GHz and a low signal amplitude of 0.10 V. It is observed that the insertion of indium nanosheets between layers of WO3 remarkably increases the width of the tunneling barrier from 55 to 70 nm without altering the tunneling barrier height. This also enhances the cutoff frequency at a quad-band frequency of 1.80 GHz from 10 GHz to 1.46 THz and increases the return loss values from ≈5 to 21 dB. A widely tunable cutoff frequency extending from 0.30 GHz to 1.46 THz can be obtained based on the selected driving signal frequency. The microwave-controlling features of the Pt/WO3/In/WO3/Pt devices, with their high cutoff frequency and high power transmission ratios at the quad-band frequency, make them attractive for 6G technology.
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    n-Si/p-BaO/p-SiO2 Heterojunctions Designed as Negative Capacitance and Negative Conductance Sources, 6G Technology Frequency Stabilizers, and Current Rectifiers
    (Physica Scripta (IOP), 12.02.2025) QAsrawi Atef Fayez; M. Y. Al-Harbi; Seham Alharbi
    Barium oxide thin films were deposited on n-type Si wafers and coated with silicon oxide nanosheets to develop multifunctional electronic devices. Two channels, n-Si/p-BaO (SB) and n-Si/p-BaO/p-SiO₂ (SBS), were fabricated under high vacuum (10⁻⁵ mbar). The SB channel served as a microwave resonator and a negative capacitance (NC) source, while the SBS channel exhibited suppressed NC and a negative conductance (NG) effect. NC and NG effects dominate in the frequency ranges of 1.18-1.80 GHz and 1.16-.80 GHz, respectively. Both channels demonstrated high cutoff frequencies exceeding 200 GHz, making them effective as 6G band filters and high-frequency stabilizers. Additionally, the current-voltage characteristics revealed strong temperature dependent asymmetry, with ratios of 52 and 132 at 5.0 V for SB and SBS, respectively, enabling their use as electronic switches and current rectifiers even at 433 K. These devices combine NC and NG features, high-frequency stabilization, and current rectification, showcasing their potential for advanced multifunctional applications.
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    Thermally Deposited Pt/InSe/Nb2O5/Ag Stacked Layers Designed as Negative Capacitance Sources and Antennas for 5 G/6 G Networks
    (Physica Status Solidi a (Wiley), 09.112024) QAsrawi Atef Fayez; Alhatbi Seham; Algarni Sabah
    Herein, Pt/InSe/Nb2O5/Ag (ISNO) stacked layers are designed as multichannel 5 G/6 G network antennas and negative capacitance (NC) sources. The devices are fabricated using thermal deposition technique to coat Pt/InSe thin films with transparent Nb2O5 dielectric windows. While Pt thin films induce the crystallinity of InSe, the Nb2O5 layer remains amorphous. The impedance spectroscopy studies show that the Pt/InSe/Ag (IS) and (ISNO) antenna channels exhibit resonance–antiresonance peaks at driving frequencies of ≈0.4 and ≈1.1 GHz, respectively. Both the IS and ISNO antenna channels exhibit the NC effect in a wide range of frequency domain. In addition, ISNO antennas show signal transmission above 1.70 GHz with a return loss value of 28 dB and voltage standing wave ratios of 1.20. The range of frequencies over which the antenna performs well (bandwidth) extends from 1.54 to 1.80 GHz. Practical tests of one-port and two-port reflection/transmission using a network analyzer operative in the frequency domain of 0.01–6.0 GHz highlight the system's differing isolation and coupling characteristics at 2.43 and 6.0 GHz, respectively. The high levels of isolation at 6.0 GHz assure the suitability of the system for applications requiring minimal reverse transmission and high signal integrity. The NC effect, wide bandwidth, and high signal isolation characteristics are preferable in electronics and 5 G/6 G networks.
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    Thickness-Controlled Ti Optical Filters Designed for Tunable Terahertz Technology
    (Physica Status Solidi b (Wiley), 15.02.2025) QAsrawi Atef Fayez
    Herein, titanium (Ti) thin films deposited by a vacuum ion coating technique under a high vacuum pressure of 10 5 mbar are designed to perform as optical filters operatives in the terahertz frequency domain. The performance of these amorphous optical filters is controlled by varying the filter thickness in the range of 100–500 nm. Increasing the thickness of the filters decreases the optical transmittance, the absorption coefficient, the optical conductivity (σ), the terahertz cutoff frequency ( fT), the drift mobility, and the free carrier concentration. The thickness-based bulk limit of these filters is ≈300 nm. On the other hand, the increase in the optical filter thickness results in an increase the dielectric constant. Drude–Lorentz analyses on σ of the filters have shown the domination of four oscillators with oscillator frequencies of 1016, 859, 508, and 317 THz. These oscillators guarantee the good response of the Ti optical filters to optical excitations in the infrared, visible, and UV spectral domains. Based on the filter thickness, an extremely wide range of fT extending from ≈3.8 to 1248 THz can be achieved. The wide tunability of fT and σ of the Ti optical filters makes them promising for terahertz applications.