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    Enhanced performance of Pb/FeSe2 interfaces designed for electrical applications
    (Springer, 2024) Alharbi, Seham R.; Qasrawi, Atef Fayez; Algarni, Sabah E.
    In this work, iron selenide layers are deposited onto glass and lead substrates to perform as terahertz filters. The layers are deposited by the thermal evaporation technique under a vacuum pressure of 10–5 mbar. Glass/FeSe2 (GFS) and Pb/FeSe2 (PFS) films are structurally, morphologically and electrically characterized. The atomic composition of the GFS films contained excess selenium that reacted with Pb forming a PbSe layer. This layer induced the crystallinity of iron selenide. The preferred crystal structure of FeSe2 was cubic with cell parameters of a = b = c = 3.04 Å and space group Pm3m . Lead substrates increased the room temperature electrical conductivity of GFS films from of 1.52 ×10?5(?cm)?1 to 6.88 ×10?2(?cm)?1 . Analyses of the electrical conduction mechanism in the temperature range of 25–330 K have shown that coating the films onto Pb substrates shifted the accepter level from 182 to 58 meV, decreased the degree of structural disor-der, shorten the average hopping range from 59 to 19 Å and increased the density of localized states near Fermi level by two orders of magnitude. The conductivity of PFS films exhibited degenerate semiconductor characteristics in the temperature range of 120–28 K. This feature is followed by an evidence of exhibiting superconductivity at critical temperatures lower than 24 K. On the other hand the impedance spectroscopy measurements in the driving signal frequency domain of 0.01–1.0 GHz have shown that Pb/FeSe2/Ag interfaces can perform as band filters showing microwave cutoff frequency values reach-ing 100 GHz at driving signal frequency of 1.0 GHz. These band filters are ideal for 6G technology nominating PFS films for high frequency applications.
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    Fast crystallization of InSe thin films via pulsed laser welding technique and effect of crystallinity on the optical and dielectric properties
    (IOP Publishing, 2024) Khusayfan, Najla M.; Qasrawi, Atef Fayez; Khanfar, Hazem K.; Alharbi, Seham R.
    Physica Scripta Inclusive Publishing Trusted Science, find out more. ACCEPTED MANUSCRIPT Fast crystallization of InSe thin films via pulsed laser welding technique and effect of crystallinity on the optical and dielectric properties Najla M. Khusayfan1, A F Qasrawi2, Hazem Khanfar3 and Seham Alharbi4 Accepted Manuscript online 18 January 2024 • © 2024 IOP Publishing Ltd What is an Accepted Manuscript? DOI 10.1088/1402-4896/ad2040 DownloadAccepted Manuscript PDF Download PDF Article metrics 3 Total downloads Submit Submit to this Journal MathJax Turn on MathJax Permissions Get permission to re-use this article Share this article Share this content via email Share on Facebook (opens new window) Share on Twitter (opens new window) Share on Mendeley (opens new window) Hide article and author information Author e-mails atef.qasrawi@aaup.edu Author affiliations 1 Department of Physics, University of Jeddah, Jeddah, Jeddah, Makkah, 21959 , SAUDI ARABIA 2 Physics Department, Arab American University, Telfit,, Jenin, P298, Palestine, State of 3 Computer system Engineering , Arab American University, Telfit,, Jenin, Jenin, P298, Palestine, State of 4 Physics Department, University of Jeddah, jeddah, Jeddah, Makkah, 21959 , SAUDI ARABIA ORCID iDs A F Qasrawi https://orcid.org/0000-0001-8193-6975 Hazem Khanfar https://orcid.org/0000-0002-3015-4049 Dates Received 5 October 2023 Revised 17 December 2023 Accepted 18 January 2024 Accepted Manuscript online 18 January 2024 Journal RSS Sign up for new issue notifications Abstract In the current study the crystalline phase of indium selenide thin films which were grown by the thermal evaporation technique is achieved via pulsed laser welding technique (PLW) in a second. The films crystallinity is achieved under various welding conditions including the pulse width (PW), repetition frequency (f_r ) and pulse diameter (d). The optimum parameters for obtaining well crystalline phase are PW=1.0 ms, f_r=10Hz and d=1.0 mm. PLW induced crystallinity showed preferred structure relating to monoclinic phase of InSe. Compositionally while amorphous films exhibited In2Se3 chemical structure, crystalline ones preferred InSe phase. Associated with this type of crystallinity, direct and indirect energy band gap values of 2.32 eV and 3.12 eV are determined. The crystalline films showed lower dielectric constant value accompanied with higher optical conductivity and higher terahertz cutoff frequency in the infrared range of light. In addition the dielectric dispersion spectra were treated using Drude-Lorentz model to read the optical conductivity parameters for the PLW assisted crystalline InSe terahertz resonators. The treatment showed that the crystallinity of the films resulted in improved free carrier density, longer relaxation times at femtosecond level, larger plasmon frequencies and higher drift mobility values. These features together with the response of terahertz cutoff frequency to IR excitations make crystalline InSe thin films promising for optoelectronic and terahertz technology applications.
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    Growth and characterization of (glass, Ag)/SeO2 thin films
    (Elsevier, 2022) Alharbi, Seham R.; Qasrawi, Atef Fayez; Algarni, Sabah E.
    Herein, thin films of SeO2 coated onto glass and Ag thin film substrates are studied and characterized. The films which are prepared by a vacuum evaporation technique, displayed Ag-metal induced crystallization process. The grown films are composed of tetragonal structure of SeO2 as major phase and orthorhombic as minor phase. The optical studies showed that the films exhibit an energy band gap of 3.69 eV. In addition, the analyses of the dielectric dispersion spectra indicated the nonlinear character of dielectric response. The SeO2 films response to oscillatory electromagnetic field is accompanied with drift mobility values in the range of 5.02–12.06 cm2/Vs. Moreover, polycrystalline SeO2 films coated onto Ag substrates are found appropriate for use as negative capacitance (NC) sources in the frequency domain of 0.41–1.80 GHz. Accompany with the NC effect, negative conductance (NG) effect was observed near 0.410 GHz and near 1.53 GHz.
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    In/MgSe Terahertz filters with enhanced optical conduction and light absorption
    (Springer, 2023) Alharbi, Seham R.; Qasrawi, Atef Fayez
    In this work, semitransparent indium thin films with thickness of 200 nm were used as substrates for depositing magnesium selenide thin films (200 nm). Both indium and MgSe films were coated onto ultrasonically cleaned glass substrates under vacuum pressure of 10– 5 mbar. The structural and morphological studies on these thin films showed that indium conducting layers suppressed the formation of cubic MgSe2 phase in the films. Optically, it was observed that semitransparent indium substrates improved the light absorption in the visible and infrared ranges of light. The light absorption increased by more than 14 times at 1.20 eV. In addition, coating MgSe onto In substrates resulted in a shift in the direct allowed transitions band gap from 2.54 eV to 1.92 eV. It also decreased the dielectric constant values. The optical conductivity and terahertz cutoff frequency values increased at the In/MgSe interfaces. Fitting of the optical conductivity spectra of In/MgSe interfaces by Drude–Lorentz approaches showed that indium substrates increased the drift mobility by two times and increased the plasmon frequency of MgSe. The enhanced optical conductivity and increased terahertz cutoff frequency values which are achieved via coating MgSe onto semitransparent indium substrates make MgSe films applicable in terahertz technology as band filters.
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    Lead selenide thin films designed for laser sensing and visible light communications
    (Springer, 2023) Khusayfan, Najla M.; Qasrawi, Atef Fayez; Khanfar, Hazem K.; Alharbi, Seham R.
    Herein thin films of PbSe are coated onto amorphous glass, amorphous silicon (a?Si) and crystalline n?type Si (n?Si) wafers by the thermal evaporation technique under a vacuum pressure of 10? 5 mbar. The films are structurally, morphologically, compositionally, optically and electrically characterized. Strong effect of the nature (amorphous or crystalline) and type (Si or glass) of the substrate on the physical properties of lead selenide films is detected. Of these properties the crystallite sizes decreased and the microstrain, the stacking faults and defect density increased and the energy band gap is blue shifted when (a, n)-Si substrates replaces glass. In addition, the use of crystalline n?Si substrates instead of a?Si removed the free carrier absorption from a?Si/ p?PbSe improving the quantum efficiency of the devices. Opto-electronically, n?Si/p?PbSe films showed photosensor characteristics that suit both visible light and infrared technology applications. The photosensors displayed high current responsivity, external quantum efficiency percentages and response times reaching respective values of 1.4 A/W, 172% and 60 ?s. In addition, the n?Si/p?PbSe photosensors which were used as detectors to receive wireless light signals generated from light pulses of 10 kHz frequencies showed smart features nominating them as promising devices for laser sensing and visible light communication technology.
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    p-Si/n-CrSe2 Heterojunctions Designed as High-Frequency Capacitors and Photosensors
    (Springer, 2024) Algarni, Sabah E.; Qasrawi, A. F.; Khusayfan, Najla M.; Alharbi, Seham R.; Alfhaid, Latifah Hamad Khalid
    In this work, polycrystalline n-CrSe2 nanosheets with thickness of 100 nm are grown on p-type Si wafers by the thermal deposition technique under vacuum pressure of 10(-5) mbar. Structural and optical investigations showed the preferred growth of the trigonal phase of CrSe2 on Si substrates. Direct allowed transitions within an energy band gap of 2.60 eV were found to be dominant in the films. Silver contacts on the layers allowed construction of hybrid optoelectronic device structure formed from Ag/p-Si Schottky arm and p-Si/n-CrSe(2)pn junction. The device runs in such a way that forward biasing of the Schottky arm is accompanied by a reverse biasing of the pn junction. It is observed that the hybrid device structure can perform as a high-frequency capacitor. The capacitance-voltage characteristic curves show that these capacitors can respond to ac signals with frequencies of 100 MHz. They also exhibit bandstop filter characteristics allowing the passing of signals with return loss and voltage standing wave ratios exceeding 10 dB and 1.76, respectively, at 60 MHz. The device under study displayed rectifying and photo-sensing properties with an asymmetry ratio of 60 in the dark and 217 under excitation of visible light. Visible light excitation of these photosensors displayed voltage biasing dependence in their current responsivity, external quantum efficiency and specific detectivity, reaching values of 0.24 A/W, 65.2% and 4.83 x 10(9) Jones, respectively. The features of the hybrid devices which use CrSe2 nanosheets as active media make them good candidates for use in radio wave and visible light communication technologies.
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    Pb/FeSe interfaces designed for optical communication technology
    (Wiley, 2023) Alharbi, Seham R.; Qasrawi, Atef Fayez; Algarni, Sabah E.
    Herein, thin films of FeSe are coated onto glass and semitransparent Pb substrate of thicknesses of 200 nm. The produced glass/FeSe (GFS) and Pb/FeSe (PFS) are structurally, compositionally, and optically characterized. It is observed that Pb substrates induced the crystallinity of cubic FeSe and cubic PbSe. On average, 21% of the phases in FeSe films are identified as PbSe. Due to the strong orbital overlapping between Pb and FeSe, Pb substrate increases the light absorption, the dielectric constant, the optical conductivity, and the terahertz cutoff frequency by ?150 %, 180 %, 263 %, and 101 %, respectively. In addition the direct and indirect energy bandgaps shrink from 2.49 and 2.80 to 2.41 and 2.50 eV, respectively. Moreover, treating GFS and PFS as terahertz optical resonators have shown that Pb substrates enhanced the drift mobility and increased the plasmon frequency making it adequate for 6G technology applications. An important feature of the PFS optical resonator is the stability of the terahertz cutoff frequency at 16 THz in the visible range of light. This feature together with the enhanced optical absorption in the visible light region makes the PFS films attractive for visible light communication technology.