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    Effects of ZnPc substrates on the electro‑optical properties of MgSe thin films and the applications of Al/ZnPc/MgSe/ (Ag, C, Au) hybrid devices as resonant negative capacitance sources
    (Optical and Quantum Eletronics, Springer link, 11/07/2024) Qasrawi Atef Fayez
    Herein, polycrystalline magnesium selenide (MgSe) thin films are deposited onto glass and monoclinic-structured zinc phthalocyanine (ZnPc) thin film substrates under high vacuum pressure using the thermal evaporation technique. ZnPc substrates improved the crystallinity of the MgSe films and decreased the stacking faults percentages and defect concentration by 31.57 and 52.49%, respectively. MgSe films deposited onto ZnPc substrates exhibited a notable increase of up to 32% in light absorption within the visible spectrum, while maintaining the energy band gap value of MgSe without significant alteration. In addition, as both the substrate and the epilayer exhibited p-type conductivity, an isotype heterojunction device structure is formed at the ZnPc/MgSe interfaces. The valence and conduction band offsets for this interface are 0.81 and 1.16 eV, respectively. On the other hand, re-fabrication of the ZnPc/MgSe heterojunctions onto Al thin film substrates and forming three Ag/MgSe, C/MgSe, and Au/MgSe Schottky channels on the epilayer surface allowed wide control of the negative capacitance effect and the resonance-antiresonance (RA) peaks in the capacitance spectra of the Al/ZnPc/MgSe/(Ag, C, Au) hybrid devices. These two important RA and NC features of the device can also be engineered by altering the DC biasing of the device. Moreover, Lorentz model analyses on the capacitance spectra showed an increased density of oscillators and increased scattering time constant with decreasing built-in potential at the metal/MgSe interfaces. The features of the hybrid devices presented make the device promising for microwave and electro-optical applications
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    Electro-optical dynamics in SnO2 designed as negative resistance sources and gigahertz/terahertz band filters
    (Optical and Quantum Electronics, springer link, Mayis 2024) Qasrawi Atef Fayez; Kmail Bayan
    Amorphous thin films of SnO2, prepared by a vacuum evaporation technique under a pressure of 10− 5 mbar, are employed as electro-optical filters suitable for microwave, infrared, and visible light communication technologies. The filters perform as optical layers, exhibiting optical transitions within an energy band gap of 3.62 eV, with the band gap containing energy band tails of widths of 0.63 eV. In addition, dielectric dispersion analyses on the optical filters show their ideality for high k-gate dielectric applications. Wide tunability in the dielectric response is observed in these films. Moreover, analyses of the optical conductivity and terahertz cutoff frequency spectra have shown that SnO2 films exhibit resonance of optical signals suitable for infrared and visible light communication technology as well. When excited with infrared light of energy of 1.38 eV, the drift mobility and free hole concentration in these films reach 11.72 cm2/Vs and 2 × 1017 cm− 3, respectively. Furthermore, the device exhibits a negative resistance effect in the microwave range of 0.1–1.80 GHz, and terahertz cutoff frequency values in the range of 10 GHz − 48 THz. The features of the SnO2 electro-optical band filter make them attractive for communication technology extending from 5G/6G to IR and reaching visible light communications.
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    Enhanced Performance of Fe/WO3 Terahertz Dielectric Lenses
    (Crystal Research and Technology, Wiley, Nisan 2024) Qasrawi Atef Fayez; Hazem Khanfar
    Herein transparent iron nanosheets deposited by the ionic coating technique onto glass and WO3 dielectric lenses are studied and characterized. The thickness of Fe nanosheets is varied in the range of 70–350 nm. It is observed that the transmittance and reflectance of the Fe nanosheets are highly affected by the layer roughness. Coating of iron nanosheets onto WO3 dielectric lenses increases the light absorption of WO3 by more than 240 times and red-shifts the energy bandgap. Remarkable enhancements in the dielectric constant and in the optical conductivity are achieved via Fe coatings. In addition, iron coated dielectric lenses show higher terahertz cutoff limits varying in the range of 1.0–30 THz. Iron nanosheets remarkably increase the free charge carrier density and plasmon frequency in the infrared range of light. Moreover, the temperature dependent electrical conductivity shows high temperature stability and an increased electrical conductivity by more than 7 orders of magnitude by coating WO3 with 70 nm thick Fe nanosheets. The stability of the electrical conductivity at low temperatures and the wide range of terahertz cutoff limits in addition to the well-enhanced light absorbability makes the iron coated tungsten oxide dielectric lenses promising for multifunction optoelectronic applications.
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    Enhanced performance of Pb/FeSe2 interfaces designed for electrical applications
    (Applied Physics A materials science and processing, Mart 2024) Qasrawi Atef Fayez; Seham Alharbi; Sabah E Algarni
    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(Ω cm)−1 to 6.88 ×10−2(Ω 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 disorder, 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 reaching 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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    Optical, dielectric and electrical properties of Ba/Sb nanosheets designed for electro-optical application
    (Phyisca Scripta (IOP), 10.10.2024) Qasrawi Atef Fayez; Najar S. H.; Elayyat Shadia M. S.
    Herein, stacked nanosheets of barium and antimony are fabricated using a vacuum deposition technique under a vacuum pressure of 10-5 mbar onto cleaned glass substrates. The Zintl Ba/Sb nanosheets exhibit an amorphous nature of growth with equal atomic contents. Notably, they present interesting properties such as low average roughness, high light transmittance and absorption, and low reflectance. Two optical transitions within energy bands with values of 3.40 eV and 0.75 eV are determined for these stacked nanosheets. Additionally, Ba/Sb nanosheets displayed dielectric lens and optical filter characteristics with high optical conductivity exceeding 5.0 (Ωcm)-1, 20 (Ωcm)-1, and 100 (Ωcm)-1 in the infrared, visible, and ultraviolet ranges of light, respectively. The optical conductivity parameters, including the free charge carrier density, drift mobility, and plasmon frequency, exhibit values in the ranges of 1.3-25×1019 cm-3, 3.53-9.41 cm2/Vs, and 3.92-17.18 GHz, respectively. Moreover, Ba/Sb nanosheets display characteristics of terahertz band filters, demonstrating terahertz cutoff frequency values of 18-100 THz in the incident photon energy range of 1.13-3.64 eV. On the other hand, temperature-dependent electrical conductivity measurements on these stacked nanosheets reveal the domination of two impurity levels centered at 136 meV and 500 meV, with one being dominant below and the other above 380 K, respectively. The features of the Ba/Sb nanosheets reported here highlight their potential as optical filters, surface plasmon resonators, and terahertz band filter
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    Thermal annealing effects on the structural and electrical properties of Ag2La thin films deposited by thermal evaporation technique
    (Digest Journal of Nanomaterials and Biostructures Vol. 19, No. 2, April - June 2024, p. 909 - 917, 17.06.2024) Qasrawi Atef Fayez; Zakarneh Wafa
    thermal annealing process. The thermally heated of films at 200 oC increased the crystallite sizes and improved the crystalline structure of the films. For these films the electrical conductivity measurements which were handled in the temperature range of 300- 440 K. The conductivity analyses indicated that the transport of charged particles is dominated by the thermionic emission and by the variable range hopping conduction mechanisms. The annealing of films shifted the impurity levels and decreased; the degree of disorder, the average hopping distance and the average hopping energy.
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    Thermal annealing effects on the structural and electrical properties of Ag2La thin films deposited by thermal evaporation technique
    (Digest Journal of Nanomaterials and Biostructures, 17/06/2024) Qasrawi Atef Fayez; Zakarneh Wafa
    thermal annealing process. The thermally heated of films at 200 oC increased the crystallite sizes and improved the crystalline structure of the films. For these films the electrical conductivity measurements which were handled in the temperature range of 300- 440 K. The conductivity analyses indicated that the transport of charged particles is dominated by the thermionic emission and by the variable range hopping conduction mechanisms. The annealing of films shifted the impurity levels and decreased; the degree of disorder, the average hopping distance and the average hopping energy.
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    ZnPc based multifunctional devices designed as fast capacitors, rectifiers, infrared detectors and microwave resonators adequate for 6G technology applications
    (Physica Scripta, Mart 2024) Qasrawi Atef Fayez; Daragme Rana B.
    Herein Zinc phthalocyanine (ZnPc) based multifunctional devices are fabricated and characterized. The device fabrication included formation of an Au nanosheets onto n-Si wafers and coating these nanosheets with 500 nmthick ZnPc layer. Silver and platinum were used to form a Schottky and an ohmic contacts with n-Si and ZnPc, respectively. The device hybrid structure (Ag/n-Si/Au/p-ZnPc/ Pt; abbreviated as ASZ) is composed of Ag/n-Si Schottky arm and p- and n- layers forming pn junction separated by Au nanosheets. Electrical and photoelectrical measurements on the ASZ devices have shown their ability to perform as conventional metal-oxide-semiconductor capacitors (CMOS). TheseCMOSdevices showed light and frequency controlled charge accumulation, depletion and inversion mechanisms within the range of 1.0–50 MHz. The flat band and threshold voltages of the ASZ capacitors are engineered by the imposed ac signal frequency and by infrared (IR) light. In addition, ASZ devices performed as biasing controlled IR photosensors and as current rectifiers. A rectification ratio of 103, IR light sensitivity of 39, specific detectivity of .96 ´109 Jones and current responsivity exceeding 9.0 mAW−1 are recorded at biasing voltage of 4.5 V. Moreover ASZ devices displayed microwave resonator characteristics presented by negative capacitance effect, resonance – antiresonance phenomena and high microwave cutoff frequency. The latter is larger than 10 GHz nominating the device for 6G technology applications.