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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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    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.