Seham Reef Alharbi

Amorphous Ge thin films coated with rare-earth yttrium (Y) and ytterbium (Yb) nanosheets were investigated as multifunctional materials for electronic and microwave applications. Electrical characterization of as-grown Ge and coated Ge (Y, Yb) structures over 30–300 K and 0.01–6.0 GHz showed that Y and Yb coatings enhanced the low-temperature electrical conductivity by factors of 23.7 and 11.3, respectively. Charge transport was governed by thermally activated conduction and variable range hopping above about 120 K, while tunneling dominated in the 20–120 K range, indicating that rare-earth coating strongly modifies carrier localization and interfacial electronic states in Ge. In the 0.001–1.8 GHz range, Ge/Y and Ge/Yb also exhibited negative conductance and negative capacitance, supporting their potential for signal processing and sensing technologies. In parallel, sub-6 GHz two-port microwave measurements showed that the Y-coated sample exhibited the broadest common matched frequency range of 2.01–3.90 GHz and a balanced two-port response near 2.40 GHz. For Ge/Y, the minimum reflection coefficients were S₁₁ = −37.84 dB at 2.61 GHz and S₂₂ = −38.06 dB at 2.34 GHz, while S₂₁ and S₁₂ reached −24.12 dB and −23.96 dB, respectively, at 0.21 GHz. These results establish rare-earth coating as an effective approach for tuning the electrical and microwave network response of amorphous Ge thin-film structures and motivate their further investigation for sub-6 GHz microwave and wireless-device applications.

Herein, molybdenum sulfide (MoS ₂ ) powder ceramics, pressed into pellet form and sintered at a low temperature (200 °C) for 1 h and 20 h, are studied and analyzed for potential use in high-frequency microwave technology design. It is observed that longer sintering times lead to enhanced crystallinity (fewer defects and larger crystallites), increased grain sizes, and reduced pore density, resulting in improved electrical conductivity and a conductivity type conversion from p-type to n-type. The porosity percentage decreased from 48.5% to 39.0% as a result of increasing the sintering time from 1 h to 20 h, respectively. The donor and acceptor centers, along with the variable range hopping parameters—such as degree of disorder, hopping distance ( R ( 200 K ) ), hopping energy, and density of localized states near the Fermi level ( N ( E F ) ) - are found to be strongly dependent on the sintering time. Numerically, N ( E F ) decreased from 9.80 × 10 18 cm ³ eV ⁻¹ to 2.81 × 10 17 cm ³ eV ⁻¹ and R ( 200 K ) increased from 6.78 nm to 15.50 nm as the sintering time increased from 1 h to 20 h, respectively. Furthermore, the ceramics, when designed as antennas and evaluated through return loss and voltage standing wave ratio ( VSWR ) measurements in the 9.0 kHz–6.0 GHz spectral range, demonstrate strong potential for 5G/6G technology applications. Notably, the sample sintered for 1 h exhibited a main resonant frequency at 3.3 GHz, whereas the sample sintered for 20 h showed a resonant frequency at 5.46 GHz. Both devices achieved return loss values better than −40 dB, VSWR of 1.02, and bandwidths of ∼2.0 GHz, highlighting their suitability for high-frequency applications.

Herein, amorphous copper oxide thin films are irradiated with laser pulses of various pulse widths ( PW ) and repetition frequencies ( f R ) to achieve ultrafast crystallinity and obtain enhanced features suiting electro-optical systems. Pulsed laser irradiated (PLI) films exhibited crystalline orthorhombic-hexagonal structure when irradiated with PW of 5.0 ms and f _R = 1.0 Hz and preferred the hexagonal structure as a major phase at PW value of 50.0 ms and f R = 1.0 Hz . The crystallinity is enhanced with increasing PW and f R values. Films irradiated with pulsed laser of f R = 1.0 Hz exhibited interesting morphology presented by growth of nano-grains at PW = 5.0 ms that converts to textured microspheres at PW = 50 ms. Optically, the films transmittance increased and reflectance decreased with increasing PW value leading to widening of the energy band gap for most of the irradiated films. The PLI films were used for the design of planner waveguides suitable for global system for mobile communications technology showing negative capacitance effect and excellent impedance match and signal transfer properties presented by return loss value of 29 dB and reflection coefficient value of 0.036 at quad band frequency of 1800 MHz. These ideal features of the PLI films make them suitable for applications concerned communication technology.

Herein CdS thin films deposited onto glass and CuO substrates by the thermal evaporation technique are treated as electro-optical devices. Investigations on the structural properties of the CuO/CdS (CS) heterojunctions have shown that the preferred growth of hexagonal CdS onto amorphous CuO results in strained structure that increased the defects concentration in CdS. Optically the energy band gap of CdS is narrowed and the light absorption and dielectric response increased by 1590% at 1.70 eV and 565% at 1.60 eV, respectively. CS exhibited a valence band aligned heterojunction and a conduction band offset of 0.43 eV. As terahertz band filters CS heterojunction exhibited cutoff frequency in the range of 5–77 THz and high optical conductivity exceeding 100 Ω cm − 1 in the infrared range of light. The drift mobility and free carrier concentration varied in the range of 5.74–10.44 cm² V⁻¹s⁻¹ and 1.7 × 10 18 − 1.6 × 10 19 cm⁻³, respectively. Electrically, a planar waveguide benefiting from CS interfaces as a high k − dielectric media showed negative capacitance effect and negative cutoff frequency as a response to signal carriers in the frequency domain of 0.01–1.0 GHz. The waveguides with these features are promising as signal stabilizers and negative capacitance sources in addition to its ability to perform as terahertz band filters.