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<p>In this work, niobium diselenide (NbSe<sub>2</sub>) thin films were deposited by thermal evaporation under a base pressure of ~10<sup>−5</sup>&#xa0;mbar and investigated as broadband frequency-selective reflective surfaces spanning the microwave, infrared, visible, and ultraviolet spectral regions for high-frequency applications. X-ray diffraction indicated weak crystallinity with reflections assignable to the hexagonal NbSe<sub>2</sub> phase. Surface morphology and topographical analyses revealed an average grain size of ~80&#xa0;nm and an average surface roughness of ~12&#xa0;nm. Optical characterization yielded an energy bandgap of 1.50&#xa0;eV and an Urbach energy of 0.21&#xa0;eV. For photonic terahertz applications, NbSe<sub>2</sub> exhibited pronounced dielectric tunability from the infrared to the ultraviolet, accompanied by an increase in optical conductivity and a corresponding rise in terahertz cutoff frequency across 1.38–4.50&#xa0;eV. In addition, when employed as a dielectric coating on metallic substrates, an Al/NbSe<sub>2</sub>/Ag one-port reflective stack produced multiple impedance-matched resonances within the 9.0&#xa0;kHz–6.0&#xa0;GHz range, with reflection-loss minima approaching ~45&#xa0;dB (|<InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(S_{11}\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>S</mi> <mn>11</mn> </msub> </math></EquationSource> </InlineEquation>| ≈ 0.0056). A practical operating bandwidth of ~2.9&#xa0;GHz was achieved under the reflection-loss criterion, while the most strongly matched conditions yielded a voltage standing-wave ratio of approximately 1.01. These findings demonstrate sub-6-GHz impedance engineering enabled by a thin NbSe<sub>2</sub> dielectric layer, supporting the development of compact frequency-selective surfaces for 5G/6G stopband implementation and microwave packaging integration.</p>

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Thermally Evaporated NbSe2 Thin Films Designed as Frequency-Selective Reflective Surfaces

  • 期刊论文

  • 发表日期：

    2026年7月18日

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  • Seham R. Alharbi,
  • A. F. Qasrawi,
  • Laila H. Gaabour

摘要

In this work, niobium diselenide (NbSe2) thin films were deposited by thermal evaporation under a base pressure of ~10−5 mbar and investigated as broadband frequency-selective reflective surfaces spanning the microwave, infrared, visible, and ultraviolet spectral regions for high-frequency applications. X-ray diffraction indicated weak crystallinity with reflections assignable to the hexagonal NbSe2 phase. Surface morphology and topographical analyses revealed an average grain size of ~80 nm and an average surface roughness of ~12 nm. Optical characterization yielded an energy bandgap of 1.50 eV and an Urbach energy of 0.21 eV. For photonic terahertz applications, NbSe2 exhibited pronounced dielectric tunability from the infrared to the ultraviolet, accompanied by an increase in optical conductivity and a corresponding rise in terahertz cutoff frequency across 1.38–4.50 eV. In addition, when employed as a dielectric coating on metallic substrates, an Al/NbSe2/Ag one-port reflective stack produced multiple impedance-matched resonances within the 9.0 kHz–6.0 GHz range, with reflection-loss minima approaching ~45 dB (| \(S_{11}\) S 11 | ≈ 0.0056). A practical operating bandwidth of ~2.9 GHz was achieved under the reflection-loss criterion, while the most strongly matched conditions yielded a voltage standing-wave ratio of approximately 1.01. These findings demonstrate sub-6-GHz impedance engineering enabled by a thin NbSe2 dielectric layer, supporting the development of compact frequency-selective surfaces for 5G/6G stopband implementation and microwave packaging integration.