Yogesh Kumar Srivastava, Rajour Tanyi Ako, Manoj Gupta, Madhu Bhaskaran, Sharath Sriram, Ranjan Singh,
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| Nanometer-scale thin film sensing with quasi-BIC Fano resonance. (a) Optical image of the fabricated TASR metamaterial. The inset depicts the geometrical parameters of the unit cell, gap g = 3 μm, width w = 6 μm, length l = 60 μm, periodicity p = 75 μm, and asymmetry d = 10 μm. (b) Image of the fabricated metamaterial showing robustness and flexibility. (c) The Q factors of quasi-BICs of an ideal (dots, PEC) and a realistic (star, metallic) metamaterial array with varying asymmetry d. Inset: simulated transmission spectra of the metallic TASR metamaterial with an asymmetry of d = 10 μm. (d) and (e) Change in the simulated transmission amplitude (ΔT) and phase (Δϕ, degree) on coating Ge of thicknesses ranging from 7 to 20 nm on the TASR metamaterial. |
https://aip.scitation.org/doi/abs/10.1063/1.5110383
The fingerprint spectral response of several materials with terahertz electromagnetic radiation indicates that terahertz technology is an effective tool for sensing applications. However, sensing few nanometer thin-films of dielectrics with much longer terahertz waves (1 THz = 0.3 mm) is challenging. Here, we demonstrate a quasibound state in the continuum (BIC) resonance for sensing of a nanometer scale thin analyte deposited on a flexible metasurface. The large sensitivity originates from the strong local field confinement of the quasi-BIC Fano resonance state and extremely low absorption loss of a low-index cyclic olefin copolymer substrate. A minimum thickness of 7 nm thin-film of germanium is sensed on the metasurface, which corresponds to a deep subwavelength scale of λ/43 000, where λ is the resonance wavelength. The low-loss, flexible, and large mechanical strength of the quasi-BIC microstructured metamaterial sensor could be an ideal platform for developing ultrasensitive wearable terahertz sensors.
The authors acknowledge valuable and timely assistance from Zhang Qiannan in performing the thickness measurements of the analyte layer using Atomic Force Microscopy. Y.K.S., M.G., and R.S. acknowledge the research funding support from the Ministry of Education AcRF Tier 1 Grant No. RG191/17 and Tier 2 Grant No. MOE2017-T2-1-110. S.S. and R.S. acknowledge support from an RMIT Foundation Research Exchange Fellowship. This work was performed in part at the Micro Nano Research Facility at RMIT University in the Victorian Node of the Australian National Fabrication Facility (ANFF).
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