# Terahertz sensing of 7nm dielectric film with bound states in the continuum metasurfaces

## TL;DR

This paper demonstrates a highly sensitive terahertz sensor capable of detecting nanometer-scale dielectric films using bound states in the continuum metasurfaces, enabling ultrasensitive wearable sensing applications.

## Contribution

It introduces a novel quasi-BIC resonance metasurface that can detect 7 nm thin dielectric films at terahertz frequencies, surpassing previous sensing limitations.

## Key findings

- Detects 7 nm germanium film, corresponding to λ/43000 scale.
- Utilizes strong local field confinement for high sensitivity.
- Features low-loss, flexible, and mechanically robust design.

## Abstract

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-film of dielectrics with much longer terahertz waves (1 THz = 0.3 mm) is challenging. Here, we demonstrate a quasi-bound state in the continuum (BIC) resonance for sensing of nanometer scale thin analyte deposited on a flexible metasurface. The large sensitivity originates from 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 length scale of {\lambda}/43000, where {\lambda} is the resonance wavelength. The low-loss, flexible and large mechanical strength of the quasi-BIC micro structured metamaterial sensor could be an ideal platform for developing ultrasensitive wearable terahertz sensors.

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Source: https://tomesphere.com/paper/1908.03662