High aspect plasmonic nanotrench structures as sensors in the near- and Mid-IR frequency range

Titanium nitride (TiN) and aluminum-doped zinc oxide (AZO) high-aspect trench structures are fabricated using a combination of deep reactive ion etching and atomic layer deposition. These structures may be used as sensors in the near-infrared (IR, 820 - 900 nm wavelength range) and mid-IR (8 μm wavelength), respectively.

We show that the refractive index sensitivity reached values up to 430 nm/RIU for TiN trenches in the near-IR region and enhanced sensitivity of molecules in AZO trenches for mid-IR wavelengths.Due to the high achievable confinement of the electric field at a metal-dielectric interface, plasmons are one of the avenues exploited for high-sensitivity sensing [1].

This confinement at the surface allows tracking of very small amounts of analytes, for example in label-free biosensing. One of the possible designs of the sensors involves grating structures [2], [3]. Depending on the analyte to be measured, either near- or mid-IR ranges can be used. In particular, the mid-IR absorption spectroscopy operating in the wavelength range of 2 - 20 μm (5000 - 500 cm−1) can be used to detect molecules by measuring the vibrational modes in their chemical bonds.

They generally have specific absorption bands in this wavelength range [4]-[6], enabling label-free detection of specific molecules in solid, liquid, and gas phases. The research into these fields may enable various applications from medical diagnosis to gas sensing for environmental monitoring.