Nanogap-Enhanced Infrared Spectroscopy with Template-Stripped Wafer-Scale Arrays of Buried Plasmonic Cavities

TL;DR

This paper introduces wafer-scale arrays of buried plasmonic cavities created through atomic layer lithography and template stripping, achieving high SEIRA enhancement and precise nanogap control for advanced infrared sensing.

Contribution

It presents a novel fabrication method for buried nanocavities with controlled nanogaps, enabling high enhancement in infrared spectroscopy at wafer scale.

Findings

Achieved a SEIRA enhancement factor of 10^5 with 3 nm gaps.

Generated strong infrared resonances and dense hotspots.

Demonstrated precise gap control and long-term stability.

Abstract

We have combined atomic layer lithography and template stripping to produce a new class of substrates for surface-enhanced infrared absorption (SEIRA) spectroscopy. Our structure consists of a buried and U-shaped metal-insulator-metal waveguide whose folded vertical arms efficiently couple normally incident light. The insulator is formed by atomic layer deposition (ALD) of Al2O3 and precisely defines the gap size. The buried nanocavities are protected from contamination by a silicon template until ready for use and exposed by template stripping on demand. The exposed nanocavity generates strong infrared resonances, tightly confines infrared radiation into a gap that is as small as 3 nm ({\lambda}/3300), and creates a dense array of millimeter-long hotspots. After partial removal of the insulators, the gaps are backfilled with benzenethiol molecules, generating distinct Fano resonances due to strong coupling with gap plasmons, and a SEIRA enhancement factor of 10^5 is observed for a 3 nm gap. Because of the wafer-scale manufacturability, single-digit-nanometer control of the gap size via ALD, and long-term storage enabled by template stripping, our buried plasmonic nanocavity substrates will benefit broad applications in sensing and spectroscopy.