Phonon‐polaritonic resonances on nanopillars of hexagonal boron nitride for surface enhanced infrared absorption

Phonon polaritons (PhPs) in hexagonal boron nitride enable sharp mid‐infrared optical resonance with strong spatial confinement, making them promising for surface enhanced infrared absorption spectroscopy. Here, using colloidal nanosphere lithography, we have fabricated hBN nanopillar antennas and demonstrated their PhP resonances in a cost‐effective way. By varying the diameters of the hBN nanopillars, the PhP resonance can be readily tuned to match the molecular vibrations of CBP (4,4′‐bis(N‐carbazolyl)‐1,1′‐biphenyl) molecules. Upon frequency matching, the coupling between the PhP resonance and the molecular vibration shows pronounced mode splitting, illustrating the SEIRA behaviour with a coupling strength approaching the strong coupling regime. While, with slight frequency mismatching around 10 cm‐1, the coupling strength decrease significantly, indicating a high sensitivity of the SEIRA activities to the resonance frequency of hBN nanopillar antennas. Our findings provide a new method for the fabrication of PhP nanoantennas and may promote the development of PhPs in SEIRA‐based mid‐infrared sensing applications.This article is protected by copyright. All rights reserved.