Antenna enhanced infrared photoinduced force imaging in aqueous environment with super-resolution and hypersensitivity

TL;DR

This paper introduces a novel antenna-enhanced photoinduced force microscopy technique that achieves super-resolution and hypersensitivity for IR imaging in aqueous environments, enabling nanoscale interface analysis with high sensitivity.

Contribution

It demonstrates the first application of photoinduced force microscopy in water using resonant antennas to significantly enhance sensitivity and resolution.

Findings

Achieved sub-10 nm spatial resolution in aqueous IR imaging.

Successfully identified a 1-2 nm PDMS layer in water.

Demonstrated sampling of ~604 chemical bonds with high sensitivity.

Abstract

Tip enhanced IR spectra and imaging have been widely used in cutting-edge studies for the in-depth understanding of the composition, structure and function of interfaces at the nanoscale. However, molecular monolayer sensitivity has only been demonstrated on solid/gas interfaces. In aqueous environment, the reduced sensitivity due to strong damping of the cantilever oscillation and background IR absorption extremely limits the practical applications of tip enhanced IR nanospectroscopy. Here, we demonstrate hypersensitive nanoscale IR spectra and imaging in aqueous environment with the combination of photoinduced force (PiF) microscopy and resonant antennas. The highly confined electromagnetic field inbetween the tip end and antenna extremely amplifies the photoinduced force to the detectable level, while the excitation via plasmon internal reflection mode minimizes the environmental absorption. A polydimethylsiloxane (PDMS) layer (~1-2 nm thickness) functionalized on the AFM tip has been successfully identified in water with antennas of different sizes. Sampling volume of ~604 chemical bonds from PDMS was demonstrated with sub-10 nm spatial resolution confirmed by electric (E) field distribution mapping on antennas, which strongly suggests the desired requirements for interfacial spectroscopy. This platform demonstrates for the first time the application of photoinduced force microscopy in aqueous environments, providing a brand-new configuration to achieve highly enhanced nanoscale IR signals, which is extremely promising for future research of interfaces and nanosystems in aqueous environments.