Photoacoustic Sensing of Trapped Fluids in Nanoporous Thin Films: Device Engineering and Sensing Scheme

TL;DR

This paper proposes a photoacoustic sensing method for quantifying fluid infiltration in nanogranular ultrathin films, using hypersonic mode frequency shifts for highly sensitive detection of liquid presence and distribution.

Contribution

It introduces a novel photoacoustic sensing scheme combining multiscale modelling and hypersonic mode analysis for fluid detection in nanogranular coatings, with potential for broad nanoscale applications.

Findings

Predicted sensitivity exceeds 26,000 cm^2/g.

The scheme can discriminate different infiltration patterns.

Applicable to various nanoscale porous materials.

Abstract

Accessing fluid infiltration in nanogranular coatings is an outstanding challenge, of relevance for applications ranging from nanomedicine to catalysis. A sensing platform, allowing to quantify the amount of fluid infiltrated in a nanogranular ultrathin coating, with thickness in the 10 to 40 nm range, is here proposed and theoretically investigated by multiscale modelling. The scheme relies on impulsive photoacoustic excitation of hypersonic mechanical breathing modes in engineered gas-phase synthesised nanogranular metallic ultathin films and time-resolved acousto-optical read-out of the breathing modes frequency shift upon liquid infiltration. A superior sensitivity, exceeding 26x103 cm^2/g, is predicted upon equivalent areal mass loading of a few ng/mm^2. The capability of the present scheme to discriminate among different infiltration patterns is discussed. The platform is an ideal tool to investigate nano fluidics in granular materials and naturally serves as a distributed nanogetter coating, integrating fluid sensing capabilities. The proposed scheme is readily extendable to other nanoscale and mesoscale porous materials.