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

G Benetti and M Gandolfi and MJ Van Bael and L Gavioli and C Giannetti and C Caddeo and F Banfi, ACS APPLIED MATERIALS & INTERFACES, 10, 27947-27954 (2018).

DOI: 10.1021/acsami.8b07925

Accessing fluid infiltration in nanogranular coatings is an outstanding challenge, of relevance for applications ranging from nanomedicine to catalysis. A sensing platform, allowing quantifying the amount of fluid infiltrated in a nanogranular ultrathin coating, with thickness in the 10-40 nm range, is here proposed and theoretically investigated by multiscale modeling. The scheme relies on impulsive photoacoustic excitation of hypersonic mechanical breathing modes in engineered gas- phase-synthesized nano granular metallic ultrathin films and time- resolved acousto-optical read-out of the breathing modes frequency shift upon liquid infiltration. A superior sensitivity, exceeding 26 x 10(3) 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 nanofluidics 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.

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