Ultrasonic force microscopy on 'poly(vinyl alcohol)/SrTiO3' nano-perovskites hybrid films

TL;DR

This study uses Ultrasonic Force Microscopy to characterize poly(vinyl alcohol)/SrTiO3 hybrid films, revealing nanoscale interface effects and aggregation behaviors not visible with traditional AFM.

Contribution

It demonstrates the effectiveness of UFM in resolving nanostructures and interface properties in PVA/SrTiO3 composites, highlighting the role of ultrasonic damping at interfaces.

Findings

UFM better resolves STO nanoparticle morphology than contact-mode AFM.

STO nanoparticles form nanoclusters and microaggregates at high concentrations.

Ultrasound damping at PVA/STO interfaces influences UFM contrast.

Abstract

Atomic Force Microscopy (AFM) and Ultrasonic Force Microscopy (UFM) have been applied to the characterization of composite samples formed by SrTiO 3 (STO) nanoparticles (NPs) and polyvinyl alcohol (PVA). The morphological features of the STO NPs were much better resolved in UFM than in contact-mode AFM topography. For high STO concentrations the individual STO NPs formed nanoclusters, which gathered in microaggregates. The STO aggregates, covered by PVA, exhibited no AFM frictional contrast, but were clearly distinguished from the PVA matrix using UFM. Similar aggregation was observed for NPs in the composite samples than for NPs deposited on top of a flat silicon substrate from a milliQ water solution in the absence of polymer. In the hybrid films, most STO nanoparticles typically presented a lower UFM contrast than the PVA matrix, even though stiffer sample regions such as STO should give rise to a higher UFM contrast. STO NPs with intermediate contrast were characterized by an UFM halo of lower contrast at the PVA/STO interface. The results may be explained by considering that ultrasound is effectively damped on the nanometer scale at PVA/ STO interfaces. According to our data, the nanoscale ultrasonic response at the PVA/STO interface plays a fundamental role in the UFM image contrast.