Quantitative subsurface contact resonance force microscopy of model polymernanocomposites**Publication of NIST, an agency of the US government, not subject to copyright.

Abstract

We present experimental results on the use of quantitative contact resonance forcemicroscopy (CR-FM) for mapping the planar location and depth of 50 nm diameter silicananoparticles buried beneath polystyrene films 30–165 nm thick. The presence of shallowlyburied nanoparticles, with stiffness greater than that of the surrounding matrix, isshown to locally affect the surface contact stiffness of a material for all depthsinvestigated. To achieve the necessary stiffness sensitivity, the CR-FM measurementsare obtained utilizing the fifth contact eigenmode. Stiffness contrast is found toincrease rapidly with initial increases in force, but plateaus at higher loads. Over theexplored depth range, stiffness contrast spans roughly one order of magnitude,suggesting good depth differentiation. Scatter in the stiffness contrast for single imagesreveals nonuniformities in the model samples that can be explained by particle sizedispersity. Finite element analysis is used to simulate the significant effect particle sizecan have on contact stiffness contrast. Finally, we show how measurements at arange of forces may be used to deconvolve particle size effects from depth effects.