Poisson's ratio of 0.38, we can expect that a 30 nm radius probe indented to 250 nN force will have aFF of 10 nm depending on the observed adhesion force. This means that we should be able to resolve an interphase extending at least 50 nm from the SiO2 surface. This estimate compares well with the results of Zhang, et al. , where PMMA films of varying thickness were sandwiched between two silica plates. In that study, no plateau was observed across a 60 nm film between plates, but a 156 nm film clearly showed an interphase spanning both plates. Cheng, et al. reported an interphase gradient extended ~100 nm from an isolated silica-PMMA interface. On the other hand, assuming a carbon black substrate and a styrene-butadiene rubber matrix with a