The normalized modulus-distance profiles for a range of artificial interphase thicknesses, and three different probe radii are shown in Figure . Each profile was plotted with the master curve (dark solid line), and the difference between the obtained modulus and the modulus predicted by the master curve (E/EFF-EMC) are shown in the inset figures. With a relatively thin I layer (λphase = 90, 180 nm), the data tracks the master curve for a probe radius of R = 300 nm. Increasing deviations from the master curve are seen for measurements with decreasing probe radius, i.e., R = 30 nm and R = 15 nm. The deviation from the pure substrate effect becomes more significant for a thicker I layer (i.e., λphase = 486 ,1168 nm) at all probe radii. These are conditions in which the I layer is always much thicker than each contact radius. In addition, for the thickest I layer (i.e., λphase = 1168 nm) a clear plateau region and a step-like transition from the interphase modulus to the matrix modulus for all tip radii is observed. This contrasts with the smooth transitions observed for thinner interphases. The lack of plateau region for a thin interphase suggests that the effects of chemical interdiffusion in forming a natural interphase is on the same length scale as that produced by our fabricated interphases. These observations show that the effect of the interphase on the modulus profile can be distinguished only when the contact radius is sufficiently small compared to the interphase thickness.