Fig. 2. The PiF signal and cantilever amplitude as a function of tip-sample distance on 10-nm-thick PS-r-PEDCPMA brush prepared on Si and excited with 1733 cm⁻¹.

The black curve is the amplitude curve of the second resonance, which probes the topography in a dynamic AFM mode. The green curve is the amplitude of the first mechanical resonance, used for probing the photoinduced force with direct-drive modulation to measure both the localized and nonlocalized forces. The blue curve is the amplitude of the first mechanical resonance, used for probing the photoinduced force with sideband modulation to measure mostly the localized force behavior. The orange curve is the amplitude at the contact resonance frequency, which measures the sample dilation once the tip is in physical contact with the surface. The three curves (blue, green, and red) are normalized by the maximum signal obtained in the sideband excitation. a.u., arbitrary unit.