Figure 1: Experimental set-up.
(a) Schematic of the set-up. A particle is glued to the quartz-tuning fork based AFM, immersed in the liquid and approached to the substrate, made of casted particles. (b) SEM image of a 0.6 μm radius PVC bead glued to the tungsten tip. Scale bar, 1 μm. (c) During the experiment, the tuning fork is excited at two distinct frequencies, corresponding to mechanical oscillation of both normal (N, blue) and tangential/shear (T, red) modes. Two phase-locked loops (PLL) track the frequency of the resonance peaks, allowing characterization of normal and tangential force gradients ∇F (equation (1)) and dissipative frictional forces FD (equation (2)). (d) Typical resonance curve of the normal mode, for a bead in liquid (black) and in contact to another bead on the substrate (red).
