Fig. 4.

Capacitance gradient (dC/dz) images of unmodified, cationic and anionic cellulose films were obtained over a 1 µm² sample. The capacitance coupling of the tip to the sample was measured and determined by the capacitance of the probed sample volume. The scale is in mV as a signal is generated that is linearly proportional to dC/dz. The black/white scale indicates the magnitude of dC/dz signal of the sample, whereby black = 0 and white = 10 mV. The cationic cellulose surface is a lighter shade which reflects a higher capacitive coupling dC/dz