FIGURE 3.

Lateral force images of a COOH-NH₂ SAM patterned substrate taken with an OH-functionalized nanosized probe tip probe tip (R ∼50 nm, nominal cantilever spring constant, k ∼0.06 N/m) under ∼5 nN applied normal force in 0.01 M NaCl solutions at pH ∼10.3 and 2.4 (pH was adjusted by adding HCl or NaOH; COOH-SAM was outside the hexagon, NH₂-SAM inside).