Fig. 1.

Source of force drift in an atomic force microscope (AFM). (A) Schematic of a force spectroscopy experiment. The AFM tip is attached to a molecule and retracted from the surface. Force is determined by the deflection (z_tip−z₀), as measured on a quadrant photodiode (QPD). (B) With no molecule attached, the zero force position z₀ (gold) of a cantilever (short BioLever) was measured as a function of time 2 h after wetting. A similar record (green) was measured after repositioning the detection laser onto the chip holding the cantilever. These measurements were scaled using the cantilever’s sensitivity (S = 0.043 V/nm) and stiffness (k = 37 pN/nm). This comparison demonstrates that the primary source of force drift is the cantilever. PZT: piezoelectric stage. This figure is reprinted from [5] with permission from the American Chemical Society.