Fig. 1

Schematic for I–V measurements in contact-mode AFM. a In this schematic, the tip is biased with respect to the bottom electrode which is grounded. Current flows are detected and amplified by use of a high-gain current amplifier, with the output fed into a data acquisition system. b In an S-IV measurement, a slowly varying DC waveform is applied to the tip (or sample) and the current is measured; each step in the voltage results in a relaxation in the measured current due to the capacitance in the circuit. By neglecting some portion of this current and averaging over some integration time Δt, a single value of the current I _j at V _j is recorded. In general-mode I–V, the waveform is fast (see c) (generally, sinusoidal but not limited to this case), and the full current stream is recorded, allowing filtering after collection as appropriate