Fundamentals of AFM

Video credit Oxford Asylum Research

Depending on the type of interaction between the probe and the sample, AFM can be operated in multiple modes

Static modes are sometimes also called contact modes, and include lateral force microscopy (LFM). They track constant deflection across the photodiode quadrants.

These can have various names including AC/AM/AFM, and track changes in peak-to-peak amplitude of oscillation and phase lag relative to the drive frequency/set phase.
(see embedded video below)

Conductive AFM (CAFM), scanning Kelvin probe microscopy (SKPM) and Magnetic force microscopy (MFM) modes require specialized conductive probes (CAFM and SKPM) or magnetic probes (MFM), and dual-pass scanning configurations (SKPM and MFM) to isolate electrical potentials/magnetic fields from underlying topography.

If you are interested to learn more, see these video tutorials (opens in new windows):

Scanning capacitance microscopy

KPFM

Video credit Oxford Asylum Research

Let's summarise the various AFM operation modes

The tip is in continuous, hard contact with the surface. A feedback loop adjusts the Z-piezo actuator to keep a constant cantilever deflection (and constant force) while rastering in X and Y.
A relative of contact mode where the fast scan direction is orthogonal to the cantilever length. It measures the torsional twisting of the cantilever to map surface frictional forces.
The cantilever is mechanically oscillated near its resonant frequency. Topography is tracked by monitoring changes in the oscillation amplitude as the tip taps the surface.
An AC bias applied to a conductive tip induces localized material strain (expansion/contraction) in piezoelectric or ferroelectric samples, measuring local electromechanical response.
(see embedded video below)
Drives the cantilever at two frequencies flanking the contact resonance. By tracking the amplitude difference, it eliminates topographic crosstalk while maintaining resonance amplification.
(see embedded video below)
Measures electrical current passing through a conductive tip and the sample under an applied bias to map localized electrical conductivity or resistance.
A two-pass technique where the first pass records topography and the second pass lifts the tip to a specified delta height to measure long-range forces (e.g., electrostatic, magnetic).
Uses a high-voltage biased conductive AFM tip to purposefully reverse or manipulate local ferroelectric domain polarization profiles on the nanoscale.