Kelvin Probe Force Microscopy

Measure contact potential difference ΔΦ = (φ_tip − φ_sample)/e via AC bias nulling

Tip work function (eV): 4.50 AC bias (V): 0.5 Scan position: 0

KPFM applies an AC voltage V_AC·sin(ωt) to the cantilever tip. The electrostatic force has a component at ω: F_ω ∝ (V_CPD − V_DC)·V_AC. A feedback loop adjusts DC bias V_DC until F_ω = 0, directly reading the contact potential difference CPD = (φ_tip − φ_sample)/e. Spatial resolution <10 nm enables work function mapping of individual grains, defects, and molecular adsorbates.