AFM Calibration Issues

Atomic force microscopy (AFM) is a powerful tool to investigate molecular interactions and mechanical properties at biointerfaces, with nanometric spatial resolution and pN force sensitivity (Binnig et al., 1986, Martin et al., 1987). However, to fully exploit the quantitative spectroscopic and imaging capabilities of an atomic force microscope, the instrument must be accurately calibrated. The calibration regards several components of an AFM. First of all, the scaling factors of the force and deflection detection apparatus, that is, the cantilever spring constant (intrinsic and effective) and the deflection sensitivity of the optical beam deflection system must be determined. The displacement of the sample with respect to the AFM tip must be controlled with sub-nanometer accuracy, which requires the proper calibration of the sensitivities of the piezoelectric scanners of the instrument along the three directions x,y,z. The tip radius of curvature and the tip geometry are important parameters in the modelling of tip–sample interactions, as in the case of indentation experiments; these parameters must be accurately characterized. This chapter presents a critical overview of the most important calibration procedures for AFM and discusses the related issues and how to mitigate them.