Time-resolved tapping-mode atomic force microscopy

There is an increasing interest in the use of atomic force microscopy for quantitative mapping of material-specific surface properties. Unfortunately, methods that have been developed for local stiffness measurements suffer from low operational speeds and they apply large forces to the surface, limiting their resolution and use on soft materials such as polymers and biological samples. On the other hand, tapping-mode AFM, which is well suited to soft materials due to its gentle interaction with the surface, cannot be used to recover information on the tip-sample interaction (and hence, on the material properties) due to limited mechanical bandwidth offered by the resonant AFM probe.;In this work, a technique for rapid quantitative material characterization with nanoscale spatial resolution is introduced. This technique is based on time-resolved measurement of tip-sample interaction forces during tapping-mode AFM imaging by a special micromachined AFM probe. In this probe, a high-bandwidth interferometric force sensor at the end of the cantilever is coupled to the tip motion and is used to resolve tip-sample interaction forces with high sensitivity and temporal resolution. Combined with a real-time signal processing software that we developed, these probes provide quantitative maps of peak interaction forces and elastic properties simultaneously with conventional AFM data. High-contrast compositional mapping, peak force imaging and quantitative material characterization by mapping surface Young's modulus acquired using this technique are demonstrated on various samples.