Dynamic Atomic Force Microscopy and applications in biomolecular imaging

The Atomic Force Microscope (AFM) is a key member of the Scanning Probe Microscope (SPM) family. Its versatility allows it to image and manipulate nanoscale features with high precision, making it one of the main instruments in
nanotechnology for surface characterization. The aim of this thesis is to improve robustness, reproducibility, resolution and data interpretation in ambient conditions
for dynamic AFM of heterogeneous samples.

The AFM is particularly notorious for lack of reproducibility with apparent height and width being the two main measured parameters where accuracy is sought. Here
i) the origins of reproducibility, or lack thereof, have been investigated experimentally via a systematic approach to imaging for the whole range of parameter space and relative humidity, ii) smooth and step-like transitions have been investigated both experimentally and with simulations, iii) a method to mechanically stabilise the tip radius and calculate the effective area of interaction in the dynamic mode has been developed and used to predict the number of eV dissipated per atom per cycle, iv) a method to predict the tip radius in situ has been developed, v) three types of dynamic behaviour have been categorised and distinguished (Type I, II and III) allowing to both predict the tip radius and noise patterns, vi) a general interpretation of a mechanism behind height reconstruction and vii) a novel high resolution and low wear imaging technique (SASS) have been developed, modelled,
implemented and interpreted with the help of simulations.

The most general outcome of this work is that the tip radius has to be well characterised since it plays a major role in any AFM experiment. The investigation is
general for nano-mechanical forced oscillators in ambient conditions and the calculations will lead to mapping of local chemistry and mechanics at higher resolution.