NTNU - Norwegian University of Science and Technology Michael R. P. Ragazzon
Postdoc. — PhD Engineering Cybernetics


My main area of research is on the topic of atomic force microscopy (AFM). By utilizing tools from control engineering, our efforts in improving AFM can be divided into two main areas of interest:

(I) Improving the performance of the microscope. In dynamic mode AFM, the imaging bandwidth is governed by the slowest component in the open-loop chain consisting of the vertical actuator, cantilever and demodulator. Of which, the latter has been our main concern. Our efforts include (1) development and utilization of new high-bandwidth demodulators, (2) studying possibilities for entirely circumventing the demodulator, as well as (3) investigating and comparing state-of-the-art demodulators in AFM.

(II) Model-based approach to revealing nanomechanical properties using AFM. Revealing nanomechanical properties of soft samples is possible using AFM due to its ability to measure forces. Traditionally, static load-unload force curves have been used to measure elasticity of the sample by fitting the measurements to the Hertz contact model. More recently, dynamic approaches allow one to additionally reveal properties such as viscosity and multifrequency amplitude and phase. We are currently investigating a new model-based approach to revealing viscoelasticity and other properties. Utilizing this online identification approach allows monitoring of e.g. a time-varying elastic modulus in real-time. Additionally, as more data is gathered, the sample model can be iteratively improved to account for the measured signal. The resulting dynamic sample model could be useful for investigating or simulating the sample.

Experiments are conducted at the Nanopositioning lab at the Department of Engineering Cybernetics. In addition to custom-built nanopositioning devices, a commercial AFM is available for implementation of novel control and identification strategies.

Figure: Lyapunov estimator for high-bandwidth amplitude demodulation.
Figure: AFM experiment employing parameter identification on a two-component polymer sample.