Novel developments and applications of bimodal atomic force microscopy and 3D-AFM

Abstract

Understanding surface and interfacial properties of materials is fundamental to employ them for novel applications. The Atomic Force Microscope is one of the most versatile tools for that purpose. It can be applied in vacuum, air or liquid solution, for the study of materials of very different nature, and with the purpose of unraveling intrinsic properties other than resolving morphological features with sub-nm resolution. All together, these are characteristics that make the AFM unique. Among the different AFM techniques developed so far, dynamic modes stand out for their flexibility. Dynamic AFM methods consist in a oscillatory excitation of the AFM cantilever. The two main dynamic AFM techniques are called Amplitude Modulation (AM) and Frequency Modulation (FM), which differ for the mechanism exerted by the electronic controllers. Their use has reached a widespread popularity in academia and industry. Recently, novel advanced dynamic AFM techniques have been developed with three general purposes: (i) higher sensitivity, (ii) faster acquisition time, (iii) ability to analyze material properties not accessible before. In this thesis, bimodal AFM and 3D-AFM are the advanced dynamic methods of interest. Bimodal AFM is a multifrequency AFM technique based on the simultaneous excitation of two eigeinmodes of the AFM cantilever. It can be applied to unravel different types of material properties, e.g. mechanical and magnetic characteristics. For that purpose, proper force models have to be combined with a theoretical description of the cantilever movement, and corroborate through simulations and experiments. 3D-AFM is a novel AFM technique which allows to map with high resolution a three-dimensional volume. It has been applied to study forces happening at solid-liquid interfaces, and it has unraveled how liquid molecules arrange at the surface of a variety of materials. This thesis comprises six chapters with two main focuses, being the first the further development and improvement of bimodal AFM and 3D-AFM, and the second to show their feasibility to be applied for the study of nanoscale phenomena otherwise difficult to probe with other techniques. The details of the chapters are briefly listed in the following