Atomic force microscopy
An Atomic Force Microscope (AFM) enables the topographic visualization of nanostructured surfaces with a resolution in the sub-nanometer range. Image generation is based on the control and detection of intermolecular forces, respectively, which act between surface atomes and molecules and the atoms of the imaging probe.
AFM is a powerful tool for the characterization of surfaces in terms of their morphology and chemistry. The working principle of AFM relies on the detection of interaction forces between the tip and the surface by means of measuring the bending of a cantilever with a reflected laser beam. Different operation modes can be utilized to obtain topography, adhesion and stiffness information. The main advantage of ambient AFM lies however in the possibility of performing in-situ measurements.
All of the AFM setups at TMC are equipped with flow cells to test metal oxide surfaces for their stability in corrosive media and to perform in situ adsorption/desorption experiments. Moreover, some of the setups also offer the possibility to perform electrochemical AFM studies. In this case the flow cells also contain counter and reference electrodes to obtain the three electrode configuration necessary for the simultaneous cyclic voltammetry and impedance experiments.
AFM is a very important technique for all working groups in TMC. Depending on the research focus, different measurement modes are applied.
The group of Adhesion and Corrosion Science is investigating the fundamental mechanisms of adhesion and de-adhesion processes. In this case, Single Molecule Force Spectroscopy (SMFS), being one of the few methods providing information on binding strengths of individual bonds, has been successfully applied to single-crystalline and heterogeneous systems. The measurements of interaction forces between the polymer chains with various functional groups and the respective surface under pH control can be used to obtain information on the electrostatic, van der Waals and chemical forces as a function of the environment pH.
In the group of Interfacial Engineering of Advanced Materials the Chemical Force Microscopy (CFM) is widely applied to model and technical systems to determine the chemical properties of adsorbed organic layers. Here a very thin film of organofunctional molecules is deposited onto the AFM cantilever and the overall interaction forces between the functionalized tip and the surface is measured by collection of force-distance curves as a function of pH. Depending on the pKa value of the functional films on the surface and the cantilever it is possible to obtain chemical information and to determine the orientation of the molecules on the surface.
The Nanobiomaterials group employs single-molecule AFM imaging in order to investigate the interaction of medically relevant proteins with small-molecules, the stability and denaturation of DNA nanostructures under various application-specific conditions, and the adsorption and surface diffusion of various biomolecules at model surfaces. For the latter, high-speed AFM is often employed in order to capture biomolecular dynamics with a temporal resolution down to the few-seconds level.