AFM is a powerful tool to characterize 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 on the cantilever with a reflected laser beam. Different operation modes can be utilized to obtain topography, adhesion and stiffness information. The main advantage of atmospheric AFM lays however in the possibility of performing in situ measurements.
All of the AFM setups at TMC are equipped with flow cells to test the 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 Laboratory of Adhesion Science and Engineering 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 crystalline1 and heterogeneous systems2. 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 Advanced Surface and Interface Analysis 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.
One of the research topics in the group of Nanostructured Thin Films is the investigation of plasma deposited layers in terms of their mechanical stability. For these studies the combination of the AFM with a uni-axial stretching device enables the in situ observation of defect formation and crack propagation.
1. M. Valtiner, G. Grundmeier, Langmuir (2010), 26, 2, 815-820.
2. B. Ozkaya, O. Ozcan, P. Thissen and G. Grundmeier, Langmuir (2010), 26, 11, 8155-8160