Surface Potential Energy of Spinel Catalyst from Atomic Friction Measurements

Itai Shahar, Department of Chemical-Engineering, Ben-Gurion University, Beer Sheva , Israel

Friction is a force that opposes motion. Since it is proportional to the contact area and properties of the materials in contact, it can disclose information on the interfacial interaction potential. The underlying mechanism of friction involves energy dissipation, which together with the surface potential is related to fabrication, catalysis, adhesion and so on. Hence, measuring frictional forces can provide direct quantification of the interaction free energy landscape of the system. This requires high quality data which can be attained with Atomic Force Microscope (AFM). The AFM can probe nanoscale frictional forces with lattice resolution. And measure the dynamical interaction between a cantilever tip and the surface of interest, resulting with atomic stick-slip force pattern. Here we perform FFM experiments on NaCl in ethanol  as a reference material and apply the Prandtl-Tomlinson phenomenological framework to estimate the amplitude of the surface energy corrugation, and show how it scales with the applied normal load. From this scaling we can extrapolate the surface potential in the low friction regime. This methodology was then extended to Spinel catalyst, which was measured for the first time, and displayed higher surface energy than the NaCl crystal. This provides a proof of concept for the application of FFM in the field of catalyst characterization and design.