Novel Electrochemical Surface Forces Apparatus and Electrochemical AFM Setups for the Study of Interfacial Phenomena

With the rapid progress in the design and fabrication of micro- and nanometer-scaled devices at smaller and smaller length scales, a fundamental understanding of, and the ability to control the interfacial interactions between materials across ultra small distances plays a critical role in advancing these technologies. The ability to ‘tune’ the forces in various device components remains a critical hurdle to optimizing device performance and reliability of, for example nanofluidic and lab-on-a-chip systems, aqueous-based MEMS, sensor devices; as well as devices where adhesion and adsorption can be controlled, surface contacts and wetting properties tuned, and single molecules and bi-layer interactions manipulated. Surface morphology (including roughness) and electrostatic potential-dependent interaction forces significantly affect the physical and mechanical properties of surfaces and play a critical role in all of these systems.

We present novel setups for both an improved electrochemical AFM [1] and a newly developed electrochemical surface force apparatus [2], and compare the two techniques. We discuss surface force measurements under electrochemical potential control between a metal and a ceramic surface across a liquid medium (water). Our experiments also reveal how increasing levels of surface roughness and dissimilarity in the surface potentials of the interacting surfaces influence the strength and range of electric double layer, van der Waals, hydration, and steric forces, and how these contribute to deviations from DLVO theory, particularly at distances less than two Debye lengths, or 2-3 times the rms rougness, whichever is greater [2].

[1] Markus Valtiner, G. Ankah, A. Bashir and F. Renner, Rev. Sci. Instrum. 82, 023703 (2011)

[2] Markus Valtiner, Kai Kristiansen, George W. Greene, Jacob N. Israelachvili, Advanced Materials, DOI: 10.1002/adma.201003709 (2011)