Materials Science of Electrochemical Formation of Tungsten Nanosharp Probes

This dissertation is centered on the development of a methodology that aims to engineer millimeter long and ten microns thin nanosharp tungsten probes. The current state of the art of electropolishing techniques is reviewed. We discuss the probes produced by electrochemical etching of a wire until it breaks into two pieces. This process is difficult to control because of the complexity of the associated hydrodynamic flows. These techniques were called convection-limited electropolishing (CLE) because the kinetics of wire etching is controlled by the convective diffusion of ions. We introduced a newly developed technique, precipitation-limited electropolishing (PLE), which enables production of the long probes with nanosharp tips. In the PLE regime, the electrochemical reaction leads to formation of the porous surface layer that hinders the flow of the electrolyte. The probe’s sharpness and length are controlled by choosing an appropriate thermodynamic pathway of metal to metal oxide/hydrates transformations. As an example of the treatable metals, we use tungsten wires. However, the developed methodology might be applicable for other metals