Defect Control with the Electron Wind Force

The flow of current generates Joule heating as electrons are scattered by the lattice or ordered atoms. However, when they are scattered by defects, such as grain boundaries, they transfer all their momentum to the defects. This momentum transfer gives rise to the so-called electron wind force (EWF), which is purely mechanical in nature. The well-known damage phenomenon of electromigration results from the combined influences of EWF and Joule heating. However, this study focuses on exploiting the EWF constructively. We hypothesize that if we can suppress the temperature rise, the EWF can impart significant mobility to defects and anneal them in a very short amount of time. This is because temperature-driven diffusion is mostly random, whereas EWF-driven diffusion follows the direction of electron flow, exhibiting convection-diffusion behavior.<br/> <br/>We performed experiments on a diverse set of materials to investigate our hypothesis. The first set involved atomic layer deposited tin disulfide and tin oxide in thin film and electronic device forms. The EWF was observed to cause a remarkable increase in current-voltage characteristics. Since the slope of this curve represents defect density (via electrical resistance), the results indicate appreciable annealing at room temperature in less than a minute. Similar results achieved via thermal annealing require several hours at 350°C. The second set involved metals and alloys. We present evidence of unique grain reconfiguration through controllable rotation, which is not possible with conventional heat treatment. At room temperature, we observed up to 18 degrees of grain rotation, which could be reversed by varying the current flow direction. The ability to control Joule heating provides a unique tool to manipulate microstructure: at low temperatures, we can induce grain refinement while maintaining low-angle grain boundary (LAGB) density, and at moderate temperatures, we can increase grain size and eliminate LAGBs.<br/><br/>The findings of this study highlight the potential of 'convective diffusion' of defects that are specifically targeted by electrical current-based materials processing for microstructural control at room temperature.