Electrochemically Controlled Reversible Formation of Organized Channel Arrays in Nanoscale-Thick RuO₂ Films: Implications for Mechanically Stable Thin Films and Microfluidic Devices

Arrays of notched holes were fabricated with shapes that serve to initiate and guide crack formation during electrochemical delithiation of RuO2 films. It is demonstrated that these structures cause the formation of organized microchannel arrays during delithiation and that the channels reversibly close when the films are re-lithiated. Moreover, the maximum width of the channels is a function of the hole spacing, and the widths can be controlled by controlling the state of lithiation. Also, there is a striking improvement in the overall mechanical stability of the films when crack formation is guided in this way. These results are consistent with models for stress accommodation through reversible sliding at the film–substrate interface. The ability to use electrochemical methods to reversibly open and close channels with controlled widths could be of use in microfluidic devices and sensors.