A general approach for controllable surface structuring of metals via through-mask electrochemical micromachining under isotropic etching mode

Surface structuring has attracted growing interest in the industry due to its potential to improve the macroscopic properties of workpieces. This work investigated the surface structuring of metals by combining thermal oxide film mask and laser lithography with isotropic etching. The metals were thermally oxidized to form a protective oxide film, laser ablation patterned the thermal oxide film, while electrochemical etching operated in the isotropic mode obtained an array of hemispherical cavities. The isotropic etching potential for different metals is taken from the mass transport region of the polarization curve. The effects of thermal oxide film thickness and laser ablation area on the uniformity of the etching holes were studied. The thermal oxidation of TA2 at 350 °C formed a 20-nm-thick oxide film, while an array of 10 μm radius hemispherical microcavities was fabricated on the laser patterning surface via electrochemical etching at 2 V for 1 min. The surface structuring of stainless steel, pure nickel, and tungsten is highly dependent on the ability of the oxide film to avoid electrochemical reactions. The feasibility of combining thermal oxidation and laser lithography with electrochemical etching is of great value for the surface structuring of metallic materials for biomedical and microsystem applications.