Based on wet etching and ultrasonic cavitation, an ultrasonic etch method was proposed for fabricating micro- and nanoscale hierarchical structures. By ultrasonic etching with isopyknic mixture of nitric acid/ethanol(4%, volume fraction) and hydrogen peroxide(30%, mass fraction) for 2—10 min at room tempe-rature, several hierarchical structures were fabricated on the surfaces of 60Si2Mn, 60#, T10, Cr06, 65Mn and silicon steel. After decorated with fluorosilane, the aforementioned surfaces become superhydrophobic and show water contact angles of 156.0°, 154.8°, 156.4°, 153.9°, 156.6° and 155.8°, respectively, and the corresponding roll angles are 6.5°, 19.2°, 6.1°, 7.8°, 6.7° and 7.2°, respectively. Compared to the regular etching, the chemical corrosion of ultrasonic etching was enhanced and modified by coupling with cavita-tion, and therefore could fabricate hierarchical structures. Due to the differences in microstructure morphologies and wetting states of solid/liquid interfaces, the superhydrophobic surfaces prepared show different wetting behavior. The ultrasonic method proposed is simple, inexpensive and available for other metals, thus having potential values in constructing micro- and nanoscale hierarchical structures and superhydrophobic surfaces.
