Cone Angle Modulation of Silicon Nanocones through Double Etching Processes in Metal-Assisted Chemical Etching

All-wet metal-assisted chemical etching (MACE) has been demonstrated as a simple and effective method to fabricate silicon nanocones (SiNCs). The properties of SiNCs strongly depend on their structure parameters such as the cone angle and can be optimized through modulating the cone angle. However, cone angle modulation of SiNCs in all-wet MACE processes has not been achieved. Here, we report the fabrication of SiNCs with different cone angles through double etching processes in all-wet MACE. Large-size silver nanoparticles (AgNPs) were first obtained by solution deposition. After a common etching process, a double etching process with diluted etching solutions was introduced. In the etching step, AgNPs gradually reduced with the Si etching, which resulted in the formation of SiNCs. The cone angles of SiNCs depend on the changing rate of AgNP sizes. Based on this mechanism, SiNCs with different cone angles from 5°-20° were successfully fabricated by changing the concentration of the diluted etching solution in the double etching process. The contact angle of SiNCs with different cone angles was also investigated. It is found that the wettability of the SiNCs becomes poorer with increasing cone angles. Cone angle modulation of SiNCs in all-wet MACE will benefit the property control and the wide applications of SiNCs.