Nanoscale sharpening of Ag tip apexes using high-frequency pulsed electrochemical machining

Fabrication of metal nanostructures, including the Ag tips with a nanoscale apex that is crucial for optical scanning probe microscopy, has triggered intense research into nanophotonics. Here, we report an advanced fabrication of Ag tips using pulsed electrochemical machining (EM). It was found that sharper tips can be obtained by using high-frequency pulsed EM. In order to elucidate the sharpening mechanism, the EM system was analyzed using an equivalent circuit. The smaller capacitance of the electrical double layer at high frequency is believed to be responsible for the sharpening. Additionally, the EM process was traced by taking a schlieren photograph, which revealed that the electrolyte contribution to the EM process comes only from the flow of the reaction products.