Preparation of metal nano-needles using ion-track membranes

Koshikawa, Hiroshi; Yamamoto, Shunya; Sugimoto, Masaki; Kitamura, Akane; Sawada, Shinichi; Yamaki, Tetsuya

Chemical etching of polymer films irradiated with heavy ions leads to the formation of ion-track membranes with nanoscale pores in different shapes. Particularly, conically-shaped pores are expected to have a potential to create metallic nanoneedles by combination of vapor-deposition and electroplating methods. In this study, we prepared copper nanoneedles inside the conical pores of polyimide (PI)-based ion-track membranes and investigated their morphology. The PI films were irradiated with Ar ions. The irradiated films were etched in a sodium hypochlorite solution at 60C for 0.5 h, leading to the formation of conical pores with a surface diameter of ca. 500 nm. A very thin Au layer was deposited on this pore side of the ion-track membranes; then, it was used as a cathode for electroplating copper into the pores. After dissolving the PI templates, we obtained the copper needles ca. 500 nm in base diameter and 1.2 m in height on copper plates.