Fabrication of nanostar arrays by nanoimprint lithography

Abstract

Using a low-cost and high-throughput process, this work demonstrates the fabrication of nanostar arrays over a large surface area, which would be an efficient substrate for surface enhanced Raman scattering applications. In the method, the nanostar is defined by the gap between four nanoholes “touching” each other. The two-dimensional periodic hole array was fabricated by nanoimprint lithography, and then the array pattern was transferred into a polymer layer sandwiched between two hard mask layers. Next, the holes in the polymer layer were enlarged by oxygen reactive ion etching (RIE) until its diameter was equal to the array period. The nanostar array was formed in the bottom hard layer after RIE, or it can be further transferred into a noble metal layer by lift-off steps. The authors fabricated a nanostar array with 200 nm tip-tip distance (equal to array period) and down to sub-10-nm apex and gap between adjacent stars. Numerical simulation confirmed the great enhancement of electromagnetic field near the star apexes.