Stacking of nanoscale metal dot array using liquid transfer imprint lithography with roll press

Abstract

The stacking of metal nanodot patterns is useful for plasmonic devices and metamaterials. Metal nanodot patterns are conventionally fabricated using a combination of lithography and a metal lift-off process, which is time consuming and complex. On the other hand, there is demand for an expanding the patterning area of the metal nanodot. Therefore, the fabrication method with high throughput is required. For more efficient fabrication, we have developed a novel stacking technique that combines ultraviolet nanoimprint lithography (UV-NIL), contact printing, and liquid transfer imprint lithography (LTIL). UV-NIL was used to obtain a replica mold with a nanoscale hole pattern, and the metal layers were deposited onto the mold by using a vacuum evaporator. Contact printing removed a metal layer on the mold surface, leaving a metal nanodot array in the holes of the replica mold. This metal layer was transferred by UV-NIL, and LTIL with a roll press was employed to reduce the thickness of the UV-curable resin; the excess resin was split from the mold in the liquid phase. The replica mold with the metal dots and an intermediate layer was then transferred to a polyester film. In this study, this process was repeated to obtain five stacked layers. The stack consisting of gold nanodots displayed a red plasmonic color, whereas the stack of silver nanodots displayed a blue plasmonic color. Scanning electron microscopy was used to confirm the stacked structures through tilted angle and cross-sectional view images. The advantages of this process are that nanodot patterns can be fabricated using a mold-based process and that the thickness of the stacking layer can be controlled by LTIL. This process can therefore be used for high-throughput fabrication of stacking metal devices such as plasmonic memory.