Large area sub-100 nm direct nanoimprinting of palladium nanostructures $(document).ready(function() { if (!$("html").hasClass("ie8")) { $.ajax({ url: "https://crossmark-cdn.crossref.org/widget/v2.0/widget.js", dataType: "script", cache: true }).done(function() { $(".crossmark-button").addClass("visible"); }); } });

Abstract

Direct imprinting of metals is predominantly achieved by using polydimethylsiloxane (PDMS) molds to pattern metal nanoparticles and subsequently melting them to form continuous structures. Although such a combination can successfully imprint metals, the yield and reproducibility are usually low when sub-100 nm features over large areas are desired. In this work, we demonstrate a simple method involving the addition of a cross-linker ethylene glycol dimethacrylate (EDMA) to a palladium metal precursor, and its in situ free radical polymerization during imprinting, which not only dramatically increases the yield to ∼100% but also enables high reproducibility. Palladium mercaptide resist was formed by dissolving acetoxy(benzylthio)palladium, EDMA and azobis-(isobutyronitrile) in an organic solvent mixture. The resist underwent polymerization when imprinted using a silicon mold at 120 °C with pressures as low as 30 bar. Polymerization rigidly shapes the imprinted patterns, traps the metal atoms, reduces the surface energy and strengthens the structures, thereby giving ∼100% yield after demolding. Heat-treatment of the imprinted structures at 330 °C resulted in the loss of organics and their subsequent shrinkage without the loss of integrity or aspect ratio and converted them to palladium nanostructures as small as ∼35 nm wide, over areas >1 cm × 1 cm. With suitable precursors, our technique can potentially be extended to pattern noble metals such as platinum, gold and silver.