Fabrication Of Metal Nanostructure By Nanoimprint Lithography And Study Of Their SERS Effect

Noble metallic microstructures have recently attracted considerable interest in the fields of photonic,photovoltaics,photocatalysis and biological and chemical sensors due to their extraordinary characteristics such as light scattering and absorption,and giant enhancement of the local electric fields.O f particular interest is the combination of plasmonic nanostructures and Raman spectroscopy,which provides a powerful analytical technique,namely,surface-enhanced Raman scattering(SERS)for the ultra-sensitive detection even to single molecular levelThe nanofabrication techniques for metallic micro structure such as E-beam lithography(EBL)and focus ion beam(FIB)offer high fidelity and high controllability,while they suffer from low throughput and high cost On the other hand,self-assembly approaches,such as nanosphere lithography and block copolymer lithography provide a new strategy to fabricate high-resolution nanostructures over a large area with low cost,while it is difficult to obtain highly uniform and uncontrollable structures of arbitrary symmetries across whole area.Apractical SERS substrate with high average enhancement factor(EF),uniformity and reproducibility,large area and low cost is still strongly desired.In this paper,we develop simple and low-cost methods to fabricate SERS substrates over a large area by nanoimprint lithography with anodic aluminum oxide(AAO)templating.1.The fabrication of gold nanodot arrays on Si wafers and its SERS performance.We developed a novel and facile method to prepare gold nanodot arrays using a hybrid nanoimprint lithography with the AAO templating combined with ICP,e-beam evaporation and standard lift-off processes.The structural parameters such as the diameter of the gold nanodots and the gap size between them could be easily tuned by changing the AAO molds with different hole sizes and their spacings.A high Raman EF is achieved on the gold nanodot array SERS substrate with diameter of 90 nm,pillar spacing of 20 nm.2.Gold/PC nanopillar arrays and its SERS effect We demonstrated a simple and low-cost way to fsbricate flexible SERS substrates over a very large area.A method based on combination of nanoimprint lithography and e-beam evaporation of gold was used to fabricate gold/PC nanopillar arrays with different geometrical parameters,of which the diameter of the gold-coated nanopillars and the gap size between them could be easily tuned by changing the AAO molds with different hole diameters and spacings,different thicknesses of deposited gold layer.The effect of different parameters on SERS enhancement was investigated by three-dimensional numerical simulations and experimental SERS measurements.When the diameter of PC nanopillars was 90 nm and the thickness of deposited gold was 90 nm,the structure showed the optimized SERS perfomrance for trans-1,2-bis(4-pyridyl)ethylene(BPE)molecular with an EF of 4.4 × 108 due to the dense nanogaps(namely,SERS hot-spots)smaller than 10 nm that are created not only between the gold coated nanopillars but also between the gold caps on the tops of the nanopillars and the gold film at the bottom of the nanopillar arrays.As a SERS template,it shows a large-area uniformity with a relative standard deviation of 15%and an excellent reproducibility with a relative standard deviation of 18%.