Jun 23, 2014
Cheap and replicable nano-pillar arrays
Arrays of high aspect-ratio pillars have applications in solar cells, surface acoustic sensors, bio-inspired adhesives and as platforms for tissue growth. The cost of preparing these structures is relatively high and this impedes the development and batch fabrication of them as a promotable product. Reporting in Nanotechnology, a low-cost and high-yield replica molding method is demonstrated by researchers from Simon Fraser University. The aim is to prepare similar structures in different materials while reducing the cost by enabling multiple replications based on one master.
Scanning electron microscopy (SEM) images of the PMMA nano-pillar arrays, the epoxy replica pillar arrays and the polyurethane replica of pillar arrays
Anodic aluminum oxide (AAO) membranes, having finely ordered arrays of nano-holes, are used to emboss polymethyl methacrylate (PMMA) on a hot plate. This controls the aspect ratio of the resulting nano-pillars and it serves as a master for further molding steps. The PMMA master is coated by a silane release layer and replicated using polydimethylsiloxane (PDMS). Utilizing this PDMS negative mold, different materials can be molded to create a replica of the nano-pillar arrays. Demonstrated in the scanning electron microscope images above, the fidelity of the replica structure is mostly preserved from the master.
Non-collapsing PMMA nano-pillars permit visible light from the back, as shown in the photo with a SFU logo underneath a transparent PMMA sample. This sample is prepared by one embossing process which takes only 1.5 hours. Equipment for preparing the sample is easily found in a regular lab environment and the cost of preparing such arrays of nano-pillars is greatly reduced by the molding process.
As an example of a potential application, polymeric nano-pillars are prepared as bio-inspired dry adhesives and studied for their adhesion properties. By choosing a high surface energy material, the epoxy nano-pillars adhesive is able to produce three times more adhesion force than the original PMMA nano-pillars adhesive. Uniformity of the array of replicated nano-pillars and their surface chemistry can be observed from the force map acquired by a scanning probe microscopy technique.
More information about the research can be found in the journal Nanotechnology 25 285303.
Study compares light trapping in hexagonal and square nano arrays (June 2012)
Roll-to-roll nanoimprinting to change nanolithography landscape (Nov 2012)
Nanoimprint lithography: anisotropic remastering reduces feature size (June 2012)
About the author
Yasong Li is a PhD candidate at the Simon Fraser University in the school of engineering science, supervised by Carlo Menon and Byron Gates. Her research focuses on the preparation and characterization of gecko-inspired dry adhesives.