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DESIGN IDEAS


NANOSCALE PRINTING CAN BEAT COUNTERFEITERS


 Encoding different colours onto a single pixel and shining light with different polarisation (below) creates the ability to display two distinct images within the same plane (bottom)


Research fromthe University of Glasgow outlines howengineers have developed nano- scale plasmonic colour filters that display different colours depending on the orientation of the lightwhich hits it. This technique allows the “printing” of two


different but exceptionally detailed full-colour imageswithin the same surface area using “structural colour” techniques – something which has never been done before. Instead of relying on dyes and pigments,


as in traditional printing, structural colour uses specially structured nanomaterials to render colours. The nanomaterials allowfor much higher-resolution printswhich do not fade over time. A typical printed image in a magazinemight consist of around 300 coloured dots per square inch of page (300dpi). A page “printed”with structural colour techniques, however, could reach a resolution of 100,000dpi ormore. The breakthrough comes fromincluding an


additional nanoscale element in the structural colour process, created at the University’s JamesWattNanofabrication Centre. Biomedical engineering lecturer Dr


Alasdair Clark said: “We’ve discovered that if wemake colour pixels fromtiny cross-shaped indents on a strip of aluminiumfilm, the colour they display becomes polarisation- dependent, allowing us to encode two colours into a single pixel, and then selectwhich colour is displayed by shining different polarisations of light at the surface. By changing the size and shape of the nanoscale indent,we can create awide range of different colours at very high resolutions.” The team, fromthe university’s School of


Engineering, have demonstrated their techniquewith several examples, including a nanoscale imagewhich shows the university’s crestwhen the light reaches it in one orientation, and an image of the university towerwhen the orientation of the light is reversed. “There are a lot of potential applications


for our plasmonic colour technology,which we’re really excited about. It is ideal for long-termdata archival due to its ultra-high resolution, and because the colourswon’t fade evenwhen exposed long-termto the harshest sunlight.We’veworked out thatwe could store 1.46GB per square centimetre, so a single A4 sheet could holdmore than 900GB of data,” added Clark. “Secondly, the process to produce the


plasmonic colours is difficult to replicate without access to dedicated facilities, so it could be ideal for creating a newkind of anti-counterfeitingmaterial for banknotes. Lastly, it offers the possibility of developing newtypes of colour filters for digital photography.”


8 /// Environmental Engineering /// October 2017


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