February 2019
Spotlight Summary by Johann Toudert
Micro-tags for art: covert visible and infrared images using gap plasmons in native aluminum oxide
Imprinted micro-tags hidden in a painting, card, or banknote and showing different motifs when inspected with visible or near-infrared light are appealing for anticounterfeiting applications. This is because the information carried by them cannot be read with the naked eye, and because replicating them requires state-of-the-art fabrication tools. In this context, Ray Jia Hong Ng and coworkers report the fabrication of micro-tags where each few-micrometer pixel consists of an array of aluminium nanostructures on a surface-oxidized aluminium film. The few-nanometer native aluminium oxide layer separating the nanostructures from the film enables gap plasmon resonances. The wavelength of such resonances can be tuned in the visible and near-infrared by properly choosing the nanostructure size and array pitch. This enables achieving pixels with the desired visible color and near-infrared brightness, with a low visible/near-infrared crosstalk. By using four types of pixels with two different visible colors and two different near-infrared brightnesses, the authors designed a 240-micrometer × 240-micrometer micro-tag showing a quick-response code when illuminated with visible light and a barcode when illuminated with near-infrared light.
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Article Information
Micro-tags for art: covert visible and infrared images using gap plasmons in native aluminum oxide
Ray Jia Hong Ng, Ravikumar Venkat Krishnan, Zhaogang Dong, Jinfa Ho, Hailong Liu, Qifeng Ruan, Kin Leong Pey, and Joel K. W. Yang
Opt. Mater. Express 9(2) 788-801 (2019) View: Abstract | HTML | PDF