The method involves making very fine perforations into a sandwich structure of nanomaterials. A bottom layer of silver 100nm thick is topped with a silica dielectric spacer 45nm thick, followed by a second 25nm layer of silver on top.
The material is then treated with focused ion beam milling. This punches holes into the top layer of silver. By carefully calibrating the size of holes created it was possible to vary the wavelengths of light reflected from different areas of the nanostructured film to create colour effects.
To demonstrate the potential of their new technology the academics reproduced a Missouri S&T logo in full colour – including cyan, dark blue, orange and magenta areas – measuring roughly 50nm x 40nm.
The developers believe the process has various potential applications, including in imparting security marks to branded goods and components – though in its current form a scanning electron microscope is necessary to read the symbols.
The work is summarised in a paper published in the journal Scientific Reports on 5 June.
Co-author Jie Gao says: ‘Unlike the printing process of an inkjet or laserjet printer – where mixed colour pigments are used – there is no colour ink used in our structural printing process – only different hole sizes on a thin metallic layer.
This article comes from Digital Demand World, which provides exclusive news and analysis on developments in digital print trends, markets, and technologies.