Metasurfaces are structures designed to control, for example, electromagnetic radiation using repeating structures, typically with sub-micrometer dimensions for light.Routes to forming these structures include etching away parts of a surface or to deposit onto the surface – the contours of which the team refers to as topography: “The resulting surface topography is often undesirable and can strongly limit the device performance when embedded into a stack of many independent layers.”To leave a flat surface instead, the Soton researchers stated with the transparent conductive oxide aluminium-doped zinc oxide (Al:ZnO).This has a high electron density, making it dielectric to visible light but metallic as far as infra-red is concerned.The new technique is based on the discovery that an oxygen plasma can greatly reduce the electron concentration in certain metal oxides – up to five orders of magnitude in Al:ZnO. A patterned silicon nitride coating protects areas that are not to be treated, and is later removed.Two devices have been made to demonstrate the technique: a planar metasurface optical solar reflector for satellite radiant cooling, and a multi-band metasurface that absorbs selected wavelengths while reflecting.“Plasma patterning provides a new route to form electrical and optical devices with structures beyond existing manufacturing limitations,” said researcher Kai Sun. “Here, we have shown for the first time that a planar metasurface, based on aluminum-doped zinc oxide, can be achieved with an optical metasurface function but physically flat. The metasurface devices in this work are only a start of this new technique’s applications and its full potential impact is still to be seen.”The work is published as ‘Embedded metal oxide plasmonics using local plasma oxidation of AZO for planar metasurfaces‘ in Advanced materials. Funded came from the Dstl MultiMeta project.
Source: This news is taken from www.electronicsweekly.com
