FIB‐fabricated complex‐shaped 3D chiral photonic silicon nanostructures

• Published in: Journal of microscopy (Oxford) 2017-12, Vol.268 (3), p.254-258
• Main Authors: ROGOV, O.Y., ARTEMOV, V.V., GORKUNOV, M.V, EZHOV, A.A., KHMELENIN, D.N.
• Format: Article
• Language: English
• Subjects: Biosensors; Chiral metasurfaces; Chirality; Damage; Filtration; focused ion beam; Ion beams; nanofabrication; Nanostructure; Optical properties; Oxidation; Photonics; Prototyping; Sapphire; Silicon; Stimulated emission; thermal oxidation; Thin films
• ISSN: 0022-2720; 1365-2818
• DOI: 10.1111/jmi.12644

Summary Technologies capable of fabricating complex shaped silicon metasurfaces attract increasing attention. The focused ion beam fabrication technique is considered traditionally as causing thick damaged layers in silicon resulting in a significant rise of the optical absorption loss. We examine the structure of the FIB‐fabricated nanostructures on the silicon‐on‐sapphire (SOS) platform and its optical characteristics before and after thermal oxidation. We show that being thermally oxidised the FIB‐patterned silicon subwavelength nanostructure tends to regain its chiral optical features. The impact of the oxidation process on the silicon nanostructure optical behaviour is discussed. Lay description Structuring metal and semiconductor films at the scales of tens and hundreds of nanometres gives rise to fundamentally new functional optical properties, often inaccessible with conventional materials. Such nanostructures – metasurfaces – have been confirmed to perform efficient spectral and polarisation light filtering, gas‐ and biosensing, to amplify the stimulated emission etc. Silicon based metasurfaces are attracting much attention as they are able of versatile optical properties being very well technologically compatible. Focused ion beam (FIB) milling technique is widely used for experimental prototyping of optical nanostructures. However, in silicon it is known to produce thin damaged layers, which strongly absorb light and make the nanostructures useless in the visible range. We have performed microscopic examination of the FIB‐fabricated metasurface on the silicon‐on‐sapphire platform and confirmed the relation between strong optical loss and FIB‐induced damage. We have shown that a proper thermal oxidation restores the metasurface transparency and, at the same time, preserves the main features of its complex‐shaped nanostructure. Using the example of 3D‐chiral silicon pattern we show that such approach allows creating silicon metasurfaces that combine high transparency with strong optical chirality.