Optical properties of cicada wings covered by graphene studied by nano‐Raman spectroscopy

Some biological systems exhibit nanoscale constructions to produce optical effects. This study utilises Atomic Force Microscopy (AFM) and Tip-Enhanced Raman Spectroscopy (TERS) to study the complex bionanometric structure of cicada wings. Topographical irregularities of the wings due to <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:semantics><mml:mi>α</mml:mi> <mml:annotation>$\alpha$</mml:annotation></mml:semantics> </mml:math> -chitin nanopillars hinder the probe's approach to the sample, a crucial step in overcoming the light diffraction limit in TERS measurements. To mitigate this issue, graphene was deposited, promoting surface smoothing and ensuring a reliable TERS measurement. Combined analyses of AFM and TERS mapping revealed a significant enhancement of the graphene 2D band, particularly in the regions surrounding the nanometric pillars, while the characteristic <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:semantics><mml:mi>α</mml:mi> <mml:annotation>$\alpha$</mml:annotation></mml:semantics> </mml:math> -chitin Raman peaks are evident on top of the pillars, clarifying details of how light passed through the material.