Moth Eyes Inspire Antireflective Skins for UAVs

  • Published
  • By Molly Lachance
  • Air Force Office Of Scientific Research
ARLINGTON, Va. --  Researchers at National Taiwan University are expanding upon the antireflective properties of moth eyes to make better protective skins for Air Force unmanned air vehicles. With funding from the Asian Office of Aerospace Research and Development--an international detachment of AFRL--Professor Li-Chyong Chen produced an antireflective nanostructure surface using arrayed silicon nanotips.

Prof Chen's silicon nanotip surface mimics the naturally formed surfaces found on many plants and animals. The color on butterfly wings, camouflage of cicadas, and night vision of moths are all made possible by tiny surface structures that absorb certain wavelengths of light. A key aspect of Prof Chen's research has been finding an efficient and easy-to-integrate approach for preparing the nanotips on a single surface. Her patented electron-cyclotron-resonance method offers the opportunity to do so in only one step.

This plasma-assisted method selectively dry-etches a single silicon wafer by masking and unmasking certain portions. The unetched portions form an array of nanotips. Because of the high density of plasma in the ECR method, Prof Chen has been able to create a thick forest of silicon nanotips. Of equal importance, she can produce them uniformly over a large area, recently demonstrating the approach on a 6 in. wafer. The resulting nanostructure surface not only mimics the moth eye, but also surpasses its function in antireflection by absorbing almost all of the direct light that falls on it.

The new silicon nanotip surface demonstrates a low hemispherical reflectance of <1% from the ultraviolet to the infrared region and shows significant suppression of specular reflection in the far-infrared to terahertz region. In addition, these findings are nearly unaffected by the angle of the light source shining on the surface, allowing Prof Chen to add broadband antireflection and quasi-omni-directional antireflection to the list of properties that show promise for AF optical defensive applications.