Wafer-scale highly-transparent and superhydrophilic sapphires for high-performance optics

We reported the wafer-scale highly-transparent and superhydrophilic sapphires with antireflective subwavelength structures (SWSs) which were fabricated by dry etching using thermally dewetted gold (Au) nanomasks. Their optical transmittance properties were experimentally and theoretically investigated. The density, size, and period of the thermally dewetted Au nanopatterns can be controlled by the Au film thickness. For the sapphire with both-side SWSs at 5 nm of Au film, the average total transmittance (T-avg) of similar to 96.5% at 350-800 nm was obtained, indicating a higher value than those of the flat sapphire (T-avg similar to 85.6%) and the sapphire with one-side SWSs (T-avg similar to 91%), and the less angle-dependent transmittance property was observed. The calculated transmittance results also showed a similar tendency to the measured data. The SWSs enhanced significantly the surface hydrophilicity of sapphires, exhibiting a water contact angle (theta(c)) of < 5 degrees for Au film of 5 nm compared to theta(c)similar to 37 degrees of the flat sapphire. (C) 2012 Optical Society of America