title: Broad-band antireflection coating at near-infrared wavelengths by a breath figure.
abstract: We prepared a porous thin film by spin-coating of a cellulose acetate butyrate (CAB) solution in tetrahydrofuran under a humid environment. Due to evaporative cooling during spin-coating, condensed water droplets were formed by a breath figure on the CAB solution, and these developed a porous structure after complete drying. By varying the solution concentration and rotating speeds, two distinct morphologies were generated: top and bottom layers with higher and lower porosities, respectively. We found that the two-layer porous film coated on glass exhibited low reflectance of less than 1% in the near-infrared (NIR) regime corresponding to wavelengths between 900 and 2200 nm. Since the porous structure was very uniform over a large area, the film could be easily employed for broad-band antireflection coating at NIR wavelengths.
authors.affiliation: Department of Chemical Engineering and Polymer Research Institute, Electric and Computer Engineering Division, Pohang University of Science and Technology, Kyungbuk 790-784, Korea.
authors.forename: Min Soo
authors.initials: MS
authors.lastname: Park
authors.forename: Jin Kon
authors.initials: JK
authors.lastname: Kim