Thermally Stable Antireflective Coatings Based on Nanoporous Organosilicate Thin Films

Thermally stable nanoporous organosilicate thin films were realized by the microphase separation of pore-generating polymers mixed with an organosilicate matrix to be antireflective coatings (ARCs), for which a thin film with a refractive index (n) of 1.23 for zero reflection is required. The refractive index of such nanoporous organosilicate films can be tuned from 1.39 down to 1.23 by incorporating nanopores within the films. With a nanoporous single layer with n ~ 1.23, the light transmittance of the glass above 99.8% was achieved in the visible range (λ ~ 550 nm). To overcome the limitation on the narrow wavelength for high transmittance imposed by a single antireflective nanoporous thin film, bilayer thin films with different refractive indices were prepared by placing a high refractive index layer with a refractive index of 1.45 below the nanoporous thin film. UV−vis transmittance of a glass coated with the bilayer films was compared with nanoporous single-layer films and it is demonstrated that the novel broadband antireflection coatings in a wide range of visible wavelength can be easily obtained by the organosilicate bilayer thin films described in this study. Also, ARCs developed in this study demonstrate excellent AR durability owing to the hydrophobic nature of the organosilicate matrix.This work was supported by the NANO Systems Institute - National Core Research Center (NSI-NCRC) from the Korea Science and Engineering Foundation (KOSEF) and the Brain Korea 21 Program endorsed by the Ministry of Education of Korea. We are very grateful to Mr. Y. J. Park at Postech for assistance during X-ray reflectivity experiments at Pohang Light Source (PLS) supported by the Ministry of Science and Technology of Korea.Wealso thank Dr. Steve Kline (NIST), Prof. S.-M. Choi, and Mr. J. Lee for their help during smallangle neutron scattering experiments at the National Institute of Standards and Technology (NIST) in the United States. J.C. acknowledges the financial support from the ERC Program of the MOST/ KOSEF (R11-2005-048-00000-0)