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Template‐Free Sol‐Gel Preparation of Superhydrophobic ORMOSIL Films for Double‐Wavelength Broadband Antireflective Coatings
Author(s) -
Zhang XinXiang,
Cai Shuang,
You Dan,
Yan LiangHong,
Lv HaiBing,
Yuan XiaoDong,
Jiang Bo
Publication year - 2013
Publication title -
advanced functional materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 6.069
H-Index - 322
eISSN - 1616-3028
pISSN - 1616-301X
DOI - 10.1002/adfm.201203059
Subject(s) - anti reflective coating , materials science , ormosil , refractive index , thin film , sol gel , coating , transmittance , layer (electronics) , surface modification , contact angle , chemical engineering , optics , optoelectronics , nanotechnology , composite material , physics , engineering
A double‐layer double‐wavelength antireflective (AR) coating with 100% transmittance at both 1064 nm and 532 nm, which is very important in high power laser systems, is designed using thin film design software (TFCalc). The refractive indices for the bottom and top layers of the designed AR coating are about 1.30 and 1.14. A simple, template‐free sol‐gel route is proposed to prepare the superhydrophobic ORMOSIL (organically modified silicate) thin film, which has an ultralow refractive index, by silica particle surface modification using hexamethylisilazane (HMDS); this treatment decreases the refractive index of the silica thin film from 1.23 to 1.13. The formation mechanism of the ultralow refractive index thin film is proposed. The particle surface modification with HMDS significantly improves the hydrophobicity of the coated film; the water contact angle of the film increases from 23.4° to 160°. The bottom layer, which has a refractive index of 1.30, is prepared from acid‐catalyzed and base‐catalyzed mixed silica sol. A double‐layer silica AR coating is obtained with transmittances of 99.6% and 99.8% at 532 nm and 1064 nm, respectively.