Latex-templated porous silica films for antireflective applications

Thin films with low-refractive index are of great interest to adjust the optical properties of optical components, e.g. reflectivity. In this respect, sol-gel coatings are very efficient for flat glass functionalisation because of ease of application, low cost and versatility. Mesoporous silica films prepared by surfactant self-assembly have been extensively studied but show poor refractive index stability as capillary condensation of atmospheric water can occur in the pores. One way to tackle this issue is to prepare films with larger pores for which capillary condensation is impossible at ambient humidity. Starting from custom made latex nanoparticles, we successfully prepared sol-gel porous silica film with pore size above 30nm and no microporosity in the silica walls. We are then able to independently and accurately tailor pore size, pore volume fraction and pore surface chemistry, leading to a stable refractive index that can be tuned in a large range (from 1.15 to 1.40 at 600 nm). Pore accessibility as a function of pore size and porous fraction was investigated through ellipsometry-porosimetry for ethanol adsorption, and a transition between open and closed pore structure at decreasing volume fraction was shown. Below the threshold, the films showed a closed porosity structure with a low stable refractive index (down to 1.29 at 600 nm), opening the way to their use for antireflective applications.

[1]  Lisa C. Klein,et al.  Sol-Gel Technology for Thin Films, Fibers, Preforms, Electronics and Specialty Shapes , 1988 .

[2]  D. Meyerhofer.  Characteristics of resist films produced by spinning , 1978 .

[3]  Á. Morales,et al.  Silica antireflective films on glass produced by the sol-gel method , 2003 .

[4]  J. Boilot,et al.  Reactivity of 3D hexagonal mesoporous silica films to environment studied by infrared ellipsometry , 2003 .

[5]  C. Laberty‐Robert,et al.  Design, Synthesis, and Properties of Inorganic and Hybrid Thin Films Having Periodically Organized Nanoporosity† , 2008 .

[6]  Alfred Grill,et al.  Ultralow-k dielectrics prepared by plasma-enhanced chemical vapor deposition , 2001 .

[7]  F. Palumbo,et al.  From Low-k to Ultralow-k Thin-Film Deposition by Organosilicon Glow Discharges , 2006 .

[8]  Thierry Gacoin,et al.  Phase diagram for mesoporous CTAB–silica films prepared under dynamic conditions , 2003 .

[9]  A. Falqui,et al.  Hierarchical Porous Silica Films with Ultralow Refractive Index , 2009 .

[10]  R. Ryoo,et al.  Improvement of Hydrothermal Stability of MCM-41 Using Salt Effects during the Crystallization Process , 1997 .

[11]  J. Boilot,et al.  Latex-Templated Silica Films: Tailoring Porosity to Get a Stable Low-Refractive Index , 2010 .

[12]  L. C. Hsia,et al.  Characterization of tetra methyl cyclo tetra siloxanes-based low-k dielectric film , 2004 .

[13]  E. Fred Schubert,et al.  Optical thin-film materials with low refractive index for broadband elimination of Fresnel reflection , 2007 .

[14]  Thierry Gacoin,et al.  Mesoporous 3D-hexagonal organosilicate films: Post-synthesis grafting vs. direct synthesis , 2006 .

[15]  C. Sanchez,et al.  Determination of pore size distribution in thin organized mesoporous silica films by spectroscopic ellipsometry in the visible and infrared range , 2003 .

[16]  K. Sing.  Reporting physisorption data for gas/solid systems with special reference to the determination of surface area and porosity (Recommendations 1984) , 1985 .

[17]  A. Volinsky,et al.  Fracture toughness, adhesion and mechanical properties of low-K dielectric thin films measured by nanoindentation , 2003 .

[18]  Jun Liu,et al.  Low K mesoporous silica films through template-based processing , 1996 .

[19]  Karen Maex,et al.  Low dielectric constant materials for microelectronics , 2003 .

[20]  Din-Guo Chen,et al.  Anti-reflection (AR) coatings made by sol–gel processes: A review , 2001 .

[21]  Björn Karlsson,et al.  Optical and mechanical properties of sol-gel antireflective films for solar energy applications , 1999 .

[22]  Guido Groeseneken,et al.  Influence of absorbed water components on SiOCH low-k reliability , 2008 .

[23]  D. Avnir,et al.  Recommendations for the characterization of porous solids (Technical Report) , 1994 .

[24]  P. Albouy,et al.  One pot synthesis of hierarchical porous silica membrane material with dispersed Pt nanoparticles using a microwave-assisted sol–gel route , 2008 .

[25]  S. Torquato,et al.  Random Heterogeneous Materials: Microstructure and Macroscopic Properties , 2005 .

[26]  Moon-Ho Jo,et al.  Application of SiO2 aerogel film with low dielectric constant to intermetal dielectrics , 1997 .

[27]  James G. Berryman,et al.  Random close packing of hard spheres and disks , 1983 .

[28]  M. Baklanov,et al.  Internal matrix structure of low-κ mesoporous silica and its relation to mechanical properties , 2004 .

[29]  K. Defriend.  A simple approach to hierarchical ceramic ultrafiltration membranes , 2003 .

[30]  Bruce Dunn,et al.  Continuous formation of supported cubic and hexagonal mesoporous films by sol–gel dip-coating , 1997, Nature.

[31]  Galo J. A. A. Soler-Illia,et al.  Fundamentals of Mesostructuring Through Evaporation‐Induced Self‐Assembly , 2004 .

[32]  A. Julbe,et al.  New approaches in the design of ceramic and hybrid membranes , 2008 .

[33]  Hyung‐Ho Park,et al.  Phase behavior of ordered mesoporous silica film prepared by Brij-76 block copolymer , 2008 .

[34]  E. Schubert,et al.  Engineered nanoporous and nanostructured films , 2009 .

[35]  M. Baklanov,et al.  Non-destructive characterisation of porous low-k dielectric films , 2002 .