MEL-type pure-silica zeolite nanocrystals prepared by an evaporation-assisted two-stage synthesis method as ultra-low-k materials

作者：Liu Yan^*; Sun Minwei; Lew Christopher M; Wang Junlan; Yan Yushan

来源：Advanced Functional Materials, 2008, 18(12): 1732-1738.

DOI：10.1002/adfm.200701134

A MEL-type pure-silica zeolite (PSZ), prepared by spin-on of nanoparticle suspensions, has been shown to be a promising 1 ultra-low-dielectric-constant (k) material because of its high mechanical strength, hydrophobicity, and chemical stability. In our previous works, a two-stage synthesis method was used to synthesize a MEL-zeolite nanoparticle suspension, in which both nanocrystal yield and particle size of the zeolite suspension increased with increasing synthesis time. For instance, at a crystal yield of 63 %. the particle size is 80 nm, which has proved to be too large because it introduces a number of problems for the spin-on films, including large surface roughness, surface striations, and large mesopores. In the current study, the two-stage synthesis method is modified into an evaporation-assisted two-stage method by adding a solvent-evaporation process between the two thermal-treatment steps. The modified method can yield much smaller particle sizes (e.g., 14 vs. 80 nm) while maintaining the same nanocrystal yields as the two-stage synthesis. Furthermore, the nanoparticle suspensions from the evaporation-assisted two-stage synthesis show a bimodal particle size distribution. The primary nanoparticles are around 14 nm in size. and are stable in the final suspension with 60% solvent evaporation. The factors that affect nanocrystal synthesis are discussed, including the concentration, pH value, and viscosity. Spin-on films prepared by using suspensions synthesized this way have no striations and improved elastic modulus (9.67 +/- 1.48 GPa vs. 7.82 +/- 1.30 GPa), as well as a similar k value (1.91 +/- 0.09 vs. 1.89 +/- 0.08) to the previous two-stage synthesized films.

• 出版日期2008-6-24