Low-temperature synthesis of nanoscale silica multilayers - atomic layer deposition in a test tube

Herein we demonstrate a simplified, 'poor-man's' form of the Atomic Layer Deposition (ALD) technique to grow uniform silica multilayers onto hydrophilic surfaces at low temperatures, including room temperature (RT). Tetramethoxysilane vapor is used alternately with ammonia vapor as a catalyst, with very common benchtop lab equipment in an ambient environment. This deposition method could be applied in a wide range of fields for growing nanoscale layers of silica from an inexpensive vapor source, without the sophisticated vacuum systems or high temperatures that are generally required for ALD. Conditions for uniform deposition are demonstrated for 20-nm-thick silica shells grown around polymer spheres at RT, and in the interstitial space of a colloidal crystal film. This approach is shown to provide a controlled means of sintering the silica spheres and thereby is an easy way to modify the photonic and mechanical properties of the resulting material. We believe this method has an advantage compared to other more sophisticated methods of ALD and provides a simple technique for broad applications in MEMs, nanoporous structures, sintering of components, cell encapsulation, and organic/inorganic layered composites.