Chemical Vapor Deposition of Silica Micro- and Nanoribbons Using Step-Edge Localized Water

• Published in: The journal of physical chemistry. B 2003-06, Vol.107 (23), p.5393-5397
• Main Authors: Zach, Michael P, Newberg, John T, Sierra, Luiza, Hemminger, John C, Penner, Reginald M
• Format: Article
• Language: English
• ISSN: 1520-6106; 1520-5207
• DOI: 10.1021/jp034452k

Amorphous silica (SiO2) ribbons were prepared by hydrolyzing SiCl4 at highly oriented pyrolytic graphite (HOPG) surfaces on which water had condensed. Exposure to humid air (>30% relative humidity (RH)) at room temperature caused water to condense selectively at hydrophilic step edges on an otherwise hydrophobic graphite surface. Upon exposure of this surface to SiCl4 vapor, a reaction with condensed water at step edges caused the formation of SiO2 according to the reaction SiCl4 + 2H2O → SiO2 + 4HCl. The shape and size of the SiO2 nanostructures varied with the RH:  Below 20% RH, nanoparticles of SiO2, aligned at step edges, were observed. For RH of 35−50%, continuous nano- and microribbons of SiO2 were obtained. For higher RH, micron-scale silca particles and ribbons were both observed. At a RH of 35%, silica ribbons as small as 80 nm (width) x 20−40 nm (height) up to 500 μm in length could be prepared. Repetitive dosing of the HOPG surface in the humid environment with SiCl4 produced nano- and microribbons with a height and width that increased in proportion to square root of the SiCl4 dose.