Hierarchical Silicon Etched Structures for Controlled Hydrophobicity/Superhydrophobicity

• Published in: Nano letters Vol. 7; no. 11; pp. 3388 - 3393
• Main Authors: Xiu, Yonghao, Zhu, Lingbo, Hess, Dennis W, Wong, C. P
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 01-11-2007
• Subjects: Anisotropy; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Hydrofluoric Acid - chemistry; Hydrogen Peroxide - chemistry; Hydrophobic and Hydrophilic Interactions; Hydroxides - chemistry; Low-dimensional structures (superlattices, quantum well structures, multilayers): structure, and nonelectronic properties; Materials science; Mechanical and acoustical properties of condensed matter; Mechanical properties of nanoscale materials; Methods of nanofabrication; Microscopy, Electron, Scanning; Models, Statistical; Nanolithography; Physics; Potassium Compounds - chemistry; Pressure; Silanes - chemistry; Silicon - chemistry; Substrate Specificity; Surface Properties; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Temperature; Time Factors; Water - chemistry; Silanes; Gold; Lithography; Mechanical properties; Surface treatments; Etching; Contact angle; Nanostructures; Adhesion; Surface structure; Anisotropy; Hafnium; Droplets; Silicon; Hysteresis; Tribology
• ISSN: 1530-6984; 1530-6992
• DOI: 10.1021/nl0717457

Silicon surface hydrophobicity has been varied by using silane treatments on silicon pyramid surfaces generated by KOH anisotropic etching. Results demonstrated that by altering the surface hydrophobicity, the apparent contact angle changed in accord with the Wenzel equation for surface structures with inclined side walls. Hierarchical structures were also constructed from Si pyramids where nanostructures were added by Au-assisted electroless HF/H2O2 etching. Surface hydrophobicity and superhydrophobicity were achieved by surface modification with a variety of silanes. Stability of the Cassie state of superhydrophobicity is described with respect to the Laplace pressure as indicated by the water droplet meniscus in contact with the hierarchical structures. The contact angle hysteresis observed is also discussed with respect to water/substrate adhesion.