Multifunctional Porous Silicon Nanopillar Arrays: Superhydrophobicity, Antireflection, and Sensitive SERS Performance
Open Access
- Author:
- Kiraly, Brian Thomas
- Graduate Program:
- Engineering Science
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- June 18, 2012
- Committee Members:
- Jun Huang, Thesis Advisor/Co-Advisor
- Keywords:
- porous
nanopillar
SERS
superhydrophobic
antireflection - Abstract:
- Silicon nanostructures are of intense interest because of their applications in biology, biochemical sensing, energy storage, energy harvesting, photonic materials, electronic materials, and optical thin films. Perhaps more significantly, SiNPs can be fabricated with conventional silicon and CMOS processes, making them easily integrated into a variety of current electronic and photonic architectures. One-dimensional silicon nanostructures can either be grown with a bottom-up approach or fabricated with top-down methods. Growth generally involves chemical synthesis mediated by catalytic particles, whereas top-down methods utilize a chemical or physical etch and a surface nanopattern to fabricate the structures. While both methods have shown advantages and disadvantages, the ability to produce single-crystalline structures with highly controllable orientation and location has proven an overwhelming advantage for top-down methods and has greatly expanded the list of potential applications for these materials. The sub-micron dimensions of silicon nanostructures gives them a variety of unique electronic, optical, and mechanical properties. Collections of aligned nanostructures strongly influence the reflection of light from a surface and the way liquids expand across a surface. When the size of individual structures is reduced below 10 nm, quantum effects are introduced into the band structure, altering electronic conduction and light interaction and emission. Individual properties have been studied and utilized for a variety of nano-enabled devices, but only recently have researchers looked to simultaneously utilize multiple properties to for enhanced performance. In this work, we fabricate one-dimensional silicon nanopillar (SiNP) arrays with a top-down approach that utilizes nanosphere lithography to pattern a metallic surface and a wet-chemical etch of silicon to produce free-standing nanostructures. The SiNPs show unique longitudinal features along their entire length and have surface porosity with dimensions on the single-nanometer level. The SiNP substrates reduced reflection nearly fivefold from planar silicon in the visible range without any optimization. The same substrates also approached superhydrophobic behavior with increasing aspect ratio, demonstrating contact angles up to 138°.. Finally, the pillars were made into sensitive surface enhanced Raman scattering (SERS) substrates by depositing metal onto the pillars. The performance of the substrates was demonstrated using a chemical dye R6G. To emphasize the unique and versatile attributes of the SiNP arrays, all of the characterization and applications in this work were accomplished on the same set of substrates. Combining multiple unique properties of SiNPs and SiNP arrays into a single device can have important effects on low-analyte detection sensitivity, solar harvesting efficiency, dynamic biological monitoring, and many other potential nanoscale systems.