The unprecedented ability of plasmonic metal nano-structures to concentrate light into deep-subwavelength volumes has propelled their use in a vast array of nanophotonics technologies and research endeavors. They are used in sensing, super-resolution imaging, SPP lithography, SPP assisted absorption, SPP-based antennas, light manipulation, etc. To take full advantage of the attractive capabilities of CMOS compatible low-cost plasmonic structures based on Al and Cu, nanolaminate coatings are investigated to improve their long-term stability in corrosive physiological environments. The structures are fabricated using phase-shifting PDMS masks, e-beam deposition, RIE, Atomic Layer Deposition and Rapid Thermal Annealing. An alternate approach using Nanosphere Lithography (NSL) was also investigated. Films were examined using ellipsometry, atomic force microscopy and transmission measurements. Accelerated in-situ tests of Hafnium Oxide/Aluminum Oxide nanolaminate shells in a mildly pH environment with temperatures akin to physiological environments emulated using PBS show greatly enhanced endurance, with stable structures that last for more than one year. / Master of Science / When light (electromagnetic radiation) interacts with the free (conduction) electrons of a metallic nanostructure it leads to a coupling resulting in collective excitations (oscillations) that lead to strong enhancements of the local electromagnetic fields surrounding the nanoparticles, this phenomenon is called Localized Surface Plasmon Resonance (LSPR) and plasmonics are structures that are capable of exhibiting this phenomenon. The condition for LSPR to occur is that the dimension scale of the structure is less than the wavelength of the electromagnetic radiation interacting with it. This implies that the structure has to be in nanoscale dimensions. LSPR based plasmonic structures are compact, sensitive and can be integrated with electronic devices and can be used in various applications like implantable biological sensors (blood pH sensing, diabetics sensing, etc.), devices that integrate several laboratory testing functionalities on a single chip, studies to determine the dynamics of chemical reactions, increasing the efficiency of solar power generation, etc. LSPR is exhibited by metallic nano-particles like gold, silver, copper and aluminum. Metals like copper corrode at a rapid rate in water at room temperature and hence nano scale structures made from them that can exhibit LSPR cannot be used in higher temperature ionic environments without a protective coating. High density, uniform coatings with less defect density can be deposited using Atomic layer deposition (ALD). In this research Atomic Layer Deposited Aluminum Oxide and Hafnium Oxide nanolaminate structures are explored to increase the long-term stability of plasmonic structures in physiological solutions. In-situ tests are carried out in a Phosphate-buffered Saline (PBS) solution with a pH value of 7.2 (simulating physiological conditions) at a temperature of 37℃ (physiological temperature) and 85.1℃ (accelerated testing). The results demonstrate that the dielectric nano coatings investigated in this project can increase the stability of the plasmonic structures in the corrosive physiological environment from a few days to more than one year.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/78280 |
| Date | 28 June 2017 |
| Creators | Daniel, Monisha Gnanachandra |
| Contributors | Electrical and Computer Engineering, Zhou, Wei, Hsiao, Michael S., Stilwell, Daniel J. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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