Date of Award
Doctor of Philosophy
Chemical and Biological Engineering
Chemical Engineering; Electrical Engineering
Andrew C. Hillier
The focus of this dissertation is two-pronged: 1. Extending the capability of laser interference lithographic technique to fabricate novel nanostructured surfaces and 2. Application of the fabricated nanostructured surfaces to modulate interfacial processes, e.g. coupling of light with metallic nanostructures to excite surface plasmon resonance (SPR) and directing self-assembly of colloidal crystals.
The first part of the dissertation focuses on modifying the laser interference lithography (LIL) technique. The traditional LIL is limited to fabrication of only single-pitch linear gratings. We mitigated this drawback by incorporating non-planar Lloyds mirror to the LIL technique. The proposed modified LIL technique has the ability to control the pitch profile and the shape of gratings using curvatures of non-planar Lloyd’s mirrors. This enabled LIL to fabricate chirped gratings with pitch values changing continuously from ~10 μm to ~500 nm over a controllable length. The shape of the grating could also be changed from linear to arc-shaped curves of various degree of curvatures. Such novel gratings were shown to be useful as variable bandpass filter and dually diffractive-focusing element. The dissertation also includes work to further the capability of LIL using subsequent multi-exposure techniques to fabricate 2D quasicrystals and Moiré lattices.
The second part of the dissertation is directed towards applications of the novel nanostructures fabricated by modified LIL to modulate interfacial processes. We used a chirped pitch grating as a template for colloidal crystal self-assembly. The method elucidated unique relationships between the pitch values and the crystal lattices formed on it. We demonstrated that grating structure can induce formation of unique lattice geometries, not favored by natural self-assembly, e.g. square lattice, rhombic lattice, graphite-like lattice structures. A thin film of silver coating on the different lattice structures imparted interesting optical characteristics. In addition to templating colloidal crystal growth, the nanostructures were metallized and applied to engineer SPR responses for sensing applications and enhancement of vibrational spectroscopic techniques. In the first case, we used index matching technique to enhance coupling efficiency of light with metallic nanostructures. This bolstered the transmission efficiency from ~5 fold to ~100 fold. The enhanced electric field was demonstrated in refractive index sensing application. In the second case, we used modified LIL in conjunction with nanoimprint lithography to fabricate metallic nanohole arrays of varying periodicity. The nanohole arrays could support SPR at different spectral locations and proved useful in enhancing vibrational stretching mode of -CH. The enhancement factor achieved for -CH mode was about ~40 fold.
In summary, this work aimed to improve versatility of LIL as a nonconventional lithographic technique for fabrication of novel nanostructures with various applications. We demonstrated their application in manipulating light at subwavelength scale, optical sensing, enhancing spectroscopic technique and control self-assembly at nanoscale.
Mahmood, Russell, "Nanostructured surfaces fabricated by modified interference lithographic technique for modulation of interfacial processes" (2019). Graduate Theses and Dissertations. 17049.