Hierarchical nanopatterning with block copolymer lithography and template-stripping
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The interest in confining light within the sub-wavelength regime has been motivated by the urgency in replacing electronic integrated circuits with optical ones for elevated computational efficiency. This can be achieved by using light as the signal-carrier instead of electrons. Like electrons, light needs circuits and components for the guidance of the signal. Consequently, the field of plasmonics studies the propagation, localization, and guidance of light in metal nanostructures (NSs) and metal thin films. The hybridization of surface plasmon resonance (SPR) in periodic structures and localized surface plasmon resonance (LSPR) in metal NSs for light confinement and subsequent localization/enhancement is studied in this thesis. Fabrication of SPR inducing metal structures with feature sizes of 2 microns and 400 nm is achieved by photo- and nano-imprint lithography, respectively. LSPR inducing metal NSs with a diameter between 45-55 nm and periodicity of 75 nm is realized by template- stripping of 150 nm thin Au film from silicon (Si) templates that were prepared by utilizing novel block copolymer (BCP) lithography. Optical measurement and numerical modeling showed strong absorption of light at the wavelength of 687 nm for periodic Au nanodisks and at 708 nm for periodic Au nanodisks with metal NSs by BCP lithography, providing support for the existence of SPR and LSPR. However, BCP metal NSs without periodic Au nanodisks showed no plasmon resonance but exhibited an absorption of ≈ 20% for wavelength range 350- 800 nm. The efficacy of BCP directed self-assembly (DSA) for large-area hierarchical nanopatterning over other patterning schemes promises appealing prospect for sub-wavelength hierarchical nanopatterning.