Using Nanoimprint Lithography to Develop Metallic Micro/Nano Hybrid Structure-Based Plasmonic Devices
Date Issued
2014
Date
2014
Author(s)
Yu, Chen-Chieh
Abstract
Plasmonic micro/nano hybrid structures are an emerging idea in recent optical device. The hybrid structures possess advantages of both the individual micro- and nano-structures. Typically, electron beam lithography and photolithography are used to fabricate the designed structures. However, the low throughput or high cost of these lithography methods limit the development of such hybrid structures. Nanoimprint lithography is well-known as a rapid, high-throughput, and robust method for fabricating micro- and nano-structures. Therefore, it will be much suitable to construct micro- and nano-structures by using nanoimprint lithography. In this thesis, an improved lithography—the direct nanoimprint-in-metal method—is used to develop nanoparticle (NP) -based micro/nano hybrid structures. Metallic NP-film hybrid structure has attracted great interests due to the unique, anisotropic plasmonic gap modes. The coupling between the localized surface plasmon resonance (LSPR) and the surface plasmon resonance (SPR) supported by the metal film largely enhances the electromagnetic field. In this thesis, I develop an ultrasensitive nanoparticle (NP)-film caliper that functions with high resolution (angstrom scale) in response to both the dimensions and refractive index of the spacer sandwiched between the NPs and the film. The anisotropy of the plasmonic gap mode in the NP-film caliper can be characterized readily using spectroscopic ellipsometry (SE) without the need for further optical modeling. To the best of our knowledge, this paper is the first to report the use of SE to study the plasmonic gap modes in NP-film calipers and to demonstrate that SE is a robust and convenient method for analyzing NP-film calipers. The high sensitivity of this system originates from the plasmonic gap mode in the NP-film caliper, induced by electromagnetic coupling between the NPs and the film. The refractometric sensitivity of this NP-film caliper reaches up to 314 nm/RIU, superior to those of other NP-based sensors. The NP-film caliper also provides high dimensional resolution, down to the angstrom scale. In this study, the shift in wavelength in response to the change in gap spacing is approximately 9 nm/A. Taking advantage of the ultrasensitivity of this NP-film caliper, a platform for discriminating among thiol-containing amino acids was developed. On the other hand, the low-cost, rapid, and direct nanoimprint-in-metal method is used to improve the origin NP-film hybrid structures. The direct nanoimprint-in-metal is used to prepare an incident angle–tuned, broadband, ultrahigh-sensitivity plasmonic antennas from nanoparticles (NPs) and imprinted metal mirrors. By changing the angle of incidence, the nanoparticle-imprinted mirror antennas (NIMAs) exhibit broadband electromagnetic enhancement from the visible to the near-infrared (NIR) regime, making them suitable for use as surface-enhanced Raman scattering (SERS)–active substrates. Unlike other SERS-active substrates that feature various structures with different periods or morphologies, the NIMAs achieve broadband electromagnetic enhancement from single configurations. The enhancement of the electric field intensity in the NIMAs originate from coupling between the LSPR of the NPs and the periodic structure–excited surface plasmon resonance (SPR) of the imprinted mirror. Moreover, the coupling wavelengths can be modulated because the SPR wavelength is readily tuned by changing the angle of the incident light. Herein, this thesis demonstrate that such NIMAs are robust substrates for visible and NIR surface-enhanced resonance Raman scattering under multiple laser lines (532, 633, and 785 nm) of excitation. In addition, the NIMAs are ultrasensitive SERS-active substrates that can detect analytes (e.g., rhodamine 6G) at concentrations as low as 10^–15 M. Moreover, a simple hybrid configuration based on high-index dielectric nanoparticles (NPs) and plasmonic nanostructures is proposed for nanofocusing of submicron-short-range surface plasmon polaritons (SPPs). The excited SPPs are locally bound and focused at the interface between the dielectric NPs and the underlying metallic nanostructures, and greatly enhance the local electromagnetic field. Besides, taking advantages of the surface property of dielectric NPs, versatile functionality for this system can be achieved. For example, the nanofocusing of submicron-short-range SPPs can be applied on enhancing the Raman signals of molecules adsorbed on the dielectric NPs. Besides, the interfacial reaction rate on the dielectric NPs surface can be improved by the local strong electromagnetic field. Therefore, the proposed nanofocusing configuration can promote and probe the interfacial reactions simultaneously. Promoting and probing the desorption of ethanol gas molecules as well as the photo-degradation of MB molecules are demonstrated in this study. Moreover, the nanofocusing of SPPs is demonstrated on relatively cheap metal surface (Al) in the ultraviolet (UV) regime, which is not achieved by conventional tapered waveguide nanofocusing structures. Therefore, the nanofocusing of submicron-short-range SPPs by dielectric NPs on plasmonic nanostructures is not limited to lossless, noble metals, and reveals the potential on future light management and on-chip green devices and sensors. In the last, the metallic corrugated structures was prepared for use as highly sensitive plasmonic sensors. Relying on the direct nanoimprint-in-metal method, fabrication of this metallic corrugated structure is readily achieved in a single step. The metallic corrugated structures are capable of sensing both surface plasmon resonance (SPR) wavelengths and index-matching effects. The corrugated Au films exhibit high sensitivity (ca. 800 nm/RIU), comparable with or even higher than those of other reported SPR-based sensors. Because of the unique index-matching effect, refractometric sensing can also be performed by measuring the transmission intensity of the Au/substrate SPR mode—conveniently, without a spectrometer. In the last, this thesis demonstrate that the NP-corrugated Au film hybrid structure is capable of sensing biomolecules, revealing the ability of the structure to be a highly sensitive biosensor.
Subjects
micro/nano hybrid structure
nanoimprint lithography
surface plasmon resonance
plasmonic coupling
surface-enhanced Raman scattering
nanofocusing
plasmonic device
Type
thesis
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