Archive
Multifunctional Plasmonic Nanopillar Arrays Using Nanoimprint Lithography
Art der Abschlussarbeit
Dissertation
Autoren
- Chen, Sheng-Chieh
Betreuer
- Prof. Dr.-Ing. habil. Wolf-Joachim Fischer
Weitere Betreuer
Prof. M. Mertig, Prof. H. Schenk
Abstract
Plasmonic nanostructures are poised to lead to a revolution in optics. For centuries, optical techniques were constrained by Abbe’s classical diffraction limit, which states that the minimum resolvable distance between two closely spaced objects is at best half the wavelength of light. This prevents control over light at the nanoscale. However, plasmon resonance exhibits unique optical properties when optically excited, which supports optical charge-carrier resonance, namely, the so-called surface plasmon resonance (SPR). The SPR can be generated at the subwavelength scale and offers a way of bypassing the diffraction limit, allowing the manipulation of light at the nanoscale and below the diffraction limit. In this study, a periodic array of nanopillars was used to support plasmonic effects. These periodic nanostructures were fabricated using a simple and low-cost soft thermal nanoimprinting process, which allowed the fabrication of a large-area nanopillar array. This array structure, which is shown in Chapter 3, was constructed with the aim of increasing the hotspot region and thus the absorbance efficiency and the refractive index sensitivity. An array of nanopillars with a diameter of 230 nm was fabricated in a triangular lattice using soft thermal nanoimprinting. Nanoimprint lithography (NIL) was firstly introduced by Prof. S.Y. Chou in 1995 as a simple, low-cost, and high-throughput method for fabricating nano- and microdevices. It creates patterns by mechanical deformation and is a reproducible process. Using NIL, one can produce large-area, low-cost devices.
This thesis presents two applications that extend plasmonics into the realm of practical devices. In the first part of this thesis, the above-described nanostructure is demonstrated as a highly sensitive refractive index sensor. The three-dimensional structure consisted of two types of plasmonic structures: a nanodisk array and a nanohole array, such that the plasmonic modes of the nanodisk and nanohole arrays could be coupled. Based on the transmission spectra, it was found that the strong coupled mode resulted in a higher sensitivity compared to that corresponding to the normal surface plasmon polariton mode. In order to realize a simple and low-cost sensor capable of determining the refractive indices of the surrounding media, bright-field optical images of the array were obtained using a commercial microscopy system equipped with a charge-coupled device camera. The corresponding variations in the color of the reflected images could be seen clearly. Thus, a simple refractive index sensor could be realized by analyzing the change in the color of the sensor with respect
to liquids with different refractive indices. A sensitivity of 4700 was achieved. The second half of this thesis demonstrates the use of the array structure as a plasmonic absorber in the near-infrared (NIR) region. The high absorbance of the plasmonic nanopillar array as well as its large area, low-cost fabrication process, and excellent biocompatibility make it a highly promising structure for various practical applications. Photothermal bubble generation is demonstrated using a nanoimprinted NIR plasmonic absorber. Under NIR illumination, the plasmonic absorber becomes a highly efficient nanosource of heat because of the enhanced light absorption at the localized SPR wavelength. The plasmonic substrate is capable of generating size-tunable bubbles, depending on the illumination power and exposure time. Further, a biotoxicity test is performed by cultivating colon carcinoma cells on the plasmonic substrate. The cells cultivated on the two halves of the substrate exhibit no morphological changes when compared to the normal cell line, indicating the high biocompatibility of the plasmonic substrate. This study should lead to new approaches for chemical synthesis through solvothermal chemistry as well as to novel biomedical applications. In summary, this foundational work paves the way for the use of NIL as a technique for fabricating low-cost plasmonic nanostructures that can access the NIR region of the spectrum, can be produced at a low cost, and allow for the mass production of plasmonic devices.
This thesis presents two applications that extend plasmonics into the realm of practical devices. In the first part of this thesis, the above-described nanostructure is demonstrated as a highly sensitive refractive index sensor. The three-dimensional structure consisted of two types of plasmonic structures: a nanodisk array and a nanohole array, such that the plasmonic modes of the nanodisk and nanohole arrays could be coupled. Based on the transmission spectra, it was found that the strong coupled mode resulted in a higher sensitivity compared to that corresponding to the normal surface plasmon polariton mode. In order to realize a simple and low-cost sensor capable of determining the refractive indices of the surrounding media, bright-field optical images of the array were obtained using a commercial microscopy system equipped with a charge-coupled device camera. The corresponding variations in the color of the reflected images could be seen clearly. Thus, a simple refractive index sensor could be realized by analyzing the change in the color of the sensor with respect
to liquids with different refractive indices. A sensitivity of 4700 was achieved. The second half of this thesis demonstrates the use of the array structure as a plasmonic absorber in the near-infrared (NIR) region. The high absorbance of the plasmonic nanopillar array as well as its large area, low-cost fabrication process, and excellent biocompatibility make it a highly promising structure for various practical applications. Photothermal bubble generation is demonstrated using a nanoimprinted NIR plasmonic absorber. Under NIR illumination, the plasmonic absorber becomes a highly efficient nanosource of heat because of the enhanced light absorption at the localized SPR wavelength. The plasmonic substrate is capable of generating size-tunable bubbles, depending on the illumination power and exposure time. Further, a biotoxicity test is performed by cultivating colon carcinoma cells on the plasmonic substrate. The cells cultivated on the two halves of the substrate exhibit no morphological changes when compared to the normal cell line, indicating the high biocompatibility of the plasmonic substrate. This study should lead to new approaches for chemical synthesis through solvothermal chemistry as well as to novel biomedical applications. In summary, this foundational work paves the way for the use of NIL as a technique for fabricating low-cost plasmonic nanostructures that can access the NIR region of the spectrum, can be produced at a low cost, and allow for the mass production of plasmonic devices.
Schlagwörter
-
Berichtsjahr
2016