대면적 금속나노필러 형성 및 SERS sensor 연구

Abstract

The nanostructures found in nature have sometime an elaborate three-dimensional structure made up with the soft and flexible constituents, and they exhibit diverese mechanical and optical functions. By mimicking elaborate nature structures, we have been achieved outstanding technologies such as spider`s webs, moth`s wings and diatom`s micro-holes. To fabricated fine and exquisite nano-patterns, various techniques have been developed for multi-functional devices. Nanoimprint lithograpy (NIL) process is a low-cost and facile nanofabrication technique that can enable the replication of sub-micro and nano-scale patterns on various substrates. Especially, a mass-production could be realized by a semi-permanent duplicating method and the patterns can be transferred to transparent substrates by aid of its direct-contact fabrication. Based on those virtues, NIL has been applied in various fields such as electronics, photonics and bio-sensors. In this thesis, we employed NIL to fabricate polymer resist masks for one-dimensional nanowire synthesis. Elaborate nano-patterns were fabricated on silicon (Si) substrate by using E-beam lithography and metal was deposited as an etching mask. Using reactive-ion etching (RIE), we manufactured Si nano-pillars on Si substrate and it was used as a master template for copying duplicated polydimethylsiloxane (PDMS) molds. We checked the morphologies of a Si master template by a field emission scanning electron microscope (FE-SEM) and it showed square arrays of circular pillars with uniform diameter of 160 nm and height of 300 nm, and with the center-to-center spacing between the pillars of 410 nm. In addition, highly aligned ZnO nanostructures were fabricated by a duplicated mold. We deposited zinc oxide (ZnO) seed layers on Si and gallium nitride substrates by using metal-organic vapor phase epitaxy (MOVPE) in large-area. NIL was employed to fabricate nano-holes on ZnO seed layer substrates by using polymethyl methacrylate (PMMA) and duplicated molds. O2 plasma treatments were executed for removing residual PMMA layers (30 sec, 30 W). For achieving high quality ZnO nanowires, we used a hydrothermal growth method and checked various morphologies of grown ZnO nanowires using a FE-SEM. Furthermore, we executed a hot-embossing technique for a flexible SERS device fabrication. Elaborate nano-pillars were transferred on flexible polystyrene (PS) substrate and the morphologies of patterned PS films were analyzed by FE-SEM. The substrates consist of a large array of circular pillars with uniform diameter of 150 nm and height of 200 nm, and with the center-to-center spacing between the pillars of 500 nm. Sputter was employed to coat gold on nano-pillars conformally for applying in a surface-enhanced Raman spectroscopy (SERS) sensor. The Au nano-pillars display a smooth surface and uniform diameter along the vertical direction. Methylene blue (MB) was used as a Raman detecting molecules and a low concentration of its solution (5×10-4M) was deposited on SERS platforms. UV-vis spectroscopy showed flat gold surface and Au nano-pillars absorption spectra and Raman spectroscopy analysis revealed that our platforms exhibited 3×103 and 7.3 enhancements of Raman peak at 1624cm-1, compared with bare planar silicon and gold coated planar PS substrates, respectively. Contact angle was measured to confirm a good wettability of our SERS Platforms. With these analyses, we confirm the possibilities of this device as a flexible SERS sensor.