Field Enhancement using Noble Metal Structures

Resonance may be one of the most fundamental rules of nature. Electromagnetic resonance at nanometer scale could produce a giant field enhancement at optical frequency, providing a way to measure and control the process of atoms and molecules at single molecule scale. For example, the giant field enhancement would provide single molecule sensitivity for Raman scattering, which provides unique tools in measuring the quantity in extremely low concentration. In addition, light-emitting diodes could have high brightness but low input power that would be revolutionary in the optoelectronic industry. Although light enhancement is promising in several key technology areas, there are several challenges remain to be tackled. In particular, since the field enhancement is so strongly geometry dependent that slight modification of the geometry can lead to large variations in the outcome, a thorough understanding in how the geometry of the structure affects the field enhancement and creating proper methods to fabricate these structures reproducibly is of most importance. This thesis is devoted to design, fabrication and characterization of field enhancement generated on the surface of noble metals such as silver or gold with 1D structure.;The s-polarized field enhancement arising from one-dimensional metal gratings is designed and optimized by using Rigorous Coupling Wave Analysis (RCWA). After optimization, the strongest enhancement factor is found to be 9.7 for 514nm wavelength light. The theoretical results arc confirmed by angle-dependent reflectivity measurements and the experimental results are found to support the theory.;A novel single slit structure employing surface plasmon polaritons (SPPs) for enhancing the electric field is studied. SPPs are first generated on a 50 nm thick metal film using attenuated total reflection coupling, and they are subsequently coupled to the cavity mode induced by the single slit. As a result, the field enhancement is found at least 3 times the surface plasmon background adjacent to the slit, as predicted by using RCWA. The mechanism for enhancement is theoretically studied both numerically and analytically.;Two novel convenient methods for fabricating nanoslits with high aspect ratio are proposed. One is creating nanoslits by cracking the thin glass substrates with metal film. Sub-5nm wide slits with fair uniformity are created, as confirmed by Scanning Electron Microscopy images and comparing the Confocal Two Photon Emission (CTPE) spectroscopy with finite difference in time domain simulations. The other is creating slits by fatiguing the metal film on a flexible substrate. Enhanced CTPE and second harmonic generation are observed arising from these less than 20nm wide slits.;Nanoslits fabricated using Electron Beam Lithography (EBL) are characterized using CTPE. The overall emission enhancement of excitation and collection wavelengths is separated by a proposed method. It is surprisingly found that the pulsing laser can tune the resonant wavelength of the EBL samples to the laser wavelength. A mechanism is proposed for this phenomenon. It is shown this can be developed into a tool to fabricate field enhancement hot spots.