UC Irvine

In this thesis, we use plasmonic materials to achieve enhanced optical properties, including the enhancement of Raman scattered light, the enhancement of optically induced electron tunneling, and the enhancement of the magnetic field component of light interacting with matter.

Our first focus is the development of a teaching lab, which introduces the concept of Surface Enhanced Raman Scattering (SERS) to students in general chemistry lab settings. In the lab, students synthesize gold nanoparticles and perform Raman measurements, examining the concentration dependent spectrum of thiocyanate in aqueous solution with and without gold nanoparticles. Through this experience, students learn the chemical and physical foundations of SERS measurements in a simple, elegant manner. This helps students recognize the capabilities and fundamentals of advanced Raman spectroscopy, a topic often underrepresented in chemistry teaching labs.

Next, our focus is shifted to the fabrication of devices to generate rectified currents upon illumination. The rectifying element is a nm-sized slit between two gold electrodes. Dc current is produced upon illumination due to asymmetries in the junction. Such photo-induced currents are enhanced by surface-plasmons in the nanogap, excited by remote surface plasmon polaritons (SPPs) launched 10 microns from the gap. We describe the fabrication of nanogaps ranging 4-20nm in size in Au bowties using a combination of Focused Ion Beam (FIB) and electromigration techniques. We observe SPP-driven electron tunneling events in the devices, elucidating the natural transition of Tien-Gordon type tunneling into Fowler-Nordheim field emission with increasing illumination power, and demonstrate that these two mechanisms have similar physical origins.

Finally, we describe the use of surface plasmons to enhance and control the interaction between the magnetic field component of light and matter. To do so, we fabricate and explore plasmonic Au nanostructures designed to enhance local magnetic fields at optical wavelengths. The tunability of the device is described as a function of gap size. In addition, we propose a method for optically probing enhanced magnetic fields generated in the devices using trivalent lanthanide ions. Finally, we discuss scattering experiments on a single Er2O3 nanoparticle illuminated with azimuthally polarized light, indicating the possible involvement of a magnetic resonance near 800nm.