Tuning the Optical Response of Graphene and Metamaterials
The following dissertation examines the tunability of two types of proof-of-concept devices centering around post-fabrication modification of the infrared optical response. The first device, created through the hybridization of the metamaterials and the phase-transition oxide vanadium dioxide (VO2), is probed using Fourier transform infrared spectroscopy. We demonstrate that, through application of voltage pulses to this initially uniform device, a gradient in the optical properties can be obtained. This macroscopic control mechanism enables persistent modification of the device, though the hysteretic nature of the VO2 insulator to metal transition (IMT), on spatial scales on the order of a few wavelengths of the probing light. In addition to effects from current-induced heating, we show that the optical response can also be modified through the use of an ionic gel to oxidize or reduce the vanadium ions in VO2, thereby driving its IMT. These measurements also demonstrate the potential for metamaterials as a means of probing metal-to-insulator transitions, allowing for enhanced optical probing of changes in VO2 properties due to electric fields from the ion gel. The second device we explored is a graphene based device used for examining the modification of graphene’s plasmonic response in conjunction with the ferroelectric high-κ dielectric lead zirconium titanate (PZT) employed as a gate dielectric. By using PZT, the carrier concentration, and therefore the optical properties of graphene, can be heavily modified with small back-gate voltages. Additionally, the use of a ferroelectric dielectric enables a form of memory in the device where transient voltage application leads to persistent changes in graphene properties. Examination of this device using scanning near-field optical microscopy allows us to determine the usefulness of similar devices in future plasmonic device.