| dc.description.abstract | The collective oscillation of conduction band electrons in metal nanostructures, known as the localized surface plasmon resonance (LSPR), can be engineered to absorb photons at desired wavelength. Plasmonic nanostructures have received significant research interests not only because this flexible optical response tailorability, but also because the hot carriers excited within plasmonic metals after the non-radiative decay of LSPR have remarkable photocatalytic performance. Therefore, the dynamics of hot carriers and the behavior of hot carriers at steady state are of great interest in the field of photodetection, photocatalysis and optical power conversion devices.
In this dissertation, my study is divided into three distinct yet connected projects. In the first project, a free-electron jellium model is used to calculate the energy distribution of non-thermal carriers. Additionally, a theoretical framework describing tunneling phenomena of carriers in a metal is derived. With the electric field provided by the full-wave optical simulation (FDTD method), an asymmetric plasmonic tunnel junction is proposed and a 20% output energy efficiency is calculated. The second project studies the Raman scattering from plasmonic metals, in which a two-temperature anti-Stokes Raman thermometry is developed. Within this thermometry, not only the material temperature but also a subpopulation of hot carriers with energy distribution described by a second temperature, electronic temperature, is accurately probed. Furthermore, we proposed that the inelastic scattering from non-thermal carriers contributes in the Stokes Raman scattering.
A good agreement between theory and experiment is achieved and the plasmon dephasing time, which dictates the decay of LSPR, is extracted from steady state measurement. To prove the presence of hot carriers at steady state, an independent thermionic emission experiment is conducted in the third project. Patterned gold nanostructures are fabricated using electron-beam lithography, and a thermionic emission device consists of gold nanostructures and an ITO electrode is constructed. The current-voltage characteristics not only proves the presence of hot carriers but also tells the information about the size and energy distribution of hot carriers.
The study of hot carriers at steady state is crucial in designing hot carrier devices with better performance. The results and analyses presented in this dissertation shall provide insightful perspective of hot carrier behavior at steady state and broaden the horizon of hot-carrier-mediated photocatalysis and light-harvesting applications. | en |
