Dynamics of plasmon-induced hot carriers in metallic nanoparticles
Doctor of Philosophy
Plasmon-induced hot carriers have attracted lots of interests due to the extraordinary applications on hydrogen photocatalysis and solar energy harvesting. Although many great features of hot electrons have been studied through previous works, the generation process and dynamics of them are still less understood. A more comprehensive theoretical model is needed to build the basic framework to predict and explain the behavior of hot carriers. In this work, we develop a theoretical model for the hot carrier dynam- ics using a silver nanosphere where the conducting electrons are treated as free electrons in a finite spherical potential well. We calculate the plasmon-induced hot carrier production by using Fermi’s golden rule. We show that the many-body interactions during generation have merely a minor effect on the results by comparing with density functional meth- ods. Our research shows that particle size and hot carrier lifetime play an important role in determining both the production rate and the en- ergy distribution of the hot carriers. Larger nanoparticle sizes and shorter lifetimes result in higher carrier production rates but smaller energies. After illumination, the master equations are employed to obtain the time-dependent evolution of carrier occupations in each quantum state,involving the electron-electron, electron-photon and electron-phonon in- teractions. The electron-electron relaxation is proved to be the most es- sential one during the entire decay of energetic hot carriers. In order to apply this method to larger systems and make it capable for nanoparticles of different shapes, we parameterize the electron-electron interaction, and produce nearly the same dynamics process fantastically compared with that under calculations with exact transition matrix elements, indicat- ing its validity throughout the energetic decay evolution. Then, with the help of parameterization, we calculate the energy distribution of hot car- riers and corresponding photoluminescence as a function of time, based on which we obtain the lifetime for hot carriers in different energy ranges. Moreover, we consider the continuous illumination and discuss the effect of Purcell factor on blue shift of photoluminescence. At last we discuss the tunability of photoluminescence profile using nanorod, and calculate the influence of photon density of states on photoluminescence.
hot carriers; plasmon; e-e scattering