Coherent Multidimensional Spectroscopy as a Probe for Femtosecond Relaxation Dynamics of Metal Colloids

Book excerpt: Electronic carrier dynamics are integral in the design of functional metal transducers. Moreover, the optical properties and dynamics of colloidal metals depend sensitively their structures. Hence, a comprehensive understanding of how structural factors like size, geometry, and composition influence electronic relaxation processes allows for the development of predictive models for judicious selection of nanoscale metals for photonic applications. This dissertation focused on the usage of time-resolved nonlinear spectroscopy techniques, specifically femtosecond transient absorption and two-dimensional electronic spectroscopy (2DES) to probe electronic relaxation dynamics in colloidal metals, including: monolayer-protected clusters (MPCs), plasmonic gold nanorods, metal hybrid nanostructures, and 2-D semiconductors. The ultrafast relaxation mechanisms in all of these systems were understood in relation to structure-specific and state-resolved dynamics. 2DES results resolved excited-state symmetry-dependent relaxation dynamics in 38-atom gold nanoclusters that were influenced by specific metal kernel and inorganic semiring structures. It is shown that Fermi liquid dynamics can be resolved in plasmonic metal ensembles. It is also shown that synthetic modification to size and composition of a single domain in composite metal nanostructures can be used to overcome bulk-like contributions that govern phonon-mediated thermalization. In addition, phonon-mediated renormalization rates across different materials thicknesses (i.e. number layers) in 2-D semiconductors is described. All of these results indicate that specific nanostructures (size, composition, thickness, and geometry) play integral roles in governing ultrafast relaxation dynamics in complex nanoscale metal colloids, which in turn can be leveraged to develop predictive models for optimal design of functional metal transducers.