(472e) Carrier Dynamics of Photocatalytic Two-Dimensional Semiconductors Decorated with Plasmonic Nanoparticles

Layered transition metal dichalcogenides (TMDs), MX₂ structures where M = Mo or W and X = S, Se, or Te, are an emergent source of 2D semiconductors with intriguing catalytic and optoelectronic properties. Concurrently, plasmonic metal nanoparticles (NPs), featuring an extraordinary ability to concentrate light and energy in sub-wavelength dimensions, can enhance light harvesting and catalytic activity in adjacent semiconductors. Mechanisms of plasmonic enhancements includes local heating, light scattering, local field confinement, resonant energy transfer, and interfacial charge transfer. However, these underlying physical mechanisms are poorly understood in situ, and most devices have exhibited poor performance due to the localized nature of plasmon resonances and their picosecond carrier relaxation. The work herein utilizes transient absorption spectroscopy, with pump tunability and broadband visible-NIR probing, to monitor the carrier excitation and dynamics in AuNP-decorated TMDs. A combination of this time-resolved and steady-state optical spectroscopies unveiled the presence of a sub-gap absorption feature in gold NP-decorated molybdenum diselenide (MoSe₂). Optical excitation of this low-energy feature generates long-lived, charge carriers in MoSe₂. Improved understanding of interaction between plasmonic NPs and adjacent 2D semiconductors represents an important advance in the design and implementation of these emerging hybrid materials in solar photoelectrochemistry.