Influence of Band Alignment on Electronic Relaxation in Plasmonic Metal-Semiconductor Hybrid Nanoparticles

Recent advances in colloidal synthesis enable the generation of multicomponent metal-semiconductor nanoparticles that share a solid-state interface, thus providing a tunable platform for the tailored electronic and optical properties of nanoscale heterostructures. Here, the influence of size and material composition on electron-phonon scattering was investigated for a series of gold-metal chalcogenide (PbS, ZnS, and Cu_2-xS) hybrid nanoparticles using femtosecond time-resolved transient extinction spectroscopy. The influence of semiconductor size on electron-phonon coupling in the hybrid nanoparticles was studied using two Au-PbS systems having different PbS diameters, 6 ± 1 and 17 ± 3 nm. For Au-PbS (PbS = 6 ± 1 nm), an approximately 30% acceleration of the electron-phonon scattering rate was observed with respect to 5 ± 1 nm gold nanoparticles. In contrast, the system having the larger PbS domain size exhibited a decelerated rate when compared to gold nanoparticles. The nanostructure dependence of the electron-phonon scattering rates was attributed to differences in band edge alignment with respect to the Au Fermi level. Electron-phonon scattering was accelerated for Au-Cu_2-xS where the conduction band edge is in close alignment with the gold Fermi level. In contrast, the ultrafast response of Au-ZnS displayed no significant difference from pure AuNPs, which is consistent with minimal energy alignment between the two domains; the ZnS domain is an effective insulator in this case. These results demonstrate that controlled and selective modifications to both the size and composition of the semiconductor domain in metal-semiconductor hybrid nanoparticles impact band alignment, which in turn can be leveraged to modulate electronic thermalization in plasmon-supporting heterostructures.