Ultrafast Charge Dynamics in Plasmonic Metal–Metal Phosphide Nanohybrids

Understanding and controlling the hot charge carrier processes in hybrid plasmonic nanomaterials is crucial when designing systems for applications in energy harvesting, biosensing, photocatalysis, and nanophotonics. Over the years, ultrafast charge dynamics studies have extensively been conducted on bimetallic systems involving noble metals for tuning the relaxation time of hot electrons, with slower relaxation for applications involving harvesting of hot electrons and faster relaxations for applications requiring temperature increase via effective thermalization. In this study, we investigate the charge dynamics in CoNiP–Au and Ni2P–Au heterodimers. Using ultrafast transient absorption spectroscopy, we demonstrate that the relaxation time of Ni2P–Au is much faster than that of CoNiP–Au and Au, while CoNiP–Au shows an intermediate decay time. These results track with variations in the DOS at the Fermi level of the different samples. Additionally, we develop a theoretical model to extract the charge carrier dynamics in the nanohybrids quantitatively. Using the model, we identified that the Ni2P domain acts as a hot electron sink, resulting in very fast relaxation dynamics in Ni2P–Au. Through the two-temperature model and power-dependent energy measurements, we calculated the intrinsic relaxation time for each domain of the hybrids. The relaxation time of 105 ± 29 fs in Ni2P is twice as fast as the fastest temporal response reported for Pt–Au. The intrinsic relaxation time of CoNiP–Au was found to be very similar to that for Au at 501 ± 102 fs and 520 ± 170 fs, respectively. The insights gained from this work can contribute to the understanding of hot carrier dynamics and the design of plasmonic hybrid materials for targeted applications.