Charge separation in Pt-decorated CdSe@CdS octapod nanocrystals.

We synthesize colloidal CdSe@CdS octapod nanocrystals decorated with Pt domains, resulting in a metal-semiconductor heterostructure. We devise a protocol to control the growth of Pt on the CdS surface, realizing both a selective tipping and a non-selective coverage. Ultrafast optical spectroscopy, particularly femtosecond transient absorption, is employed to correlate the dynamics of optical excitations with the nanocrystal morphology. We find two regimes for capture of photoexcited electrons by Pt domains: a slow capture after energy relaxation in the semiconductor, occurring in tipped nanocrystals and resulting in large spatial separation of charges, and an ultrafast capture of hot electrons occurring in nanocrystals covered in Pt, where charge separation happens faster than energy relaxation and Auger recombination. Besides the relevance for fundamental materials science and control at the nanoscale, our nanocrystals may be employed in solar photocatalysis.