Elucidating the electronic cross-talk dynamics across the heterointerface of janus CdSe/PbSe nanocrystals

Abstract

CdSe/PbSe Janus heteronanocrystals (HNCs) were synthesized in one pot, and the underlying reaction mechanism along with the epitaxy at the hexagonal CdSe–cubic PbSe heterojunction were investigated. During the initial stages of reaction, unusually large CdSe nanocrystals were formed due to rapid growth in the presence of Pb-oleate which cation exchanged asymmetrically to form the Janus structures. Distinct PbSe and CdSe domains were visualized after sufficient growth as seen from the high-resolution transmission electron microscopic images with a unique rock salt PbSe and wurtzite CdSe interface. The core Pb–Se bonds were differentiated from interfacial Pb–Se bonds through the X-ray photoelectron spectroscopy measurements. Transient absorption spectroscopy of the Janus NCs revealed intriguing spectroscopic signatures in both the spectral and time domains as manifested by the early population of higher excitonic states upon pulsed laser excitation along with broad TA spectra rich in higher excitonic states due to the intricate hybridization between the electronic states of two disparate materials. The TA measurements were well correlated with the formation of the Janus structure as new states emerged at the longer wavelength side in the TA spectra due to PbSe accompanied by a slow ∼5 ps additional electron cooling component arising due to hole localization in the PbSe domain.