Semiconducting quantum-dot nanocrystals have emerged as a promising class of materials with optoelectronic properties controllable through quantum-confinement effects. Despite recent successes in this field, an important factor that remains difficult to control is the impact of the nanocrystal surface structure on the photophysics and electron transport in nanocrystal-based materials. In particular, the presence of surface defects and irregularities can result in the formation of localized sub-bandgap states that can dramatically affect the dynamics of charge carriers and electronic excitations. Here we use Scanning Tunneling Microspcopy/Spectroscopy (STM/S) to investigate, in real space, sub-bandgap states in individual ligand-free PbS nanocrystals. Furthermore, we examine the relationship between surface reconstruction and the observed sub-bandgap states in PbS nanocrystals through ab-initio DFT simulations. This study provides insight into the possible mechanisms of sub-bandgap state formation which may result from post synthesis processing techniques, such as ligand exchange and annealing steps, leading to the under-coordination of surface atoms.

Impact of surface reconstruction on the electronic structure of PbS QD nanocrystals: Experiment and theory

253rd National Meeting (2017)

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