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On the Nature of Trapped-Hole States in CdS Nanocrystals and the Mechanism of Their Diffusion
journal contribution
posted on 2018-06-01, 00:00 authored by R. Peyton Cline, James K. Utterback, Steven E. Strong, Gordana Dukovic, Joel D. EavesRecent
transient absorption experiments on CdS nanorods suggest
that photoexcited holes rapidly trap to the surface of these particles
and then undergo diffusion along the rod surface. In this Letter,
we present a semiperiodic density functional theory model for the
CdS nanocrystal surface, analyze it, and comment on the nature of
both the hole-trap states and the mechanism by which the holes diffuse.
Hole states near the top of the valence band form an energetic near
continuum with the bulk and localize to the nonbonding sp3 orbitals on surface sulfur atoms. After localization, the holes
form nonadiabatic small polarons that move between the sulfur orbitals
on the surface of the particle in a series of uncorrelated, incoherent,
thermally activated hops at room temperature. The surface-trapped
holes are deeply in the weak-electronic coupling limit and, as a result,
undergo slow diffusion.
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CdS nanocrystal surfaceCdS nanorodssurface-trapped holesnonbonding sp 3 orbitalstheory modelhole statesphotoexcited holessurface sulfur atomssulfur orbitalsTrapped-Hole Stateshole-trap statesabsorption experimentsholes form nonadiabaticCdS Nanocrystalsdiffusionvalence band formrod surfaceroom temperaturesemiperiodic density