Kinetics of Isovalent (Cd2+) and Aliovalent (In3+) Cation Exchange in Cd1-xMnxSe Nanocrystals.
Ion exchange, in which an in-diffusing ion replaces a lattice ion, has been widely exploited as a synthetic tool for semiconductor doping and solid-to-solid chemical transformations, both in bulk and at the nanoscale. Here, we present a systematic investigation of cation-exchange reactions that involve the displacement of Mn2+from CdSe nanocrystals by Cd2+or In3+. For both incoming cations, Mn2+displacement is spontaneous but thermally activated, following Arrhenius behavior over a broad experimental temperature range. At any given temperature, cation exchange by In3+is approximately 2 orders of magnitude faster than that by Cd2+, illustrating a critical dependence on the incoming cation. Quantitative analysis of the kinetics data within a Fick's-law diffusion model yields diffusion barriers (ED) and limiting diffusivities (D0) for both incoming ions. Despite their very different kinetics, indistinguishable diffusion barriers of ED≈ 1.1 eV are found for both reactions (In3+and Cd2+). A dramatically enhanced diffusivity is found for Mn2+cation exchange by In3+. Overall, these findings provide unique experimental insights into cation diffusion within colloidal semiconductor nanocrystals, contributing to our fundamental understanding of this rich and important area of nanoscience.
Department of Chemistry, University of Washington , Seattle, Washington 98195-1700, United States.
Pradip
P
Chakraborty
Department of Electrical Engineering, University of Washington , Seattle, Washington 98195-2500, United States.
Yu
Y
Jin
Department of Chemistry, University of Washington , Seattle, Washington 98195-1700, United States.
Charles J
CJ
Barrows
Department of Electrical Engineering, University of Washington , Seattle, Washington 98195-2500, United States.
Scott T
ST
Dunham
Department of Chemistry, University of Washington , Seattle, Washington 98195-1700, United States.
Daniel R
DR
Gamelin