Figure 4. ‘Vacancy-mediated' mechanism versus ‘kick-out' mechanism.

(a,b) Schematic representations of the ‘vacancy-mediated' mechanism (a) and the ‘kick-out' mechanism (b). The blue and red circles represent Pb and Cd, respectively. The green circles denote the Pb ions migrating at the PbS/CdS interface. The pink circle is a Cd interstitial kicking the Pb ion out of the PbS core region. The lower panels of (a,b) schematically show the energy landscapes of these two different mechanisms. (c) Typical snapshots from MD simulations showing the ‘kick-out' mechanism. Left and right parts of (c) are the configurations of the NC before and after the jump of a Pb ion (the green sphere) out of the PbS core, respectively. The Pb jump is initiated by a Cd interstitial (the pink sphere) in the PbS region. The blue, red and white spheres are Pb, Cd and S, respectively. The lower panels of (c) are magnifications of the region where the ‘kick-out' motion takes place.