 we studied cation exchange ( ce ) in 
 core / shell cu2xse / cu2xs nanorods 
 with two cations , ag+ and hg2 + , which are known 
 to induce rapid exchange within metal chalcogenide nanocrystals ( ncs ) 
 at room temperature . at the initial stage of the reaction , the guest 
 ions diffused through the cu2xs shell and reached the cu2xse 
 core , replacing first cu+ ions within the latter region . 
 
 these experiments prove that ce in copper chalcogenide ncs is facilitated 
 by the high diffusivity of guest cations in the lattice , such that 
 they can probe the whole host structure and identify the preferred 
 regions where to initiate the exchange . 
 for both guest ions , ce is 
 thermodynamically driven as it aims for the formation of the chalcogen 
 phase characterized by the lower solubility under the specific reaction 
 conditions . 
Supplementary Material