Annealing of sulfide stabilized colloidal semiconductor nanocrystals

Abstract

The effect of thermal annealing on layers of CuInS2 nanocrystals (NCs) stabilized with (NH4)2S was \ninvestigated using in situ transmission electron microscopy (TEM), in situ X-ray diffraction (XRD), \nthermogravimetric analysis combined with mass spectrometry (TGA-MS) and X-ray photoelectron \nspectroscopy (XPS). It is shown that these inorganic, chalcogen containing ligands inhibit NC sintering up \nto 450 C in an inert atmosphere. On the other hand, sintering can be promoted by annealing in \nhydrogen gas. A similar behavior is found with Cu2ZnSnSe4 and CdSe NCs. We attribute the inhibited \nsintering to the oxidation of the S2 originally stabilizing the NCs to sulfite or sulfate moieties, where \noxidation is possible either by exposure of the films to air or by thermal decomposition of residual \nsolvent molecules present in the film under inert conditions.