Amine-assisted facetted etching of CdSe nanocrystals

The treatment of CdSe nanocrystals (NCs) in a 3-amino-1-propanol (APOL)/water (v/v = 10:1) mixture at 80 °C in the presence of O₂ causes them to undergo a slow chemical etching process, as evidenced by spectroscopic and structural investigations. Instead of the continuous blue shift expected from a gradual decrease in NC dimensions, a bottleneck behavior was observed with distinct plateaus in the peak position of photoluminescence (PL) and corresponding maxima in PL quantum yield (i.e., 34 ± 7%). It is presently argued that such etching behavior is a result of two competitive processes taking place on the surface of these CdSe NCs: (i) oxidation of the exposed Se-sites to acidic SeO_x entities, which are readily solubilized in the basic APOL/H₂O mixture, and (ii) coordination of the underlying Cd-sites with both amines and hydroxyl moieties to temporally impede NC dissolution. This is consistent with the HRTEM results, which suggest that the etched NCs adopt pyramidal morphologies with Cd-terminated facets (i.e., (0001) bases and either {0111} or {2111} sides) and account for the apparent resistance to etching at the plateau regions.