ABSTRACT
It was recently shown that, by controlling the O(2) concentration, the seeded-growth of CdSe nanocrystals (NC) can be manipulated to proceed either unidirectionally (from the (0001) facet) or three-dimensionally. In this contribution, we investigate two new Se precursors (i.e. SeO(2) and NaHSe) and compare them with Se obtained from etching of smaller NC seeds. Under anaerobic conditions, both precursors led to successful 3-dimensional (3D) NC growth. At high O(2) concentrations, the seeded growth of rods was enhanced by the NaHSe precursor, while impeded by the use of SeO(2). Mechanistic studies showed that the reduction of SeO(2) to Se(2-) produces an excessive amount of O(2). This leads to rod fragmentation due to etching as well as the production of deep traps that quench their luminescence. These new precursors, along with a heightened understanding of oxygen's role, expand the synthetic repertoire of the redox-assisted, seeded-growth of CdSe and better position this low temperature (125 °C) methodology towards realizing advanced NC heterostructures.
ABSTRACT
The role of oxygen in directing the low temperature (125 degrees C), redox-assisted, unidimensional and unidirectional growth of CdSe nanocrystals (NCs) was investigated. In the presence of oxygen, CdSe quantum dots grow selectively along their c axis with little to no change in their width. Reduction of oxygen in the growth medium results in three-dimensional growth. Moreover the one-dimensional growth was found to occur only from one of the two inequivalent polar (0001) facets, as supported by the seeded growth of Cd(x)Hg(1-x)Se onto CdSe seeds. This is in agreement with density functional theory simulations, which indicate that due to selective oxygen passivation growth can occur only along the [0001] direction. The ability to control seeded NC growth with respect to morphology and directionality opens new possibilities toward the low temperature synthesis of complex nanostructures.
