Growth schemes of tunable ultrathin CdS_xSe_1-x alloyed nanostructures at low temperatures

The new 2D colloidal semiconductor ultrathin nanosheets provide an appealing combination of properties. Controlling both their morphology and composition offers another path to control their physical properties. Homogeneously alloyed structures with tunable properties were obtained using NaBH₄ which controls the precursor reactivity. The effect of NaBH₄ on the degree of alloying, shape control, and optical properties of the alloyed colloidal nanosheets is presented here. The alloyed structures are a monolayer thicker than the pure CdS or CdSe. In relatively low Se contents, the addition of NaBH₄ produced high quality alloyed nanosheets that are uniform, in the wurtzite phase and with small thickness distribution as evident from transmission electron microscopy (TEM), X-ray diffraction (XRD), and optical characterization. Atomic resolution phase images provide evidence to both stacking faults formation across the entire width of the sheet as well as local disorder, suggesting a combined mechanism of oriented attachment of patches that are fused and extended by unidirectional growth.