Synthesis of copper and zinc sulfide nanocrystals via thermolysis of the polymetallic thiolate cage

In this paper report on the synthesis of copper and zinc sulfide nanocrystals (NCs) via the formation of polymetallic thiolate cages. Cu2S NCs derived from Cu-dodecanethiol complex formed well-defined spherers, which were sufficiently monodisperse (with a size distribution of ∼10% standard deviation of approximately 4.7 nm diameter on average) to generate ordered self-assemblies. An electron diffraction pattern and UV-vis spectrum of Cu2S NCs indicate that this process can provide pure β-chalcocite (Cu2S). Nearly monodisperse ZnS NCs with a size ranging from 3 to 7 nm were obtained by thermolysis of the S-Zn-dodecanethiol precursor. The electron diffraction pattern indicates that zinc sulfide NCs are either wurtzite or a mixture of wurtzite and zincblende. TEM observation and UV-vis spectra revealed that the growth rate of ZnS NCs depends strongly on the annealing temperature. UV-vis spectra of 3 nm ZnS NCs show sharp excitonic features and a large blue shift from the bulk material. The photoluminescence spectra exhibit a large red shift from the absorption band edges. These shifts could be attributed to recombination from the surface traps. The narrow size distribution of Cu2S and ZnS NCs led to the formation of ordered self-assemblies with various well-defined but nonclosed-packing.