Synthesis of Zinc Sulfide Nanocrystals and Fabrication of Nanocrystal Superlattice

Abstract

We report synthesis of zinc sulfide nanocrystals (NCs) via formation of polymetallic thiolate cages. Nearly monodisperse ZnS NCs with size ranging from 2.2 to 7 nm were obtained by thermolysis of S-Zn-dodecanethiol precursors. The electron diffraction pattern of zinc sulfide NCs indicates that precipitates are wurtzite or mixture of wurtzite and zincblende. TEM observation and UV-vis spectra reveal that the growth rate of ZnS NCs considerably depends on the annealing temperature. UV-vis spectra of ZnS NCs with size smaller than 3 nm show sharp excitonic features and a large blue shift from the bulk material. The photoluminescence spectra exhibit large red shift from the absorption band edges, being attributed to electron-hole recombination by surface traps. The narrow size distribution of ZnS NCs leads to formation of ordered self-assemblies with various well-defined structures, where non-closed-packing structure is predominant.

Synthesis and Characterization of Copper Sulfide‐Manganese Sulfide Nanoparticles with Chestnut Morphology and Study on the Semiconducting Properties

“…The materials exhibit a direct band gap with values of 1.74, 3.5 and 2.2 eV for copper sulfide, manganese sulfide and the copper sulfide – manganese sulfide particles, respectively. The bulk band gap of copper sulfide ranges from 1.2 to 2.0 eV depending on composition,, but nanoparticle samples of djurleite (Cu 1.94 S) and anilite (Cu 1.75 S) possess band gap values of 1.73 and 1.70 eV respectively, while manganese sulfide is about 3.8 eV, which matches closely with the values measured for the nanoparticles here. The band gap for the copper sulfide‐manganese sulfide particles is intermediate that of the pure materials, supporting the formation of phase segregated heterostructured particles.…”

“…In this experimental approach to forming copper sulfide – manganese sulfide heterostructured particles, the copper sulfide disks are formed first, then manganese precursor is added to initiate manganese sulfide growth on the pre‐formed copper sulfide seeds. The formation of both materials is driven by thermolysis, which is a decomposition facilitated by the catalytic cleavage of the sulfur alkane bond in the alkanethiol molecules used in the synthesis . In this case, the manganese sulfide grows on only one face of the copper sulfide disk, because the disk is anisotropic with one of the broad 001 faces being cationic and the other anionic ,.…”

“…Copper chalcogenides have been shown to be versatile semiconducting materials and copper sulfide is particularly interesting because the naturally disordered and defect prone atomic structure has a large effect on the semiconducting properties. The thermolysis based synthetic approach offers a simple and straightforward path to the creation of copper sulfide nanomaterials, and using copper sulfide nanoparticles as a template has been documented to preferentially form heterostructures because of the unique formation mechanism during thermolysis . Nanostructured copper sulfide composed of mixed copper deficient phases possesses modest semiconducting properties including maximum electrical conductivity of 3,500 S/cm and Seebeck coefficient of 85 μV/K which has traditionally led to exploration of the material for use in a wide range of semiconducting technologies, including energy generation and storage, sensors, diagnostics and medical therapy, optically emissive materials, and others .…”

Prospects of Colloidal Copper Chalcogenide Nanocrystals

“…Colloidal binary copper chalcogenide (Cu 2− x A; A=S, Se, and Te) NCs have attracted increasing attention over the last decade, because their properties make them interesting materials for implementation into several applications, such as solution‐processable photovoltaic and nanoplasmonic devices, photocatalysis, photothermal therapy, and biomedical sensing . Some of these applications will be addressed in more detail in Section 2.4.…”

“…Cabot and co‐workers have proposed an oriented attachment pathway through which hexagonal nanodisks form hexagonal Cu 2− x S bifrustums and eventually hexagonal bipyramids . Other groups have presented evidence that Cu thiolate lamellar complexes act as both Cu precursors and shape‐templating agents . Recent work has demonstrated that the crystallographic phase and composition of Cu 2− x S NCs (see Section 2.1) can be controlled by proper choice of reaction parameters (namely, temperature, molar ratio of Cu/S, and volume ratio between the noncoordinating solvent 1‐octadecene and the ligand oleylamine) .…”