Title : Synthesis of anisotropic wurtzite copper indium sulfide nanocrystals
Abstract:
Colloidal semiconductor nanocrystals have become a topic of extensive scientific research in the last several decades, due to their unique size- and shape-dependent properties, with applications ranging from energy devices to biomedical imaging. Over many years, semiconductor nanomaterial research was dominated by binary systems containing toxic heavy metals such as cadmium and lead. However, recently, ternary I-III-VI systems have emerged as promising alternatives to these toxic heavy-metal containing systems. I-III-VI systems, such as CuInS2 (CIS) offer several distinct advantages over the existing binary systems, such as greater tunability, large Stokes shifts and enhanced stability. While the shape dependent properties of the existing binary systems have been studied, with the synthesis of anisotropic Cd-based binary systems widely reported, anisotropic ternary systems have been much less explored in the literature, with reports of CIS dominated by small, spherical particles in the thermodynamically stable chalcopyrite phase.
Herein we present the synthesis and anisotropic growth of metastable wurtzite CIS nanocrystals with a unique tapered hexagonal prismatic morphology, which can be tuned by varying the sulfur source and co-ligand. These single crystalline structures exhibit a broad absorption range across the entire UV-VIS region into the NIR. Quaternary CuInZnS nanostructures with a blue-shifted band gap were also produced. Transmission Electron microscopy, X-Ray Diffraction and Energy dispersive X-ray spectroscopy were employed to study the morphology, crystal phase and composition of the nanostructures. Detailed investigation of the nanocrystal growth revealed the initial formation of uniform CuS hexagonal nanorods, which then grow anisotropically with the incorporation of indium, producing anisotropic wurtzite CIS nanocrystals with a unique tapered hexagonal prismatic morphology. These broad absorption CIS nanostructures have potential application in photovoltaic cells and other devices, while the study of the anisotropic growth can contribute to further development of new anisotropic I-III-VI type colloidal semiconductor nanomaterials with an extensive range of potential applications.
