The Influence Of Surface Ligands On Morphology, Self-assembly Properties And Optical Properties Of Inorganic Semiconductor Nanocrystals

In the past few years, nanomaterials attract tremendous attention in recent researches. Variousresearch fields including physics, chemists, material scientists, and engineers of mechanical and electricalare involved in this research because of its unique physical and chemical properties. Among thesenanomaterials, semiconductor nanocrystals possess size-dependent properties, which make them interestingcandidates for a variety of applications, e.g., in solar energy conversion, lighting, display technology, orbiolabelling. A vast amount of synthetic procedures allowing for precise size and shape control has beendeveloped and a number of studies were conducted in recent years, which shed light on the underlyingreaction mechanisms of the nanocrystals formation and growth. Meanwhile, the surface of nanocrystals hasa strong influence on properties of nanocrystals. In order to make the nanocrystal to be used in the relatedfields, the size, shape and properties of semicondutor nanocrystals must be precisely controlled. Therefore,in this article we study the impact of surface ligand on the performance of semiconductor nanocrystals, tomake semiconductor nanocrystals can be better applied to the relevant devices, including two aspects: First,to research the impact of organic ligands for morphology, self-assembly properties of inorganicsemiconductor nanocrystals; Second, design of surface ligands of semiconductor nanocrystals, all-inorganiccolloidal nanocrystals can be successfully obtained by replacing bulky and insulating organic ligands withinorganic ligands, which can enhance charge transport capacity of nanocrystals.The main contents are as follows:1. Capric acid and oleylamine were selected as the organic surface ligands, high quality PbSeand PbTe nanocrystals were synthesized with non-injection one-pot method which could be scale up easily,to study the influence of surface ligands on morphology and self-assembly properties of nanocrystals. Seand Te precursors were prepared, the use of any pyrophoric reagents such as TBP and TOP was avoided.The size and shape of nanocrystals were controlled by the reaction time, reaction temperature, andcombination of two kinds of surfactants, DA and OAM, with different molar ratios. We can synthesisspherical PbSe nanocrystals (particle size of6.5and8.3nm), cube-shaped PbSe nanocrystals (edge lengthbetween12and16nm) and spherical PbTe nanocrystals (particle size of8.5nm), cube-shaped PbTenanocrystals (edge length between14and18nm). X-ray diffraction (XRD) and selective area electron diffraction (SAED) characterizations demonstrated the rock salt cubic structures; the transition electronmicroscopy (TEM) images show narrow size distributions of as-synthesized PbSe and PbTe nanocrystals.The uniform size of as-synthesized nanocrystals promoted the self-assemble of PbSe and PbTe nanocrystalsinto ordered superstructures under the action of oleylamine.2. According to the influence of inorganic surface ligands on properties of inorganicsemiconductor nanocrystals, all-inorganic colloidal CuInS2nanocrystals can be successfully obtained byreplacing bulky and insulating organic ligands with small and electronically transparent (NH4)4Sn2S6inorganic ligands, which can enhance charge transport capacity of nanocrystals. A facile method for thesynthesis of size-controlled triangular CuInS2(CIS) semiconductor nanocrystals in the organic phase, then,molecular metal chalcogenide complexes (MCCs) capped CuInS2nanocrystals can be synthesized byexchanging organic compounds with (NH4)4Sn2S6inorganic ligands in environmentally benign solvent. Thecharacteristics of CuInS2nanocrystals (coated by organic and inorganic ligands) were characterized byUV vis spectroscopy, Fourier-transform infrared (FTIR), transmission electron microscopy (TEM), X-raydiffraction (XRD), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS) anddynamic light scattering (DLS). The results show that [Sn42S6]--CuInS2nanocrystals were successfullyprepared by this ligand exchange method. The charge transport properties of CIS NCs films were sharplyincreased due to the improved electronic coupling after ligands exchange.