The role of morphology and surface chemistry on the properties of colloidal nanomaterials

The work described in this thesis focuses on the role of morphologies and surface chemistry on the properties of nanomaterials. First, the role of organic surface ligands in the synthesis of nanoheterostructures is discussed. It shows that the length of the alkyl chain of surface ligands can shift the equilibrium between the wurtzite and zinc blende polytypes of CdSe nanocrystals (NCs). In-situ wide-angle X-ray scattering measurements reveal that short-chain (e.g., propyl) phosphonic acids stabilize CdSe NCs with the zinc blende phase whereas octadecylphosphonic acid stabilize NCs with the wurtzite phase. It is also demonstrated how this effect can be used to improve the shape selectivity in the synthesis of anisotropic CdSe/CdS and ZnSe/CdS nanoheterostructures. Then we describe the effect of morphologies on the electronic and optical properties of NCs. The quantum-confined stark effect of CdSe/CdS nanoheterostructures embedded in polymer matrix is studied. Single-particle spectroscopy of CdSe/CdS nanoheterostructures is used to explore interfacial energy transfer in NCs. We further discuss inorganic ligands capped NCs and the enhanced electronic coupling in all-inorganic NCs arrays. Oxo-ligands is explored as a new group of inorganic ligands to functionalize NCs. The chemistry of ligand exchange is discussed in detail and the binding affinity of different inorganic ligands is compared. We also demonstrated the catalytic properties of POMs retain after capping on NCs.