Fundamental studies of the adsorption of cadmium selenide quantum dots to surfactant-functionalized titania films

Our research group studies the adsorption of semiconductor quantum dots to self-assembled monolayers on metal oxide films and the interfacial electron transfer reactivity of these materials. This thesis will focus on understanding how the properties of the monolayer-functionalized titanium oxide (TiO 2) film and the cadmium selenide (CdSe) quantum dots themselves affect the saturation surface coverages of these quantum dots. We performed equilibrium binding experiments to characterize the adsorption of mercaptoalkanoic acids (MAAs) onto nanocrystalline TiO2 films and CdSe onto these functionalized films. As the chain length of the MAAs increased, the maximum surface coverage of MAAs on TiO2 remained constant at 10-8 mol/cm 2, and the surface adduct formation constant remained constant at around 104 M-1. However, the surface coverages of TOPO-capped CdSe on MAA-functionalized TiO2 films, varied with the MAA chain length. The longer chained MAAs showed a surface coverage of 10-6 mol/cm2 while those of chain lengths of 8 carbons or less showed a surface coverage an order of magnitude lower. We believe that the structure of the CdSe capping agent might play a role in this trend where the alkyl chain length of MAA must be equal to or greater than the capping agent for significant coverage of the CdSe. Further experiments using other capping agents such as amines bore out this affinity of quantum dots for surfactant-functionalized TiO2 films.