Synthesis and characterization of a size series of extremely small thiol-stabilized CdSe nanocrystals

As an expansion to the wet chemical route for the preparation of quantum-si zed II-VI semiconductor materials, a series of thiol-capped crystalline CdS e nanoparticles has been synthesized in aqueous solution using mercapto-alc ohols (a-mercaptoethanol, 1-thioglycerol), and mercapto acids (thioglycolic acid, thiolactic acid) as stabilizers. The smaller (app. 1.4-2.2 nm diamet er) CdSe particles were obtained using thioalcohols as capping agents; the use of thioacids as stabilizers produced larger (2.1-3.2 nm diameter) CdSe particles. CdSe nanoparticles were separated from the crude solutions as re dissolvable powder samples with narrow size distributions using a size-sele ctive fractionation and have been characterized by UV-vis absorption and ph otoluminescence spectroscopy, X-ray diffraction, high-resolution transmissi on electron microscopy, and energy-dispersive X-ray analysis. A calculation of the HOMO-LUMO gap of CdSe particles as a function of their size has bee n done using an extended effective mass approximation.