Electrodeposition of CdS quantum dots and their optoelectronic characterization by photoelectrochemical and scanning probe spectroscopies

CdS quantum dots (QDs) have been electrodeposited onto textured gold substrates from a nonaqueous electrolyte containing Cd(ClO4)2and elemental S. The initial deposit consisted of very small (about 3 nm) nanocrystals of CdS which were partially oriented with the Au substrate. With increasing deposit thickness, the crystal size increased and the degree of orientation decreased. Photocurrent spectroscopy and I-V spectroscopy, using a conducting scanning force microscope tip, were used to measure the CdS bandgap variations due to size quantization. The latter method also revealed room temperature conductivity peaks assigned to Coulomb charging of the QDs and evidence for charge tunneling into higher discrete energy levels.