Mechanism of the Electrophoretic Deposition of CdSe Nanocrystal Films: Influence of the Nanocrystal Surface and Charge

Electrophoretic deposition (EPD) leads to equally thick films of distinct colloidal CdSe nanocrystals on the positive and negative electrodes due to the deposition of equal numbers of negatively and positively charged nanocrystals, even though their concentrations are not equal in solution. EPD stops when the lower concentration charged nanocrystals, here the negatively charged nanocrystals, are depleted. These and other mechanistic features of EPD are analyzed using electrophoretic mobility (ζ-potential) analysis, photoluminescence, inductively coupled plasma−atomic emission spectroscopy, thermogravimetric analysis, and related measurements, which also show that the surface charge of nanocrystals can be substantially altered by the presence of coordinating ligands. Several cycles of nanocrystal washing are needed so the nanocrystals are able to transfer charge and/or “stick” to the electrodes upon electrophoretic deposition.