Layer-by-layer depositions of polyelectrolyte/CdTe nanocrystal films controlled by electric fields

Electric fields are used to control the layer-by-layer deposition of positively charged poly(diallyldimethylammonium chloride) (PDDA) and negatively charged CdTe nanocrystals on Au substrates following the method of 'Electric Field Directed Layer-by-layer Assembly' (EFDLA) described in reference 7. Experimental results demonstrate that the depositions of PDDA and CdTe can be facilitated by maintaining the polarity of the electrode opposite to the sign of the charge of the deposited material (favorable deposition). In contrast, the deposition can also be prohibited when the polarity of the electrode is always the same as the sign of the charge of the deposited material (unfavorable deposition). Quartz crystal microbalance (QCM) results reveal that the prohibition of deposition on Au electrodes is realized by effectively blocking the adsorption of PDDA and desorbing in the meantime the previously adsorbed CdTe during the unfavorable deposition of PDDA. As a result, at most one bilayer of PDDA/CdTe can be deposited on the Au surface under unfavorable deposition at a voltage of 0.6 V. As for the favorably deposited PDDA/CdTe multilayer films, no obvious electrochemical degradation is observed with respect to CdTe nanocrystals in the film that is obtained by a series of favorable depositions of PDDA and CdTe performed alternately under 0.6 V. Atomic force microscopic measurements reveal that a six-bilayer PDDA/CdTe film obtained by favorable deposition has a relatively smooth surface with a surface roughness of 1.9 nm.