Lateral patterning of CdTe nanocrystal films by the electric field directed layer-by-layer assembly method

The electric field directed layer-by-layer assembly (EFDLA) method is used to fabricate a pattern of two different types of CdTe nanocrystals on a structured indium-tin-oxide (ITO) substrate. Such a pattern can be used to fabricate pixel arrays of CdTe light-emitting devices that emit electroluminescence of different colors. The highly fluorescent CdTe nanocrystals are negatively charged and alternated by a polycation, poly(diallyldimethylammonium chloride) (PDDA), in the fabrication of multilayer PDDA/CdTe films on ITO and An surfaces by the EFDLA method. The depositions of the charged species on different electrodes are controlled by the polarity of an applied bias voltage. We define the deposition that becomes easier in the electric fields as favorable deposition and that becomes more difficult as unfavorable deposition. Experimental results obtained by quartz crystal microbalance reveal that a series of unfavorable depositions of CdTe and PDDA performed in an alternate way can at most result in one bilayer of PDDA/CdTe on the Au surface at 0.6 V, whereas favorable depositions show a net growth of deposited mass with the increased number of deposition cycles. Similar results can also be obtained by using ITO electrodes, but a relatively high voltage of 1.4 V is required to achieve a contrast of 99% between favorable and unfavorable depositions. The large contrast enables the fabrication of dual-color photoluminescence and electroluminescence patterns of PDDA/CdTe films by successively depositing two differently sized CdTe nanocrystals on different ITO electrodes on one common substrate by the EFDLA method.