Filling behavior of ZnO nanoparticles into opal template via electrophoretic deposition and the fabrication of inverse opal Discussion

Combining colloidal crystal template (artificial opal) and electrophoretic deposition (EPD) process, well-ordered ZnO inverse opal can be formed by finding the optimum driving potential of EPD. Through providing the various driving potentials from -25V, -10V, -5V to -2.5V, the different mechanism of electrophoretically depositing ZnO nanoparticles into the colloidal crystal template was determined by the SEM observation of the filled templates. Because the nano-channels of colloidal crystal template are the network type, the results of surface jam, incomplete filling and perfect filling are found under specific applied voltages. The high-quality ZnO inverse opal can be only fabricated under the perfect nano-channel-filling condition. The filling behavior can be monitored dynamically by tracing the current transients, and the Optimum conditions for filling the interstitial spaces of templates constructed from colloidal particles with 180 nm and 300 nm diameter can be obtained by applying a voltage of -5V and -15V, respectively. After the complete filling of ZnO nanoparticles into the colloidal crystal template consisting of 300 nm colloids, high-quality ZnO photonic crystal possessing an absorptive peak at the wavelength of 560 nm can be fabricated by removing the template. It is expected that the EPD can find extensive applications for preparing photonic crystals of various oxides only if their nanoparticles are available. (C) 2009 Elsevier Ltd. All rights reserved.