Photochemical growth of metal nanoparticles on domain patterned ferroelectric surfaces

摘要

In this work, the growth of metal nanoparticles on domain patterned ferroelectricPb(ZrxTi1-x)O3 and LiNbO3 by photochemical reaction is demonstrated. Thephotochemical properties and phenomena occurring on the surface of Pb(ZrxTi1-x)O3 andLiNbO3 under ultraviolet illumination are investigated. Ferroelectric materials possess areversible spontaneous polarisation that has an effect on photochemical reactivity of asurface. Since the spontaneous polarisation is reversible, a desired pattern can be drawnon a ferroelectric surface in the form of domains. A combination of domain patterningand domain specific surface reactions can lead to fabrication of complex nanostructures.It is found that on a PZT (30/70) thin film, under UV irradiation, metal depositionoccurred only on C+domains and no deposition occurred on C-domains. Hence, thechemical reactivity of ferroelectric surface was found to be dependent on the polarisationof domain that is underlying the surface. Annealing of PZT samples at high temperaturesalters the defect concentration of the PZT as shown by an increase in the deposition ofsilver on the surface. When the PZT samples were annealed in air at temperatures rangingfrom 530-690°C the silver deposition increased by more than 150% and the size ofdeposited silver clusters increased by four times. The photochemical properties of PZTthin films of different compositions PbZr0.3Ti0.7O3, PbZr0.52Ti0.48O3 and PbZr0.7Ti0.3O3were investigated by undertaking silver nanocluster deposition experiments. Thecomposition of PZT film (Zr/Ti ratio) affects silver deposition such that on PbZr0.3Ti0.7O3silver deposits only on C+domains, whereas PbZr0.52Ti0.48O3 and PbZr0.7Ti0.3O3experience deposition on both C+and C-domains. This difference in silver depositionpattern is shown to be due to the difference in width of the space charge region and bandiigap of the three samples. The impact of size of poled pattern on silver deposition at thesurface is shown. It is found that for smaller size of C+domains (smaller than 1 μm) theamount and size of deposited silver decreased with the decrease in domain size. On aPZT surface, formation of spherical, triangular and hexagonal nanoplates of gold viaphotoreduction has also been demonstrated.Silver cation reduction on C+and C-domains of ferroelectric lithium niobate (LN) byphotochemical and photoelectric process is demonstrated. The interaction of photoelectricand domain dependent influences can be observed in LiNbO3 due to the low electronaffinity (ca 1.1-1.5eV). The impact of composition of LN on the photoreduction of silverhas been shown. It is found that the photochemical reactivity of MgO-doped LN issignificantly higher as compared to non-doped LN. The energy and intensity of incidentphoton is also found to have an impact on the photoreduction of silver on LN surface. Inaddition to this, deposition of Al and Mn nanoparticles on LN surface by means ofphotoreduction reaction has been demonstrated. It is shown that for a metal tophotoreduce on C+domain of a ferroelectric material, the reduction potential of the metalhas to be within the band-gap of the material. It is shown that under atmosphericconditions, it is possible to selectively adsorb molecules of opposite charge on the surfaceof LN due to uncompensated polarisation charge.