Preparation And Characterization Of ABO₃ Perovskite Nanodots On A Substrate

The ABO₃ type materials have been used in memeries and photoelectric fields due to its excellent electrical properties such as piezoelectric,pyroelectric effect.With the development of modern science and nanotechnology,the needs for small devices are growing,and the preparation of ABO₃ nano-materiais with smaller size and high property can promote the development of the photoelectric field.ABO₃ nanodots on a substrate are considered to be a superior form in utilizing zero-dimensional effect.In this paper,lead titanate(PT),zirconium lead titanate(PZT) and barium titanate(BT) multicomponet nanodots were investigated.Size-and density controlled multicomponet nanodots were prepared successfully on different substrates through phase separation induced self-assembly which combines sol-gel and spin coating technology.PT nanodots were prepared on Si substrate by adjusting the densities of Pb ion concentration,PVP concentration, acetylacetone concentration and the heat treatment temperature.Tthe size of PT nanodots increased with decreasing PVP concentration and increasing Pb ion concentrations;Acetyl acetone concentration could affect the morphology of PT nanodots with triangular shape,square shape or nano-flower shape;Heat treatment temperature could affect the formation of PT phase,PT could be formed after 700℃treatment and the phase was determined by XRD and HRTEM.The size of PT nanodots was between 20nm to 100nm,and the density could be controlled in the range of 0.4×10¹⁰-3.7×10¹⁰ dots cm^-2.For PZT nanodots,there exited the same phenomenon that the size of PZT nanodots increased when the PVP concentration decreased and Ti concentration increased.The high ratio of Zr:Ti led to no appearance of nanodot structure because the high ratio increased the viscosity of the sol,which hintered the occurrence of the phase separation during spin-coating.Silicon(Si),quartz(SiO₂) and strontium titanate (SRO) substrates were used to prepared PZT nanodots,and the size and distribution of PZT nanodots could be more homogeneous on SiO₂ or SRO substrate.For BT nanodots,it was difficult to form BT nanodots on Si substrate because the sol had poor phase separation ability,and if the heat treatment temperature increased,only film was formed.An excellent room temperature field emission property of PT nanodots was observed.The minimum turn-on voltage was about 5.3 V/mm;while the emission current density reached about 270μAcm^-2 at an applied field of about 9.25 V/mm. The cathode-luminescence image recorded using a CCD camera of the fluorescence of a phosphor screen at daylight and the luminescence was very bright and homogeneous.The FN plots of PT nanodots showed good linearity within the measurement range suggesting that electron emission from the PbTiO₃ nanodots follows the FN behavior.The photoluminescence property was found in PT and PZT nanodots.The photoluminescence peak of PT nanodots had blue shift from 373nm(3.33eV) to 363nm(3.42eV) with different Pb ion content;the photoluminescence peak of PZT nanodots was at 350nm(3.54eV).The following two considerations are suggested for luminescence mechanisms of the nanodots.(1) The presence of amorphous PT will introduce localized tail states in which electrons or holes may be trapped.(2) It has been demonstrated both experimentally and theoretically that there exist two kinds of Ti coordination in amorphous PT,fivefold oxygen Ti coordination([TiO₅]square base pyramid) and sixfold oxygen Ti coordination([TiO₆]octahedron).The coexistence of[TiO₅]and[TiO₆]clusters will yield a charge imbalance that encourages the trapping of holes in previously mentioned localized states.