C.J. Lu

The effect of grain size on domain structure in unsupported thin films

The effect of grain size on domain structure in unsupported thin films with grains (70 - 250 nm) was studied by using TEM. It is found that there probably exists a critical grain size near 200 nm, at which an abrupt change in domain structure occurs. Above this size, domains, which are lamellar microtwins, appear in almost all of the coarse grains. The domain width decreases with grain size. Below this size, however, most of the grains are single-domain ones, while some irregular and curved domain walls appear only in a small portion of the fine grains. The number of the single-domain grains increases with decreasing grain size. Such a grain-size dependence of domain structure is correlated with the anomalous behaviours of the coercive field and dielectric constant in ferroelectric thin films. This interesting result has not been reported before.

The oriented growth of thin films deposited by a sol - gel process on substrates without lattice match

thin films were deposited by a sol - gel process onto various substrates without lattice match and their preferred orientations were investigated. Preferentially a axis-oriented films were obtained on Si(111) and quartz glass. The films on r-sapphire exhibited a highly preferred orientation along both the (101) and the (110) axes. Both a and c axis-oriented thin films were prepared on (111) Pt-coated Si substrates. It is demonstrated that the films fired at lower temperatures are difficult to align with the substrates. The degree of grain orientation of thicker films is lower than that of thin films. The origin of the orientations found in our thin films is discussed. However, the mechanism by which nuclei of the orientations form at the film/substrate interface is not yet known.

Grain size effect on the phase transitions in oriented PbTiO3 thin films deposited by the sol-gel method on (111) Pt/Si

Abstract Oriented PbTiO 3 thin films with different average grain sizes were prepared by the sol-gel method on (111) Pt Si substrates. The phase transitions in the films were investigated by using high-temperature XRD measurements. It was found that the phase transition from tetragonal to cubic in the film of grain size ~ 210 nm occurs at about 480 °C, whereas it occurs at around 460 °C in the film of grain size ~ 130 nm. The transition is reversible but with about 20 °C hysteresis between cooling and heating. The Curie temperatures T c measured for both films are lower than that of the bulk. The T c decreases with grain size. Although an abrupt 90 °-domain absence occurs between the two films, no major change in the T c was observed. In addition, it was observed that the change in the c -parameter with temperature is almost the same in both heating and cooling cycles whereas the a -value exhibits hysteresis. This results just the reverse of those reported previously.

X-ray diffraction study on the grain-size-dependences of orientation and 90 °-domain structure in oriented PbTiO3 thin films on (111) Pt

Abstract Both (100) and (001) oriented PbTiO 3 thin films were prepared on (111) Pt substrates using a sol-gel process. It is indicated that very-fine-grained ( 3 . As the average grain size decreases to 130 nm with annealing temperature, the intensity of the peak (100) increases drastically while that of (001) decreases rapidly. The sudden changes in the relative intensities of the two peaks suggest that at grain size below a critical size between 130 and 210 nm most of the grains in the films no longer show 90 °-domains, which is in good agreement with our TEM investigations for randomly oriented PbTiO 3 thin films. These interesting results have not been previously reported.

The growth and phase transitions of epitaxial Pb(Zr0.95Ti0.05)O3 thin films prepared by sputter deposition combined with post-annealing on SrTiO3(1 0 0)

Epitaxial Pb(Zr0.95Ti0.05)O-3 thin films of an orthorhombic perovskite structure have been grown on SrTiO3(100) substrates using radio-frequency sputter deposition from a stoichiometric ceramic target. The films were deposited without substrate heating and then annealed at 700 degrees C in a conventional furnace. The single-crystal nature of the films was confirmed by the cross-section scanning electron microscopy, X-ray diffraction (XRD) including theta-2 theta scan and phi-scan, as well as reflection high energy electron diffraction. The films are a mixture of a- and c-domains. The experiments of high-temperature XRD indicated that the Curie point of the films is close to that for the stoichiometric ceramic target. On heating, however, the orthorhombic-rhombohedral phase transition in the epitaxial films occurred at about 190 degrees C, far higher than the corresponding transition temperature (51.6 degrees C) for its bulk counterpart

Transmission electron microscopy study of 180° domain structure in PbZrO3

Abstracts are not published in this journal