G.K.H. Pang

ZnO-based film bulk acoustic resonator for high sensitivity biosensor applications

Zinc oxide (ZnO)-based film bulk acoustic resonator consisting of a piezoelectric element (Au∕ZnO∕Pt) and a Bragg reflector (ZnO∕Pt multilayer structure) has been fabricated by magnetron sputtering. The transmission electron microscopy and x-ray diffraction measurements revealed that all thin film layers in the device were well crystallized and highly textured. By electrical measurements, it was found that the device had a high resonant frequency (3.94GHz) and mass sensitivity (8970Hzcm2∕ng). The use of the device as a biosensor was demonstrated by comparing the resonant properties of the device with/without coatings of biospecies.

Room temperature synthesis of rutile nanorods and their applications on cloth

In order to achieve better photocatalytic performance, rutile nanorods dispersed in anatase and brookite phases were synthesized from titanium isopropoxide (TIP) in a concentrated HNO3 solution at room temperature (23 °C). X-ray diffraction results indicated that the percentage of rutile increased with increasing peptization time. Scanning electron microscopy and and high-resolution transmission electron microscopy measurements revealed that the nanosized titania particles mainly consisted of granular anatase and brookite, and rod-like rutile. It was interesting that the stability of the colloid increased with increasing nanoparticle concentration, and the tricrystalline titania showed a photocatalytic activity higher than that of pure anatase. These nanocrystals were applied onto cotton fabrics, and achieved a promising bactericidal photocatalytic activity and excellent protection against UV radiation.

Topographic and phase-contrast imaging in atomic force microscopy

Phase-contrast imaging in the tapping mode atomic force microscopy (AFM) is a powerful method in surface characterization. This method can provide fine details about rough surfaces, which are normally obscured in topographic imaging. To illustrate some of the capabilities of phase-contrast imaging, AFM studies of Pt/Ti/SiO2/Si and Pb(Zr0.52Ti0.48)O3 (PZT) films were carried out. Phase-contrast imaging revealed fine details of their microstructures, including grain boundaries, triple junctions and twinning, which could not be detected by topographic imaging. The studies showed that phase-contrast imaging is capable of providing superior information about surface characteristics when compared to the standard topographic imaging.

Synthesis of wurtzite ZnSe nanorings by thermal evaporation

In this study, free standing crystalline ZnSe nanorings and nanowires have been fabricated on Au coated Si substrates by simple thermal evaporation of ZnSe powders. Ring- or wirelike morphology can be achieved in a controllable manner by using different reactor pressures during growth, while all the other conditions remain the same. Our results show that the ZnSe nanorings are wurtzite phase instead of the zinc-blende phase, observed in typical one-dimensional ZnSe nanostructures. The growth mechanism of the nanorings has been discussed, and the cathodoluminescence of the nanorings has been described.

Effect of lattice-misfit strain on the process-induced imprint behavior in epitaxial Pb(Zr0.52Ti0.48)O3 thin films

The effect of lattice-misfit strain on the process-induced imprint behavior in Pb(Zr0.52Ti0.48)O3 (PZT) capacitors with Pt (top), and SrRuO3, La0.7Sr0.3MnO3 or LaNiO3 (bottom) electrodes has been studied. With the different oxide electrodes and by changing the deposition oxygen pressure, various lattice-misfit strains in the epitaxial PZT films have been produced. It was found that after in situ annealing at reduced oxygen pressures, the capacitors showed an increased voltage offset in the polarization-electric field hysteresis loops with increasing the misfit strain, irrelevant to the oxide electrodes employed, while lattice disorder at the bottom interface can effectively eliminate the voltage shift. Our results suggest that the imprint behavior is caused by oxygen loss via dislocations generated by the misfit strain relaxation at the growth temperature.

Microstructure and enhanced in-plane ferroelectricity of Ba0.7Sr0.3TiO3 thin films grown on MgAl2O4 (001) single-crystal substrate

The microstructure and in-plane dielectric and ferroelectric properties of highly oriented Ba0.7Sr0.3TiO3 (BST) thin film grown on MgAl2O4 (001) single-crystal substrate through pulsed laser deposition were investigated. X-ray diffraction measurements indicated that BST had a distorted lattice with a tetragonality a∕c=1.012. The cross-sectional observation under transmission electron microscope revealed that, while most of BST grains grew epitaxially on MgAl2O4, the film also contained a noticeable amount of misoriented grains and dislocations. The electrical measurements indicated that the film had a shifted Curie temperature (TC=78°C) and an enhanced in-plane ferroelectricity (remnant polarization Pr=7.1μC∕cm2) when compared with BST ceramic (TC≈33°C and Pr≈0).

Epitaxial and highly electrical conductive La0.5Sr0.5TiO3 films grown by pulsed laser deposition in vacuum

The target material with nominal composition of La0.5Sr0.5TiO3 sintered in air is an insulator and not a single-phase compound. By pulsed laser ablation in vacuum at the multiphase La–Sr–Ti–O target, however, highly electrical conductive and epitaxial La0.5Sr0.5TiO3 films have been fabricated on LaAlO3(001) substrates. Structural characterization using three-axis x-ray diffraction (θ–2θ scan, ω-scan rocking curve, and φ scan) reveals that the films have a pseudocubic structure and grow on the substrates with a parallel epitaxial relationship. Atomic force microscopy images show the films have quite smooth surface, for a film 200 nm thick, the roughness Ra is about 0.31 nm over the 1 μm×1 μm area. Resistivity versus temperature measurements indicate that the films are metallic at 2–300 K and have resistivity of 64 μΩ cm at 300 K, which is about one order lower than that of the single-phase La0.5Sr0.5TiO3 bulk materials. After the same deposition procedure, epitaxial La0.5Sr0.5TiO3 films have also been grow...

Mn and Sm doped lead titanate ceramic fibers and fiber/epoxy 13 composites

Manganese and samarium doped lead titanate [Pb0.85Sm0.10(Ti0.98Mn0.02)O3, PSmT] fibers were prepared by sol-gel method. The micrographs obtained using scanning electron microscope show that PSmT ceramic fibers are round and dense. The diameter of the fibers was in the range of 30–35 μm. The crystalline grains size is ∼2.5 μm. The micrographs obtained using transmission electron microscope also unveiled the layer-by-layer 90° domains in the grains. X-ray diffraction patterns of the fibers show that PSmT ceramics have a pure perovskite structure. The c/a ratio of the unit cell was 1.04. The PSmT fiber/epoxy 1-3 composites were fabricated by filling the ceramic fiber bundle with epoxy. The dielectric permittivity e, electromechanical coefficient kt, and the piezoelectric constant d33 of PSmT fiber/epoxy 1-3 composites with 68% fiber loading were 118, 0.51, and 48 pC/N, respectively. The hysteresis loop of the composites was measured by the Sawyer–Tower method. It was also found that the composites could with...

Characterization of butterfly single crystals of by atomic force, optical and scanning electron microscopy techniques

A comparative study of ferroelectric domain configurations and surface morphology of butterfly single crystals of by the techniques of atomic force microscopy, optical microscopy and scanning electron microscopy is described. An unusual array of defects on the surface of a highly stressed region of the crystal was investigated in detail. Surface microstructural features displaying complex and distinct morphology associated with barium-rich phases were also studied.

Correlation between domain evolution and asymmetric switching in epitaxial Pb(Zr0.52Ti0.48)O3 thin films

The process-induced domain evolution and asymmetric switching in epitaxial Pb(Zr0.52Ti0.48)O3 (PZT) thin films have been studied by reciprocal space mapping, transmission electron microscopy, high-temperature x-ray diffraction, and the polarization-electric field hysteresis loop measurements. After annealing at reduced oxygen pressures, it was evidenced that an oxygen loss at the PZT bottom interface can occur at temperatures well below the Curie temperature TC, and more importantly, the oxygen loss can induce a large positive voltage offset and drive simultaneously the polydomain formation in the PZT films. Our results indicate that the structure evolution is correlated with the coercive voltage shift, and an oxygen-loss-related internal stress at the interface would be responsible for the large internal electric field in epitaxial PZT films.