http://hdl.handle.net/10397/2469 Search the Channel search http://repository.lib.polyu.edu.hk/jspui/simple-search http://hdl.handle.net/10397/4996 Title: Spectroellipsometric study of sol–gel derived potassium sodium strontium barium niobate films<br/><br/>Authors: Mak, Chee-leung; Lai, Brian; Wong, Kin-hung; Choy, Chung-loong; Mo, D.; Zhang, Y. L.<br/><br/>Abstract: Spectroscopic ellipsometry (SE) was used to characterize the sol–gel derived(K₀.₅Na₀.₅)₀.₄(Sr₀.₆Ba₀.₄)₀.₈Nb₂O₆(KNSBN) thin films as a function of sol concentration. In the analysis of the measured SE spectra, a modified double-layer Forouhi–Bloomer model was adopted to represent the optical properties of the KNSBN films. In this model, the films were assumed to consist of two layers—a bottom bulk KNSBN layer and a surface layer that composed of bulk KNSBN as well as void. Good agreement was obtained between the measured spectra and the model calculations in the chosen spectral region. Effective medium approximation theory was used to evaluate the effective refractive index for the surface layer. The results of SE have been correlated with atomic force microscopy measurements of surface roughness. Our analyses have shown that the surface layer had a lower refractive index than the bottom one. In addition, the refractive index and the surface roughness of the KNSBN films increase with the sol concentration.<br/><br/>Description: DOI: 10.1063/1.1355283 http://hdl.handle.net/10397/4987 Title: Modeling of anomalous shift and asymmetric hysteresis behavior of ferroelectric thin films<br/><br/>Authors: Wong, Chung-kwan; Shin, Franklin G.<br/><br/>Abstract: An analytical bilayer model has been developed to consider the effect of the existence of a dead layer (e.g., due to polarization degradation) at the film-electrode interface in an otherwisehomogeneous ferroelectric thin film. By introducing asymmetric conductivity in the dead layer, the anomalous horizontal (along the field axis) shift behavior of hysteresis loops in ferroelectric thin films is successfully reproduced. Assuming that the ferroelectric P-E hysteresis loops of the layers are parallelogramlike, explicit expressions are derived for calculating the internal fields in the film, as well as the “apparent” D-E loop as measured from a Sawyer-Tower circuit. The general switchingsequence for the ferroelectric phases will be considered. Using the ferroelectric-ferroelectric bilayer model, other anomalous phenomena, including vertical shift and deformed loop shape are also modeled.<br/><br/>Description: DOI: 10.1063/1.1810634 http://hdl.handle.net/10397/4985 Title: Measurement of mechanical properties for dense and porous polymer films having a low dielectric constant<br/><br/>Authors: Xu, Yuhuan; Tsai, Yipin; Zheng, D. W.; Tu, K. N.; Ong, C. W.; Choy, Chung-loong; Zhao, Bin; Liu, Q.-Z.; Brongo, Maureen<br/><br/>Abstract: We measured the mechanical properties of dense and porous polymeric films, the modified polyarylethers, which have a low dielectric constant varying from 2.7 to 1.8, by combining three different methods; membrane bulge test, nanoindentation, and single-substrate bending beam method. The elastic modulus and initial stress measured from these three methods are in goodagreement. The substrate effect was observed in the measurements by nanoindentation. Dataobtained by nanoindentation show a significant dependence on the film thickness and the displacement depth of the indenter. However, the hardness of the low dielectric constant thin film does not depend on thickness and only slightly depends on the indentation depth. A tentative analysis is proposed to explain the results.<br/><br/>Description: DOI: 10.1063/1.1287756 http://hdl.handle.net/10397/4979 Title: Epitaxial and highly electrical conductive La₀.₅Sr₀.₅TiO₃films grown by pulsed laser deposition in vacuum<br/><br/>Authors: Wu, Wenbin; Lu, Fei; Wong, Kin-hung; Pang, Geoffrey Kin-hung; Choy, Chung-loong; Zhang, Y. H.<br/><br/>Abstract: The target material with nominal composition of La₀.₅Sr₀.₅TiO₃sintered 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 La₀.₅Sr₀.₅TiO₃films have been fabricated onLaAlO₃(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 onthe 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 R[sub a] is about 0.31 nm over the 1 μmX1 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 La₀.₅Sr₀.₅TiO₃bulk materials. After the same deposition procedure, epitaxial La₀.₅Sr₀.₅TiO₃films have also been grown on TiN buffered (001) Si substrates.<br/><br/>Description: DOI: 10.1063/1.373724