[en] An aperiodic optical superlattice is designed. The designing method is universal and can be applied to all frequency conversion processes by using the coupling of quasiphase matching, without any limitations to special materials and to given fundamental wavelengths. Copyright 2001 American Institute of Physics

[en] We study nonlinear Cerenkov radiation generated from a nonlinear photonic crystal waveguide where the nonlinear susceptibility tensor is modulated by the ferroelectric domain. Nonlinear polarization driven by an incident light field may emit coherently harmonic waves at new frequencies along the direction of Cerenkov angles. Multiple radiation spots with different azimuth angles are simultaneously exhibited from such a hexagonally poled waveguide. A scattering involved nonlinear Cerenkov arc is also observed for the first time. Cerenkov radiation associated with quasi-phase matching leads to these novel nonlinear phenomena

[en] It is always expected that the conversion efficiency is as high as possible for nonlinear interactions at any pump intensity. We present a method of controlling the conversion efficiency of sum-frequency generation in the periodic optical superlattices with different duty cycles, which is based on the controllable linear gratings induced by electro-optic effect here. The calculated results verify that this method is feasible and very efficient in attaining the complete transfer between the pump and sum-frequency waves at any given pump intensity. In addition, we demonstrate the electric-optic control is better than temperature control

[en] Pb(Zr_0.52Ti_0.48)O₃ (PZT) nanocrystals and transparent polycarbonate (PC) composite thin films with useful properties for ferroelectric, piezoelectric and electro-optic devices were prepared by a spin-coating technique. Ultra-fine PZT (∝40-50 nm) nanocrystals with pure perovskite tetragonal phase were synthesized by a hydrothermal method. The structure and morphology of the composite thin films were studied by means of X-ray diffraction and scanning electron microscopy. To obtain the optimum electro-optic properties of poled composite films, the poling condition under an external electric field was optimized through the dielectric properties of PZT and PC polymer and effective field intensity theory. The electro-optic coefficient of the poled PZT/PC composite film is estimated to be 30.5 pm/V. The transparency spectra were measured and the optical band gaps of the unpoled, poled at 145 C and poled at 165 C composite thin films are estimated to be 4.26 eV, 4.21 eV and 4.18 eV, respectively. The measured dielectric constants of PZT/PC are in good agreement with the calculated values for the composite with a very small PZT volume fraction, based on the Onsager effective-field theory. This offers a reliable and indirect way to predict the dielectric constant of nanocrystals. (orig.)

[en] LaAlO₃ (LAO) gate dielectric films were deposited on Si substrates by low-pressure metalorganic chemical vapor deposition. The interfacial structure and composition distribution were investigated by high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), secondary-ion mass spectroscopy (SIMS), and Auger-electron spectroscopy (AES). HRTEM confirms that there exists an interfacial layer between LAO and Si in most samples. AES, SIMS, and XPS analyses indicate that the interfacial layer is compositionally graded La-Al silicate and the Al element is severely deficient close to the Si surface. Electrical properties of LAO films were evaluated. No evident difference in electrical properties between samples with and without native SiO₂ layers was observed. The electrical properties are discussed in terms of LAO growth mechanisms, in relation to the interfacial structure. (orig.)

[en] c-axis epitaxial and polycrystalline Sr₃Bi₄Ti₆O₂₁ (SBTi) thin films were fabricated on (001)SrTiO₃ (STO) single-crystal substrates and Pt/Ti₂/SiO₂/Si substrates respectively, by pulsed laser deposition (PLD). Structures of the films were systematically characterized by x-ray diffraction (XRD), including θ-2θ-scans, rocking curve scans and φ-scans, atomic force microscopy and transmission electron microscopy (TEM). The epitaxial orientation relation of the SBTi films on STO is established by selected-area electron diffraction and XRD φ-scans to be (001)SBTi || (001)STO, [11-bar 0]SBTi || [010]STO. Cross-sectional high-resolution TEM studies on the epitaxial SBTi film revealed that SBTi is a single-phase material. A special kind of irrational atomic shift along the [001] direction was observed and is discussed in detail. By using an evanescent microwave probe (EMP), the room-temperature dielectric constant of the epitaxial SBTi film was measured to be 211 ± 20. Excellent electrical properties of the polycrystalline SBTi films with Pt bottom and top electrodes were exhibited: the P_r and E_c values were 4.1 μC cm^-2 and 75 kV cm^-1 respectively, the nonvolatile polarizations decreased by less than 5% after 2.22 x 10⁹ switching cycles and the dielectric constant and loss tangent were 363 and 0.04 at 100 kHz