Improvement of the ferroelectric properties of ABO(3) (A= Pb, Ca, Ba; B=Ti, Zr) films

High-quality ABO(3)/LaNiO3 (A = Ph, Ca, Ba; B = Ti, Zr) hetero structures have been grown on LaAlO3 (1 0 0) substrate by the chemical solution deposition method and crystallized by a microwave oven technique. The structural, morphological and electric properties were characterized by means of X-ray diffraction (XRD), atomic force microscope (AFM), and dielectric and ferroelectric measurements. XRD patterns revealed single-phase polycrystalline and oriented thin films whose feature depends on the composition of the films. The AFM surface morphologies showed a smooth and crack-free surface with the average grain size ranging from 116 to 300 nm for both LaNiO3 electrode and the ferroelectric films. Dielectric measurements on these samples revealed dielectric constants as high as 1800 at frequency of 100 KHz. Such results showed that the combination of the chemical solution method with the microwave process provides a promising technique to grow high-quality thin films with good dielectric and ferroelectric properties. (c) 2005 Elsevier Ltd. All rights reserved.

Piezoresponse force microscopy characterization of rare-earth doped BiFeO3 thin films grown by the soft chemical method

The multiferroic behavior with ion modification using rare-earth cations on crystal structures, along with the insulating properties of BiFeO3 (BFO) thin films was investigated using piezoresponse force microscopy. Rare-earth-substituted BFO films with chemical compositions of (Bi 1.00-xRExFe1.00O3 (x=0; 0.15), RE=La and Nd were fabricated on Pt (111)/Ti/SiO2/Si substrates using a chemical solution deposition technique. A crystalline phase of tetragonal BFO was obtained by heat treatment in ambient atmosphere at 500 °C for 2 h. Ion modification using La3+ and Nd3+ cations lowered the leakage current density of the BFO films at room temperature from approximately 10-6 down to 10-8 A/cm2. The observed improved magnetism of the Nd3+ substituted BFO thin films can be related to the plate-like morphology in a nanometer scale. We observed that various types of domain behavior such as 71° and 180° domain switching, and pinned domain formation occurred. The maximum magnetoelectric coefficient in the longitudinal direction was close to 12 V/cm Oe. © 2012 Elsevier Ltd and Techna Group S.r.l.

Synthesis and characterization of ZnO nanoflowers grown on AIN films by solution deposition

ZnO nanoflowers are synthesized on AIN films by solution method. The synthesized nanoflowers are composed of nanorods, which are pyramidal and grow from a central point, thus forming structures that are flower-shaped as a whole. The nanoflowers have two typical morphologies: plate-like and bush-like. The XRD spectrum corresponds to the side planes of the ZnO nanorods made up of the nanoflowers. The micro-Raman spectrum of the ZnO nanoflowers exhibits the E-2 (high) mode and the second order multiple-phonon mode. The photoluminescence spectrum of the ZnO nanoflowers exhibits ultraviolet emission centred at 375 nm and a broad green emission centred at 526 nm.

Chemical etching of a GaSb crystal incorporated with Mn grown by the Bridgman method under microgravity conditions

A GaSb crystal incorporated with Mn has been grown by the Bridgman method on the Polizon facility onboard the FOTON-M3 spacecraft. Structural defects and growth striations have been successfully revealed by the chemical etching method. By calculating various parameters of the convection, the striation patterns can be explained, and the critical value of the Taylor number, which characterizes the convective condition of the rotating magnetic field induced azimuthal flow, was shown. The stresses generated during crystal growth can be reflected by the observations of etch pit distribution and other structural defects. Suggestions for improving the space experiment to improve the quality of the crystal are given.

Preparation of polymer/silica nanoscale hybrids through sol-gel method involving emulsion polymers (PMMA/SiO2)

The different poly (methyl methacrylate) (PMMA) /SiO2 hybrids were prepared through sol-gel method involving PMMA emulsion (emulsion method) and PMMA/THF solution (solution method). The samples were characterized by differential scanning calorimetry(DSC), thermogravimetry analysis(TGA), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results showed that PMMA/SiO2 composites in nanoscale were prepared by emulsion method, and its size of phase heterogeneity was less than that of solution method. Meanwhile, the polymer emulsion as the reactive medium was more suitable for the formation of SiO2 network.

Investigation on the corrosion inhibitive effect of 2H-pyrazole-triazole derivatives in acidic solution

Four research methods, such as weight loss test, electrochemical techniques, adsorption isotherm, and quantum chemical calculation, were employed in this paper to study the inhibition efficiency (IE) and inhibition mechanism of three 2H-pyrazole-triazole derivatives, BHOT, FHOT, and CHOT in 1 M HCl solution for mild steel. Using the electrochemical technique, three inhibitors were proved to show a mixed-type character for mild steel by suppressing both anodic and cathodic reactions on the steel surface. The adsorption models of three compounds were established at different temperatures according to their adsorption isotherms. The results of the quantum chemical calculation method indicated that the adsorption sites of 2H-pyrazole-triazole derivatives were strongly centralized on benzene ring, triazole ring, or other substituents. All the results showed that the three derivatives were excellent inhibitors in I M HCl solution for mild steel.

Chemical deposition of La0.7Ca0.3MnO3±δ films on ceramic substrates

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

LaNiO3 nanotubes produced using a template-assisted method

We have studied the experimental conditions needed to produce LaNiO3 (LNO) nanostructures using a template-assisted method. In this route, a mesoporous anodic aluminum oxide template was filled with a chemical solution that had been prepared with polymeric precursors route. The precursor solutions and synthesized samples were characterized by X-ray diffraction (XRD), thermogravimetric analysis, infrared spectroscopy and high-resolution scanning electron microscopy (HRSEM). The XRD results for the samples that were heat-treated at 700 degrees C revealed that these samples crystallize in a perovskite-like LaNiO3 structure. HRSEM images revealed that the samples prepared with different deposition times (0.5, 1 and 2 h) promoted the formation of LaNiO3 nanotubes with different wall thicknesses.

Semi-analytic method of contact modelling

An algorithm to improve the accuracy and stability of rigid-body contact force calculation is presented. The algorithm uses a combination of analytic solutions and numerical methods to solve a spring-damper differential equation typical of a contact model. The solution method employs the recently proposed patch method, which especially suits the spring-damper differential equations. The resulting semi-analytic solution reduces the stiffness of the differential equations, while performing faster than conventional alternatives.

An FETI-preconditioned conjuerate gradient method for large-scale stochastic finite element problems

In the spectral stochastic finite element method for analyzing an uncertain system. the uncertainty is represented by a set of random variables, and a quantity of Interest such as the system response is considered as a function of these random variables Consequently, the underlying Galerkin projection yields a block system of deterministic equations where the blocks are sparse but coupled. The solution of this algebraic system of equations becomes rapidly challenging when the size of the physical system and/or the level of uncertainty is increased This paper addresses this challenge by presenting a preconditioned conjugate gradient method for such block systems where the preconditioning step is based on the dual-primal finite element tearing and interconnecting method equipped with a Krylov subspace reusage technique for accelerating the iterative solution of systems with multiple and repeated right-hand sides. Preliminary performance results on a Linux Cluster suggest that the proposed Solution method is numerically scalable and demonstrate its potential for making the uncertainty quantification Of realistic systems tractable.

Transport studies on La0.8-xPr0.2SrxMnO3 manganite films

In this communication, we report the results of the studies on structural, microstructural, transport and magnetotransport behavior of L0.8-xPr0.2SrxMnO3 (LPSMO) (x=0.1, 0.2 and 0.3) manganite films grown on (100) single crystalline SrTiO3 (STO) substrate using low cost chemical solution deposition (CSD) method. Films with similar compositions were also grown using sophisticated pulsed laser deposition (PLD) technique and results of structural and transport studies obtained for CSD grown films were compared with PLD grown films. Structural studies show that all the CSD and PLD grown films possess single crystalline nature with compressive and tensile strain, respectively. Surface morphology, studied using atomic force microscope (AFM), reveals the island like grain morphology in CSD grown films while PLD grown films possess smooth film surfaces. Carrier density dependent transport properties of the films have been discussed in the context of zener double exchange (ZDE) mechanism. Lower resistivity and higher transition temperature (T-p) observed in CSD grown films as compared to PLD grown films have been discussed in the light of structural strain and surface morphology of the films. Various models and mechanisms have been employed to understand the charge transport in CSD and PLD grown films. Also, observation of low temperature resistivity minima behavior in all the CSD and PLD grown LPSMO films has been explained in the context of electron-electron scattering mechanism. (C) 2015 Elsevier B.V. All rights reserved.

静动结合的化学腐蚀法制备近场光学探针的理论分析

理论上分析了静动结合的化学腐蚀法制备探针的具体机理及过程。在静态腐蚀的过程中, 利用流体力学Young-Laplace方程的一级近似解获得了光纤插入到HF酸中形成的新月形高度。在动态腐蚀过程中, 详细分析了当静态腐蚀时间和动态腐蚀时间分别取不同值时, 光纤移动速度对光纤探针结构的影响。利用此法可制备出尖端锐利、大锥角或多锥体等各种结构的光纤探针。这为实验上制备出性能优良的探针, 为拓宽扫描近场光学显微镜的应用范围奠定基础。将上述理论分析的结果与本文实验中所得初步结果进行了比较, 所得结果一致。

Effect of incorporating nonlanthanoidal indium on optical properties of ferroelectric Bi4Ti3O12 thin films

Bi4Ti3O12 (BTO) and Bi3.25In0.75Ti3O12 (BTO:In) thin films were prepared on fused quartz and LaNiO3/Si (LNO) substrates by chemical solution deposition (CSD). Their microstructures, ferroelectric and optical properties were investigated by X-ray diffraction, scanning electron microscope, ferroelectric tester and UV-visible-NIR spectrophotometer, respectively. The optical band-gaps of the films were found to be 3.64 and 3.45 eV for the BTO and BTO:In films, respectively. Optical constants (refractive indexes and extinction coefficients) were determined from the optical transmittance spectra using the envelope method. Following the single electronic oscillator model, the single oscillator energy E-0, the dispersion energy E-d, the average interband oscillator wavelength lambda(0), the average oscillator strength S-0, the refractive index dispersion parameter (E-0/S-0), the chemical bonding quantity beta, and the long wavelength refractive index n(infinity) were obtained and analyzed. Both the refractive index and extinction coefficient of the BTO:In films are smaller than those of the BTO films. Furthermore, the refractive index dispersion parameter (E-0/S-0) increases and the chemical bonding quantity beta decreases in the BTO and BTO:In films compared with those of bulk. (C) 2007 Published by Elsevier B.V.

High-mobility Ga-polarity GaN achieved by NH3-MBE

GaN epilayers were grown on (0001) sapphire substrates by NH3-MBE and RF-MBE (radio frequency plasma). The polarities of the epilayers were investigated by in-situ RHEED, chemical solution etching and AFM surface examination. By using a RF-MBE grown GaN layer as template to deposit GaN epilayer by NH3-MBE method, we found that not only Ga-polarity GaN films were repeatedly obtained, but also the electron mobility of these Ga-polarity films was significantly improved with a best value of 290 cm(2)/V.s at room temperature. Experimental results show it is an easy and stable way for growth of high quality Ga-polarity GaN films.

Large-area silver-coated silicon nanowire arrays for molecular sensing using surface-enhanced Raman spectroscopy

A new and facile method to prepare large-area silver-coated silicon nanowire arrays for surface-enhanced Raman spectroscopy (SERS)-based sensing is introduced. High-quality silicon nanowire arrays are prepared by a chemical etching method and used as a template for the generation of SERS-active silver-coated silicon nanowire arrays. The morphologies of the silicon nanowire arrays and the type of silver-plating solution are two key factors determining the magnitude of SERS signal enhancement and the sensitivity of detection; they are investigated in detail for the purpose of optimization.