Photoluminescent behavior of SrZrO3/SrTiO3 multilayer thin films

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Structure and ferro/piezoelectric properties of SrBi(4)Ti(4)O(15) films deposited on TiO(2) buffer layer

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

Effect of niobium dopant on fatigue characteristics of BiFeO3 thin films grown on Pt electrodes

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Retention Characteristics of CBTi144 Thin Films Explained by Means of X-Ray Photoemission Spectroscopy

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

Multi-functional properties of CaCu3Ti4O12 thin films

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

Visible emission from Er-doped SnO2 thin films deposited by sol-gel

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

Epitaxially grown LiNbO3 thin films by polymeric precursor method

LiNbO3 thin films were grown on (0001) sapphire substrates by a chemical route, using the polymeric precursor method. The overall process consists of preparing a coating solution from the Pechini process, based on metallic citrate polymerization, the precursor films, deposited by dip coating, are then heat treated to eliminate the organic material and to synthesize the phase. In this work, we studied the influence of the heat treatment on the structural and optical properties of single-layered films. Two routes were also investigated to increase the film thickness: increasing the viscosity of the coating solution and/or increasing the number of successively deposited layers. The x-ray diffraction theta -2 theta scans revealed the c-axis orientation of the single- and multilayered films and showed that efficient crystallization can be obtained at temperatures as low as 400 degreesC, the phi-scan diffraction evidenced the epitaxial growth with two in-plane variants, A microstructural study revealed that the films were crack free, homogeneous, and relatively dense. Finally, the investigation of the optical properties (optical transmittance and refractive index) confirmed the good quality of the films. These results indicate that the polymeric precursor method is a promising process to develop lithium niobate waveguides.

Ferroelectric phase transition in Pb0.60Sr0.40TiO3 thin films

Polycrystalline Pb-0.Sr-60(0).40TiO3 thin films with the tetragonal perovskite structure were grown on platinum-coated silicon substrates by a chemical method. Raman results reveal that A1 (1 TO) symmetry modes, also known as soft modes, persist above the phase transition 14 temperature. This is due to the high structural distortion caused by the substitution effect of Sr2+ for Pb2+ ions. In contrast, the E(1TO) symmetry mode vanishes at 498 K, characterizing the ferroelectric-paraelectric transition phase. However, the Raman spectra, as a function of temperature, reveal that the ferroelectric-paraelectric phase transition may be correlated with a diffuse phase transition. The experimental data obtained from measurements of the dielectric constant as a function of temperature and frequencies showed a classical behavior of ferroelectric phase transition in Pb-0.Sr-60(0).40TiO3 thin films, rather than a relaxor ferroelectric phase transition. (C) 2004 Elsevier B.V. All rights reserved.

Nanocrystalline anatase thin films prepared from redispersible sol-gel powders

Transparent thin films of nanocrystalline anatase were obtained by dip-coating process using an ethanolic suspension of redispersed nanoparticles. This suspension was prepared by sol-gel route and their redispersability achieved by surface grafting of para-toluene-sulfonic acid and acetylacetone. The effects of the acetylacetone content on the powder redispersibility and on the structural evolution of films were determined by small angle X-ray scattering, X-ray reflectometry and X-ray diffraction for different firing temperatures. The results demonstrated that the porous structure of the studied films consist of agglomerates of primary particles with two levels of porosity. The control of the amount of capping ligand allows for a fine-tuning of the average pore size of the dried films. Upon increasing the firing temperature up to 500 degrees C, progressive increase in apparent density, average pore size of films and average crystallite size of powders were observed. (c) 2005 Elsevier Ltd. All rights reserved.

Photoluminescence at room temperature in amorphous SrTiO3 thin films obtained by chemical solution deposition

Intense photoluminescence in highly disordered strontium titanate amorphous thin films prepared by the polymeric precursor method was observed at room temperature (300 K). The luminescence spectra of SrTiO3 amorphous thin films at room temperature revealed an intense single-emission band in the visible region. X-ray absorption near edge structure was used to probe the local atomic structure of SrTiO3 amorphous and crystalline thin films. Photoluminescence intensity in the 535 nm range was found to be correlated with the presence of non-bridging oxygen defects. A discussion is presented of the nature of this photoluminescence, which may be related to the disordered structure in SrTiO3 amorphous thin films. (C) 2002 Elsevier B.V. B.V. All rights reserved.

SrBi2Nb2O9 thin films crystallized using a low power microwave oven

SrBi2Nb2O9 thin films were produced by the polymeric precursor method using an aqueous solution. The crystallization of the films was carried out using a domestic microwave oven by means of a SiC susceptor in order to absorb the microwave energy and rapidly transfer the heat to the film. Low microwave power and short time have been used. The films obtained are well-adhered, homogeneous and with good specularity, even when treated at 600 degreesC for 10 min. The microstructure and the structure of the films can be tuned by adjusting the crystallization conditions. Depending on the direction of the heat flux it is possible to obtain preferential oriented or polycrystalline films in the microwave oven for 10 min. The microstructure presented a polycrystalline nature with spheroid small mean grain size when the susceptor is placed above the substrate. When the susceptor is placed below the substrate, the films presented platelet grains with mean grain size around 250 nm and a 001 orientation. For comparison, films were also prepared by the conventional method at 700 degreesC for 2 h. (C) 2003 Elsevier Ltd. All rights reserved.

Soft chemical deposition of BiFeO3 multiferroic thin films

BiFeO3 thin films free of secondary phases were obtained by the soft chemical solution on Pt(111)/Ti/SiO2/Si substrates after annealing at 500 degrees C for 2 h. The film grown in the (100) direction presented a remanent polarization P-r of 31 mu C/cm(2) at room temperature. Electrical measurements using both quasistatic hysteresis and pulsed polarization confirm the existence of ferroelectricity with a switched polarization of 60-70 mu C/cm(2), Delta P=(P-*-P). Low leakage conduction and an out-of-plane piezoelectric (d(3)) coefficient of 40 pm/V were obtained by the improvement of preparation technology.

Nature of defects for bismuth layered thin films grown on Pt electrodes

The authors investigated the influence of defects on the piezoelectric and dielectric properties of Bi4Ti3O12 (BIT), SrBi4Ti4O15 (SBTi) and CaBi4Ti4O15 (CBTi144) thin films by x-ray photoemission spectroscopy measurements. In the SBTi film, Sr which is a nonpolarizable ion restricting the movement of Ti4+ ions and thus leads to a low piezoresponse. Meanwhile, the oxygen environment is quite different in the BIT and CBTi144 films exhibiting excellent piezoelectric properties. The piezoelectric coefficient and the dielectric behavior were larger for a-b axis oriented than for c axis-oriented films due to the defects created during the films crystallization. (c) 2007 American Institute of Physics.

Epitaxial growth of LiNbO3 thin films in a microwave oven

Oriented LiNbO3 thin films were prepared using a polymeric precursor solution deposited on (0001) sapphire substrate by spin coating and crystallized in a microwave oven. Crystallization of the films was carried out in a domestic microwave oven. The influence of this type of heat treatment on the film orientation was analyzed by X-ray diffraction and electron channeling patterns, which revealed epitaxial growth of films crystallized at 550 and 650 degreesC for 10 min. A microstructural study indicated that the films treated at temperatures below 600 degreesC were homogeneous and dense, and the optical properties confirmed the good quality of these films. (C) 2003 Elsevier B.V. B.V. All rights reserved.

Investigation of phase transition in ferroelectric Pb0.70Sr0.30TiO3 thin films

We have carried out dielectric and Raman spectroscopy studies at the 298-623 K temperature range in polycrystalline Pb0.70Sr0.30TiO3 thin films grown by a soft chemical method. The diffuse phase-transition behavior of the thin films was observed by means of the dielectric constant versus temperature curves, which show a broad peak. Such behavior was confirmed later by Raman spectroscopy measurements up to 823 K, indicating that a diffuselike phase transition takes place at around 548-573 K. The damping factor of the E(1TO) soft mode was calculated using the damped simple harmonic oscillator model. on the other hand, Raman modes persist above the tetragonal to cubic phase transition temperature although all optical modes should be Raman inactive. The origin of these modes was interpreted in terms of a breakdown of the microscopic local cubic symmetry by chemical disorder. The lack of a well-defined transition temperature and the presence of broad bands at some temperature interval above the ferroelectric-paraelectric phase-transition temperature suggested a diffuse nature of the phase transition. This result corroborates the dielectric constant versus temperature data, which showed a broad ferroelectric phase transition in this thin film. (C) 2004 American Institute of Physics.