Ferroelectric and microstructural characteristics of SrBi2Ta2O9 thin films crystallized by the rapid thermal annealing process

Ferroelectric SrBi2Ta2O9 thin films on Pt/Ti/SiO2/Si were successfully synthesized by the modified polymeric precursor method. The films were deposited by spin coating and crystallized by rapid thermal annealing in a halogen lamp furnace, followed by postannealing at temperatures ranging from 700 degreesC to 800 degreesC in an oxygen atmosphere. Microstructural and phase evaluations were followed by x-ray diffraction and atomic force microscopy. The films displayed spherical grain structures with a superficial roughness of approximately 3-6 nm. The dielectric constant values were 121 and 248 for films treated at 700 degreesC and 800 degreesC, respectively. The P-E curve showed a voltage shift toward the positive side, which was attributed to crystallization under the halogen illumination. The remanent polarization (2P(r)) and coercive field (E-c) were 7.1 muC/cm(2) and 113 kV/cm, and 18.8 muC/cm(2) and 93 kV/cm for the films treated at 700 degreesC and 800 degreesC, respectively. (C) 2001 American Institute of Physics.

Control of retention and fatigue-free characteristics in CaBi4Ti4O15 thin films prepared by chemical method

Ferroelectric CaBi4Ti4O15 (CBTi144) thin films were deposited on Pt/Ti/SiO2/Si substrates by the polymeric precursor method. The films present a single phase of layered-structured perovskite with polar axis orientation after annealing at 700 degrees C for 2 h in static air and oxygen atmosphere. The a/b-axis orientation of the ferroelectric film is considered to be associated with the preferred orientation of the Pt bottom electrode. It is noted that the films annealed in static air showed good polarization fatigue characteristics at least up to 10(10) bipolar pulse cycles and excellent retention properties up to 10(4) s. on the other hand, oxygen atmosphere seems to be crucial in the decrease of both, fatigue and retention characteristics of the capacitors. Independently of the applied electric field, the retained switchable polarization approached a nearly steady-state value after a retention time of 10 s. (C) 2006 Elsevier B.V. All rights reserved.

A study on X-ray irradiation of composite polyaniline LB films

Composite Langmuir-Blodgett (LB) films from polyaniline and cadmium stearate have been irradiated with ionizing X-rays for various exposure times. In the initial stages of X-ray irradiation the absorption peak at 580 nm of an as-deposited film was seen to decrease with a concomitant increase in the absorption in the long wavelength region (700-1100 nm). Upon prolonging the irradiation, the absorption maximum shifted to 800 nm with the LB film color changing to green, characteristic of acid doped polyaniline. The changes in the Fourier transform infrared (FTIR) spectra upon irradiation are also similar to those observed upon acid doping of polyaniline. When compared with acid doping, two major differences were observed for the LB films exposed to X-rays. First, the packing order of the cadmium stearate domains in the composite LB films - as observed by X-ray diffraction - is not affected by the X-ray irradiation. In addition, no significant increase in the DC conductivity was noted after the X-ray exposure whereas similar LB films have their conductivity increased by an order of magnitude upon acid doping. These differences may be explained by considering that the inter-domain contribution to the conductivity is increased by the acid doping because the insulating cadmium stearate domains are destroyed, which does not occur with the X-ray irradiation. (C) 1998 Elsevier B.V. S.A. All rights reserved.

Potentialities and practical limitations of absolute neutron dosimetry using thin films of uranium and thorium applied to the fission track dating

Neutron dosimetry using natural uranium and thorium thin films makes possible that mineral dating by the fission-track method can be accomplished, even when poor thermalized neutron facilities are employed. In this case, the contributions of the fissions of (235)U, (238)U and (232)Th induced by thermal, epithermal and fast neutrons to the population of tracks produced during irradiation are quantified through the combined use of natural uranium and thorium films.If the Th/U ratio of the sample is known, only one irradiation (where the sample and the films of uranium and thorium are present) is necessary to perform the dating. However, if that ratio is unknown, it can be determined through another irradiation where the mineral to be dated and both films are placed inside a cadmium box.Problems related with film manufacturing and calibration are discussed. Special attention is given to the utilization of thin films having very low uranium content. The problems faced suggest that it may be better to substitute these films by uranium doped standard glasses calibrated with thicker uranium films (thickness greater than 1.5 x 10(13) mu m).

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.

Microstructural, dielectric and ferroelectric properties of calcium-modified lead titanate thin films derived by chemical processes

Ferroelectric Pb1-xCaxTiO3 (x = 0.24) thin films were formed on a Pt/Ti/SiO2/Si substrate by the polymeric precursor method using the dip-coating technique for their deposition. Characterization of the films bq X-ray diffraction showed a perovskite single phase with a tetragonal structure after annealing at 700 degreesC. Atomic force microscopy (AFM) analyses showed that the film had a smooth and crack-free surface with low surface roughness. In addition, the PCT thin film had a granular structure with an 80 nm grain size. The thickness of the films observed by the scanning electron microscopy (SEM) is 550 nm and there is a good adhesion between the film and substrate. For the electrical measurements metal-ferroelectric-metal of the type capacitors were obtained, where the thin films showed good dielectric and ferroelectric properties. The dielectric constant and dissipation factor at 1 kHz and measured at room temperature were found to be 457 and 0.03. respectively. The remanent polarization and coercive field for the: deposited films were P-r = 17 muC/cm(2) and E-c = 75 kV/cm, respectively. Moreover. The 550-nm-thick film showed a current density in the order of 10(-8) A/cm(2) at the applied voltage of 2 V. The high values of the thin film's dielectric properties are attributed to its excellent microstructural quality and the chemical homogeneity obtained by the polymeric precursor method. (C) 2001 Elsevier science Ltd. All rights reserved.

Characterization and application of PZT/PU and graphite doped PZT/PU composite

Composites, made of lead zirconate titanate (PZT) ceramic powder and castor oil-based polyurethane (PU), were prepared in the film form. The films were obtained in the thickness range 100-300 mum using up to 50/50 vol.% of ceramic. Another composite (PZT/C/PU) was obtained by adding a small amount (1.0 vol.%) of graphite (C) to the PZT/PU composite. By increasing the conductivity of PU-containing graphite, polarization of PZT could be carried out with better efficiency. A comparison of piezo- and pyroelectric activities and spatial distribution of polarization between graphite doped and undoped composites reveal the advantages of using semiconductor filler. These composites were used as sensors to detect acoustic emission (AE). The detection was made using two simulated sources of AE, i.e., ball bearing drop and pencil lead break. PZT/C/PU composite was able to detect both flexural and extensional components of wave vibration. (C) 2002 Elsevier B.V. B.V. All rights reserved.

Temperature dependence of photoinduced birefringence in polystyrene doped with Disperse Red-1

A theoretical model on the basis of the free-volume concept is presented explaining the temperature dependence of photoinduced birefringence in polystyrene films that contain Disperse Red-1. Birefringence increases with temperature up to 180 K as the free volume for isomerization increases, and then decreases as thermally activated processes dominate. The fast process of birefringence decay has a time constant that increases with temperature at low temperatures, due to the change kin photoisomerization.

Improvement of the dielectric and ferroelectric properties in superlattice structure of Pb(Zr,Ti)O-3 thin films grown by a chemical solution route

Making heterolayered perovskite materials constitutes an approach for the creation of better dielectric and ferroelectric properties. In the experiment reported here, heterolayered PZT40/PZT60 films were grown on Pt/Ti/SiO2/Si (100) by a chemical solution deposition. The dielectric constant of the heterolayered thin film was significantly enhanced compared with that of pure PZT40 and PZT60 thin films. A dielectric constant of 701 at 100 kHz was observed for a stacking periodicity of six layers having a total thickness of 150 nm. The heterolayered film exhibited greater remanent polarization than PZT60 and PZT40 films. The values of remanent polarization were 7.9, 18.5, and 31 muC/cm(2), respectively, for pure PZT60, PZT40, and heterolayered thin films, suggesting that the superior dielectric and ferroelectric properties of the heterolayered thin film resulted from a cooperative interaction between the ferroelectric phases made from alternating tetragonal and rhombohedral phases of PZT, simulating the morphotropic phase boundary of this system. (C) 2004 American Institute of Physics.

Photoluminescence at room temperature in disordered Ba(0.50)Sr(0.)5(0)(Ti0.80Sn0.20)O-3 thin films

Photoluminescence (PL) properties at room temperature of disordered Ba0.50Sr0.50(Ti0.80Sn0.20)O-3 (BST:Sn) thin films were obtained by the polymeric precursor method. X-ray diffraction data and corresponding PL properties have been measured using the 488 nm line of an argon ion laser. The PL spectra of the film annealed at 350 degrees C for 21 h are stronger than those of the film annealed at 350 degrees C for 28 h, indicating a disorganized structure. The energy band gaps of the crystalline and amorphous BST:Sn thin films were 3.35 and 2.25 eV, respectively. The doped BST thin films also tend to a cubic structure, resulting from TiO6 deformations. (c) 2006 American Institute of Physics.

Preparation and properties of ferroelectric Pb1-xCaxTiO3 thin films produced by the polymeric precursor method

Pb1- xCaxTiO3 thin films with x = 0.24 composition were prepared by the polymeric precursor method on Pt/Ti/SiO2/Si substrates. The surface morphology and crystal structure, and the ferroelectric and dielectric properties of the films were investigated. X-ray diffraction patterns of the films revealed their polycrystalline nature. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) analyses showed the surface of these thin films to be smooth, dense and crack-free with low surface roughness. The multilayer Pb1-xCaxTO3 thin films were granular in structure with a grain size of approximately 60-70 nm. The dielectric constant and dissipation factor were, respectively, 174 and 0.04 at a 1 kHz frequency. The 600-nm thick film showed a current density leakage in the order of 10(-7) A/cm(2) in an electric field of about 51 kV/cm. The C-V characteristics of perovskite thin films showed normal ferroelectric behavior. The remanent polarization and coercive field for the deposited films were 15 muC/cm(2) and 150 kV/cm, respectively. (C) 2001 Kluwer Academic Publishers.

Planar waveguides based on nanocrystalline and Er3+ doped SnO2

Luminescent SnO2: x%mol Er3+ (x=0.1-2.0) thin films have been spin coated on borosilicate and silica substrates from water colloidal suspensions that could be prepared containing up to 40% in weight SnO2 nanocrystalline powders. High Resolution Transmission Electron Microscopy results show the well known SnO2 cassiterite structure and nanocrystallites around 10 nm in diameter, corroborating results from X-ray diffraction. Mono and multi layers have been prepared from the stable colloidal suspensions and films thickness was observed to increase linearly, up to 200 nm, with the colloidal suspensions nanoparticles amount. Excitation and emission spectra have been measured and Er3+ ions were found to be essentially incorporated into the cassiterite structure, substituting for Sn4+, for doping concentration lower than 0.05 mol%. Er3+ ions also appear segregated at the grains surface for higher doping concentration. The optical parameters (refractive index, thickness and propagating modes) of a waveguide sample were measured at 632.8 and 543.4 nm by the prism coupling technique. A monomodal waveguide was obtained with attenuation loss of 3.5 dB/cm along a 2.5 cm optical path.

Structural and electrical properties of SrBi2Nb2O9 thin films prepared by chemical aqueous solution at low temperature

SrBi2Nb2O9 (SBN) thin films were prepared by the polymeric precursors method and deposited by dip coating onto Pt/Ti/SiO2/Si(100) substrates. The dip-coated films were specular and crack-free and crystallized during firing at 700 degrees C. Microstructure and morphological evaluation were followed by grazing incident X-ray diffraction (GIXRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The films exhibited somewhat porous grain structure with rounded grains of about 100 nm. For the electrical measurements, gold electrodes of 300 mu m in diameter were sputter deposited on the top surface, forming a metal-ferroelectric-metal (MFM) configuration. The remanent polarization (P-r) and coercive field (E-c) were 5.6 mu C/cm(2) and 100 kV/cm, respectively. (C) 1999 Elsevier B.V. B.V. All rights reserved.

Thickness dependence of leakage current in BaBi2Ta2O9 thin films

BaBi2Ta2O9 thin films having a layered structure were fabricated by metalorganic solution deposition technique. The films exhibited good structural, dielectric, and insulating properties. The room temperature resistivity was found to be in the range of 10(12)-10(14) Omega cm up to 4 V corresponding to a field of 200 kV/cm across the capacitor for films annealed in the temperature range of 500-700 degrees C. The current-voltage (I-V) characteristics as a function of thickness for films annealed at 700 degrees C for 1 h, indicated bulk limited conduction and the log(I) vs V-1/2 characteristics suggested a space-charge-limited conduction mechanism. The capacitance-voltage measurements on films in a metal-insulator-semiconductor configuration indicated good Si/BaBi2Ta2O9 interface characteristics and a SiO2 thickness of similar to 5 nm was measured and calculated. (C) 1999 American Institute of Physics. [S0003-6951(99)00830-X].

UV-visible absorption characteristics of TEOS-derived and Cr-doped silica sonogels aged in different pH solutions and heat treated up to 600 degrees C

Cr-doped xerogels were obtained by sol-gel process from the acid-catalyzed and ultrasound-stimulated hydrolysis of tetraethoxysilane (TEOS) with addition of CrCl3.6H(2)O in water solution during the liquid step of the process. The gels were aged immersed in different pH solutions for about 30 days, after that they were allowed to dry. The samples were annealed at temperatures ranging from 40 to 600degreesC and analyzed by UV-visible absorption spectroscopy. Cr3+ is the preferable oxidation state of the chromium ion in the gels annealed up to 250-300degreesC, in the case of aging in solutions of pH=5 and 11. A high UV absorption below similar to320 nm, due to the host gel, and different absorption bands, depending on the temperature, due to the chromium ion were observed in the xerogels at temperatures below similar to250degreesC, in the case of aging in solutions of pH=1 and 2. These absorption bands have not been assigned. Above 300degreesC up to 600degreesC, Cr5+, and possibly Cr6+, are the preferable oxidation states of the chromium ion independent of the pH of the aging solution, so the xerogels turn to a yellowish appearance in all cases.