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Barium strontium titanate ͑Ba 0.8 Sr 0.2 TiO 3 ͒ thin films have been prepared on Pt/Ti/SiO 2 /Si substrates using a soft solution processing. X-ray diffraction and also micro-Raman spectroscopy showed that the Ba 0.8 Sr 0.2 TiO 3 thin films exhibited a tetragonal structure at room temperature. The presence of Raman active modes was clearly shown at the 299 and 725 cm Ϫ1 peaks. The tetragonal-to-cubic phase transition in the Ba 0.8 Sr 0.2 TiO 3 thin films is broadened, and suppressed at about 35°C, with a maximum dielectric constant of 948 ͑100 kHz͒. Electrical measurements for the prepared Ba 0.8 Sr 0.2 TiO 3 thin films showed a remnant polarization ͑P r ͒ of 6.5 C/cm 2 , a coercive field ͑E c ͒ of 41 kV/cm, and good insulating properties. The dispersion of the refractive index is interpreted in terms of a single electronic oscillator at 6.97 eV. The direct band gap energy ͑E g ͒ and the refractive index ͑n͒ are estimated to be 3.3 eV and n ϭ 2.27-2.10, respectively.

Charge transport and shelf-degradation of MEH-PPV thin-films were investigated through stationary (e.g. current versus voltage -JxV) and transient (e.g. Time-of-Flight -ToF, Dark-Injection Space-Charge-Limited Current -DI-SCLC, Charge Extraction by Linearly Increasing Voltage -CELIV) current techniques. Charge carrier mobility in nanometric films was best characterized through JxV and DI-SCLC. It approaches 10 − 6 cm 2 /Vs under a SCLC regime with deep traps for light-emitting diode applications. ToF measurements performed on micrometric layers (i.e.~3 μm) confirmed studies in 100 nm-thick films as deposited in OLEDs. All results were comparable to a similar poly(para-phenylene vinylene) derivative, MDMO-PPV. Electrical properties extracted from thin-film transistors demonstrated mobility dependence on carrier concentration in the channel (~10 − 7 -10 − 4 cm 2 /Vs). At low accumulated charge levels and reduced free carrier concentration, a perfect agreement to the previously cited techniques was observed. Degradation was verified through mobility reduction and changes in trap distribution of states.

Pb 1Ϫx Ca x TiO 3 (0.10рxр0.40) thin films on Pt/Ti/SiO 2 /Si(100) substrates were prepared by the soft solution process and their characteristics were investigated as a function of the calcium content ͑x͒. The structural modifications in the films were studied using x-ray diffraction and micro-Raman scattering techniques. Lattice parameters calculated from x-ray data indicate a decrease in lattice tetragonality with the increasing content of calcium in these films. Raman spectra exhibited characteristic features of pure PbTiO 3 thin films. Variations in the phonon mode wave numbers, especially those of lower wave numbers, of Pb 1Ϫx Ca x TiO 3 thin films as a function of the composition corroborate the decrease in tetragonality caused by the calcium doping. As the Ca content ͑x͒ increases from 0.10 to 0.40, the dielectric constant at room temperature abnormally increased at 1 kHz from 148 to 430. Also calcium substitution decreased the remanent polarization and coercive field from 28.0 to 5.3 C/cm 2 and 124 to 58 kV/cm, respectively. These properties can be explained in terms of variations of phase transition ͑ferroelectric-paraelectric͒, resulting from the substitution the lead site of PbTiO 3 for the nonvolatile calcium.

Persistent photoconductivity (PPC) in vanadyl phthalocyanine (VOPc) organic light-emitting diodes was investigated using photoconductive time response, photocurrent–voltage characteristics and charge extraction in linearly increasing voltage (CELIV) measurements. The experiments were performed in phase 1 (amorphous) and in phase 2 (crystalline) samples obtained by the physical vapour deposition (PVD) technique over ITO/glass electrodes with an Al covering electrode. The results indicated a photoconductivity with a long decay time in phase 1 VOPc described by a stretched exponential relaxation. The device showed a rectifying behaviour and the mobility of holes was measured by CELIV, following a dispersive model. In crystalline samples the PPC effect was not observed and the dominant mechanism of transport of holes was hopping in a Gaussian density of states.