Incorporation of PbF2 into Heavy Metal Oxide Borate Glasses. Structural Studies by Solid State NMR

A series of heavy metal oxide (HMO) glasses with composition 26.66B(2)O(3)-16GeO(2)-4 Bi2O3-(53.33-x)PbO-xPbF2 (0 <= x <= 40) were prepared and characterized with respect to their bulk (glass transition and crystallization temperatures, densities, molar volumes) and spectroscopic properties. Homogeneous glasses are formed up to x = 30, while crystallization of beta-PbF2 takes place at higher contents. Substitution of PbO by PbF2 shifts the optical band gap toward higher energies, thereby extending the UV transmission window significantly toward higher frequencies. Raman and infrared absorption spectra can be interpreted in conjunction with published reference data. Using B-11 and F-19 high-resolution solid state NMR as well as B-11/F-19 double resonance methodologies, we develop a quantitative structural description of this material. The fraction of four-coordinate boron is found to be moderately higher compared to that in glasses with the same PbO/B2O3 ratios, suggesting some participation of PbF2 in the network transformation process. This suggestion is confirmed by the F-19 NMR spectra. While the majority of the fluoride ions is present as ionic fluoride, similar to 20% of the fluorine inventory acts as a network modifier, resulting in the formation of four-coordinate BO3/2F- units. These units can be identified by F-19{B-11} rotational echo double resonance and B-11{F-19} cross-polarization magic angle spinning (CPMAS) data. These results provide the first unambiguous evidence of B-F bonding in a PbF2-modified glass system. The majority of the fluoride ions are found in a lead-dominated environment. F-19-F-19 homonuclear dipolar second moments measured by spin echo decay spectroscopy are quantitatively consistent with a model in which these ions are randomly distributed within the network modifier subdomain consisting of PbO, Bi2O3, and PbF2. This model, which implies both the features of atomic scale mixing with the network former borate species and some degree of fluoride ion clustering is consistent with all of the experimental data obtained on these glasses.

Femtosecond laser processing of glassy and polymeric matrices containing metals and semiconductor nanostructures

Tailoring properties of materials by femtosecond laser processing has been proposed in the last decade as a powerful approach for technological applications, ranging from optics to biology. Although most of the research output in this field is related to femtosecond laser processing of single either organic or inorganic materials, more recently a similar approach has been proposed to develop advanced hybrid nanomaterials. Here, we report results on the use of femtosecond lasers to process hybrid nanomaterials, composed of polymeric and glassy matrices containing metal or semiconductor nanostructures. We present results on the use of femtosecond pulses to induce Cu and Ag nanoparticles in the bulk of borate and borosilicate glasses, which can be applied for a new generation of waveguides. We also report on 3D polymeric structures, fabricated by two-photon polymerization, containing Au and ZnO nanostructures, with intense two-photon fluorescent properties. The approach based on femtosecond laser processing to fabricate hybrid materials containing metal or semiconductor nanostructures is promising to be exploited for optical sensors and photonics devices.

Comparative degradation of ZnO- and SnO(2)-based polycrystalline non-ohmic devices by current pulse stress

The degradation behaviour of SnO(2)-based varistors (SCNCr) due to current pulses (8/20 mu s) is reported here for the first time in comparison with the ZnO-based commercial varistors (ZnO). Puncturing and/or cracking failures were observed in ZnO-based varistors possessing inferior thermo-mechanical properties in comparison with that found in a SCNCr system free of failures. Both systems presented electric degradation related to the increase in the leakage current and decrease in the electric breakdown field, non-linear coefficient and average value of the potential barrier height. However, it was found that a more severe degradation occurred in the ZnO-based varistors concerning their non-ohmic behaviour, while in the SCNCr system, a strong non-ohmic behaviour remained after the degradation. These results indicate that the degradation in the metal oxide varistors is controlled by a defect diffusion process whose rate depends on the mobility, the concentration of meta-stable defects and the amount of electrically active interfaces. The improved behaviour of the SCNCr system is then inferred to be associated with the higher amount of electrically active interfaces (85%) and to a higher energy necessary to activate the diffusion of the specific defects.

Electrical characterization of poly(amide-imide) for application in organic field effect devices

The admittance spectra and current-voltage (I-V) characteristics are reported of metal-insulator-metal (MIM) and metal-insulator-semiconductor (MIS) capacitors employing cross-linked poly(amide-imide) (c-PAI) as the insulator and poly(3-hexylthiophene) (P3HT) as the active semiconductor. The capacitance of the MIM devices are constant in the frequency range from 10 Hz to 100 kHz, with tan delta values as low as 7 x 10(-3) over most of the range. Except at the lowest voltages, the I-V characteristics are well-described by the Schottky equation for thermal emission of electrons from the electrodes into the insulator. The admittance spectra of the MIS devices displayed a classic Maxwell-Wagner frequency response from which the transverse bulk hole mobility was estimated to be similar to 2 x 10(-5) cm(2) V(-1)s(-1) or similar to 5 x 10(-8) cm(2) V(-1)s(-1) depending on whether or not the surface of the insulator had been treated with hexamethyldisilazane (HMDS) prior to deposition of the P3HT. From the maximum loss observed in admittance-voltage plots, the interface trap density was estimated to be similar to 5 x 10(10) cm(-2) eV(-1) or similar to 9 x 10(10) cm(-2) eV(-1) again depending whether or not the insulator was treated with HMDS. We conclude, therefore, that HMDS plays a useful role in promoting order in the P3HT film as well as reducing the density of interface trap states. Although interposing the P3HT layer between the insulator and the gold electrode degrades the insulating properties of the c-PAI, nevertheless, they remain sufficiently good for use in organic electronic devices. (c) 2012 Elsevier B.V. All rights reserved.

Preparação de vidros e vitrocerâmicas de óxidos de metais pesados contendo prata: propriedades ópticas, estruturais e eletroquímicas

Silver containing heavy metal oxide glasses and glass ceramics of the system WO3-SbPO4-PbO-AgCl with different AgCl contents have been prepared and their thermal, structural and optical properties characterized. Glass ceramics containing metallic silver nanoparticles have been prepared by annealing glass samples at temperatures above the glass transition and analyzed by transmission electron microscopy and energy dispersive X-ray microanalysis. The presence of the metallic clusters has been also confirmed by the observation of a surface plasmon resonimce band in the visible range. Cyclic voltammetric measurements indicated the presence of metallic silver into the glasses, even before to perform the thermal treatment.

Chemical mechanism of controlled nitric oxide release from trans-[RuCl([15]aneN(4))NO](PF6)(2) as a vasorelaxant agent

The nitrosyl ruthenium complex, trans-[RuCl([15]aneN(4))NO](PF6)(2), ([15]aneN(4) = 1,4,8,12-tetraazacyclopentadecane), exhibits vasorelaxation characteristics attributed to its nitric oxide release properties. The observed in vitro and in vivo vasodilation is dependent on noradrenaline concentration. We report here the chemical mechanism of the reaction between noradrenaline and trans-[RuCl([15]aneN(4))NO](PF6)(2) in aqueous phosphate buffer solution at pH 7.40. NO measurement by NO-sensor electrode, cyclic voltammetry, (PNMR)-P-31 and HPLC analysis were used to investigate the reduction process as the fundamental step for NO release characteristic of trans-[RuCl([15]aneN(4))NO](PF6)(2). A supramolecular species containing HPO4 (2-) as a bridging group between noradrenaline and trans-[RuCl([15]aneN(4))NO](PF6)(2) is suggested as an intermediate prior to the reduction of the nitrosyl ruthenium complex.

Vanadium and Titanium Mixed Oxide Films: Synthesis, Characterization and Application as Ion Sensor

Vanadium/titanium mixed oxide films were produced using the sol-gel route. The structural investigation revealed that increased TiO2 molar ratio in the mixed oxide disturbs the V2O5 crystalline structure and makes it amorphous. This blocks the TiO2 phase transformation, so TiO2 stabilizes in the anatase phase. In addition the surface of the sample always presents larger amounts of TiO2 than expected, revealing a concentration gradient along the growth direction. For increased TiO2 molar ratios the roughness of the surface is reduced. Ion sensors were fabricated using the extended gate field effect transistor configuration. The obtained sensitivities varied in the range of 58 mV/pH down to 15 mV/pH according to the composition and morphology of the surface of the samples. Low TiO2 amounts presented better sensing properties that might be related to the cracked and inhomogeneous surfaces. Rising the TiO2 quantity in the films produces homogeneous surfaces but diminishes their sensitivities. Thus, the present paper reveals that the compositional and structural aspects change the surface morphology and electrical properties accounting for the final ion sensing properties of the V2O5/TiO2 films. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.053206jes] All rights reserved.

Structural and mechanical analysis for the optimization of PVD oxide coatings for protection against metal dusting

The evolution of the structure and properties of Cr/Cr oxide thin films deposited on HK40 steel substrates by reactive magnetron sputtering (RMS) was investigated and linked to their potential protective behavior against metal dusting. Deposition time, mode of oxygen feeding, and application of bias voltage were varied to assess their effect on the density, adhesion, and integrity of the films. All the films showed a very fine columnar microstructure and the presence of amorphous Cr oxide. Both, an increasing time and a constant oxygen flow during deposition led to the development of relatively low density films and mud-like cracking patterns. A graded oxygen flow resulted in films with fewer cracks, but a careful control of the oxygen flow is required to obtain films with a truly graded structure. The effect of the bias voltage was much more significant and beneficial. An increasing negative bias voltage resulted in the development of denser films with a transition to an almost crack-free structure and better adhesion. The amorphous oxide resulted in low values of hardness and Young's modulus. (C) 2012 Elsevier B.V. All rights reserved.