Modeling electrical characteristics of thin-film field-effect transistors: III. Normally-on devices

The thin-film field-effect-transistor model recently developed is applied to devices based on materials that already show current even without a bias present at the gate resulting in so-called normally-on transistors. These fall in three categories: (i) narrow-band-gap semiconductors, where the thermal energy is sufficient to excite carriers across the band-gap, here analyzed for unipolar and ambipolar materials, (ii) doped semiconductors, and (iii) metals. It is shown what the impact is on the IV and transfer curves.     

Polyaniline-related ion-barrier anticorrosion coatings: I. Ionic permeability of polyaniline,cationic, and bipolar films

Ionic permeabilities of coating films were studied with a variety of experimental methods including measurements of membrane potential, salt diffusion, and electron spectroscopy for chemical analysis (ESCA). The results show that polyaniline (PAn) allows diffusion of anions (if PAn is dispersed in a cationic polymer matrix, the resulting film may have cationic defects that allow the passage of cations), a cationic film is permeable to cations, and the combination of a PAn containing primer with the cationic topcoat is an ion-barrier which delays penetration of both anions and cations.     

Polyaniline-related ion-barrier anticorrosion coatings: II. Protection behavior of polyaniline,cationic, and bipolar films

A polyaniline (PAn) containing coating layer leads to substrate corrosion in an environment of aggressive anions. A cationic coating results in delamination or blistering. A bipolar coating consisting of a PAn primer and a cationic topcoat inhibits both corrosion and delamination.     

Synthesis and third-order nonlinear optical studies of a novel four-coordinated organoboron derivative and a bidentate ligand: The effect of the N → B coordinative bond

The third-order nonlinear optical characterization of a new boronate (2) derived from 4-dimethylaminocinnamaldehyde was performed by third-harmonic generation (THG) at the infrared wavelength of 1550 nm. Compound 2 was prepared from the reaction of diphenylboronic acid and the bidentate ligand (1) and characterization was made through UV, IR, ¹H, ¹¹B, and ¹³C NMR and X-ray diffraction. The THG experiments showed that the N → B coordinative bond in 2 enhanced the second molecular hyperpolarizability of the type γ⁽³⁾(−3ω, ω, ω, ω) by a factor of three with respect to the value exhibited by the ligand 1. On the other hand, Z-scan studies at 800 nm (femtosecond (fs) pulses) also showed that such coordinative bond increased the nonlinear absorption (two-photon absorption (TPA)) in 2 with respect to 1. These studies demonstrate that the N → B coordinative bond facilitates the polarization of the electronic π-system, a situation that optimizes the third-order NLO response. Results on the excited state absorptions in these compounds are also presented.     

Synthesis, luminescence and quantum yields of Eu(III) mixed complexes with 4,4,4-trifluoro-1-phenyl-1,3-butanedione and 1,10-phenanthroline-N-oxide

The new complex tris(4,4,4-trifluoro-1-phenyl-1,3-butanedionate)(1,10-phenanthroline-N-oxide)europium(III) has been synthesized, characterized, and its photophysical properties (excitation and luminescence spectra, and quantum yields) investigated down to 4.2 K. A similar complex containing H₂O instead of phenNO molecules was also investigated for comparison. The more pronounced temperature dependence of the quantum yield q and the larger difference between the q values upon ligand and direct Eu³⁺ excitation for the hydrated compound show that there are other quenching processes operative, besides the expected multiphonon relaxation via the H₂O vibrations. The results clearly show that the substitution of the water molecules by phenNO leads to greatly enhanced quantum yields (i.e. 30% vs. 66%, upon ligand excitation at 300 K) and longer ⁵D₀ lifetimes (380 μs vs. 670 μs respectively). This can be ascribed to a more efficient ligand-to-metal energy transfer and to less efficient non-radiative ⁵D₀ relaxation processes.     

Corrosion of reinforcing steel in simulated concrete pore solutions: Effect of carbonation and chloride content

The corrosion susceptibility of as-received reinforcing steel bars (rebars) in solutions simulating the pore liquid of alkaline and carbonated concrete has been studied by means of potentiodynamic polarisation tests and polarisation resistance measurements. The effect of different degrees of carbonation and the presence of several chloride contents in the simulated pore solutions was investigated. Results show the beneficial effect of high alkalinity on the localised corrosion of steel caused by chloride ions. From the results of the potentiodynamic tests a critical chloride concentration above which pitting could take place was evaluated for each solution. The chloride threshold values here found are of the same order than those previously reported in the literature for film-free steel. The results obtained in solutions simulating carbonated concrete showed that under weak carbonation conditions carbon steel does not passivate while in the presence of high levels of carbonate and bicarbonate the resistance to localised corrosion is improved.     

Microwave plasma assisted preparation of disperse chromium oxide supported catalysts: Adsorption and decomposition of chromium acetylacetonate

Microwave plasma enhanced chemical vapour deposition (PECVD) is a promising method for the solvent free preparation of catalytic materials. In this work, microwave low temperature plasma technology has been used for the deposition of catalytic active chromia species on zirconia and lanthanum doped zirconia supports. The obtained materials were characterized by inductive coupled plasma-optical emissions spectroscopy (ICP-OES), Fourier-transform infrared spectroscopy (FTIR), thermo gravimetric analysis-difference thermo analysis (TG/DTA) investigations and transmission electron spectroscopy-energy dispersive X-ray analysis (TEM-EDX).The results reveal that the PECVD method is a solvent free one step method suitable for preparation of chromia containing catalysts. During the PECVD process the adsorption of Cr(acac)₃ probably takes place by cleavage of one ligand on both supports. The anchoring of the formed active component CrO_x is more stable on La_0.1Zr_0.9O_1.95 than on ZrO₂. Furthermore, the utilization of the PECVD method can inhibit the formation of large CrO_x agglomerates or α-Cr₂O₃ on both supports. After upscaling, this method can be used for the preparation of catalysts for fine chemicals in larger scale.     

The transpassive dissolution mechanism of highly alloyed stainless steels: I. Experimental results and modelling procedure

The transpassive dissolution of austenitic stainless steels (AISI 316L, AISI 904L, 254SMO and 654SMO) in a 0.5 M sulphate solution with pH 2 was studied by conventional and rotating ring-disc voltammetry, as well as electrochemical impedance spectroscopy. The main process in the transpassive potential region was found to be the release of soluble Cr(VI), while small amounts of lower-valency Cr or Mo species are released as well. Secondary passivation readily occurs for AISI 316L, whereas the remaining highly alloyed steels dissolve at high current densities in the whole potential range studied. The dissolution rate was found to increase in the order AISI 904L<254SMO<654SMO. Thus it can be correlated to the increase in the Cr and especially Mo content of the steel substrate. The impedance spectra contain contributions from the transpassive dissolution of Cr and secondary passivation, probably due to enrichment of Fe in the outermost layer of the surface film. A kinetic model of the process is proposed, including a two-step transpassive dissolution of Cr via a Cr(VI) intermediate and the dissolution of Fe(III) through the anodic film. The model was found to be in quantitative agreement with steady state current vs. potential curves and electrochemical impedance spectra. The kinetic parameters of transpassive dissolution were determined and the relevance of their values is discussed.     

Mechanical properties of thermal barrier coatings after isothermal oxidation.: Depth sensing indentation analysis

Thermal barrier coatings (TBC) are extensively used to protect metallic components in applications where the operating conditions include aggressive environment at high temperatures. Isothermal oxidation degrades the performance of these coatings, so this work analyses the mechanical properties (Young's modulus, E, and hardness, H) of TBC and its evolution after thermal exposure in air. ZrO₂(Y₂O₃) top coat and NiCrAlY bond coating were air plasma sprayed onto an Inconel 600 Ni base alloy. The TBC were isothermally oxidized in air at 950 °C and 1050 °C for 72, 144 and 336 h. Depth sensing indentation tests were carried out on the ceramic coating to evaluate E and H in the as-sprayed materials and after isothermal oxidation. An approach based on multiple tests at different loads was used to determine size independent apparent E an H. These mechanical properties, measured perpendicular to the surface, clearly decreased after isothermal oxidation as a consequence of microcracking within the ceramic coating.