No abstract available

[en] Taking into consideration the importance of the anodic effect in the technological process of tantalum elctrowinning, the authors studies the influence of Ta₂O₅ and K₂TaF₇ on the critical anodic current density. The Ta₂O₅ has a beneficial effect, increasing this current density. K₂TaF₇ acts indirectly, by increasing the Ta₂O₅ solubility in the electrolyte. These effects are evident in the current-voltage curves obtained for different K₂TaF₇ and Ta₂O₅ concentrations. (author)

[en] Studies of the L-Ta₂O₅ defect structure are reviewed. It is shown that the overall results are inconsistent with a simple oxygen-vacancy defect model. A new defect model based on infinitely adaptive structures is proposed, and according to this model a monophasic structure is maintained without site conservation in the sub-lattices. For L-Ta₂O₅-type structures it is proposed that the oxygen sub-lattice may change its density of sites independent of the metal sub-lattice. These processes may involve extremely long equilibration periods, even at temperatures as high as 1400⁰C. 27 refs.; 3 figs

[en] Peroxo-tantalic acid solution was obtained by direct reaction of Ta(OC₂H₅) with H₂O₂. It turned into amorphous Ta₂O₅.nH₂O when dried. Thermal analysis revealed that Ta₂O₅.nH₂O thus formed underwent three-step thermal decomposition. Final product up to 700degC was hexagonal tantalum oxide. Electrical conductivity of spin-coated Ta₂O₅.nH₂O was measured with ac impedance method revealing that temperature and humidity dependence of ionic conductivity (4.3x10^-7S cm^-1 at 27degC) was very small. (author). 10 refs.; 3 figs

[en] The light-addressable potentiometric sensor is a promising technology platform for multi-sensor applications and lab-on-chip devices. However, many prior LAPS developments suffer from their lack in terms of non-portability, insufficient robustness, complicate handling, etc. Hence, portable and robust LAPS-based measurement devices have been investigated by the authors recently. In this work, a 'chip card'-based light-addressable potentiometric sensor system is presented. The utilisation of ordinary 'chip cards' allows an easy handling of different sensor chips for a wide range of possible applications. The integration of the electronic and the mechanical set-up into a single reader unit results in a compact design with the benefits of portability and low required space. In addition, the presented work includes a new multi-frequency measurement procedure, based on an FFT algorithm, which enables the simultaneous real-time measurement of up to 16 sensor spots. The comparison between the former batch-LAPS and the new FFT-based LAPS set-up will be presented. The immobilisation of biological cells (CHO: Chinese hamster ovary) demonstrates the possibility to record their metabolic activity with 16 measurement spots on the same chip. Furthermore, a Cd²⁺-selective chalcogenide-glass layer together with a pH-sensitive Ta₂O₅ layer validates the use of the LAPS for chemical multi-sensor applications

[en] Only corner-sharing between the seven TaO₆ octahedra is observed in the neutral complex [H_-11Ta₇O₁₂(tdci)₆] (tdci 1,3,5-trideoxy-1,3,5-tris(dimethylamino)-cis-inositol). The structure depicts the Ta₇O₃₀ double adamantane core. In contrast to previously described structures of polyoxometalate ions, which have a predominantly edge-shared framework, this compound has an unusually open structure. (orig.)

[en] This paper presents a study of bifurcation in the time-averaged dynamics of TaO memristors driven by narrow pulses of alternating polarities. The analysis, based on a physics-inspired model, focuses on the stable fixed points and on how these are affected by the pulse parameters. Our main finding is the identification of a driving regime when two stable fixed points exist simultaneously. To the best of our knowledge, such bistability is identified in a single memristor for the first time. This result can be readily tested experimentally, and is expected to be useful in future memristor circuit designs. (paper)

[en] We report a physical model for multilevel switching in oxide-based bipolar resistive memory (ReRAM). To confirm the validity of the model, we conduct experiments with tantalum-oxide-based ReRAM of which multi-resistance levels are obtained by reset voltage modifications. It is also noticeable that, in addition to multilevel switching capability, the ReRAM exhibits extremely different switching timescales, i.e. of the order of 10⁻⁷ s to 10⁰ s, with regard to reset voltages of only a few volts difference which can be well explained by our model. It is demonstrated that with this simple model, multilevel switching behavior in oxide bipolar ReRAM can be described not only qualitatively but also quantitatively. (paper)

[en] Atomic layer deposition of highly conformal films of tantalum oxide were studied using tantalum alkylamide precursors and water as the oxygen source. These films also exhibited a very high degree of conformality: 100% step coverage on vias with aspect ratios greater than 35. As deposited, the films were free of detectable impurities with the expected (2.5-1) oxygen to metal ratio and were smooth and amorphous. The films were completely uniform in thickness and composition over the length of the reactor used for depositions. Films were deposited at substrate temperatures from 50 to 350 deg. C from precursors that were vaporized at temperatures from 50 to 120 deg. C. As deposited, the films showed a dielectric constant of 28 and breakdown field consistently greater than 4.5 MV/cm

[en] Tantalum pentoxide films grown anodically on tantalum foil have been used as reference materials for a variety of purposes. For both the calibration of depth resolution in sputter-depth profiling instruments using Auger electron spectroscopy, and for calibrating the sputtering rate in these instruments, the certified reference material BCR 261 has been developed at NPL. Tantalum pentoxide reference materials have also been developed in Paris and at Chalk River with considerable characterization. Here we bring these separate standards to one common absolute calibration, show all to be of identical composition, and show that the sputtering rate is constant with depth. This establishes the NPL/BCR material for determining sputtering flux densities, and hence for calibrating Faraday cups, and also for calibrating nuclear scattering instruments for absolute measurements