Abstract

Abstract

A solution for scalable-flow batteries

Flow batteries, in which the redox active components are held in tanks separate from the active part of the cell, offer a scalable route for storing large quantities of energy. A challenge for their large-scale development is to avoid formulations that depend on toxic transition metal ions. Lin et al. show that quinones can be dissolved in alkaline solutions and coupled with ferricyanides to make a flow cell battery (see the Perspective by Perry). This gives scope for developing flow cells with very low costs, high efficiencies at practical power densities, simplicity of operation, and inherent safety.

Science, this issue p. 1529; see also p. 1452

Abstract

Abstract

A highly volatile asymmetric iron(II) amidinate, iron(II) bis(N-tert-butyl-N′-ethylacetamidinate), was synthesized for the first time by systematically changing starting iron(II) compounds such as acetylacetonate, acetate, and chloride, in different media such as diethyl ether, toluene, and tetrahydrofuran. The amidinate has been characterized and compared with the symmetric iron(II) bis(N,N′-diisopropylacetamidinate) by NMR spectroscopy, MS, IR spectroscopy, and dynamic and isothermal thermogravimetric techniques. Different amidinates from three starting compounds exhibit almost the same NMR, MS, and IR spectra, a melting point of 85 °C, and the same solution color in the same solvents, but quite different synthetic yields, volatilities, and colors in different solvents. This implies that the amidinates show an interesting solvatochromism. In particular, the asymmetric iron(II) amidinates obtained should be a mixture of paramagnetic and diamagnetic compounds. The thermostability and sublimation kinetics of the iron(II) amidinates have been investigated in detail. It is found that the average activation energy of 106 kJ mol^–1 for the nonisothermal sublimation is slightly higher than the average activation energy of 104 kJ mol^–1 determined from the isothermal thermogravimetric experiments. The sublimation is a diffusion-controlled process because the temperature and the rate of the sublimation depend strongly on the sublimation level and the sample size. The optimal iron(II) starting compound and reaction medium should be iron(II) acetylacetonate and diethyl ether, respectively, because the combination offers the highest yield, the greatest volatilizability of 98 %, and thus the purest product. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Praseodymium aluminum oxide (PAO) thin films were grown by atomic layer deposition (ALD) from a new precursor, tris(N,N′-diisopropylacetamidinato) praseodymium, (Pr(amd)₃), trimethylaluminum (TMA), and water. Smooth, amorphous films having varying compositions of the general formula Pr_xAl_2–xO₃ were deposited on HF-last silicon and analyzed for physical and electrical characteristics. The films were pure according to Rutherford backscattering spectrometry (RBS) and secondary ion mass spectrometry (SIMS). The permittivity of the thin film with the stoichiometry of Pr_1.15Al_0.85O₃ was 18, and all annealed films displayed very low leakage currents compared to other high-k oxide films deposited using ALD. A leakage current density of 1.1 × 10^–4 A cm^–2 was achieved for a PAO film with an equivalent oxide thickness of 1.46 nm. Annealed films also displayed nearly zero flat-band voltage shifts and low hysteresis (< 10 mV). The optimal growth parameters and electrical properties were achieved with Pr_1.15Al_0.85O₃. Atomic force microscopy (AFM) determined that high temperature annealing (850 °C) had no effect on the smoothness of the films (rms of 0.17 nm).

Thin and continuous copper films serve as seed layers for electrodeposition of interconnects in microelectronic devices. Gaps in the continuity of these Cu films must be avoided, because they can generate voids that later lead to failure of the devices. It is difficult to sputter completely continuous copper-seed layers into the increasingly narrow trenches and holes in modern interconnects. Here we report a method for producing thin, completely continuous, and highly conductive copper films conformally inside very narrow holes with aspect ratios of over 40:1. The first step in our process is atomic layer deposition (ALD) of copper(I) nitride, Cu₃N, by the alternating reactions of copper(I) N,N′-di-sec-butylacetamidinate vapor and ammonia on surfaces heated to approximately 160 °C. At this temperature, Cu₃N is thermally stable, but is readily reduced to copper metal by exposure to molecular hydrogen gas (H₂). Copper layers as thin as 0.8 nm (about 3 monolayers) are electrically continuous and show the electrical resistivity predicted by a grain-boundary-scattering model for continuous films of that thickness. 3 nm thick copper films on 2 nm of ruthenium have a sheet resistance of less than 50 Ω/□, a value low enough to serve as seed layers for advanced electroplating techniques.