Thin-film oxidation

In the fifth paper of this chapter on cathodes, an investigation of thin-film oxide-hydroxide electrodes containing Cr, Ni, and Co compounds was authored by N. Vlasenko et al. The thin-films were produced by electrochemical deposition from transition metal aqueous fluorine-containing electrolytes onto steel substrates. These thin-films were tested in Li coin cells. Electrochemical activity appears to scale with the amount of fluoride used in the deposition the larger concentration of fluoride in the bath, the greater the capacity. One Ni oxide-hydroxide film electrode showed greater than 175 mAh/g reversible capacity on the 50th cycle with excellent coulombic efficiency. 

The electrochemical behavior of thin-film oxide-hydroxide electrodes containing chromium, nickel and cobalt compounds was investigated. Experimental results have shown that such compounds can be successfully used as active cathodic materials in a number of emerging primary and secondary battery applications. 

Table 1. Thin-film oxide chemical composition.

The data in the Figs. 9.1,9.2 and 9.4 nicely illustrate the complementarity of XPS and SIMS and the possibilities that thin film oxide supports offer for surface investigations. Owing to the conducting properties of the support, charging is virtually absent and typical single crystal techniques such as monochromatic XPS and static SIMS can be applied to their full potential to answer questions on the preparation of supported catalysts. 

Realistic model systems. Some techniques become much more informative if suitable model systems are used. Examples are the thin-film oxides used as conducting model supports, which offer much better opportunities for surface analysis than do technical catalysts. Another example is provided by the non-porous, spherical supports that have successfully been employed in electron microscopy. It is important that the model systems exhibit the same chemistry as the catalyst they represent. 

Table 16-3 gives some more information on nuclei used in spectroscopy. When the kinetic problem dictates small dimensions of the sample (e.g., in thin film oxidation), the concentration needed to apply a nuclear spectroscopy may be considerably higher than indicated in Thble 16-3. 

This article give an overview about the microwave properties of insulating and superconducting oxide dielectrics. In addition, microwave measurement techniques for bulk and thin film oxides will be reviewed. 

The renewed interested in ZnO as an optoelectronic material has been triggered by reports on p-type conductivity, diluted ferromagnetic properties, thin film oxide field effect transistors, and considerable progress in nanostructure fabrication. All these topics are the subject of a recently published book [11],... 

Emphasis was first placed on the adsorptive behavior of Compound D on the surface of chromium because that metal has the following desirable properties (a) it is an excellent adsorbent for carboxylic acid groups (5) (b) a large body of data is available on the properties of adsorbed, monomolecular films of aliphatic (16), partially fluorinated (13), fully fluorinated (2), and chloro-fluoro carboxylic acids (2) (c) the metal surface can be readily and reproducibly cleaned by standard metal-lographic polishing techniques and (d) there is a hard, coherent, thin-film oxide on the surface (18). 

I. Antioxidative Properties Using the Thin Film Oxidation Protocol... 

Table 2 Oxidative resistance of arachidonic acid when additized with experimental nitro- and thio-polyunsaturated fatty acids during thin film oxidation testing...

The broad band observed around 2080cm , predominating at higher particle sizes, is due to CO adsorbed on Rh particles. The RAIRS spectra obtained on oxide supported metal particles (single crystal oxides and thin film oxides) is discussed in detail in Section 5. 

This contrasts with the case of FT-RAIRS on metal supported on single crystal oxide surfaces where the local dielectric response, and the associated electric fields in IR, depend on the particle size or film thickness. It should also be mentioned that on thin film oxide substrates, because the underlying metal will always screen the parallel fields, molecules adsorbed on particle facets which result in e.g. v(C-0) being orientated parallel to the macroscopic surface will be screened and not be observed in the RAIRS spectra. 

To prepare model catalysts, metal nanoparticles were grown on the thin film oxide by evaporation (step 3 in Fig. 15.7a). Figure 15.7c and d show STM results for Pd nanoparticles grown on Al3O3/NiAl(110) at 300 and 90 K, respectively [11, 39,43,47,48]. Figure 15.8 displays the dependence of the island density (nanoparticles per cm ), the mean particle diameter, and the average number of atoms per particle on the nominal film thickness [39]. Similar nucleation studies were performed for Pt, Rh, and Ir nanoparticles [39, 46]. 

Fig. 17.2 The preparation of epitaxially grown thin film oxide model catalysts suitable for structural, spectroscopic and catalytic characterization. A schematic of the recirculated microreactor setup is shown on the right [22, 28]...

The most commonly used methods for the preparation of ultrathin oxide films are (1) direct oxidation of the parent metal surface, (2) preferential oxidation of one metal of choice from a suitable binary alloy, and (3) simultaneous deposition and oxidation of a metal on a refractory metal substrate. The detailed procedures for (1) and (2) are discussed elsewhere [7,56,57] procedure (3) is discussed here in detail. Preparation of a model thin-film oxide on a refractory metal substrate (such as Mo, Re, or Ta) is usually carried out by vapor-depositing the parent metal in an oxygen environment. These substrate refractory metals are typically cleaned by repeated cycles of Ar sputtering followed by high-temperature annealing and oxygen treatment. The choice of substrate is critical because film stoichiometry and crystallinity depend on lattice mismatch and other interfacial properties. Thin films of several oxides have been prepared in our laboratories and are discussed below. 

Michaelis reviews the application of valve metals in electronics based on the dielectric properties of ultra-thin films. Following presentation of fundamental principles and experimental details, the discussion of valve metal systems includes thin film oxide behavior of Ti, Zr, Hf, Nb, Ta, and Al. The application of these valve metal systems in electrolytic capacitor manufacturing is discussed with emphasis on current development trends and research issues. In addition, special emphasis on Si02 dielectric films is provided for integrated circuit applications associated with dynamic random access memory chip fabrication. 

Fig. 2 Schematic of the preparation method for the synthesis of supported metal clusters on thin film oxide surfaces. (View this art in color at www.dekker.com.)...

Trundle, C., and Brierley, C. J., Precursors for thin films oxides by Photo-MOCVD, Appl. Surf. Sci. 36, 102 (1989). 

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