Surface modifications passive layers

The use of iodate and periodic acid as oxidizers for noble metal CMP has also been attempted. Similar to W CMP, a surface oxidation or modification is required for the subsequent removal by mechanical force. For example, the potential use of ruthenium as bottom electrode capacitor for next-generation DRAM devices [40] has been explored. Owing to the fact that a dry-etch process can lead to the formation of toxic RUO4 [41], the possibility of using CMP to implement Ru has gained interest recently. The studies in this area have indicated that the formation of stable passive layers such as RUO2 [41,42] and RU2O5 [42] are important steps in the Ru CMP. 

Figure 6.29 shows, as an example, the effect of surface modification on the sta-bihty of sihcon electrode in an aqueous solution. The bare sihcon surface is quickly passivated in aqueous solution under illumination. Coating the electrode with a layer of either ferrocene or polypyrrole gives an improvement in the stabihty. The stability is further improved by a two-layer coating of ferrocene/polypyrrole as shown in Fig. 6.29. 

C. Chemical modification of the glued surfaces by the formation of passivating layers. The modification technique depends on the nature of the metal. The parts are most often subjected to acid pickling, e.g. aluminum alloys are anodized in sulfuric and chromic acids. It is preferable to anodize aluminum parts in sulfuric acid followed by treatment of the anodic film in a bichromate. There are several methods of pickling carbon and stainless steels, chemical oxidation of magnesium alloys as well as copper and titanium alloys before gluing [4]. 

The amount of Si ions dissolution is found to be dependent on surface modification, which was confirmed by induchvely coupled plasma-atomic emission spectrometer (ICP-AES) analysis. Table 2.2 shows the dissolution amount of Si ions with and without surface modification of fumed silica slurry. Without surface modification, the amount of Si dissoluhon was 1.370 0.002 mol/L, whereas surfaces modified with poly(vinylpyrrolidone) (PVP) polymer yielded a dissoluhon of 0.070 0.001 mol/L, almost 20 hmes less than the unmodified surface. Figure 2.6 represents the electro-kinetic behavior of silica characterized by electrosonic amplitude (ESA) with and without surface modification. When PVP polymer modified the silica surface, d5mamic mobility of silica particles showed a reduchon from -9 to -7 mobility units (10 m /Vxs). Dynamic mobility of silica particles lacking this passivation layer shows that silica suspensions exhibit negative surface potentials at pH values above 3.5, and reach a maximum potential at pH 9.0. However, beyond pH 9.0, the electrokinetic potential decreases with an increasing suspension pH. This effect is attributed to a compression of the electrical double layer due to the dissolution of Si ions, which resulted in an increase of ionic silicate species in solution and the presence of alkali ionic species. When the silica surface was modified by... 

Crystal surface modification The surface of the crystals may also be modified by the final passivation rinse. When a final rinse containing chromate or Cr(III) is used, a thin film of either ZnCr04, CrP04 [32], or CrOOH [33] is formed on the surface. Likewise, when steel is used as the substrate material, and in the presence of passivating additives such as nitrite, a thin layer of FeP04 may be formed on the surface of the crystals. Further modification of the phosphate surface may be induced if the crystals come into contact with an alkaline environment, as described below. 

Figure 2.10. Interfacial degradation mechanisms ofLi(Nii-xCo 02 electrodes in contact with a standard LiPFfcarbonates electrolyte during cycling. Structural modifications of the active material s surface and the formation of a passivation layer. (Reprintedfrom [SEG 99] with permission. Copyright 2005 Elsevier). For a color version of the figure, see WWW. iste. CO. uk/dedryvere/electrodes.zip...

Stainless steels, as well as A1-, Ni-, and Ti-based alloys have been studied extensively as possible candidates for bipolar plates. One of the most well-studied materials for bipolar plates is SS 316/316L (16-18% Cr, 10-14% Ni, 2% Mo, rest Fe) other candidates are 310,904L, 446, and 2205. Bare stainless steel plates form a passive 2-A nm chromium oxide surface layer under PEMFC conditiOTs that leads to unacceptably high ICRs. A similar trend is observed for the other alloys and therefore surface modification or surface coatings on selected substrate material has to be considered as a pathway to meet the technical targets of low ICR and high corrosion resistance. 

The inner phosphine layer passivates the particle surface the linking layer protects it while the outer functionalized layer delivers desirable chemical properties, including miscibility, the ability to copolymerize with other polymer matrices, cross-linking on the surface of the dots, and further chemical modifications such as conjugations to biomolecules. 

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