Interdiffusion prevent metallic

POWDER METALLURGY. Powder metallurgy (PM) embraces the production of finely divided metal powders and their union through the use of pressure and heat into useful articles. The temperatures required are below the fusion point of the principal constituent, and bonding depends on interdiffusion of the metal particles in the solid state. It is necessary to provide intimate contact between particles, hence reducing atmospheres are provided in the sintering process to prevent formation of oxide films Readily oxidized powders such as aluminum require special technique. 

Barrier metals, as opposed to alloys like AuGeNi, are employed in many thin film metallization systems to promote adhesion and prevent interdiffusion. Gold is an excellent conductor, however, it has very poor adhesion to both Si and GaAs. Gold also shortens the device lifetime when it diffuses into an active region of the device. For this reason it is used in multilayered structures such as Ta/Pt/Ta/Au (50), W/Au (50) and Cr/Au (51). SIMS, AES and RBS have all been used effectively in studying metal-metal interdiffusion, to extract diffusion coefficients, and to estimate device lifetimes. 

Use of suitably reactive metals and/or organics, so that a strong interaction at the top layer(s) of the organic material prevents interdiffusion. 

With this technique it was also possible to look for appropriate buffer layers between the metal hydride and Pd to prevent interdiffusion and oxidation [83], In the case of La switchable mirrors it was found that an AlO layer with a very well defined thickness (between 0.9 and 1.2 nm) is able to inhibit Pd/La interdiffusion and oxidation of La without significantly hampering hydrogen absorption. 

The final steps involve deposition of the interconnect metal (Figure 4.39, step s). Copper is now the metal-of-choice due to its more desirable electrical resistivity, relative to A1 (1.7 pO cm vs. 2.7 pQ cm, respectively) that was exclusively used in earlier ICs. Due to its low resistivity and high density, titanium nitride is an efficient barrier level that prevents surface oxidation of Cu, as well as the interdiffusion of Cu into adjacent layers. To yield the final multilayer IC shown in step t of Figure 4.39, steps (p)-(s) are repeated. Indeed, a long complex process that took weeks in the making. 

All the advantages of heterojunction II-VI sulfide-based solar cells can be utilized, with the polymer matrix preventing interdiffusion of An metal components, often the main reason for the instability observed in inorganic heterostructure II-IV solar cells produced by liquid epitaxy or thermal evaporation,... 

Figure 7.4 shows the structure of an FBMR with plate-type Pd-Ag dense metal membranes for hydrogen production [8, 9]. Two-sided planar membrane panels are suspended vertically in the reactor. Each side of the panels consists of 25 pm thick Pd-Ag foil mounted on a porous stainless steel base with a barrier layer to prevent interdiffusion... 

Inorganic (non-polymer) basecoats can provide layers to aid in adhesion (adhesion layer or glue layer) of a film to a surface. For example, in the Ti-Au metallization of oxides, the titanium adhesion layer reacts with the oxide to form a good chemical bond and the gold alloys with the titanium. The layers may also be used to prevent interdiffusion (diffusion barrier) between subsequent layers and the substrate. For example, the electrically conductive compound TiN is used as a barrier layer between the aluminum metallization and the silicon in semiconductor device manufacturing. 

The ceramic thermal barrier layer provides thermal protection to the underlying materials. Also, this layer works as a shield to protect the underlying metallic parts from erosion and corrosion. The metallic bond coat is to protect the underlying superaUoy substrate from oxidation, balance thermal mismatch between the topcoat and substrate, and prevent interdiffusion of elements in the substrate and bond coat. 

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