Metallic impurities, incorporation

The method can successfully be used in analyses of impurities in metals and alloys, for estimation of minor elements in monomolecular films of oxide layers of Fe-Cr-Ni alloys, for detection of metal impurities in environmental pollution, for studying the depression of high-grade semiconducting materials and for analysis of the corrosion products of contact junction diodes used in microelectronic circuits. Much sophistication is desirable on the instrumental side so as to incorporate an automatic recording device to make an FR polarograph suitable for wider applications and common use. 

Transition metal dopants and impurities are probably incorporated substitutionally for Ti in BaTi03. Emission spectrographic analyses indicate that the distribution coefficients for Mn and Fe dopants are on the order of 1 to 2, i.e., the crystals are slightly enriched relative to the melt. Cr and Ni may have distribution coefficients slightly less than 1. For Co, the measured concentrations in the crystals display considerable scatter we estimate that the distribution coefficient is on the order of 4. Fe is the most prevalent transition metal impurity and is typically present at a concentration of 10-15 ppm by weight. Si, Al, Mg, and Cu are also typically present at 5-50 ppmw. Fe and Cr impurities have also been observed by EPR spectroscopy, although Cr could not be detected by emission spectroscopy, with a detection limit of 10 ppmw. 

Harsher conditions may employ pressurized oxygen headspaces, for which Parr type apparatus are employed. Incorporation of added metal impurities (commonly copper and iron salts) in conjunction with oxygen headspace has been reported (60). One research group utilized high temperatures (80°C), copper (II) salts, and oxygen gas headspace to study the... 

FIGURE 7.6 Material removal and static etch rate of copper with identical formulations incorporating oxidizer from different manufacturers. The total metal impurity is the highest in hydrogen peroxide by Manufacture 1 and the lowest by Manufacturer 3 (from Ref. 12). 

Low solubility of solvent into the silicon During epitaxial process, atoms of the solvent are incorporated in the Si crystal. Their incorporation can modify the electronic properties of the layer. Actually, many metallic impurities act as recombination centre or as dopant and reduce the lifetime of minority carriers. Solvent purity is also an important parameter to avoid other impurities. 

In contrast, nonfunctional recycling means that the metal remaining incorporated in recyclates constitutes an impurity resulting in a loss of the metal s function [51]. 

The dehydration of lactic acid to make the prepolymer should start with an —OH to —COOH ratio of 1 1. All other components with —OH and —COOH functionality disrupt the stoichiometric balance and may be incorporated as comonomers during prepolymerization, which limits the final lactide production yield from lactic acid. Little public information is available on the technical and economic relationship between lactic acid quality and lactide synthesis. Only a few patents mention the effect of metal impurities on racemization [68,69]. Stereochemical purity is one of the key parameters determining lactic acid purity. 

Dopant gas/semiconductor A gas or gas mixture used to incorporate a metallic impurity into a semiconductor substrate to impart particular electrical properties. 

One expects that some impurities occupy interstitial sites, leading to fast diffusion. However, it is rather difficult to understand how some metallic impurities could be incorporated into interstitial sites, when the atomic sizes of the impurities are taken into account. Hydrogen atoms could be easily put on interstitial sites in a crystal, but are not necessarily fast diffusers. 

Semiconductors in nano-crystallized form exhibit markedly different electrical, optical and structural properties as compared to those in the bulk form [1-10]. Out of these, the ones suited as phosphor host material show considerable size dependent luminescence properties when an impurity is doped in a quantum-confined structure. The impurity incorporation transfers the dominant recombination route from the surface states to impurity states. If the impurity-induced transition can be localized as in the case of the transition metals or the rare earth elements, the radiative efficiency of the impurity- induced emission increases significantly. The emission and decay characteristics of the phosphors are, therefore, modified in nanocrystallized form. Also, the continuous shift of the absorption edge to higher energy due to quantum confinement effect, imparts these materials a degree of tailorability. Obviously, all these attributes of a doped nanocrystalline phosphor material are very attractive for optoelectronic device applications. 

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