Halide contamination

Several metal halide precursors have been applied in ALD processes, together with water as an oxygen source. However, the suitability of a particular metal halide for ALD depositions has been found to depend on the metal. Halide contamination of the film may cause problems at low deposition temperatures [45-47], although halides may be successfully used as ALD precursors. Liberation of HX (X = F, Cl, Br, I) during the deposition process may also cause problems, such as corrosion and etching. 

Propylene carbonate [108-32-7] M 102.1, b 110°/0.5-lmm, 238-239°/760mm, d 1.204, n 1.423. Manufactured by reaction of 1,2-propylene oxide with CO2 in the presence of a catalyst (quaternary ammonium halide). Contaminants include propylene oxide, carbon dioxide, 1,2- and 1,3-propanediols, allyl alcohol and ethylene carbonate. It can be purified by percolation through molecular sieves (Linde 5A, dried at 350° for 14h under a stream of argon), followed by distn under vac. [Jasinski and Kirkland AC 39 163 1967], It can be stored over molecular sieves under an inert gas atmosphere. When purified in this way it contains less... 

The incorporation of inorganic anions (halide contamination, formation of ate complexes), particularly as observed in alkyl [137] and alkoxide chemistry... 

The cationic rhodium complex [Rh(nbd)(PPh3)2]+ (nbd = norbornadiene), previously described by Osborn as a catalyst precursor for the hydrogenation of alkenes and dialkenes when dissolved, e.g., in acetone [28], has proved to be active in dialkylimidazolium PF, CuCI, or SbFf, salts [29]. Due to the very low solubility of alkanes in ionic liquids, the reaction is truly biphasic. The rhodium loss in the organic phase is under the limit of detection. The catalyst can be used repeatedly. In this case, the presence of coordinating anions, such as traces of chloride, inhibits the catalyst activity. Halide contaminants may arise from unreacted starting material used in the preparation of NAILs or from the possible decomposition of the halogenated anion (e.g., PF ). Purification and quality control of ionic liquids are then crucial [30]. 

Factors which often make the silylamide route superior to traditional salt metathesis reactions are (i) the reaction in non-coordinating solvents due to the high solubility of the monomeric metal amides, (ii) mild reaction conditions often at ambient temperature, (iii) avoidance of halide contamination, (iv) ease of product purification [removal of the released amine along with the solvent under vacuum (bp HN(SiMe3)2 125 °C)], (v) base-free products (coordination of the sterically demanding, released amine is disfavored), (vi) quantitative yield , and (vii) the facile availability of mono- and heterobimetallic amide precursors. 

Lancaster, 99%) and HPLC grade organic solvents were used as received. The ionic liquids tested were prepared in house following standard preparative procedures, the details may be found elsewhere. In each case the ionic liquid was treated under vacuum at 60 °C in order to minimise water and were then washed extensively to ensure that halide contamination from the preparation process was < 10 ppm. 10% Pd on activated carbon was obtained from Aldrich and 5% Pt on graphite, pre-treated in flowing hydrogen... 

Another method has been described for the synthesis of halide-free ILs which uses an imidazolylidene carbene as an intermediate. The starting material is an imidazolium halide which is treated with sodium tert-butoxide to form an imidazolylidene carbene. The latter is distilled in a Kugelrohr apparatus, then reacted with a Br0nsted acid. In this way, it is possible to obtain an IL free from halide contamination, but traces of N-alkylimidazole or acid may be present. 

Similarly, a one-step procedure was proposed for a series of hydrophilic or hydrophobic ILs [22]. For example, a mixture of N-methylimidazole, ethyl bromide, and sodium tetrafluoroborate is heated at 70 °C for two weeks. The filtration of the solution allows collection of the IL in nearly 90% yield. Without any subsequent purification, the residual halide contamination is very low. 

Anodic Corrosion. The spacing between components of the ICs is small, and when a voltage is applied to a device, voltaic gradients of the order of 10 -10 V/cm can exist across surfaces, accelerating electrochemical corrosion reactions and ionic migration. In ICs, positively biased aluminum metallizations are susceptible to corrosion. A combination of electric fields, atmospheric moisture, and halide contamination leads to corrosion of aluminum. Gold and copper metallization are also subject to corrosion under these conditions. 

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