Dispersion formation under vacuum

Enokida et al. (1991) measured hole mdbilities of PMPS before and after ultraviolet exposures. The exposures were of the order of 1 erg/s-cm2. Prior to the exposures, the mobilities were approximately 10-4 cm2/Vs and weakly field dependent. Following the exposures, a decrease in the mobility was observed. Under vacuum exposure conditions, a decrease of approximately 40% was observed for a 1 h exposure. Under atmospheric conditions, however, the decrease was approximately a factor of 4. Enokida et al. attributed the decrease in mobility to the formation of Si-O-Si bonds in the Si backbone chain. A similar study of PMPS was described by Naito et al. (1991). While the field and temperature dependencies of the mobility were not affected by the ultraviolet exposures, the dispersion in transit times increased significantly. The change in dispersion could be removed by subsequent annealing. The authors attributed the increase in transit time dispersion to a reduction in the hole lifetime, induced by Si dangling bonds created by the ultraviolet radiation. 

Citrate method The preparation procedure consisted in the dissolution of the metal salts, namely Mn(N03)2 4H20 and Ce(N03)3 6H20, in distilled water, the complexation of the metallic cations with citric acid and the rapid concentration of the liquid by evaporation under vacuum. The viscous liquid was dried at 80°C and the amorphous precursor obtained was decomposed in air prior to calcination. Owing to the complexing property of the citrate anion, this procedure leads to the formation of finely dispersed two-phase systems or favours the formation of mixed oxide phases upon calcination, when these exist. Samples were calcined for 5 hours at 200, 300,400 or 500°C. 

Owing to the tendency of the acid to hydrolyse, the preparation of the sodium salt is a delicate operation. The neutralisation of the acid with sodium hydroxide is therefore undertaken under intensive cooling and the salt solution is evaporated under vacuum. Maylott and Meyer (1964) recommended anhydrous reaction conditions for the formation of the salt. The reacting anhydrous acid and dry alkali compound are dispersed in liquid hydrocarbon. At the end of the reaction the sodium salt is filtered off from the reaction medium. 

The KCg binary is prepared by the direct reaction of potassium on graphite under vacuum (ref. 9). Due to the electronic transfer to the graphene plane, this compound is a strong reducii agent. If it is allowed to react with a metallic halide MQ (M = Fe,Co,Ni) dissolved in tetrahydrofuran (THF), the reaction occurs spontaneous at room temperature and leads to the formation of metal M° dispersed on graphite ... 

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