Copper silicides

Defects in a SCR, which is present under reverse bias, can be tested in a similar way. Figure 10.6 c shows the same wafer as in Fig. 10.6 e after removal of the oxide and under cathodic polarization in the dark. Hydrogen bubbles caused by the dark current now decorate nickel silicide precipitates that short-circuit the SCR. Nickel precipitates are known to increase the dark current of a p-type Si electrode under reverse bias by orders of magnitude [Wa4]. If the bias is increased the copper silicide precipitates also become visible, as shown in Fig. 10.6 d. This method, like defect etching (Fig. 10.4f), is only sensitive to precipitated metals. Metals that stay in solution, like iron, do not show up in defect mapping and have to be determined by other methods, for example diffusion length mapping. 

Silicobromoform is usually prepared by passing hydrogen bromide over heated silicon112,4,5 or a silicide such as copper silicide.3 The product, consisting of a mixture of silicon tetrabromide with a few per cent of tri- and dibromosilanes, is purified by shaking with mercury, if necessary, to remove any free bromine, and by fractional distillation. The use of metal silicides instead of silicon does not add appreciably to the yield of the bromoform and is not recommended in the following procedure. 

Cobalt Monosilidde, CoSi, is formed as prismatic needles by heating cobalt and copper silicide in the electric furnace.7 It melts at 1300° C. in hydrogen, and has a density of 6-30 at 20° C. When heated in fluorine it incandesces, yielding fluorides. Chlorine decomposes it only at a dull red heat, but it dissolves slowly in aqua regia and more rapidly in concentrated hydrogen chloride. It melts at 1393° C.6... 

Cobalt Disilicide, CoSi2, results when cobalt is heated in the electric furnace with excess of silicon or with a mixture of copper silicide and silicon.8 It forms dark crystals, probably belonging to the cubic system density 5 3 hardness 4-5. Sulphur has no action on it, and oxygen at 1200° C. only effects a superficial oxidation. It incandesces in fluorine if gently wanned chlorine attacks it at 300° C., and bromine and iodine at dull red heat. Concentrated hydrogen... 

When heated with copper silicide, Cu4Si, it yields a double silicide, PtCu2Si,4 as a dense grey substance, completely soluble in aqua regia. 

Iron silicide or Iron monosilidde, FeSi, is prepared by heating a mixture of copper silicide and iron filings in an electric furnace. The resulting product is treated with 50 per cent, nitric acid to decompose any copper silicide, and washed. Obtained in this way, iron silicide occurs as tetrahedral crystals, with a brilliant metallic lustre they are extremely hard, and have a density of 6-17 at 15° C. Fluorine attacks them at ordinary temperatures, whilst chlorine and bromine decompose them at red heat. Molten alkali hydroxides attack the silicide, as also do fused mixtures of the alkali nitrates and carbonates.11... 

Tungsten Disilicide, WSig, is obtained by heating together copper silicide and amorphous tungsten in an electric furnace. The product is washed and treated successively with nitric acid, sodium hydroxide, warm hydrofluoric acid, and water. It may also be obtained by the aluminothermic process, by ignition of a mixture containing... 

Fig. 5. Attachment of methyl halides to silicon atoms (a) copper silicide (b) silicon single crystal.

Though the copper silicide method is preferred for the production of methyl-substituted compounds, a Grignard-type synthesis is commonly used for other alkyl and aryl substituted substances ... 

As can be concluded from Fig. 4, the initial reactivity of the surface of Sited, is very high The relevant copper species present, possibly copper chlorides, which can easily form copper-silicidic phases by reaction with silicon, can easily attack the whole of the surface and react with surface silicon, resulting in Cu-Si species and finally metallic copper, e g, [26]. Due to this very fast formation of catalytically active Cu-Si species and of precursors thereof, the reaction becomes very fast already after a short time. But, on the other hand, this overall attack on the silicon surface gives copper species the possibility to be deposited practically over the whole of the silicon grain This means in terms of our model of catalytically active Cu-Si surface species, explained in the first section of this paper, that there is a lack of still free silicon surface area, which is needed in order to form the active "two-dimensional" Cu-Si species. The surface is simply blocked by thick copper-containing layers. As consequence, the reaction goes down after a short time and the contact mass reaches only low stationary activity. 

Kim, I.C. Byun, D. Lee, S. Lee, J.K (2006). Electrochemical Characteristics of Copper Silicide-Coated Graphite as an Anode Material of Lithium Secondary Batteries. Electrochim. Acta, Vol. 52, pp. 1532-1537... 

Thus, the reaction between silicon and cuprons chloride(I) can lead to the formation of not only copper metal but also copper silicides according to ... 

All the values might be slightly elevated relative to traditional reaction bonded SiC (RB-SiC as shown on the plot ) because of the reduction in residual silicon due to the copper additions. It has been found that copper additions reduce the residual silicon content and may form copper silicides. This was observed in a hybrid SiC/B4C composite with copper and iron additions to the infiltration alloy. The XRD data from that study suggested that as the metallic additions were increased, the silicon content decreased and it has been shown that the hardness increases with decreasing silicon content in reaction bonded boron carbide materials. 

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