Effective Diffusion Coefficient Deff Research Articles

Theorie der Kontraktion der positiven Säule

It is experimentally known that with increasing pressure and current the positive column of the glow discharge constricts. A qualitative discussion of the electron particle balance displays certain requirements for the effective diffusion coefficient Deff and the production coefficient αeff of the electrons With increasing distance from the axis either the diffusion coefficient Deff should increase or the production term αeff should decrease down to negative values. We discuss to which extent the Various physical proceses can meet these requirements. The constriction caused by the presence of negative ions is evaluated from the transport equations. From the solution of our eigenvalue problem we have the radial electron density distribution and the electric field as functions of the current, pressure and radius.

Enhanced Cu Concentration in Ge Containing Ni at 500°C

Penning has shown that at 500°C, Cu penetrates into Ni-doped Ge (containing ∼1016 Ni atoms cm−3) to a concentration more than 10 times its thermal equilibrium value. We have confirmed this observation and extended the experiments with the following results. At 500°C the rate of Cu64 penetration (in Ni saturated samples) indicates an effective diffusion coefficient Deff of ∼2×10−8 cm2/sec and a saturation density, n0, of ∼1016/cm3. No detectable Cu penetration occurs after 10 hrs at 400°C. The Cu penetration at 500°C is independent of dislocation density in the sample and also independent of whether or not the Ni has been previously precipitated. The extra Cu is not electrically active. We have similarly studied the rate of mixing of ordinary Cu and Cu64 by diffusion in Ge samples at 500°C and find that Deff for this process is again ∼10−8 cm2/sec. From these experiments we conclude that Cu penetration in Ge is not responsible for the 0.04-ev energy level which appears during the early stages of Ni precipitation at 400°C, as Penning suggests. The enhanced penetration of Cu64 observed at 500°C may be interpreted as resulting from exchange between interstitially diffusing Cu64 and precipitates of either Ni or Cu.