Limiting pulse current density

Figure 6.7 Influence of pulse parameters on deposit morphology for copper deposition from a copper sulfete/sulfuric acid electrolyte [6.102]. p pulse current density ipj limiting pulse current density i average current density jj limiting current density under dc conditions.

Equation (4.89) is valid if the electrodeposition process is an under activation control in the Tafel region, the limiting diffusion current density is the same in both the middle and at the edge of the electrode, and / is the cell current corresponding to i. During the current pulses, the amplitude values of current densities and current should be substituted in Eq. (4.89) producing... 

The experimental conditions were pulse off-times 16,80,400, and 16(X) s, duty cycle 0.2, pulse current density /on = 100 mA cm , current density during off-time /off = 0.2 mA cm, and RPM= 1400. Under such hydrodynamic conditions, a limiting current density for copper electrodeposition was /l(Cu) = 9.7 mA cm . The number of cycles (depending on the on-time and off-time) was 11022, 2204, 441, and 110, respectively, in order to obtain approximately 1.3 mm thick electrodeposits. The SEMs of etched cross sections presented in Fig. 7.32 illustrate the phase distribution obtained in the experiments. Except for the electrodeposit shown in Fig. 7.32d, which had the lowest Cu content, the electrodeposits exhibited a colunuiar structure. The Co alloy columns apparently go through the entire electrodeposit, indicating that atoms are added to existing growth sites in each phase [55]. 

With the applied cathodic current density pulses larger than the limiting diffusion current density, parallel to copper electrodeposition hydrogen evolution reaction occurs [52]. On the other hand, there was not any gas evolution during anodic pulses indicating that the overall gas evolution corresponds to hydrogen evolution. Then, Eq. (4.22) can be modified by Eq. (4.25) ... 

This article will outline the experimental techniques we have used in the laser spectroscopy of these atoms and briefly indicate current plans for the refinement of these measurements. As Fig. 1 shows, the laser spectroscopy of positronium and muonium is not competitive with comparable measurements in hydrogen, largely due to the low density sources of these atoms. In the case of positronium, the first measurements were done at peak densities of a few atoms/cm3 during a laser pulse. The muonium work was limited by atom densities 10 2 atom/cm3 per laser pulse. As feeble as these sources might seem to spectroscopisis of less exotic atoms, one must remember that these instantaneous densities represent many orders of magnitude improvement of above pre-existing sources of thermal positronium and muonium. Clearly, improved sources will lead to more precise measurements. 

Figure 15K represents a typical response of the electrochemical inteqjhase to constant current pulses of different magnitude. For a sufficiently low current density, a true steady state is reached before the effect of diffusion limitation can be observed. As the current density is increased, diffusion limitation sets in earlier. Extrapolation of the potential to zero time can sometimes be employed to estimate a correct value of the activation overpotential, as shown in this Fig. 15K. If such extrapolation is not practical, one may use a higher concentration of the reactant, to increase the ratio x /x (i.e., to...

Mass transport plays an important role in pulsed metal deposition. On the one hand it limits the maximum rate of deposition and influences the structure and properties of deposits. On the other hand it effects the macrothrowing and microthrowing power. Under dc conditions, the maximum deposition rate is given by the limiting current density, fg, where the metal ion concentration... 

Therefore, very high instantaneous limiting current densities can be obtained with MREF electrolysis as compared to DC electrolysis. The pulse on-time, t , may be reduced by increasing the frequency or decreasing the duty cycle. 

Figure C2. 16.ll illustrates the evolution of the threshold current density of diode lasers with the structure of the recombination region within the p-n jimction, known as the active region. The early diode lasers were based on GaAs homojunctions. Their large threshold current densities resulted from poor carrier confinement and large effective active region thickness. This is because the diffusion length of electrons is fairly long in most of the semiconductors discussed here, of the order of several micrometres. A very high threshold current density limits operation to short pulses and ciyogenic temperatures.

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