Unipolar diffusion charging

The traditional unipolar diffusion charging model is based on the kinetic theory of gases i.e., ions are assumed to behave as an ideal gas, the properties of which can described by the kinetic gas theory. According to this theory, the particle-charging rate is a function of the square of the particle size dp, particle charge numbers and mean thermal velocity of tons c,. The relationship between particle charge and time according White s... 

Arendt and Kallman (A3) have derived the following relationship for the rate of charging a particle by diffusion of unipolar ions ... 

In diffusion charging, particles are charged by unipolar ions (ions having the same sign) in the absence of an applied electric field. Collisions of ions and particles occur as a result of random thermal motion of the ions, the brownian motion of the particles being generally neglected. 

Bricard theoiy (solid lines) with that of Figure 12.2 Unipolar diffusion charging. White (dashed lines). Experimental (After Davison and Gentry, 1985.) points of Liu and Pui are also shown. 

Unlike diffusion charging, field charging takes place in an ordered field of unipolar ions, i.e., in a region where the ions are in an electric... 

Unipolar Diffusion Charging Free Molecule Range... 

In this chapter, online size classification techniques for both diameter and length of gas phase nanofibers are reviewed. In addition, unipolar diffusion charging theories for fibers are discussed. Based on the findings of this review, an approach to online size characterization of carbon nanotubes (and nanofibers) is developed and experimental results are presented. Because of the importance of TEM analysis for size measurement confirmation and for structure and compositional analysis, a brief discussion of microscopy sample preparation and analysis is also presented. 

In 4.4 the theory of 4.2 will be applied to study electro-diffusion of ions through a unipolar ion-exchange membrane, separating two electrolyte solutions. This will include the classical treatment of concentration polarization in a solution layer adjacent to an ion-exchange membrane under an electric current. The validity limits of this theory, set by the violations of local electro-neutrality and caused by the development of a macroscopic nonequilibrium space charge, will be indicated. (The effects of the nonequilibrium space charge are to be discussed at some length in Chapter 5.)... 

Abstract We review the methods used to simulate the optoelectronic response of organic solar cells and focus on the application of one-dimensional drift-diffusion simulations. We discuss how the important physical processes are treated and review some of the experiments necessary to determine the input parameters for device simulations. To illustrate the usefulness of drift-diffusion simulations, we discuss several case studies, addressing the influence of charged defects on transport in bipolar and unipolar devices, the influence of defects on recombination, device performance and ideality factors. To illustrate frequency domain simulations, we show how to determine the validity range of Mott-Schottky plots for thin devices. Finally, we discuss an example where optical simulations are used to calculate the parasitic absorption in contact layers. 

Gentry, J.W. (1972). Charging of aerosol by unipolar diffusion of ions. J Aerosol Sci 3 65-76. 

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