Ranges of photoinjected electrons

Electrons injected from a metal electrode into a liquid are under the influence of the externally applied electric field and under the image force. At the same time collisions with the atoms or molecules of the liquid lead to energy losses and eventually to a return to the cathode. The injection current into the liquid is always smaller than the vacuum current at the same energy exceeding the wotk function, i.e.. 

In the case of no applied electric field, the minimum energy necessary to inject an electron from the metal cathode into the conduction level of the liquid is given by Equation 19. Application of an external field leads to a lowering of the barrier due to the combined action of the external field and the image field of the injected charge. The external potential, V, due to the applied field E is given as. 

Injected electrons will lose their energy by collisions and become thermalized at various distances from the cathode. Their motion is then determined by the electric field and by diffusion. At any point x, the flux of electrons is given as 

At a given photon energy hv electrons are emitted with a distribution of kinetic energies up to hv - Electrons of a given excess energy will exhibit a distribution of thermalization distances. Both effects are summarized by a distribution function D(xq). The escape yield Y, given as the ratio of the transmitted current to the injected current, is then obtained as 

Here x, X, and b are the range parameters of the distribution. With a Gaussian distribution function range parameters b were obtained which are compiled in Table 1. Here a similar dependence of b on the molecular structure is apparent as in the case of ionization by high energy radiation (see Section 5.6). 

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Table 1 Range of Photoinjected Electrons in Nonpolar Liquids Ej — Kinetic Energy of the Injected Electrons...

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