Creating Thermal Electrons

EC is comparatively sensitive to ion source conditions [76,93]. The actual ion source temperature, the buffer gas, the amount of sample introduced, and ion source contaminations each play important roles. Regular cleaning of the ion source is important [80]. It much depends on the actual analyte whether EC is effective or whether competing processes (Eq. 7.19-7.21) are prevalent. 

Alternatively to direct supply from a heated filament, electrons of well-defined low energy can be delivered into the ion volume by an electron monochromator [90,93-95]. 

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The absorption of a photon creates an electron-hole pair whose wavefunctions initially overlap. After the absorption process, the electron and hole thermalize to the band edge and diffuse apart. The different thermalization mechanisms in extended and localized states are reflected in the diffusion properties. In the extended states, the thermalization time, required to emit the excess energy AE as n phonons is... 

Band-to-band kinetic models (presented in Fig. 5) allow electrons to have only valence or conduction-band energies. Absorption of the appropriate amount of thermal or electromagnetic energy creates an electron-hole pair recombination of an electron and a hole releases energy in the form of heat or light. The band-to-band model yields... 

Negative chemical ionization (NCI) is a misnomer because only rarely is there an actual chemical reaction involved. Instead, the process requires thermal electrons that are created when a gas in the ion source is used as a buffer to decelerate and... 

In pair production, a high-energy photon creates an electron-positron pair. Both the electron and the positron ionize the atoms of the material. After the positron slows down to thermal energy, it annihilates with an electron, creating most likely two so-called annihilation photons. The two photons have equal energies of 511 keV and fly off in exactly opposite directions. They may have further interactions. 

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