Ultraviolet Surface Photochemistry and Charge Transfer
Excimer lasers can initiate surface photochemistry, and are of particular importance in the fabrication of semiconductor electronics . The energy of the photons, 3.5 to 8 eV, can raise many molecules to reactive states. On a metal or semiconductor surface, however, the time for competitive quenching (energy transfer) or charge transfer to the substrate is very fast, 10−13 to 10−15 seconds , Thus only very fast photochemical processes like photodissociation via repulsive states are likely to occur on these surfaces. The surface can still perturb even such a fast process. A simple way is “kinematically”: i.e., the surface or co-adsorbates can act as third bodies for energy or momentum transfer . Also, through bonding, the surface can change the potentials along which the photochemistry proceeds. And finally, even if a surface photo-process can “out-run” competitive quenching or charge transfers, it still may be perturbed by them.
KeywordsCharge Transfer Rate Thermal Desorption Spectrum Ground State Molecule Repulsive State Resonant Transfer
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