Low-energy electron-induced processes in fluorinated copper phthalocyanine films observed by F- desorption: why so...

As an indication of damage induced by hot electrons in an organic electronic material, the desorption of F- ions from a thin perfluorinated copper phthalocyanide film on SiO2 under low-energy (0-25 eV) electron impact has been recorded mass spectrometrically. Yields and damage cross sections are very low. No strong features due to negative ion resonances are found in the electron energy dependence of the desorption yield; rather the yield function rises from a threshold at about 5-6 eV continuously (with some weak structure) throughout the measured range. We discuss these findings in terms of the electronic structure of the film, as well as parameters influencing the relevant bond breaking process. We emphasize the strong influence of energy redistribution, which quenches normally long-lived negative ion resonances and selects localized and strongly repulsive excitations, as often observed in electronically induced bond breaking at surfaces. The improved understanding should be helpful in the selection of low-damage materials for organic semiconductor devices and for selection of operation parameters.