The effects of temperature and morphology on electron transmission and stimulated desorption of H- from thin hydrocarbon films

We have measured for the 0-20 eV incident energy range, the low-energy electron transmission (LEET) spectra and electron stimulated desorption (ESD) yields of H- from pure films of n-hexane and ethyl-benzene from 20 K to sublimation. The ESD yields from both dissociative electron attachment and dipolar dissociation initially increase as the films are heated. This effect is attributed to the collapse of pores within the films. For n-hexane, a marked decrease in ESD yields is observed at film temperatures greater than or equal to 80 K, which correlates to the onset of crystallization as evidenced in LEET spectra. This decrease in anion yield is associated with the formation of a well-defined band structure that reduces the time period an excitation and/or electron resides on a particular molecule. This behavior in the ESD yields from ethyl-benzene films is not observed prior to sublimation in agreement with LEET spectra which show negligible change with film temperature indicating that there is no change of phase prior to sublimation (i.e., the film remains amorphous at all temperatures). (C) 2000 American Institute of Physics. [S0021-9606(00)70543-5].