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 elec tron transmission (LEET) spectra and electron stimulated desorption (ESD) y ields of H- from pure films of n-hexane and ethyl-benzene from 20 K to subl imation. The ESD yields from both dissociative electron attachment and dipo lar dissociation initially increase as the films are heated. This effect is attributed to the collapse of pores within the films. For n-hexane, a mark ed decrease in ESD yields is observed at film temperatures greater than or equal to 80 K, which correlates to the onset of crystallization as evidence d in LEET spectra. This decrease in anion yield is associated with the form ation of a well-defined band structure that reduces the time period an exci tation and/or electron resides on a particular molecule. This behavior in t he ESD yields from ethyl-benzene films is not observed prior to sublimation in agreement with LEET spectra which show negligible change with film temp erature indicating that there is no change of phase prior to sublimation (i .e., the film remains amorphous at all temperatures). (C) 2000 American Ins titute of Physics. [S0021-9606(00)70543-5].