Transmission of 0–15 eV monoenergetic electrons through thin-film molecular solids

Publisher Website
Google Scholar
Abstract
The transmission coefficient for monoenergetic electrons (0.04 eV FWHM) passing through thin films (∼100 Å) of molecular solids is measured as a function of electron energy in the range 0–15 eV. The visibility of sharp maxima in the transmission spectra is enhanced by measuring the negative value of the second energy derivative of the transmitted current with respect to electron energy. In benzene, fluorobenzene, pyridine, benzaldehyde, furan, cyclohexene and 1,3- and 1,4-cyclohexadiene, the spectra exhibit from six to eight maxima, whereas in pyrrole and thiophene four structures are resolved. With the exception of the first two features in fluorobenzene and the first feature for the other solids investigated, all other maxima correlate within at least ±0.5 eV with the gas-phase electronic transitions. This correlation is achieved by increasing the energy scale of the transmission spectra relative to the gas-phase electronic energy levels. These findings corroborate previous experiments on solid organic films by Hamill and co-workers who attributed peaks in the first energy derivative of the transmitted current to energy-loss events. It is shown that the transmission features can arise either from an increase in the overall transmission coefficient due to the production of inelastically scattered electrons or from the formation of an electron–exciton complex through the temporary capture of an injected excess electron by field of a Frenkel exciton. The first low-energy feature in each spectrum may possibly arise from an enhancement of vibrational excitation related to the energy dependence of the structure factor.

This publication has 91 references indexed in Scilit: