Alternation between modes of electron transmission through organized organic layers

Photoelectrons from gold covered with self-assembled monolayers of L-polyalanine were measured as a function of temperature. Spectra and asymmetries to circularly polarized light were recorded while monitoring the electric potential across the monolayer. Upon cooling, this potential changes gradually, passing through zero at 264 K. But, contrary to the gradual potential change, both the shape of spectra and the polarization asymmetry change abruptly at the edges of the temperature range Delta=264+/-10 K. Above and below Delta, opposite asymmetries are observed and the spectra are broad. Within Delta, a series of several sharp resonances appear with null asymmetry.