Helmut Zacharias: Organized helical molecules as effective electron spin filters

For spintronic applications the development of a source of spin polarized electrons operating at room temperature is still a challenge. The interaction of longitudinally spin polarized electrons with chiral molecules has been studied extensively since 1996. Later experiments with photoelectrons from gold surfaces transmitted through monolayers of DNA indicated a spin-filtering behavior of the molecules.

A new approach is based on the interaction of electrons with ordered helical molecules in a thin film. Early electron circular dichroism experiments using circularly polarized light to emit photoelectrons from gold surfaces transmitting through monolayers of stearoyl lysine [2a] and DNA [2b] indicated a spin-filtering behavior of such organic layers.

Here we present results on the electron spin polarization observed for various samples of self-assembled monolayers of helical molecules on metal and semiconductor surfaces. Samples are irradiated with circularly and linearly polarized laser radiation at λ = 213nm to generate photoelectrons in a single step. The spin of the photoelectrons is analyzed by a Mott polarimeter. Longitudinal spin polarizations of up to about 60% have been measured in case of oligo dsDNA, irrespective of the polarization of the irradiating light. Experiments with helical membrane proteins (bacteriorhodopsin) and self-assembled monolayers of α-helical oligo-peptides show also spin filtering properties. Similar to DNA a dependence of the spin polarization on the length of the molecules is observed. Recent experiments with enantiomer pure hepta-helicene and for DNA covalently bound to Si show also promising results.

For spintronic applications a source of spin polarized electrons operating at room temperature is still a challenge. A new approach is based on the interaction of electrons with chiral molecules. Early experiments with photoelectrons from gold surfaces transmitted through monolayers of …. and DNA indicated a spin-filtering behavior of the organic layer.

Results on the electron spin polarization observed for various samples of self-assembled monolayers of helical molecules on metal and semiconductor surfaces are presented. Samples are irradiated with circularly and linearly polarized laser radiation at λ = 213nm to generate photoelectrons in a single step. The spin of the photoelectrons is analyzed by a Mott polarimeter. Longitudinal spin polarizations of up to 60% have been measured in case of oligo dsDNA, irrespective of the polarization of irradiating light. Experiments with chiral membrane proteins and self-assembled monolayers of α-helical oligo-peptides show also spin filtering properties [4]. Similar to DNA a dependence of the spin polarization on the length of the molecules is observed. Recent experiments with helicene and for DNA covalently bound to Si show promising results.