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Helmut Zacharias: Organized helical molecules as effective electron spin filters

When:We 16-09-2015 13:30 - 14:30
Where:5113.0202

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.

Due to their spin filtering properties chiral molecules could be applied as a source for spin polarized electrons. In addition, this effect occurs at room temperature so that helical molecules could simplify the design of novel spintronic devices.