Chiral molecular films as electron polarizers and polarization modulators

¹ Laboratorio de Física Estadística de Sistemas Desordenados, Centro de Física, IVIC Apartado 21827, Caracas 1020A, Venezuela
² Quimicofísica de Fluidos y Fenómenos Interfaciales (QUIFFIS), Departamento de Química, Universidad de los Andes - Mérida 5101, Venezuela
³ Department of Chemistry, Northwestern University - 2148 Sheridan Rd., Evanston, IL 60208, USA
⁴ Department of Chemistry and Biochemistry, Arizona State University - Tempe, AZ 85287 USA
⁵ Center for Nanoscale Materials, Argonne National Laboratory - Argonne, IL 60439, USA

^(a) ernestomed@gmail.com

Received: 26 March 2012
Accepted: 6 June 2012

Abstract

Recent experiments on electron scattering through molecular films have shown that chiral molecules can be efficient sources of polarized electrons even in the absence of heavy nuclei as source of a strong spin-orbit interaction. We show that self-assembled monolayers (SAMs) of chiral molecules are strong electron polarizers due to the high-density effect of the monolayers and explicitly compute the scattering amplitude off a helical molecular model of carbon atoms. Longitudinal polarization is shown to be the signature of chiral scattering. For elastic scattering, we find that at least double-scattering events must take place for longitudinal polarization to arise. We predict energy windows for strong polarization, determined by the energy dependences of spin-orbit strength and multiple scattering probability. An incoherent mechanism for polarization amplification is proposed, that increases the polarization linearly with the number of helix turns, consistent with recent experiments on DNA SAMs.