Spin Polarization of Polyalanine Molecules in 2D and Dimer-Row Assemblies Adsorbed on Magnetic Substrates: The Role of Coupling, Chirality, and Coordination

Thi Ngoc Ha Nguyen, Yossi Paltiel, Lech T. Baczewski, Christoph Tegenkamp*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

Propagation of electrons along helical molecules adsorbed on surfaces comes along with a robust spin polarization effect called chirality induced spin selectivity CISS. However, experiments on the molecular scale that allow a true correlation of spin effects with the molecular structure are quite rare. Here we have studied the structure of self-assembled chiral molecules and the electronic transmission and spin polarization of the current through the system by means of ambient scanning tunneling microscopy and spectroscopy in heterostructures of various α-helix polyalanine-based molecules (PA) adsorbed on Al2O3/Pt/Au/Co/Au substrates with perpendicular magnetic anisotropy. We have found a phase separation of the molecules into well-ordered enantiopure 2D hexagonal phases and quasi-1D heterochiral-dimer structures, which allows for the analysis of the spin polarization with almost atomic precision of PA in different phases. The spin polarization reaches up to 75% for chemisorbed molecules arranged in a hexagonal phase. On the contrary, for weakly coupled PA molecules without cysteine anchoring groups in a quasi-1D phase, a spin polarization of around 50% was found. Our results show that both the intermolecular interaction as well as the coupling to the substrate are important and point out that collective effects within the molecules and at the interfaces are required to achieve a high chiral induced spin selectivity.

Original languageAmerican English
Pages (from-to)17406-17412
Number of pages7
JournalACS applied materials & interfaces
Volume15
Issue number13
DOIs
StatePublished - 5 Apr 2023

Bibliographical note

Publisher Copyright:
© 2023 American Chemical Society

Keywords

  • CISS
  • ambient STM
  • chiral molecules
  • enantiomer
  • magnetization
  • spin polarization

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