Laboratory of the Physics of Nanostructured Materials
Ecole polytechnique fédérale de Lausanne
Title : Spin-dependent charge transfer at Electrodes
Abstract: Spin-dependent charge transfer at electrodes was characterised by magnetic resonance so as to avoid magnetohydrodynamics effects. The redox probe has a free radical state. The electrodes were either GaAs or chiral electrodes made of gold functionalised with chiral molecules. The conduction band of GaAs was hyperpolarised by the well-known optical pumping method. The observed spin dependence observed in the case of GaAs validated the method. Our method allowed us to characterise chirality-induced spin selectivity (CISS) of polypeptides grafted on Au. The spin-filtering efficiency could be estimated four this measurement to be between 6 and 19%. This result was consistent with published photomession measurements carried out in ultra-high vacuum.
Our method is a form of electrically-detected magnetic resonance (EDMR). Given the electrochemical environment, it was not possible to carry out experiments at fixed potential. Instead, the lock-in detection was applied during electrode potential ramps. The lock-in frequency was selected on the basis of electrochemical impedance spectroscopy in order to work near the frequency that is characteristic of charge transfer. As the measurements were carried out at about 10 GHz, the radicals spin polarisation was very small, resulting in current changes of the order of 50 ppm only.