Functionalized GaAs Photocathodes for Spin-Dependent Charge Transfer Studies

Abstract

Chiral-Induced Spin Selectivity (CISS) is a well-documented phenomenon occurring at electrochemical interfaces, where chiral functional groups can hinder the transfer of electrons with a specific spin state, while allowing the electrons with an opposite spin state to be transferred to the electroactive species in the solution.1,2 Spin dependent electron transfer has also been observed at p-GaAs/electrolyte interface without chiral functionalities, relying on the spin selectivity between polarised electrons in the conduction band (CB) of the p-GaAs and spin-oriented radical species in the solution.3,4 Here we report spin-dependent charge transfer in electrochemistry, where the spin selectivity is achieved by manipulating the electron spins of a radical redox mediator in the sample solution using microwaves (MW) under resonance conditions. This work has required us to characterise the photocathodic behaviour of p-GaAs in contact with methyl viologen radical cation (MV+•) in organic solvents under very low light intensities, a domain not traditionally covered in semiconductor electrochemistry. We have also contrasted the behaviour of the bare p-GaAs to biphenyl- and peptide-functionalised surfaces, showing that the parasitic valence band (VB) and surface state (SS) mediated processes can be completely avoided. In the future, we hope that these functionalised surfaces allow us to increase the spin-dependent signal intensity, as the probability of electron’s spin state relaxing due to parasitic processes can be minimised. Figure 1