Chirality injected into layered semiconductors: Electrochemical writing successful

A research team including Assistant Professor Po-Jung Huang and Professor Kouji Taniguchi of the Department of Chemistry, School of Science, Institute of Science Tokyo, has successfully switched the chirality of a semiconductor repeatedly by electrochemically intercalating and deintercalating molecules with chirality corresponding to right-handed and left-handed properties into and out of the layers of the layered semiconductor material MoS₂. Through this process, they demonstrated that the spin orientation of electrons flowing through the semiconductor can be controlled. The findings were published in ACS Nano.

The control of chirality has recently attracted attention as a new method for controlling electron spins in materials. In particular, chirality-induced spin selectivity (CISS) exhibited by chiral substances holds the potential to generate spin-polarized currents without using magnets and is thus expected to find applications in next-generation spintronics.

Conventionally, however, once the chirality of a substance is determined during synthesis, it has been difficult to freely impart or eliminate it afterward, making it rarely usable as a parameter for controlling physical properties.

The research group developed a method to reversibly intercalate molecules into the layers of MoS₂ via an electrochemical reaction, using an electrolyte solution containing chiral molecular ions (S- or R-Mepy⁺). By utilizing small-sized chiral molecules and keeping crystal strain extremely low, they succeeded in repeatedly intercalating and deintercalating the molecules into and out of MoS₂.

Through X-ray diffraction, Raman spectroscopy, and electron microscopy, they confirmed that the chiral molecules were uniformly introduced throughout the entire crystal. Furthermore, they clarified that by reversing the polarity of the applied potential at the time of chiral molecule intercalation, the chiral molecules were deintercalated, and the crystal structure returned to its original state.

When investigating the electrical properties of the MoS₂ intercalated with chiral molecules in detail, CISS, where the ease of current flow changes depending on the orientation of the electron spin, was observed. In addition, they demonstrated that the onset and disappearance of CISS can be reversibly controlled in conjunction with the intercalation and deintercalation of the chiral molecules.

These results show that chirality can be reversibly imparted to semiconductors by introducing chiral molecules into the interior of the material.

By presenting a new method to electrically turn chirality on and off, this work is expected to find applications in new spintronics devices that do not use magnets, as well as low-power-consumption electronic materials independent of external magnetic fields.

Journal Information
Publication: ACS Nano
Title: Reversible On-Off Switching of Chirality via Electrochemical Intercalation Control of Enantiopure Molecular Cations in a Layered van der Waals Material
DOI: 10.1021/acsnano.6c04758