In the first WP of the project we set out to grow and characterize single atomic layers of WTe2 and TaTe2, chosen because they exhibit a monoclinic 1T’ crystal structure in their bulk form . This should have enabled them to generate out-of-plane spin orbit torques (i.e. a longitudinal current through the atomic layer results in an out-of-plane torque, capable of flipping the magnetization of an adjacent layer). Both materials were successfully synthesized, however:
- WTe2 does not form, despite the optimization of the growth process, continuous film of a single atomic layer before the seeding of a second layer is observed; the bilayer has a different symmetry to the monolayer and cannot generate out of plane torques
- TaTe2 in its monolayer forms grows in different crystallographic phases (1H and 1T), which cannot generate out of plane torques
To maximize the impact and outcome of this MSCA action, we therefore shifted our attention to the study of MoSxSe1-x alloys with different stoichiometric ratios (namely: MoS2, MoS1.5Se0.5 MoSSe, MoS0.85Se0.15 MoS2). We carried out a characterization of these crystals with a combination of microscopic and spectroscopic techniques as a function of sample thickness and chemical composition (the first in its kind for completeness of results). We observed that these samples, which are air-stable and do not exhibit phase change with temperature, have electronic and morphological properties which change smoothly as a function of chemical composition and thickness. In particular, our preliminary results indicate that the electronic bandgap in MoSxSe1-x, which is the range in which it can absorb energy i.e. from the electromagnetic spectrum, can be seamlessly tuned in the 1.6-1.9 eV range.
