Solvent-Induced Degradation of Electrochemically Exfoliated Vanadium Selenide Visualized by Electron Microscopy

Recently discovered
two-dimensional ferromagnetic materials
(2DFMs)
have rapidly gained much interest in the fields of spintronics and
computing, where they may prove powerful tools for miniaturizing devices
such as magnetic tunnel junctions and spin-transfer torque memory
bits. In addition, heterojunctions and twisted bilayer stacks of such
materials may yield exotic spin textures. However, preparation of
such devices is complicated by the air sensitivity of many 2DFMs.
Here, we report details on the preparation of few-to-monolayer flakes
of vanadium selenide (VSe2) using electrochemical exfoliation
in propylene carbonate. We also present a detailed study of the effects
of air on the structure and magnetic properties of bare and passivated
VSe2 after different concentrations of surface passivation
treatment. We characterized the microstructure of holes in the VSe2 flakes and the formation of new compounds arising from air
exposure, solvent exposure during the exfoliating process, and deliberate
electron beam irradiation (sculpting). We sculpt VSe2 flakes
while retaining the 1T-VSe2 lattice structure, opening
the door for top-down patterned high-resolution 2DFM nanostructures.
Additionally, investigation of the magnetic response of nanosheets
using magnetic force microscopy (MFM) showed that the oxidation-induced
damage only affects the surface fields locally and does not quench
large-scale magnetic signal. The findings of this study pave the way
toward practical incorporation of 2D ferromagnetic materials in nanoelectronics.