Anisotropy of the Electric Field Gradient in Two-Dimensional α-MoO3 Investigated by 57Mn(57Fe) Emission Mössbauer Spectroscopy

Van der Waals α-MoO3 samples offer a wide range of attractive catalytic, electronic, and optical properties. We present herein an emission Mössbauer spectroscopy (eMS) study the electric-field gradient (EFG) anisotropy in crystalline free-standing samples. Although is two-dimensional (2D) material, scanning electron microscopy shows that crystals are 0.5–5-µm thick. The combination X-ray diffraction micro-Raman spectroscopy, performed after sample preparation, provided evidence phase purity crystal quality eMS measurements were conducted following implantation 57Mn (t1/2 = 1.5 min), which decays to 57Fe, 14.4 keV state. spectra dominated by paramagnetic doublet (D1) with angular dependence, pointing Fe2+ probe ions being environment. It attributed asymmetric EFG at site originating from strong in-plane covalent bonds weak out-of-plane van interactions 2D material. Moreover, second broad component, D2, can be assigned Fe3+ defects dynamically generated during online measurements. results compared ab initio simulations discussed terms system.