In-Plane Anisotropic Raman Response and Electrical Conductivity with Robust Electron–Photon and Electron–Phonon Interactions of Air Stable MoO₂ Nanosheets

Abstract

The monoclinic m-MoO₂ shows strong in-plane anisotropy that is essential to design anisotropic nanodevices. However, there is not yet detailed study on the anisotropy of m-MoO₂ nanostructures. Here, the in-plane anisotropic Raman spectra and electrical conductivity of single-crystal m-MoO₂ nanosheets were investigated systematically for the first time. Angle-resolved polarized Raman spectroscopy (ARPRS) shows distinct dependence on the excitation laser wavelength and sample thickness, demonstrating the robust wavelength-dependent optical absorption, electron-photon/electron-phonon interactions, and anisotropic phonon polarization in m-MoO₂ nanosheets. Such results agree well with the semiclassical Placzek model. Moreover, the angle-dependent electrical conductivity of starburst-like m-MoO₂ nanosheet devices shows a strong anisotropy with a conductivity ratio (σ_max/σ_min) of up to 10.1, which is the largest value in the previously reported 2D materials. This work underscores the importance of understanding the in-plane anisotropic light-matter interactions for the application of m-MoO₂ nanosheets in anisotropic plasmonics and artificial synapse.