Versatile electronic properties of atomically layered ScO2

a In recent years, graphene and transition metal dichalcogenides (TMDs) have been at the forefront of candidate materials for next-generation electronic devices. In this study, we will consider transition metal oxides (TMOs), which are a class of materials that can exist in two-dimensional geometries, but exhibit unique properties due to the strong correlation between electrons. Density functional theory calculations under the generalized-gradient approximation with on-site Coulomb interactions (GGA + U) are performed to investigate the (a) geometry, (b) energetics, (c) electronic properties, (d) magnetic properties, and (e) chemical bonding of a layered TMO–scandium dioxide (ScO 2) in its octahedral (T) and hexagonal (H) phases. The T-phase is a non-magnetic wide-band gap semiconductor with a band gap of 3.75 and 3.73 eV for the monolayer and bilayer, respectively. The H-phase monolayer is an anti-ferromagnetic (AFM) metal while the bilayer is metallic and has a ferromagnetic (FM) and an AFM configuration, which degenerate in energy. The metallicity and magnetic coupling between atoms in the H-phase are predominantly governed by the O-p z states. The analysis of the chemical topology using the quantum theory of atoms in molecules (QTAIM) shows that the Sc–O bonds are highly ionic in character. Born effective charge (Z*) analysis suggests that the H-phase monolayer has more uniform chemical bonding. Furthermore, T-and H-phase bilayers respond differently to strain applied normal to the material surface; for the former, the band gap increases and then decreases with the increase of tensile strain, whereas the latter shows a metal-semiconductor-metal transition as a larger tensile strain is applied. The mechanisms for such responses are inherently different in the two phases: in the T-phase, it is due to the shift of the lowest unfilled O-p z band, and in the H-phase, it is attributed to the transformation in shape of the bands close to the Fermi level. The versatility of the electronic properties of ScO 2 in its different phases and forms (monolayer and bilayer) can thus be exploited in devices at the nanoscale.