A first-principles study on alkaline earth metal atom substituted monolayer boron nitride (BN)

Abstract

This paper presents first-principles density functional theory (DFT) calculations for the structural, electronic, magnetic and optical properties of monolayer boron nitride (BN) doped with different alkaline earth metal (AEM) atoms. We used two configurations for substituting AEM atoms in a BN layer. In the first case, nitrogen (N) was replaced with an AEM atom and in the second case, a boron (B) atom was replaced by AEM atoms. All the impurity atoms were tightly bonded to B and N atoms in the BN layer. When an AEM atom replaces an N atom, the B-AEM bond distance increases. On the other hand, when a B atom is replaced by an AEM atom, the N-AEM bond distance is decreased. It has been found that after AEM atom substitution in a BN layer, some surface states appear at the Fermi energy (E_F) level, thereby making the BN layer a half metallic material. The appearance of surface states produces some interband transitions, which in turn introduces some new trends in the optical properties of the BN layer. Pure BN is a nonmagnetic material. However, AEM atom substitution in a BN layer induces finite magnetic moments, thereby introducing ferromagnetism in the BN layer. The values of the magnetic moments vary depending upon the type of impurity atom and the position of AEM atoms in the BN layer. The optical properties, specifically the absorption coefficient and reflectivity plots, of the AEM atom-doped BN structures were investigated using DFT with random phase approximation (RPA). A pure BN layer has zero absorption at an energy interval ranging from 0 to 4 eV. After AEM atom doping, a finite value of the absorption coefficient is obtained in the said energy interval. Similarly, a higher static reflectivity is achieved in a lower energy interval after AEM atom substitution in a BN layer. Our obtained results reveal that AEM atom substituted monolayer BN has potential applications in nanoelectronics, spintronics and optoelectronic devices.