부산대학교 도서관

In this work, a first-principles study of Na2O and K2O monolayers and their Janus structure has been carried out using density functional theory calculations based on the projector-augmented plane wave method. Good structural stability is confirmed by phonon dispersion curves and formation enthalpy. The formation of the NaKO monolayer starting from either Na2O or K2O is analyzed via the surface formation energy method. The experimental feasibility with the exothermic synthesis process is demonstrated, mostly in Na-poor or K-poor conditions. Na2O and NaKO monolayers are direct gap semiconductors with band gaps of 0.97 (1.97) and 0.51 (1.21) eV, respectively, as calculated using the PBE (HSE06) functional. Meanwhile, the K2O monolayer exhibits an indirect gap semiconductor character with an energy gap of 0.52 (1.28) eV. The ionic nature is also confirmed by means of the projected density of states and charge density difference. In addition, the 2D materials studied herein exhibit good absorption in a wide energy range from the visible to ultraviolet region with large absorption coefficients of the order of 105 (cm−1), indicating their potential to be applied in optoelectronic devices. [ABSTRACT FROM AUTHOR]