Understanding the structural, electrical, and optical properties of monolayer h-phase RuO2 nanosheets: a combined experimental and computational study

Abstract

The structural, electrical, and optical properties of monolayer ruthenium oxide (RuO2) nanosheets (NSs) fabricated by chemical exfoliation of a layered three-dimensional form of K-intercalated RuO2 are studied systematically via experimental and computational methods. Monolayer RuO2 NS is identified as having a distorted h-MX2 structure. This is the first observation of a RuO2 NS structure that is unlike the t-MX2 structure of the RuO2 layers in the parent material and does not have hexagonal symmetry. The distorted h-MX2 RuO2 NSs are shown to have optical transparency superior to that of graphene, thereby predicting the feasibility of applying RuO2 NSs to flexible transparent electrodes. In addition, it is demonstrated that the semiconducting band structures of RuO2 NSs can be manipulated to be semi-metallic by adjusting the crystal structure, which is related to band-gap engineering. This finding indicates that RuO2 NSs can be used in a variety of applications, such as flexible transparent electrodes, atomic-layer devices, and optoelectronic devices. Nanosheets of ruthenium oxide could make excellent transparent electrical contacts, show researchers from Korea. Graphene is the wonder material of the last decade owing to its amazing electrical, mechanical and thermal properties. Scientists are thus keen to fabricate single layers of atoms other than carbon. Now, Dong-Su Ko, Jung-Hwa Kim and Jong Wook Roh from the Samsung Advanced Institute of Technology and co-workers have combined experiments and theory to fully characterize this unusual two-dimensional material. They created their nanosheets by exfoliating a three-dimensional block of ruthenium oxide. Transmission electron microscopy, X-ray diffraction experiments and first-principles calculations showed that the two-dimensional material has a distorted atomic arrangement, which makes it a semiconductor rather than a metal like its parent material. Furthermore, ruthenium oxide nanosheets are more transparent than graphene, making them useful for flexible transparent electrodes. As a new two-dimensional (2D) material, monolayer ruthenium oxide (RuO2) nanosheets (NSs) have distorted h-MX2 type crystal structures that lead to semiconducting properties and good optical transmittance. This study suggests that monolayer RuO2 can be useful in applications of flexible optoelectronics.