Prediction and synthesis of metal oxide nanosheets and nanoscrolls

Arizona State University, Scottsdale AZ

Investigators

Abstract

Part 1: Non-Technical Summary Metal oxide materials have many applications in electronic, chemical, and optical devices. Atomically thin materials in the form of nanosheets have further advantages due to their high surface areas and their remarkably different properties compared with their bulk counterparts. However, most metal oxides exist in bulk crystals that cannot easily be formed into nanosheets. In this project, supported by the Solid State and Materials Chemistry program in the Division of Materials Research, the research team develops a new plasma-based synthesis method to convert atomically thin metal sulfides and selenides into metal oxide nanosheets and nanoscrolls. Theory and data mining in materials databases are used to identify target materials and plasma conditions. Close integration of theory and experiment are used to determine the underlying mechanisms of the metal oxide conversion process and to establish the fundamental roles of material structures and plasma components for converting metal sulfides and selenides into metal oxides. This project will also enhance education and outreach efforts by the PI and co-PI to increase scientific engagement and participation from underrepresented groups through a range of activities aimed at the general public, high school students, undergraduate students, and graduate students. Part 2: Technical Summary Two-dimensional (2D) nanosheets offer advantages such as increased specific surface area, improved mass and charge transport, increased surface interactions, and processability into flexible thin films that can be useful in a wide range of applications. Among known 2D materials, the majority of them have layered three-dimensional (3D) bulk counterparts held together by weak van der Waals (vdW) forces. In contrast, many metal oxides do not have layered vdW bulk crystal forms so that 2D nanosheets cannot be formed from top-down exfoliation, while bottom-up growth methods require challenging development of synthesis procedures. Thus, there is a need to develop new synthesis methods for 2D metal oxides that are generalizable and cost-effective. In this project, supported by the Solid State and Materials Chemistry program in the Division of Materials Research, the research team establishes plasma-assisted conversion synthesis (PACS) as a powerful general approach to synthesize 2D metal oxide nanosheets and nanoscrolls by conversion from layered metal sulfides and selenides. Ab initio theory and data mining in materials databases are used to identify and predict new metal oxide materials that do not have layered 3D bulk counterparts, which will then be synthesized using the PACS process. This project develops a detailed fundamental understanding of how 2D metal oxides with no known layered vdW counterparts can be formed by plasma-assisted conversion from 2D metal sulfides and selenides. The underlying mechanisms of the oxidation and scrolling processes are elucidated through closely coupled theory and experiment to determine mechanistic details of the roles of point defects, grain boundaries, compositions, and reactive intermediates. The resulting metal oxide nanosheets and nanoscrolls have potential applications in electronic, magnetic, and electrochromic devices, photocatalysis, and chemical sensing. The software and computational tools developed in this project are widely applicable to other researchers in the field. The education and outreach efforts advance the PI and co-PI's goals in increasing participation from female students, first-generation and underrepresented groups via open house events for the general public, hands-on activities for high school students, and advanced research training experiences for undergraduate and graduate students. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.