Formation of two-dimensional transition metal oxide nanosheets with nanoparticles as intermediates

Juan Yang; Zhiyuan Zeng; Jun Kang; Sophia Betzler; Cory Czarnik; Xiaowei Zhang; Colin Ophus; Chang Yu; Karen Bustillo; Ming Pan; Jieshan Qiu; Lin-Wang Wang; Haimei Zheng

doi:10.1038/s41563-019-0415-3

Formation of two-dimensional transition metal oxide nanosheets with nanoparticles as intermediates

Nat Mater. 2019 Sep;18(9):970-976. doi: 10.1038/s41563-019-0415-3. Epub 2019 Jul 8.

Authors

Juan Yang^{1

2

3}, Zhiyuan Zeng¹, Jun Kang¹, Sophia Betzler¹, Cory Czarnik⁴, Xiaowei Zhang¹, Colin Ophus⁵, Chang Yu², Karen Bustillo⁵, Ming Pan⁴, Jieshan Qiu^{6

7}, Lin-Wang Wang⁸, Haimei Zheng^{9

10}

Affiliations

¹ Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA.
² State Key Lab of Fine Chemicals, School of Chemical Engineering, Liaoning Key Lab for Energy Materials and Chemical Engineering, Dalian University of Technology, Dalian, China.
³ School of Chemical Engineering and Technology, Xi'an Jiaotong University, Xi'an, China.
⁴ Gatan Inc., Pleasanton, CA, USA.
⁵ National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA, USA.
⁶ State Key Lab of Fine Chemicals, School of Chemical Engineering, Liaoning Key Lab for Energy Materials and Chemical Engineering, Dalian University of Technology, Dalian, China. jqiu@dlut.edu.cn.
⁷ State Key Laboratory of Chemical Resource Engineering, College of Chemical Engineering, Beijing University of Chemical Technology, Beijing, China. jqiu@dlut.edu.cn.
⁸ Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA. lwwang@lbl.gov.
⁹ Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA. hmzheng@lbl.gov.
¹⁰ Department of Material Science and Engineering, University of California, Berkeley, CA, USA. hmzheng@lbl.gov.

PMID: 31285617
DOI: 10.1038/s41563-019-0415-3

Abstract

Two-dimensional (2D) materials have attracted significant interest because of their large surface-to-volume ratios and electron confinement. Compared to common 2D materials such as graphene or metal hydroxides, with their intrinsic layered atomic structures, the formation mechanisms of 2D metal oxides with a rocksalt structure are not well understood. Here, we report the formation process for 2D cobalt oxide and cobalt nickel oxide nanosheets, after analysis by in situ liquid-phase transmission electron microscopy. Our observations reveal that three-dimensional (3D) nanoparticles are initially formed from the molecular precursor solution and then transform into 2D nanosheets. Ab initio calculations show that a small nanocrystal is dominated by positive edge energy, but when it grows to a certain size, the negative surface energy becomes dominant, driving the transformation of the 3D nanocrystal into a 2D structure. Uncovering these growth pathways, including the 3D-to-2D transition, provides opportunities for future material design and synthesis in solution.