Revised Electron counting models based on six-fold coordination and layers and its application in the phase change in transition metal oxides

Guest Speaker： Associate Professor Junyi Zhu，Chinese University of Hong Kong，China

Inviter: Assoc.Prof. Xiangdong Guo

Date&Time: Friday, 20. Sep., 15:00-16:30

Venue: Tencent Meeting：378-929-967 （线上腾讯会议：378-929-967）

Biography:

Academic qualification:

2003-2009  Ph.D., Materials Science and Engineering, University of Utah, Salt Lake City

1994-1998      B.S., Physics, Peking University, Beijing, China

Previous academic positions held :

08/2013 – 07/2019: Assistant professor, Physics Department, Chinese University of Hong Kong

2012- 2013   Postdoc fellow, University of Utah, Salt Lake City, UT.

2009 - 2012   Postdoctoral researcher, National Renewable Energy Lab, Golden, CO

Present academic position :

08/2019 – now: Associate professor, Physics Department, Chinese University of Hong Kong

Previous relevant research work:

First principles studies of electronic, thermodynamic, and kinetic properties of defects, dopants, surfaces, edge, and interfaces in semiconductors and low dimensional materials.

Five most representative publications in recent five years

Y. Zhang, Y. Wang, Y. Wu, X. Shu, F. Zhang, H. Peng, S. Shen, N. Ogawa, Junyi Zhu*, and P. Yu*, Artificially Controlled Nanoscale Chemical Reduction in VO2 through Electron Beam Illumination, Nat Commun 14, 4012 (2023).

CK Sin, Junyi Zhu*, “Determining Equilibrium Shapes of MoS2: Modified Algorithm, Edge Reconstructions with S and O, and Temperature Effects”, Journal of Physical Chemistry C 125, 8, 4828–4835 (2021).

Dong-Bo Zhang, Xing-Ju Zhao, Gotthard Seifert, Kinfai Tse, Junyi Zhu*, “Twist-driven separation of p-type and n-type dopants in single-crystalline nanowires”, National Science Review, 6, 3, 532–539, 2019.

Jingzhao Zhang, Wenjing Zhao, Junyi Zhu*, “Missing links towards understanding equilibrium shapes of hexagonal boron nitride: algorithm, hydrogen passivation, and temperature effects”, Nano scale, 2018,10, 17683-17690 (2018).

Wei Yao, Eryin Wang, Changhua Bao, Yiou Zhang, Kenan Zhang, Kejie Bao, Chun Kai Chan, Chaoyu Chen, Jose Avila, Maria C Asensio, Junyi Zhu*, Shuyun Zhou*, “Quasicrystalline 30° twisted bilayer graphene as an incommensurate superlattice with strong interlayer coupling”, Proceedings of the National Academy of Sciences, 115, 27, 6928 (2018).

Abstract:

Electron Counting model (ECM) has been proved to be a powerful tool in surface studies. However, most of the studies are focused on binary compound semiconductors and how to apply ECM to complex transition metal oxides is an open question. In this talk, I’ll introduce our recent discoveries on a new scheme of ECM that is based on an overall counting in a unit of one layer. Different from standard counting scheme based on atomic sites, the layer based counting can provide important physical insights to oxides composed of transition metal elements with multiple charge states and complex oxygen vacancy channels. With this new scheme, we successfully investigated surface formation energy and reconstructions on the phase change in the study of SrCoO2.5 and HSrCoO2.5 thin films and discovered that surface defects play important roles during the phase change and the change of magnetic order. In addition, we apply this new scheme to investigate the surface and interface stabilities in the interesting phase change phenomenon on the chemical reduction from VO2 and V2O3, induced by the surface electron beam illumination. The research works are based on the following literature we have published in recent years.