Direct observation and catalytic role of mediator atom in 2D materials

Gun-Do Lee; Alex W Robertson; Sungwoo Lee; Yung-Chang Lin; Jeong-Wook Oh; Hwanyeol Park; Young-Chang Joo; Euijoon Yoon; Kazu Suenaga; Jamie H Warner; Christopher P Ewels

doi:10.1126/sciadv.aba4942

Direct observation and catalytic role of mediator atom in 2D materials

Sci Adv. 2020 Jun 10;6(24):eaba4942. doi: 10.1126/sciadv.aba4942. eCollection 2020 Jun.

Authors

Gun-Do Lee^{1

2}, Alex W Robertson³, Sungwoo Lee¹, Yung-Chang Lin⁴, Jeong-Wook Oh⁵, Hwanyeol Park⁶, Young-Chang Joo^{1

2}, Euijoon Yoon^{1

2}, Kazu Suenaga⁴, Jamie H Warner⁷, Christopher P Ewels⁸

Affiliations

¹ Department of Materials Science and Engineering, Seoul National University, Seoul, Republic of Korea.
² Research Institute of Advanced Materials, Seoul National University, Seoul, Republic of Korea.
³ Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, UK.
⁴ National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba 305-8565, Japan.
⁵ Department of Chemistry, Seoul National University, Seoul, Republic of Korea.
⁶ Memory Thin Film Technology Team, Giheung Hwaseong Complex, Samsung Electronics, 445-701, Republic of Korea.
⁷ Department of Mechanical Engineering, University of Texas at Austin, 204 Dean Keeton Street, Austin, TX 78712, USA.
⁸ Institut des Matériaux Jean Rouxel (IMN), Université de Nantes, CNRS UMR 6502, 2 Rue de la Houssinière, F-44322 Nantes, France.

Abstract

The structural transformations of graphene defects have been extensively researched through aberration-corrected transmission electron microscopy (AC-TEM) and theoretical calculations. For a long time, a core concept in understanding the structural evolution of graphene defects has been the Stone-Thrower-Wales (STW)-type bond rotation. In this study, we show that undercoordinated atoms induce bond formation and breaking, with much lower energy barriers than the STW-type bond rotation. We refer to them as mediator atoms due to their mediating role in the breaking and forming of bonds. Here, we report the direct observation of mediator atoms in graphene defect structures using AC-TEM and annular dark-field scanning TEM (ADF-STEM) and explain their catalytic role by tight-binding molecular dynamics (TBMD) simulations and image simulations based on density functional theory (DFT) calculations. The study of mediator atoms will pave a new way for understanding not only defect transformation but also the growth mechanisms in two-dimensional materials.

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