Atom-by-atom Fabrication of Monolayer Molybdenum Membranes Xiaoxu Zhao, Jiadong Dan, Wu Zhou, Kian Ping Loh, & Stephen J. Pennycook, et al.

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1 Atom-by-atom Fabrication of Monolayer Molybdenum Membranes Xiaoxu Zhao, Jiadong Dan, Wu Zhou, Kian Ping Loh, & Stephen J. Pennycook, et al. NUS Graduate School of Integrative Sciences and Engineering National University of Singapore (NUS), Singapore 0

2 Acknowledgement Prof Stephen J. PENNYCOOK (NUS) Prof Kian Ping LOH (NUS) Prof Jianyi CHEN (ICCAS) Mr. Jiadong DAN (NUS) Dr. Zijing DING (NUS) Dr. Wei FU (NUS) Prof Wu ZHOU (UCAS) 1

3 Background of atomically thin 2D materials An archetypal layered 2D materials: MoS 2 Monolayer MoS 2 Bilayer MoS 2 The presence of strong in-plane covalent bonding and weak interlayer van der Waals (vdw) coupling make the preparation of atomically thin 2D materials feasible 2

4 An atlas of atomically thin 2D materials Graphene h-bn Graphene, Boron nitride, Transition metal dichalcogenides Noble metal dichalcogenides Transition metal carbides Silicene, Germanene Monolayer metal films? 3 Nature. 2018, 556,

5 Monolayer metal membranes In addition, monolayer Iridium (Ir), Iron (Fe) exhibit enhanced magnetic moments. Despite fascinating properties were predicted in monolayer metal membranes, practical fabrication so far remains elusive. Science. 2004, 306, 666; Nano Lett. 2013, 13, 4671 PRL. 2013, 111, ; PRB. 2017, 95,

6 E-beam fabrication of novel structures e-beam sculpting novel structures TMDC Fe monolayer Nat. Nanotechnol. 2014, 9, 43 Graphene BP h-bn 0.2 nm Science. 2004, 306, 666 Nano Lett. 2017, 17, 494 Nano Res ACS Nano 2014, 8, Selective e-beam ejection of one elements in a binary system to fabricate monolayer metal membranes remains elusive due to the complex interaction between the e-beam and 2D 5 materials.

7 Fabrication of Mo membranes from defective MoSe 2 films CVD grown Se deficient MoSe 1.88 Fabrication of monolayer Mo membranes from defect free MoSe 2 films, such as grown by molecular beam epitaxy, is challenging The functions of Se vacancies: Increase the conductivity which would dissipate the ionization damage Behave as the initial nucleus for growing Mo membranes 6

8 Atomic structure of monolayer Mo membranes As-grown monolayer Mo membranes Dislocation cores along the boundary 0.5 nm 2 nm The lattice of the Mo membrane is 20% lower than the parental MoSe 2 films. Dislocation cores and rippling are frequently observed along the boundary regions to accommodate the huge lattice mismatch 7

9 EELS characterizations Mo membrane and MoSe 2 Monolayer Mo 2 C D. Geng, X. Zhao, et al. Adv Mat. 2017, 10, D. Geng, X. Zhao, et al. 2D Mat. 2017, 4, No discernible carbon peaks can be found in either MoSe 2 precursors and Mo membranes The lattice constant of Mo 2 C is 3.0 Å which is 10% larger than Mo membranes 8

10 Basic structural properties of Mo membranes Domain boundary Atomic defects Edges 2 nm 0.5 nm Interlayer Stacking order 0 s 237 s 0.5 nm 0.5 nm 0.5 nm 0.5 nm AA stacking order is the most frequently observed registry in bilayer Mo membranes 9

11 Growth mechanisms Se vacancy complexes V Se2 V Se6 V Se12 V Se nm 0.5 nm 0.5 nm 0.5 nm 2 nm 0.5 nm Se vacancies are continuously ionized by e-beam irradiation 2 nm 2 nm The growth of Mo membranes are triggered by the creation and subsequent migration of Se vacancies 10

12 Growth kinetics in real time Snapshots of the same region at different time Fresh V Se Preexisting V Se Fresh V Se2 Preexisting V Se2 0.5 nm The growth of Mo membranes are triggered by the creation and subsequent migration of Se vacancies 11

13 Self-healing characteristics 2 nm 2 nm 2 nm 2 nm Holes are gradually self-healed by redeposition of adjacent Mo adatoms Conductive metal membranes mitigate the energy transferred from the e-beam e-beam irradiation rather excite the surface Mo adatoms than introduce ionization damage 12

14 Novel 1D defects Novel 1D defects, such as reconstructed double vacancy line defects (rdv) and Mo atomic wires (MoAW) were first discovered during the fabrication of Mo membranes 0.5 nm 0.5 nm 0.5 nm 0.5 nm 13

15 In conclusion Monolayer Mo membranes were delaminated from monolayer MoSe 2 by e-beam irradiation Growth kinetics was unveiled in real time by STEM at atomic scale Structural properties of Mo membranes, including the edge topology, stacking order, and self-healing characteristics were studied Novel structural defects were first atomically studied 14

16 Thank you