MOCVD Routes to 2D Crystals Joan M. Redwing Department of Materials - PowerPoint PPT Presentation

MATERIALS RESEARCH INSTITUTE MOCVD Routes to 2D Crystals Joan M. Redwing Department of Materials Science & Engineering Materials Research Institute Center for Two-Dimensional and Layered Materials (2DLM) The Pennsylvania State University University Park, PA 16802 USA

MATERIALS RESEARCH INSTITUTE 2D at Penn State 20 + Faculty and 45 + Students/Post-docs Faculty Students/Post-docs Nasim Alem Michael Abraham Minh An Nguyen Amin Azizi Theresa Mayer Lavish Pabbi Vincent Crespi Zakaria Al Balushi Nestor Perea Suzanne Mohney Ganesh Bhimanapati Ismaila Dabo Lakshmy Rajukumar Donna D. Deng Chris Rotella Joan Redwing Suman Datta Anna Domask Dr Eduardo Cruz Silva Haila Al Dosari Joshua Robinson Ivan Skachko Aman Haque Dr. Sarah Eichfeld Yifan Sun Nitin Samarth Dr. Ana Laura Elias Youjian Tang Eric Hudson Simin Feng Timothy Walter Jie Shan Tom Jackson Robert Fraleigh Junjie Wang Jarod Gagnon Jorge Sofo Yuanxi Wang Ying Liu Yiyang Gong Zefang Wang Mauricio Terrones Corey T. Janisch Xiaoxiang Xi Zhiwen Liu Ethan Kahn Kehao Zhang Sulin Zhang Kin Fai Mak Nina Kovtyukhova Xiaotian Zhang Chia-Hui (Candace) Lee Jun Zhu Liang Zhao Tom Mallouk Yu-Chuan Lin Rui Zhao Chanjing Zhou Est. 2013 Zhong Lin Debangshu Mukherjee Roger Walker Shruti Subramanian Assoc.Director Director Joshua Robinson Mauricio Terrones 2

Layered Materials MATERIALS RESEARCH INSTITUTE Q.H. Huang, et al. Nature Nanotech. 7 (2012) p. 699 • Graphene-like layered materials • Exhibit wide variety of electronic properties – insulators, semiconductors, semi-metals, superconductors

The TMD Synthesis “Atlas” S. Das, J.A. Robinson, M. Terrones, et al. Annual Review of Materials Research , 45 , 1-27 (2015) MATERIALS RESEARCH INSTITUTE 4

Tungsten Diselenide (WSe 2 ) MATERIALS RESEARCH INSTITUTE Metalorganic Chemical Vapor Deposition T = 750 o C 500 Torr 700 Torr 600 Torr 10 nm 500 nm 500 nm 500 nm I NCREASING DOMAIN SIZE P = 700 Torr 850 o C 800 o C 900 o C 0 nm 500 nm 500 nm SiO 2 WSe 2 W-rich WSe 2 • Highly scalable process 50 nm SiC • Excellent control over W:Se ratio S.M. Eichfeld, J.M. Redwing, J.A. Robinson, et al., ACS Nano , 2015, 9 (2), pp 2080 – 2087

Tungsten Diselenide (WSe 2 ) MATERIALS RESEARCH INSTITUTE WSe 2 • Defects serve as nucleation WSe 2 /Sapphire 4 WSe 2 /EG sites in 2D materials. Domain size (  m ) 3 Se:W ratio has • Typical defects are significant impact on 2 chalcogen (S,Se,Te) domain size, shape, vacancies. 1 and “defect” formation Wallace Group (UT Dallas) Temp (°C) Time (min) Pre- Anneal Pressure (Torr) 0 0.0 4 5 1.5x10 5 2.0x10 1.0x10 Se to W ratio 800 30 500C, 15min 700 Se:W Ratio: 170 Se:W Ratio: 14000 Se:W Ratio: 400 Se:W Ratio: 800

MATERIALS RESEARCH INSTITUTE WSe 2 on Free Standing Graphene Templates As Prepared After MOCVD Growth • Developed process to produce freestanding van der Waals heterostructures • Ideal for investigating layer-layer interaction with graphene A. Azizi, N. Alem, et al. ACS Nano 9 (2015) 4882. 7

WSe 2 – Epitaxy and Defects MATERIALS RESEARCH INSTITUTE ( a) HAADF-STEM image of monolayer and multilayer WSe 2 ( a) TEM image and (b) SAD pattern showing epitaxial relationship between WSe 2 and graphene HAADF-STEM images of (b) monolayer WSe 2 and (c) edge region showing W-termination (c) Structural model showing alignment of W atoms in WSe 2 and C atoms in graphene (circled in red) d) TEM image showing nucleation near grain boundary in graphene 8

MATERIALS RESEARCH INSTITUTE Pulsed MOCVD growth of GaN SiC Substrate Epitaxial Graphene Cross-section TEM of GaN growing between graphene and SiC substrate Ke Wang, PSU MCL 2 nm 9

GaN Intercalation in Epi Graphene MATERIALS RESEARCH INSTITUTE Pathways for Ga intercalation:

Atomic Structure of 2D GaN Layers MATERIALS RESEARCH INSTITUTE ABF STEM image near 𝟏 ] zone axis the [ 𝟐𝟐𝟑 Inverted image 1 nm Two structurally different 2D layers of GaN at interface:  Low buckled 2D GaN near graphene  Highly buckled 2D GaN with nitrogen termination  Only observed with graphene encapsulation Ke Wang, PSU MCL

MATERIALS RESEARCH INSTITUTE Electronic Structure of 2D GaN Layers Predicted bandgap energies: Low buckled GaN E g =4.96 eV High buckled GaN E g =4.24 eV Composite structure E g =2.02 eV Ram Krishna Ghosh and Suman Datta 12

MATERIALS RESEARCH INSTITUTE

MATERIALS RESEARCH INSTITUTE Summary • MOCVD is a promising technique for TMDs and layered materials • Graphene encapsulated MOCVD growth viable method to stabilize 2D GaN • Future work directed at heterostructure growth, alloys & doping Acknowledgements PSU Collaborators Dr. Sarah Eichfeld (MRI) Dr. Josh Robinson (MatSE) Graduate Students Dr. Nasim Alem (MatSE) Xiaotian Zhang Dr. Suman Datta (EE) Zakaria Al Balushi Dr. Ke Wang (MRI) Nathan Martin Dr. Tom Jackson (EE) Mel Hainey Jr. Financial support provided by: Postdoctoral Scholars Chen Chen Jarod Gagnon Tanushree Choudhury 14

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Wurtzite Bulk Structure of GaN MATERIALS RESEARCH INSTITUTE Materials discovery with computation

MATERIALS RESEARCH INSTITUTE Indirect bandgap 4.12 eV Stabilized Structure direct bandgap 5.28 eV

MATERIALS RESEARCH INSTITUTE The Buckled Structure for 2D III-nitrides is More Stable!

MATERIALS RESEARCH INSTITUTE Polarization-induced Topological insulators for memory and quantum computing Phys. Rev. Lett. 109, 186803 (2012) Exotic physics Single-photon emitters for quantum optics and communication Nano Lett. 14, 982 – 986 (2014) Nat. Mater. 5, 887 – 892 (2006)