Journal Article

Coherent, atomically thin transition-metal dichalcogenide superlattices with engineered strain

Poddar, Preeti, Park, Chibeom, DiStasio, Robert A., Muller, David A., Han, Yimo, Park, Jiwoong, Kang, Kibum, Lao, Ka Un, Xie, Saien, Tu, Lijie, Huang, Lujie

2018

Overview

Two-dimensional superlattices represent the atomic-thickness limit of heterostructures that enable technologies such as strain-engineered multiferroics and quantum-cascade lasers. Xie et al. were able to produce monolayer superlattices of transition metal dichalcogenides (WS 2 and WSe 2 ) with full lattice coherence, despite a 4% lattice mismatch. They used a modulated metal-organic chemical vapor deposition process that precisely controlled each precursor. Furthermore, the authors could strain-engineer the optical properties of the superlattices to observe out-of-plane rippling. Science , this issue p. 1131 Omnidirectional epitaxy produced superlattices with strain-engineered optical properties and mechanical deformations. Epitaxy forms the basis of modern electronics and optoelectronics. We report coherent atomically thin superlattices in which different transition metal dichalcogenide monolayers—despite large lattice mismatches—are repeated and laterally integrated without dislocations within the monolayer plane. Grown by an omnidirectional epitaxy, these superlattices display fully matched lattice constants across heterointerfaces while maintaining an isotropic lattice structure and triangular symmetry. This strong epitaxial strain is precisely engineered via the nanoscale supercell dimensions, thereby enabling broad tuning of the optical properties and producing photoluminescence peak shifts as large as 250 millielectron volts. We present theoretical models to explain this coherent growth and the energetic interplay governing the ripple formation in these strained monolayers. Such coherent superlattices provide building blocks with targeted functionalities at the atomically thin limit.

• Publisher: The American Association for the Advancement of Science,AAAS
• Subject: Atomic structure / Chalcogenides / Coherence / Dislocations / Epitaxial growth / Epitaxy / Heterostructures / Lasers / Lattice matching / Lattice parameters / Metalorganic chemical vapor deposition / Metals / Monolayers / Multiferroic materials / Optical properties / Optoelectronics / Organic chemicals / Photoluminescence / Photons / Quantum cascade lasers / Science & Technology - Other Topics / Superlattices