Title: Domain morphology and mechanics of the ${\mathrm{H}/\mathrm{T}}^{\text{'}}$ transition metal dichalcogenide monolayers

Abstract

The properties of two-dimensional (2D) transition metal dichalcogenide (TMD) monolayers can be dynamically controlled via strain-induced displacive structural transformations between semiconducting (H) and metallic or semimetallic ( T ' ) crystal structures. The shapes, symmetries, and kinetics of crystalline domains generated during these transformations and the mechanical response of transforming monolayers are of fundamental and applied interest in, e.g., phase change memory devices and the study of topologically protected edge states in quantum spin Hall insulating T ' crystals. We quantitatively characterize T ' domain morphologies during H → T ' transformations in both flat and bendable TMD monolayers using a combination of first principles and continuum calculations. Wulff constructions for MoTe₂ and MoS₂ show that T ' domains within much larger T ' domains are either rhombi of fixed proportions (if nonmisfitting) or rectangles whose aspect ratio $$A_R$$ increases with domain size $$L_0$$ (if misfitting). Isolated T ' domains within much larger H domains undergo a morphological crossover from compact to elongated shapes at $$L_0$$ ≈ 100 – 200 nm if the sheet is constrained to be flat or $$L_0$$ $$≳$$ 2 $$μ$$m if the sheet is free to bend. This crossover is driven by a competition between anisotropic interfacial energy and elastic misfit energy, and its position can be tuned via the monolayer-substrate interaction strength. It is shown that the aspect ratio $$A_R$$ obeys a scaling law $$A_R$$ $$~$$ $$L^{2/3}_0$$. Stress-strain response characterized as a function of strain orientation reveals extreme anisotropy in the effective elastic modulus through H / T ' coexistence. Ferroelastic multidomain T ' - WTe₂ monolayers are found to exhibit two to three regimes of reversible mechanical response, and localized buckling in freely suspended T ' monolayers is shown to qualitatively alter T ' domain symmetries.

Authors:

Berry, Joel ^[1]; Zhou, Songsong ^[2]; Han, Jian ^[2]; Srolovitz, David J. ^[3]; Haataja, Mikko P. ^[4]

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+ Show Author Affiliations

1. Univ. of Pennsylvania, Philadelphia, PA (United States); Princeton Univ., NJ (United States)
2. Univ. of Pennsylvania, Philadelphia, PA (United States)
3. Univ. of Pennsylvania, Philadelphia, PA (United States); City Univ. of Hong Kong (Hong Kong)
4. Princeton Univ., NJ (United States)

Publication Date:

Mon Nov 05 00:00:00 EST 2018

Research Org.:

Energy Frontier Research Centers (EFRC) (United States). Center for Complex Materials from First Principles (CCM); Temple Univ., Philadelphia, PA (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES)

OSTI Identifier:

1566698

Alternate Identifier(s):

OSTI ID: 1480883

Grant/Contract Number:  

SC0012575

Resource Type:

Accepted Manuscript

Journal Name:

Physical Review Materials

Additional Journal Information:

Journal Volume: 2; Journal Issue: 11; Journal ID: ISSN 2475-9953

Publisher:

American Physical Society (APS)

Country of Publication:

United States

Language:

English

Subject:

36 MATERIALS SCIENCE; catalysis (heterogeneous); electrocatalysis; solar (photovoltaic); mechanical behavior; superconductivity; magnetism and spin physics; water; materials and chemistry by design; synthesis (novel materials)