| AVS 65th International Symposium & Exhibition | |
| 2D Materials Focus Topic | Wednesday Sessions |
| Session 2D+AM+EM+NS-WeM |
| Session: | Dopants, Defects, and Interfaces in 2D Materials |
| Presenter: | Paula Mariel Coelho, University of South Florida |
| Authors: | P.M. Coelho, University of South Florida H. Komsa, Aalto University, Finland H. Coy Diaz, University of South Florida Y. Ma, University of South Florida A.V. Krasheninnikov, Institute of Ion Beam Physics and Materials Research, Germany M. Batzill, University of South Florida |
| Correspondent: | Click to Email |
Modifications of MoSe2 and MoTe2 with metallic mirror twin grain boundaries (MTB) in films grown by molecular beam epitaxy have been previously reported [1,2]. The goal of the study presented here has been to understand the formation-mechanism of MTB networks and apply this gained knowledge for controlled modifications of these 2D materials. In a combined scanning tunneling microscopy and density functional theory approach we demonstrate that excess Mo can easily diffuse into the pristine MoSe2 or MoTe2 (but not into MoS2) layer and cause crystal modifications into Mo-rich twin grain boundaries. Vapor deposited Mo atoms are first incorporated by diffusing into interstitial (or split-interstitial) sites. Then, further Mo-atoms incorporate into the crystal structure to form triangular, Mo-rich grain boundary loops. Only after a critical density of MTBs is reached, Mo is no-longer absorbed by the 2D-crystal sheet and Mo-clusters start to form at the surface. The energetics and barriers for Mo-incorporation is calculated by DFT and shows that the formation of twin grain boundaries in the presence of excess Mo is favorable for MoTe2 and MoSe2, but not for MoS2 - in agreement with the experiment. The achievable dense networks of MTBs constitute a new Mo-rich metallic phase that may be used for controlled electric contacts or creation of active sites in electro-catalysis [4] and thus adding new functionalities into transition metal dichalcogenide-based materials and devices. Moreover, DFT simulations suggest that this mechanism for incorporation of transition metals is not limited to Mo. This enables modification of the materials properties by heteroatom dopants and initial experimental work demonstrates the incorporation of both Ti and V. V-interstitials in MoTe2 are predicted to have a magnetic moment and magnetic hysteresis curves indicate the induction of ferromagnetism in MoTe2 by doping the material with less than 1% of V interstitials.
REFERENCES:
[1] Ma Y, et al. (2017) Metallic Twin Grain Boundaries Embedded in MoSe2 Monolayers Grown by Molecular Beam Epitaxy. ACS Nano 11, 5130-5139.
[2] Coy Diaz H, Ma Y, Chaghi R, Batzill M. (2016) High Density of (Pseudo) Periodic Twin-Grain Boundaries in Molecular Beam Epitaxy-Grown van der Waals Heterostructure: MoTe2/MoS2. Appl. Phys. Lett. 108, 191606.
[3] Ma Y. et al. (2017) Angle resolved photoemission spectroscopy reveals spin charge separation in metallic MoSe2 grain boundary. Nat. Commun. 8, 14231.
[4] Tomasz Kosmala et al. (2018) Metallic Twin Boundaries Boost the Hydrogen Evolution Reaction on the Basal Plane of Molybdenum Selenotellurides. Adv. Energy Mater. 2018, 1800031.