Atomically thin sheets such as graphene and monolayer transition metal dichalcogenides hosts rich structural variety and desirable properties that derive from their 2D form, such as strong light-matter interaction and mechanical flexibility. My research employs accurate first-principles calculations to model their growth and characterization, in close collaboration with several experimental teams.
Point defects in 2D material systems
I study the thermodynamics, formation kinetics, and optical properties of point defects and defect complexes in 2D solids.
- F. Zhang, Y. Wang, C. Erb, K. Wang, P. Moradifar, V. H. Crespi, N. Alem, “Full orientation control of epitaxial MoS2 on hBN assisted by substrate defects“, under review arXiv:1801.00487
- Y. Wang, V. H. Crespi, “Nanovelcro: theory of guided folding in atomically thin sheets with regions of complementary doping”, Nano Lett. 17, 6708 (2017)
- A. Azizi, Y. Wang, G. Stone, A. L. Elias, Z. Lin, M. Terrones, V. H. Crespi, and N. Alem, “Defect Coupling and Sub-Angstrom Structural Distortions in W1–xMoxS2 Monolayers“, Nano Lett. 17, 2802 (2017).
- V. Carozo, Y. Wang, K. Fujisawa, B. R. Carvalho, A. McCreary, S. Feng, Z. Lin, C. Zhou, N. Perea-López, A. L. Elías, B. Kabius, V. H. Crespi, and M. Terrones, “Optical identification of sulfur vacancies: Bound excitons at the edges of monolayer tungsten disulfide“,Sci. Adv. 3, (2017).
The calculation of resonance Raman intensities in 2D materials requires knowledge of the dielectric response including excitonic effects using many-body perturbation theory. We develop a computational framework for calculating Raman intensities from first-principles following a diagrammatic approach, which scales favorably with respect to the number of Raman modes compared to existing implementations using finite displacements.
- Y. Wang, B. Carvalho, V. H. Crespi, “Strong exciton regulation of Raman scattering in monolayer dichalcogenides”, Phys. Rev. B (Rapid Commn.) 98, 161405 (2018)
- A. McCreary, J. R. Simpson, Y. Wang, D. Rhodes,K. Fujisawa, L. Balicas, M. Dubey, V. H. Crespi, M. Terrones, A. R. H. Walker, “Intricate Resonant Raman Response in Anisotropic ReS2“, Nano Lett. 17, 5897 (2017)
- B. R. Carvalho*, Y. Wang*, S. Mignuzzi, D. Roy, M. Terrones, C. Fantini, V. H. Crespi, L. M. Malard, and M. A. Pimenta, “Intervalley scattering by acoustic phonons in two-dimensional MoS2 revealed by double-resonance Raman spectroscopy“, Nat. Commun. 8, 14670 (2017).
2D Growth control
Increasingly successful efforts are being directed to the synthesis of millimeter-scale 2D monolayers with high sample qualities. These advances motivate the nanoscale control over 2D growth by properly designing the topographies and tailoring the surface chemistry of the substrate. We employ density functional theory and empirical forcefield calculations to predict grain boundary control and epitaxial control as applicable to a broad class of sheet-substrate combinations.
- Y. Wang, V. H. Crespi, “Theory of Finite-length Grain Boundaries of Controlled Misfit Angle in Two-dimensional Materials”, Nano Lett. 17, 5297 (2017)
- A. Azizi, Y. Wang, Z. Lin, K. Wang, A. L. Elias, M. Terrones, V. H. Crespi, and N. Alem, “Spontaneous Formation of Atomically Thin Stripes in Transition Metal Dichalcogenide Monolayers“, Nano Lett. 16, 6982 (2016).
- Z. Zhang, Y. Wang, X. Leng, V. H. Crespi, F. Kang, R. Lv, “Controllable Edge Exposure of MoS2 for Efficient Hydrogen Evolution with High Current Density”, ACS Appl. Energy Mater. 1, 1268 (2018)