Research

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 unconventional thermomechanics. My research employs accurate first-principles theory to model their growth and characterization, in close collaboration with several experimental teams.

Point defects in 2D materials

The thermodynamics of defects in a solid determines their population and what are the common species. But comparing with experiments can be difficult and time-consuming – an individual defect could be hard to unambiguously pinpoint from electron microscopy. We therefore calculate defect properties, say optical ones, to compare with experimentally measured fingerprints of defects. This procedures establishes efficient and non-invasive optical probes to interrogate sample quality.

Defects can also be exploited to improve material properties rather than degrade them, e.g. detrimental defects can be neutralized by introducing another type of innocuous defect to pair with it; nucleation of 2D materials at substrate defects could paradoxially improve the orientational uniformity of the grown 2D layer.

Excited-state properties

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.

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.