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What Has Been Achieved:
The study investigated the growth of WS2 films by MOCVD comparing the properties of monolayers grown with diethyl sulfide (DES) versus hydrogen sulfide. The results show considerable carbon incorporation in WS2 when DES is used which prohibits lateral growth of domains and significantly reduces the photoluminescence intensity from the layers.
Importance of Achievement:
What Has Been Achieved:
A new physical system has been predicted, which couples together two more traditional “surface science” systems by coupling the surfaces on opposite sides of a suspended 2D layer.
Importance of Achievement:
What Has Been Achieved:
A tightly iterated closed loop between experiment and theory in the NSF Materials Innovation Platform Two Dimensional Crystal Consortium at Penn State is revealing new insights into the growth and properties of 2D materials. This includes groundbreaking work on the interpretation of optical probes – a key area for emerging data-centric approaches of 2D systems, the development of leading interatomic potentials to describe complex growth processes, and new ways to control the atomic-level structure of these systems.
What Has Been Achieved:
A new type of strong coupling between isoelectronic substitutional dopants (Mo dopants) and common lattice defects (sulfur vacancies) has been identified in WS2 by their ~80% probability of co-localization using aberration-corrected scanning transmission electron microscopy. The coupling mechanism and the Mo dopant’s ability to facilitate the charging of sulfur vacancies is identified using first-principles density functional theory calculations.
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What Has Been Achieved:
A photoluminescence feature has been identified as excitons bound to charged sulfur vacancies in 2D WS2.
Importance of Achievement
The study identifies a fast, inexpensive, and non-destructive characterization method to assess the quality of 2D transition metal dichalcogenide crystals.
Unique Features of the MIP That Enabled Project:
Close collaboration between synthesis, characterization, and theory efforts.
Publication:
What Has Been Achieved:
A family of longstanding mis-assignments of Raman signatures in 2D transition metal dichalcogenides has been corrected by the collaboration between double resonance Raman spectroscopy experiments and first-principles calculations. Selection rules for intervalley scattering processes in MoS2 have been derived from group theory and verified from first-principles.
Importance of Achievement:
What Has Been Achieved:
Finite-length grain boundaries and their topographic control using curved substrates are predicted from accurate empirical forcefield calculations.
Importance of Achievement:
The study expands the scope and generalize the concept of grain boundaries, introducing a method of controlling the density and detailed geometry of grain boundaries that is general to all 2D materials.
Unique Features of the MIP That Enabled Project:
What Has Been Achieved:
The new ReaxFF reactive potential developed for this project accurately describes both equilibrium properties and also mechanical deformations and structural defects within MoS2 , a promising material for nanoelectronics. A new type of “ripple” defect has been identified as a favorable host for sulfur vacancy defects.
Importance of Achievement:
