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A team led by scientists at the Department of Energy's Oak Ridge National Laboratory explored how atomically thin two-dimensional (2-D) crystals can grow over 3-D objects and how the curvature of those objects can stretch and strain the crystals. The findings, published in Science Advances, point to a strategy for engineering strain directly during the growth of atomically thin crystals to fabricate single photon emitters for quantum information processing.
The team first explored growth of the flat crystals on substrates patterned with sharp steps and trenches. Surprisingly, the crystals conformally grew up and down these flat obstacles without changing their properties or growth rates. However, curvy surfaces required the crystals to stretch as they grew to maintain their crystal structure. This growth of 2-D crystals into the third dimension presented a fascinating opportunity.
Strain - Crystal - Objects - Kai - Xiao
"You can engineer how much strain you impart to a crystal by designing objects for them to grow over," said Kai Xiao, who with ORNL colleagues David Geohegan and postdoctoral researcher Kai Wang (now at Intel) conceived the study. "Strain is one way to make 'hot spots' for single photon emitters."
Conformal growth of perfect 2-D crystals over 3-D objects has the promise to localize strain to create high-fidelity arrays of single photon emitters. Stretching or compressing the crystal lattice changes the material's band gap, the energy gap between the valence and conduction bands of electrons, which largely determines a material's optoelectronic properties. Using strain engineering, researchers can funnel charge carriers to recombine precisely where desired in the crystal instead of at random defect locations. By tailoring curved objects to localize strain in the crystal, and then measuring resulting shifts in optical properties, the experimentalists compelled co-authors at Rice University—theorists Henry Yu, Nitant Gupta and Boris Yakobson—to simulate and map how curvature induces strain during crystal growth.
ORNL - Wang
At ORNL, Wang and...
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