Further optimizing the sample geometry using the American Society for Testing and Materials (ASTM) standard allowed a maximum uniform tensile strain of up to 9.7%, and is close to the theoretical elastic limit of diamond. More importantly, this showed elastic straining of the microfabricated diamond arrays.
The team then performed density functional theory (DFT) calculations to estimate the impact of elastic straining from 0 to 12% on the diamond's electronic properties. The simulation results indicated that the bandgap of diamond generally decreased as the tensile strain increased, with the largest bandgap reduction rate down from about 5 eV to 3 eV at around 9% strain along a specific crystalline orientation. The team performed an electron energy-loss spectroscopy analysis on a pre-strained diamond sample and verified this bandgap decreasing trend.
Their calculation results also showed that, interestingly, the bandgap could change from indirect to direct with the tensile strains larger than 9% along another crystalline orientation. Direct bandgap in semi-conductor means an electron can directly emit a photon, allowing many optoelectronic applications with higher efficiency.
These findings are an early step in achieving deep elastic strain engineering of microfabricated diamonds. Using the nanomechanical approach, the team demonstrated that the diamond's band structure can be changed, and more importantly, these changes can be continuous and reversible, allowing different applications, from micro/nanoelectromechanical systems (MEMS/NEMS), strain-engineered transistors, to novel optoelectronic and quantum technologies.
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