Researchers foresee controllable modulation of microstructure and band structure as essential for next-generation diamond-based microelectronics and optoelectronics, with the wafer serving as a platform for diamond MEMS and nano-structures.

A joint HKU–USTB team led by Professor Yang Lu and Professor Chengming Li fabricated a free-standing ultrahard diamond wafer up to five inches in diameter and three millimeters thick, achieving a Vickers hardness exceeding 200 GPa—the first to combine inch-scale size with ultrahigh hardness.

High-resolution TEM reveals an extremely dense network of three-dimensional interlocked stacking faults, up to 4.3 × 10^9 cm^-2, which suppress dislocation motion; nitrogen is found to reduce stacking-fault formation energy, promoting their growth according to EELS and first-principles calculations.

A customized microwave plasma-enhanced chemical vapor deposition (MPCVD) system and a high-frequency pulsed nitrogen-doping strategy create a rapidly switching, non-equilibrium growth environment during diamond deposition, enabling the desired microstructure.

Mechanical tests report a Vickers hardness of 208.3 GPa, wear resistance about seven times higher than typical polycrystalline diamond substrates, and the ability to machine high-quality single-crystalline diamond surfaces, signaling strong machining potential.

The study is published in Nature Communications under the title 'Inch-scale Ultrahard Diamond Wafer with 200 GPa Hardness via High-Frequency Pulsed Local Non-Equilibrium Growth.'

The ultrahard diamond wafer is positioned for extreme-environment electronics, advanced manufacturing, and semiconductor thermal management, with potential applications in MEMS, high-power/high-frequency chip cooling, and advanced packaging.