Figure 1: Diamond wafer prepared using the customized microwave plasma chemical vapor deposition (MPCVD) method.
A research team co-led by Professor Yang Lu from the Department of Mechanical Engineering, Faculty of Engineering, The University of Hong Kong (HKU), and Professor Chengming Li from the Institute for Advanced Materials and Technology at University of Science and Technology Beijing (USTB), has successfully fabricated a free-standing ultrahard diamond wafer with a diameter of up to 5 inches, a thickness of 3 mm, and a Vickers hardness exceeding 200 GPa.
This work marks the first demonstration of simultaneously achieving inch-scale dimensions and ultrahigh hardness in diamond materials, laying an important foundation for the development of scalable ultrahard diamond for demanding applications in precision machining, semiconductor technologies, and aerospace engineering.
Diamond is widely regarded as the "ultimate semiconductor" due to its exceptional thermal conductivity, ultra-high breakdown electric field, radiation resistance, and mechanical robustness, all of which far exceed those of conventional semiconductor materials such as silicon and silicon carbide. However, the scalable fabrication of inch-scale, binder-free ultrahard diamond has long remained a critical bottleneck due to the limitations of traditional high-pressure high-temperature (HPHT) methods.
The HKU–USTB team developed a customised microwave plasma-enhanced chemical vapor deposition (MPCVD) system and introduced an innovative high-frequency pulsed nitrogen doping strategy, creating a rapidly switching local non-equilibrium growth environment during diamond deposition. By precisely controlling plasma chemistry and growth conditions, the team successfully produced a 5-inch free-standing diamond wafer. The high-frequency pulsed introduction of a nitrogen source induces rapid fluctuations in both plasma-active species composition and growth temperature, within an extremely short period, thereby breaking the limitations of traditional stable growth modes. This dynamic regulation mechanism not only enhances the surface reconstruction and defect control but also effectively promotes the formation of specific microstructures.
Mechanical characterisation revealed that the Vickers hardness of this diamond can reach up to 208.3 GPa, twice that of conventional diamonds, and that the ultra-hard diamond wafer exhibits outstanding wear resistance and structural stability. Its wear resistance is approximately seven times higher than that of commonly used polycrystalline diamond substrates, and it is capable of producing clear scratches on high-quality single-crystalline diamond surfaces, further demonstrating its exceptional machining capability. In addition, the pulsed nitrogen-doping growth strategy allows deposition on commonly used three-dimensional tool surfaces.
High-resolution transmission electron microscopy further revealed the microscopic origin of the ultrahigh hardness. The diamond wafer contains an extremely high density of three-dimensional interlocked stacking fault networks, with a density of up to 4.3 × 10¹² cm⁻², which effectively suppresses dislocation motion. Electron energy loss spectroscopy and first-principles calculations indicate that nitrogen incorporation significantly reduces the formation energy of stacking faults, promoting their stable formation during growth.
The successful fabrication of inch-scale ultrahard diamond wafers opens new opportunities for diamond applications in extreme-environment electronics, advanced manufacturing, and semiconductor thermal management. With the rapid development of ultra-wide-bandgap semiconductor technologies, diamond wafers are expected to play an increasingly important role in MEMS, thermal management for high-power and high-frequency chips, extreme-environment sensing, and advanced packaging.
"Looking ahead, controllable modulation of the microstructure and band structure will be essential for enabling next-generation diamond-based microelectronic and optoelectronic devices. Leveraging its superior hardness and mechanical stability, the ultrahard diamond wafer developed in this study is expected to serve as an ideal platform for diamond MEMS and nano-structures, facilitating the industrialisation of strain-engineered diamond devices," said Professor Lu.
The research findings have been published in Nature Communications under the title
"Inch-scale Ultrahard Diamond Wafer with 200 GPa Hardness via High-Frequency Pulsed Local Non-Equilibrium Growth."
Article link:
https://www.nature.com/articles/s41467-025-66456-7
About Professor Yang Lu
Professor Yang Lu is currently Chair Professor of Nanomechanics in the Department of Mechanical Engineering and Kingboard Professor in Materials Engineering, and serves as Associate Dean (Mainland Affairs) of the Faculty of Engineering at HKU. Professor Lu is a leading expert in experimental nanomechanics and its interdisciplinary applications in materials engineering, advanced manufacturing, and semiconductor technologies. He is recognized for his groundbreaking works on elucidating the extreme mechanical properties of crystalline solids at micro- and nanoscale, and his innovative use of nanomechanics to manipulate micro/optoelectronics and their applications in a diverse set of engineering areas. Professor Lu has published more than 300 journal articles in peer-reviewed academic journals including Science, Nature Materials, Nature Nanotechnology etc., and 7 US patents granted.
