synthetic diamonds had already met the demands of traditional engineering applications such as mechanical machining and drilling, and that future research would focus on synthesizing crystals of larger volume and higher quality while driving their transition toward functional materials (especially in the semiconductor sector). In light of current industrial developments, this direction has evolved into four frontier dimensions:

1. Breakthroughs in the Preparation of Large-Sized, Low-Defect Single-Crystal Wafers

To truly apply diamond in electronic and optical devices, the limitation of substrate size must first be overcome. While mainstream silicon wafers have achieved large-scale mass production at 12 inches, single-crystal diamond substrates have long been constrained by seed crystal dimensions and growth rates. In recent years, the academic community has primarily tackled this challenge through mosaic splicing growth and heteroepitaxial growth. Although mosaic growth using small substrates tends to induce dislocation defects or even cracking at the seams, major breakthroughs have been achieved in heteroepitaxy and the domestic production of high-power microwave plasma chemical vapor deposition (MPCVD) equipment. For instance, a research team at Xi'an Jiaotong University independently developed 2-inch heteroepitaxial freestanding single-crystal diamond substrates using MPCVD technology and achieved batch production; meanwhile, a joint research team from the Peking University Dongguan Optoelectronics Research Institute and partner institutions developed a method for the batch production of large-sized, ultra-smooth flexible diamond films. Furthermore, domestic research and industrial institutions have grown ultra-large single-crystal diamonds weighing up to 247.82 carats (approaching the 2-inch standard), and enterprises such as Ningbo Crysdiam have fabricated 3.35-inch single-crystal diamonds and are advancing toward 4-inch technology, significantly reducing the cost of high-quality seed crystals and single-crystal wafers.

2. Advancing Toward the "Ultimate Semiconductor" (Fourth-Generation Ultra-Wide Bandgap Semiconductors)

The original literature predicted that once diamond semiconductors are successfully developed, humanity will enter the "Diamond Age." In the modern semiconductor industry, diamond is widely recognized as the "ultimate semiconductor" (a core fourth-generation semiconductor material) for fabricating next-generation high-power, high-frequency, high-temperature-resistant, and radiation-hardened electronic devices, owing to its ultra-wide bandgap of 5.5 eV5.5\text{ eV}5.5 eV (far exceeding silicon carbide and gallium nitride), breakdown electric field strength of up to 10 MV/cm10\text{ MV/cm}10 MV/cm, carrier mobility more than three times that of silicon, and extremely low intrinsic carrier concentration .

Currently, using diamond directly as an active semiconductor device still faces the physical bottleneck of difficult electrical doping: its crystal lattice is extremely dense, and p-type doping primarily relies on boron atoms, which have a high ionization energy of 0.37 eV and are difficult to fully ionize at room temperature. Forced heavy doping increases lattice stress and defects, while n-type doping (such as phosphorus doping) is even more challenging. To address this issue, frontier research is improving room-temperature hole and electron mobility through surface hydrogen-terminated conductive channel modulation, deep elastic strain engineering, and the construction of heterojunctions (such as p-type diamond/n-type gallium oxide heterojunctions), laying the device foundation for new energy vehicle high-voltage platforms above 800V, smart grids, and deep-space exploration.

3. Extreme Thermal Management for High-Computing AI Chips and 5G/6G RF Devices (Heat Sink Materials)

Before active diamond chips fully mature, utilizing diamond's ultra-high thermal conductivity of 2000∼2500 W/(m⋅K)(approximately 5 times that of copper and 10 times that of silicon) as a passive heat dissipation substrate (heat sink) has become the fastest-commercializing functional material direction. As AI large-model computing chips evolve toward advanced nodes, the heat flux density per unit area increases sharply, and traditional copper, aluminum, and ceramic thermal management materials have reached their physical limits.

In this field, the industry is accelerating the deployment of "silicon/diamond 3D integrated hybrid bonding," "gallium nitride on diamond (GaN-on-Diamond)," and "diamond-copper composite" solutions. For example, a research team at MIT embedded micro GaN chiplets into pre-machined single-crystal diamond substrate microcavities, overcoming the thermal bottleneck of high-power wireless chips for 6G and high-power radar; Huawei, in collaboration with universities, achieved breakthroughs in silicon-diamond 3D integrated hybrid bonding and glass interposer integrated diamond heat dissipation, significantly reducing peak chip junction temperatures and packaging thermal resistance; and global computing giants such as NVIDIA have validated and adopted "diamond composite + liquid cooling" solutions to resolve the high-power heat dissipation challenges of next-generation GPUs, driving the transformation of industrial diamond from a ton-priced abrasive into a piece-customized, high-value-added semiconductor thermal management material.

4. Synthesis of Extreme Mechanical New Phases and Upgrading of High-Pressure Scientific Instruments

Following the direction of nanopolycrystalline diamond (NPD) and ultra-high-pressure anvils mentioned in the original paper, the scientific community continues to explore the performance limits of carbon materials. Beyond Ehime University in Japan synthesizing centimeter-scale NPD (HIME-DIA) using a large-volume press and breaking the 125 GPa pressure limit in a multianvil apparatus, Chinese research teams (such as those from Jilin University, Sun Yat-sen University, and Zhengzhou University) have recently simulated the extreme high-temperature and high-pressure environments of meteorite impacts to successfully synthesize high-quality pure bulk hexagonal diamond (Lonsdaleite) for the first time. Its hardness reaches 155 GPa(40% higher than traditional cubic diamond) and its thermal stability exceeds 1100 ∘C, further raising the performance ceiling of superhard materials and deep-earth scientific experimental anvils.