Functional Diamonds Have Potential for Cross-Field Applications

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The Characteristics of Diamond Materials
Diamond is a special material with extreme properties in mechanical, thermal, optical, chemical, electrical, etc., just to name a few here.
Mechanical properties: Diamond is currently the hardest substance on earth, with a Mohs hardness of 10. Diamond hardness is directional, and its hardness is ordered from high to low as octahedral crystal faces, rhombohedral dodecahedral crystal faces, and hexahedral crystal faces. In addition, diamond has a small friction coefficient and has extremely high anti-wear ability.
Electrical properties: Diamond has an ultra-wide band gap, ultra-high breakdown field strength, and high electron and hole mobility.
Acoustic properties: Diamond has the highest surface acoustic wave velocity and extremely high Young’s modulus among all materials.
Optical properties: Diamond can transmit photons with energy smaller than the band gap from far infrared to ultraviolet.
Thermal properties: Diamond is the substance with the highest thermal conductivity in nature. The thermal conductivity can reach 2000 W/(mK) at room temperature, the coefficient of thermal expansion is about (0.86 ± 0.1)*10-5/K, and it is insulating at room temperature.

Synthesis Methods of Diamond
Due to the cost and scarcity of large natural diamonds, finding more cost-effective solutions for the industrial synthesis of diamonds used to be a serious challenge. It wasn’t until 1992 that HPHT (high-pressure high-temperature) technology emerged, which became the standard technology used to produce industrial diamonds for decades. After that, a variety of diamond synthesis methods have been developed, including chemical vapor deposition (CVD), detonation method, static pressure synthesis, etc.
Among them, the CVD method creates a tetrahedrally bonded carbon network by adding carbon atoms to an initial template one at a time. CVD technology is often used to prepare functional diamonds, including CVD thin films (conventional diamond films, nano-diamond films, thickness less than 50 μm) and self-supporting thick films (single crystal diamond and polycrystalline diamond).

Applications of Functional Diamond
Diamond semiconductor
Diamond is considered to be the most promising material for the preparation of next-generation high-power, high-frequency, high-temperature and low-power loss electronic devices. Its electron and hole mobility are as high as 4500 cm²/(v·S) and 3800 cm²/(v·S) at room temperature, much higher than the third-generation semiconductor materials GaN and SiC. In addition, diamond can achieve high-intensity free exciton emission (light emission wavelength is about 235nm) at room temperature, and has great potential in the preparation of high-power deep ultraviolet light-emitting diodes.

Thermal Applications of Diamond
Diamond is an excellent electronic packaging material with good prospects, for example, diamond-enhanced metal-based packaging materials have been commercially available. The combination of extremely high thermal conductivity and electrical insulation makes diamond the heat sink of choice for many high-power density devices. Heat dissipation at the laser diode junction is one of the earliest applications of CVD diamond (

Optical Applications of Diamond
Diamond almost meets all the requirements for an ideal power transmission window, and there are many applications in optical windows, such as mobile phone displays and camera lenses.

Diamond Acoustic Devices
Diamond can maintain perfect vibratory motion without distortion at frequencies up to 70 kHz, providing almost perfect sound reproduction. In addition, diamond has the highest surface acoustic wave velocity and is an excellent material for surface acoustic wave filters, which can improve the filtering frequency and power handling capacity.

Nanodiamond Lubricating Oil
Nanodiamonds have a large surface area and low surface roughness. Existing experiments have shown that adding one-thousandth of spherical nanodiamonds to lubricating oil can effectively improve the anti-wear and shock-absorbing effect of lubricating oil, and can be widely used in various mechanical structures.

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