Elements, Chemical Composition and Structure

Diamond is a carbon allotrope of graphite and fullerene, in which all 4 valence electrons of each carbon atom are bonded. Its crystal structure can be viewed as two intersecting face-centered cubic lattices separated by 1/4 of the width of the unit cell in each dimension, resulting in very strong covalent bonds between atoms. It is the hardest naturally existing material, and it is the only material to have a hardness of 10 on the Mohs scale. However, because it has cleavage planes, its toughness is not as high, and therefore can easily break under high, instantaneous loads.
Natural diamond is formed 150km beneath the surface of the earth, where it is subjected to pressure as high as 50000 atm for long periods of time. However, only less than 10% of the diamond used in manufacturing is natural. Synthetic diamonds can be manufactured by reproducing these temperature and pressure conditions under the surface of the earth, using graphite as the starting material. The crystal structure and physical properties of synthetic diamond is almost identical to that of natural, and can even exhibit superior hardness, electrical and thermal conductivity and electron mobility.

Properties

With a high band gap of 5.45 eV, high dielectric strength and thermal conductivity and radiation resistance, diamond is known to possess physical properties superior to other common semiconductors like silicon, silicon carbide and gallium nitride. Despite these excellent properties for semiconductor applications, when brought to physical contact with iron, nickel or cobalt at temperatures over 800℃, carbon atoms on the surface of the diamond diffuse into the touching material, resulting in degradation.

Production

Main methods for growing synthetic diamond are High-Pressure High-Temperature (HPHT) method, Chemical Vapor Deposition (CVD) method and detonation synthesis.

High-Pressure High-Temperature (HPHT) Method
High-Pressure High-Temperature method is the synthesis of diamond by reproducing the temperature and pressure conditions (1500℃ and 5GPa) beneath the surface of the earth that the natural diamond grows in. These conditions melt the solvent metal (either iron, nickel or cobalt), which then dissolves the carbon source. A supersaturated solution is formed, and the carbon inside this solution then separated from the solution as diamond. Producing colorless, transparent diamond is also possible by removing the nitrogen from the solution by adding titanium and aluminum.

Chemical Vapor Deposition (CVD) Method
In Chemical Vapor Deposition method, a mixture of methane or another carbon containing gas and hydrogen is ionized in a high-temperature vacuum chamber. The carbon in the gas deposits on a diamond seed, growing into a crystal.

Detonation Synthesis
This method involves detonation of carbon containing materials in a inert gas, vacuum or submerged in water.

Practical Applications

Due to its higher durability compared to other semiconductor materials, diamond as a semiconductor is being studied for applications in extreme environments, like space. Moreover, it is also known that it can be used in high-frequency, high-power devices, and it is a subject of various research on energy conservation in electric vehicles, manufacturing equipments and control units. Compared to the ubiqitiuous silicon, the ideal diamond semiconductor is tens to hundreds of times faster, and is expected to open the way to even higher power and efficiency devices.

DISCO's processing solutions

DISCO performs test cuts on diamonds using grinders, dicing and laser saws on request.