Synthetic diamonds or Lab created diamonds are those that are produced in an unnatural way emulating the conditions in which natural diamonds are created. Synthetic diamond, man-made diamond that is usually produced by subjecting graphite to very high temperatures and pressures. These diamonds are chemically identical to natural diamonds (carbon) consisting of actual carbon atoms making them diamonds and also possess characteristics similar to natural diamonds. Synthetic diamond resembles natural diamond in most fundamental properties, retaining the extreme hardness, broad transparency (when pure), high thermal conductivity, and high electrical resistivity for which diamond is highly prized.
Naturally-formed diamonds and synthetic diamonds have astonishing properties that lead to their wide applications. Its molecular structure, with strong covalent bonds, results in greater hardness than all other materials, ideal for cutters used in oil and gas drilling, where it enables longer tool lifetime by minimizing wear, reduces downtime and drives down operating costs and carbon footprints.
Synthetic diamonds are widely used in end-user industries such as mining and construction, electronics, and healthcare. They are also used as gem in jewelry. Because synthesis is an expensive process, large stones of gem quality are rarely made. Instead, most synthetic diamond is produced as grit or small crystals that are used to provide hard coatings for industrial equipment such as grinding wheels, machine tools, wire-drawing dies, quarrying saws, and mining drills. In addition, diamond films can be grown on various materials by subjecting carbon-containing gas to extreme heat, and those layers can be used in cutting tools, windows for optical devices, or substrates for semiconductors. Synthetic diamond is also emerging as most versatile super material for defence that shall have significant effect in a variety of applications as diverse as high power radars, communications and electronic warfare systems, Directed Energy Weapons, MEMS applications, Aerospace applications and Quantum science among many others.
In 1880 the Scottish chemist James Ballantyne Hannay claimed that he had made diamonds by heating a mixture of paraffin, bone oil, and lithium to red heat in sealed wrought-iron tubes. In 1893 the French chemist Henri Moissan announced he had been successful in making diamonds by placing a crucible containing pure carbon and iron in an electric furnace and subjecting the very hot (about 4,000 °C [7,000 °F]) mixture to great pressure by sudden cooling in a water bath. Neither of those experiments has been repeated successfully.
During the first half of the 20th century, the American physicist Percy Williams Bridgman conducted extensive studies of materials subjected to high pressures. His work led to the synthesis by the General Electric Company, Schenectady, New York, of diamonds in its laboratory in 1955. The stones were made by subjecting graphite to pressures approaching 7 gigapascals (1 million pounds per square inch) and to temperatures above 1,700 °C (3,100 °F) in the presence of a metal catalyst. Tons of diamonds of industrial quality have been made in variations of that process every year since 1960.
Methods of creating Synthetic Diamonds
Most synthetic diamonds are typically created one of two ways. Either by a high-pressure, high-temperature process (HPHT) or a chemical vapor deposition (CVD).In both ways these diamonds are near identical to natural diamonds.
Researchers Find New Phase of Carbon, Make Diamond at Room Temperature
Researchers from North Carolina State University have discovered a new phase of solid carbon, called Q-carbon, which is distinct from the known phases of graphite and diamond. They have also developed a technique for using Q-carbon to make diamond-related structures at room temperature and at ambient atmospheric pressure in air. Phases are distinct forms of the same material. Graphite is one of the solid phases of carbon; diamond is another.
Researchers at North Carolina State University have developed a system to synthetically make microscopic diamonds — also called nanodiamonds — in specialized crystalline structures to stabilize calculations in quantum computers. The researchers tweaked the structure of a nanodiamond, which is made of carbon atoms, to stabilize the qubits at the center of quantum computers. The impure nanodiamond provides a way for the qubit to change states in a stable form.
Q-carbon has some unusual characteristics. For one thing, it is ferromagnetic – which other solid forms of carbon are not. “We didn’t even think that was possible,” Jay Narayan, the John C. Fan Distinguished Chair Professor of Materials Science and Engineering at NC State says. In addition, Q-carbon is harder than diamond, and glows when exposed to even low levels of energy. “Q-carbon’s strength and low work-function – its willingness to release electrons – make it very promising for developing new electronic display technologies,” Narayan says.
Researchers start with a substrate, such as such as sapphire, glass or a plastic polymer. The substrate is then coated with amorphous carbon – elemental carbon that, unlike graphite or diamond, does not have a regular, well-defined crystalline structure. The carbon is then hit with a single laser pulse lasting approximately 200 nanoseconds. During this pulse, the temperature of the carbon is raised to 4,000 Kelvin (or around 3,727 degrees Celsius) and then rapidly cooled. This operation takes place at one atmosphere – the same pressure as the surrounding air. nanometers and 500 nanometers thick.
By using different substrates and changing the duration of the laser pulse, the researchers can also control how quickly the carbon cools. By changing the rate of cooling, they are able to create diamond structures within the Q-carbon. “We can create diamond nanoneedles or microneedles, nanodots, or large-area diamond films, with applications for drug delivery, industrial processes and for creating high-temperature switches and power electronics,” Narayan says. “These diamond objects have a single-crystalline structure, making them stronger than polycrystalline materials. And it is all done at room temperature and at ambient atmosphere – we’re basically using a laser like the ones used for laser eye surgery. So, not only does this allow us to develop new applications, but the process itself is relatively inexpensive.” And, if researchers want to convert more of the Q-carbon to diamond, they can simply repeat the laser-pulse/cooling process
High-pressure, high-temperature diamonds are is the name given to diamonds created under pressure of 5 GPa at more than 1500 degrees Celsius. Though this is not new to diamonds, the process has been used on diamonds to treat them in the past. It has been used to add or subtract colors or enhance the diamond as a whole. Typically this process is started with cheaper less desirable stones, known as a seed. These less lucrative stones start the process to create the HPHT diamonds.
The properties of synthetic diamond depend on a large part on its manufacturing processes. CVD, has been able to achieve superior properties such as hardness, thermal conductivity and electron mobility, compared to naturally-formed diamonds.
This process of Chemical Vapor Deposition, is another way to form synthetic diamonds. This method is a crystal formation process, using carbon plasma where the carbon atoms start to form. These deposits start to form the diamond. Along with the plasma, various gases are released into the chamber to create the right environment of the process. CVD process produces diamond from a heated mixture of a hydrocarbon gas (typically methane) and hydrogen in a vacuum chamber at very low pressures. Under normal circumstances, heating this mixture at such low pressures would produce graphite or some other non-diamond form of carbon.
But in a CVD growth chamber, some of the hydrogen is converted to atomic hydrogen, which promotes diamond formation since diamond is more stable in this environment. The conversion of molecular hydrogen to atomic hydrogen is accomplished through methods such as the application of microwave energy, an electric discharge, or hot filaments.
When an atomic hydrogen is present in the gas phase, two chemical processes occur:
(1) Graphite and other non-diamond carbon react with the atomic hydrogen and evaporate in a newly formed gas phase.
(2) Atomic hydrogen reacts with the original hydrocarbon gas (methane) to form a highly reactive carbon-hydrogen species. When this species decompose, it gives up its hydrogen to form pure carbon: diamond.
GaN-on-Diamond For Next Power Devices
GaN-on-diamond offers key parameters of high thermal conductivity, high electrical resistivity and small form factor at both device and system level. These benefits make GaN-on-diamond power amplifier devices very attractive for high power RF applications, such as commercial base stations, military radar applications as well as satellite communication and weather radars,” explained Ezgi Dogmus, technology & market analyst from Yole Développement. “This innovative device technology, in development for over a decade, is expected to be launched commercially by leading industrial actors such as RFHIC, Akash Systems and Mitsubishi Electric in the next years,” he added.
A team led by the School of Mechanical Engineering at Georgia Institute of Technology has implemented a series of results based on room-temperature surface-activated bonding (SAB) to bond GaN and single-crystal diamond with different interlayer thicknesses. The newly developed technique maximizes gallium nitride performance for higher power operations.
The maximum output power of GaN-based HEMTs is limited by the high temperature of the channel substrate, which degrades system performance and reliability. Diamond is currently the material with the highest thermal conductivity, and through its integration with GaN, it helps to dissipate the heat generated near the channel. “During the HEMT device working, a large voltage drop near the gate induces localized Joule-heating. The heating area is located within tens of nanometers, which results in super-high local heat flux. The local heat flux value of GaN-based HEMTs could reach more than ten times larger than that of the sun surface. Proper heat spreading technique, such as putting diamond as close as possible to the hot-spots, could decrease the channel temperature effectively, facilitating the device stability and lifetime,” said Zhe Cheng, a recent Georgia Tech Ph.D. graduate who is the paper’s first author and now is a postdoc in UIUC.
The techniques currently used involve the direct growth of diamond deposited by chemical vapor (CVD) on GaN with a dielectric layer as a protective layer because the plasmon during diamond growth would damage GaN. The combination of the thermal resistances of the materials and the interfaces prove to play a pivotal role in heat flow management, especially for high-frequency applications for switching power supplies. The growth temperature of the CVD diamond is above700 °C. When the devices cool down to room temperature, the stress at the interfaces would crack the wafers. Additionally, the adhesion layer increases the thermal resistance of the GaN-diamond interface, which offsets for the benefit of the diamond substrates high thermal conductivity.
The research presented by the team from the Georgia Tech, Meisei University, and Waseda University used two modified SAB techniques to bond GaN with diamond substrates with different interlayers at room temperature. The two to-be-bonded surfaces are cleaned and activated by Ar ion beams, which generate dangling bonds at the surfaces. Then the two surfaces are pressed together at room temperature. The dangling bonds would form covalent bonds at the interfaces. In their work, some silicon atoms are added at the interface to enhance the interfacial bonding.
“The bonding is finished at Meisei University and Waseda University (Fengwen Mu and Tadatomo Suga). Then the bonded interfaces are measured by time-domain thermoreflectance (TDTR) at Georgia Tech (Zhe Cheng, Luke Yates, and Samuel Graham). Related thermal modeling is also performed at Georgia Tech to evaluate the impact of the bonded interface on GaN devices”, said Zhe Cheng TDTR is used to measure thermal properties. Material characterization can be performed by high-resolution scanning electron microscopy (HR-STEM) and electron energy loss spectroscopy (EELS).
Time-domain thermoreflectance (TDTR)
Time domain thermoreflectance (TDTR) is a pump-probe technique with an ultrafast femtosecond laser, which measures the thermal boundary conductance of the GaN-diamond interface. This technique uses an ultrafast laser modulated between 1 and 12 MHz to control the thermal penetration depth. The probe pulse is delayed between 0.1 and 7 ns compared to the pump pulse to allow the decay of the relative surface temperature to be measured through this time. A Lock-in amplifier allows extracting the read signal picked up by a photodetector. The temperature variation is measured by the reflectivity variations of a thin metal transducer (50-100 nm). The system is capable of measuring thermal conductivity between 0.1 and 1000 W/m-K and thermal boundary resistance between 2 and 500 m2-K/G. A Ti-sapphire femtosecond laser is used.
Fabrication and test
In this research presented by the Georgia Tech and Meisei University, GaN was bonded to diamond by adding some Silicon atoms at the interfaces to help chemical adhesion of the interface and lowering thermal contact conductance. Thermal boundary conductance (or TBC) describes the heat conduction between solid-solid interfaces. The related coefficient is a property indicating the ability to conduct heat across interfaces.
Two samples were used by the team. The first sample consisted of a thin layer of GaN (~700 nm) bound on a commercial single-crystal diamond substrate (grown by CVD) with a Si interlayer of ~10 nm thickness. The other sample had a GaN of ~1.88-μm thickness bonded on a commercial single-crystal diamond substrate grown by a high-pressure high-temperature method (HPHT). The thickness of GaN is polished to be thin enough for TDTR measurements .With the following sample structures, the thermal conductivity of the individual crystalline diamond substrates on the GaN-free area was measured. Then TDTR measurements were performed on the area with the GaN layer to measure the TBC of the GaN-diamond structure.
“The measured thermal conductivity of the diamond substrates was used as a known parameter in the adaptation of the TDTR data to extract the TBC when measuring above the GaN layer. Overall, there are three unknown parameters: Al-GaN TBC, GaN thermal conductivity, and GaN-diamond TBC. TDTR is a technique to measure the thermal properties of both nanostructured and bulk materials. A modulated laser beam heats the surface of the sample while another delayed beam detects the change in surface temperature through thermoreflectance and captured by a photodetector”, said Zhe Cheng.
The global Synthetic Diamond market is valued at 1232.6 million USD in 2020 is expected to reach 1800.5 million USD by the end of 2026, growing at a CAGR of 5.5% during 2021-2026. Natural diamonds dominated the market in 2018 as they are one of the hardest materials available on earth and are mainly utilized for jewelry applications. Industrial applications of natural diamond account for a comparatively smaller share as compared to their synthetic counterparts, while their share in jewelry application is expected to gain prominence over the coming years.
Widespread industry adoption of diamond has been slow, consistent with general delay in adoption of new materials, however some sectors have started using it. Growing environmental concern regarding the mining process that is carried out for exploring natural diamonds coupled with strict governmental regulations to extract natural diamond is likely to hamper the production of natural diamonds, thereby giving rise to the manufacture of synthetic diamond.
Synthetic diamond jewelry has been gaining popularity in the past few years on account of high affordability and low cost. Industrial application is projected to grow at a CAGR of 2.8% from 2019 to 2030 due to rising construction activities in terms of new construction as well as refurbishment activities around the globe.
Synthetic diamonds are also widely used in superabrasive tools, such as grinding wheels, cutting tools, and drilling and dressing tools, among others, for manufacturing products in the automotive, medical, aerospace, and electronics industries. Hence, increasing demand for superabrasives is also likely to boost the demand for synthetic diamonds.
North America dominated the market with a revenue share of 51.7%. The future outlook in North America is likely to be influenced by changing buying patterns of the millennials shifting from natural diamonds to synthetic or lab grown ones on account of low cost. Asia-Pacific registered large growth in the synthetic diamond market across the world, owing to the rapid growth of electronics manufacturing in countries, like China, India, and Japan.
China are making attempts for intelligent manufacturing and upgrading to high-end manufacturing. Apart from China, the ASEAN region is the largester exporter of electronics, which is equivalent to about 25% of the region’s total exports in goods. According to the ASEAN Secretariat, the bulk of the world’s consumer electronics comes from the ASEAN region. Moreover, over 80% of the world’s hard drives are produced in the ASEAN region. Owing to these factors, Asia-Pacific is likely to dominate the global market during the forecast period.
The global synthetic diamond market is highly fragmented, with various large, mid-sized, and small players focusing heavily on research and innovation, to cater to the rising demand. The market is demand-oriented, due to which, products are manufactured depending upon the specifications from the end-user industry. The major players in the market include Element Six, Sumitomo Electric Industries, Pure Grown Diamonds, and New Diamond Technology, Sandvik Hyperion, ILJIN Diamond, Zhongnan Diamond, HUANGHE WHIRLWIND, Sino-crystal Diamond, JINQU CR GEMS, HongJing, SF-Diamond, and Yalong.
Element Six have announced that its Technologies Group experienced more than 20 percent growth in 2014, marking the third consecutive year of high growth. “Building upon the company’s positive results, in 2015 Element Six will extend its research and development efforts to leverage synthetic diamond to enhance EUV optics power levels, help create environmentally friendly and cost-effective methods to treat industrial wastewater, and to create novel thermal management solutions for semiconductor devices, among others,” according to company.
Synthetic diamonds are segmented by the way they are manufactured, i.e. high-pressure high-temperature (HPHT) and chemical vapor deposition (CVD) methods. These diamonds are also categorized by type into polished or rough. By the product segment, synthetic diamonds are divided into dust, grit, stone, bort and powder. Depending on the end-user application, they are divided into jewelry, electronics, construction, mining and healthcare.
The following companies as the key players in the global synthetic diamond market: Crystallume, Element Six, ILJIN Diamond, NEW DIAMOND TECHNOLOGY, and Scio Diamond Technology. Other prominent vendors in the market are: Applied Diamond, D.NEA, Hebei Plasma Diamond Technology, New Age Diamonds, Washington Diamonds Corporation, Centaurus Technologies, Inc.and Zhengzhou Sino-Crystal Diamond.
Further, the report states that one challenge in the synthetic diamond market is complicated manufacturing process. Synthetic diamonds are mainly produced by two manufacturing processes such as the HPHT method and the CVD method. The production of synthetic diamond is complex and time consuming. These processes include multiple steps and have production limitations regarding the size of diamonds. The HPHT method is a three-step process and requires high temperature and high pressure.