Lab-Grown Diamond Production Using Chemical Vapor Deposition

Lab-Grown Diamond Production

The diamond industry represents a unique economic case study on how scarcity impacts price. For many years large diamond companies have been able to artificially stabilize diamond prices by controlling supply. Besides being used for jewelry, diamonds have a variety of industrial applications due to their chemical composition and tensile strength. High prices and high demand have spurred a growing market for lab-grown diamond manufacturing.

Companies today are making lab-grown diamonds more than ever before and this has not only helped in making this gem more accessible but has helped in shifting the worldview towards the humanitarian and environmental costs of natural diamond mining.

Synthetic diamond making using CVD process

The Asia-Pacific region has long been the epicenter of lab-grown diamond production. India and China both manufacture diamonds, but each for different purposes. India tends to use lab-grown diamonds as high-quality gem substitutes for the fashion industry, while China uses lab-grown diamonds and diamond coatings for industrial purposes. Today, manufacturing occurs in a variety of countries, and the market has become a global venture (Research, 2017).

With consistent manufacturing, lab-grown diamonds are identical to naturally formed ones. There are two processes used to make diamonds, high-pressure and high-temperature (HPHT) and chemical vapor deposition (CVD). HPHT mimics the Earth’s natural process for diamond creation and thus requires extremely high heat (about 2000°C) and high pressures (over 1.5 million PSI) to simulate what would normally happen deep underground. CVD is a more recently developed process and imitates diamond formation in interstellar gas clouds that uses energy to break chemical bonds in gases which in turn facilitates diamond formation layer-by-layer (Technologies, 2020).

Both methods can yield high-grade diamonds but CVD has taken over as the preferred approach for a few different reasons. Firstly, most CVD processes require comparatively lower temperatures and pressures than HPHT. CVD is also able to make chemically pure diamonds because additional gases, like nitrogen and boron, are not needed during the process. But perhaps most importantly, CVD can be used for diamond deposition on substrates other than diamond. This has resulted in technological advancements for many industries like optics, computer sciences, and tool production. The biggest challenge to CVD production thus far is the inability to yield diamonds over 3.2 carats.

This blog will examine how chemical vapor deposition works and explain how Alicat vacuum controllers assist in this process.

CVD requires a process seed to act as the foundation for chemical deposition; the seed can be a thin slice of diamond or a graphite source. The seed is placed in a chamber which is evacuated down to a high vacuum (about 20 millitorr) to prevent contamination. The gases usually involved in the process are: a carbon-rich gas (like methane) and hydrogen or oxygen. Once the chamber is filled the selected gases, energy is applied to break chemical bonds and build up the diamond atom-by-atom.

There are two different approaches to creating the energy needed for the CVD process: heating gases (via thermal or chemical activation) or creating ionized plasma (via electrical or electromagnetic activation). To thermally heat gases, a filament within the vacuum chamber is used to reach target temperatures (2000-2500°C). Exothermic conversion of process gases in the form of a torch can also be used within the chamber to heat the process to the desired temperature (usually between 500-1000°C), but this is an uncommon approach. Using microwaves or lasers to make ionized plasma is the most common method applied to synthetic diamond making. There are a variety of techniques that can be employed to make the plasma (in jet streams or balls) that is used for the coating process  (Michael Schwander, 2010).

In every instance, manufacturers must carefully regulate the temperature, pressure, and gas composition of their process. Changes or fluctuations in any of these three variables impact the diamond growth rate, purity, and color. The diagrams below demonstrate the balance of gas composition and the pressure/temperature ratio that is needed for diamonds to grow.

Synthetic diamond growth regions

Figure 1 Carbon – Hydrogen – Oxygen Balance (Michael Schwander, 2010)

Synthetic diamond growth regions

Figure 2 Impact of pressure and temperatures on carbon solubility (Michael Schwander, 2010)

Alicat vacuum pressure controllers ensure accurate and stable pressures to maintain this delicate balance. There is a dedicated team of Alicat vacuum experts that have worked with diamond producers to design instruments specifically made for the pressure regulation requirements of a CVD system.

Alicat Conductor integrated Vacuum Pressure Controller
A new line of innovative upstream vacuum controllers, the Alicat Conductor-Series, has resulted from these partnerships. Historically, downstream pressure control has been used for chemical vapor deposition. In a downstream system, a large throttle valve is used in combination with a separate control module to manage high volumetric flow rates. The upstream vacuum controller Alicat offers uses a fast-acting proportional valve that enables faster system response and better stability.

 

An example of upstream control for CVD diamond production is shown below in Figure 3.

Alicat Conductor pressure controller used in vacuum control process.

Figure 3 Example of conductor used in Vacuum control

There are many challenges manufacturers face when attempting to produce quality lab-grown diamonds consistently. System stability, vacuum leaks, and component costs must be carefully monitored. Alicat has addressed system stability with quality specifications: the Conductor-series boasts a 1000:1 turndown ratio and an accuracy rating of +/-0.5% of full scale. When these specifications are coupled with Alicat’s control algorithm, it provides flexible and accurate pressure control with an extremely fast, 2ms sensor response time. To tackle leaks, Alicat performs helium leak tests (to 1 × 109 atm-cc/sec) on vacuum controllers to reduce risk. Finally, in respect to cost, Alicat has designed an all-in-one instrument that doesn’t need downstream throttle valves or separate control modules.

As the lab-grown diamond industry grows, Alicat is ready to help manufacturers adapt. If you have questions, please contact one of our expert application engineers today so we can find the solution you need.

 

References:

Chih-shiue Yan, Y. K.-k. (2002). Very high growth rate chemical vapor deposition of single-crystal diamond. Proceedings of the National Academy of Sciences of the United Stated of America (PNAS), 12523-12525. https://www.pnas.org/content/99/20/12523

Michael Schwander, K. P. (2010). A review of diamond synthesis by CVD processes. Elsevier, 1287-1300. https://www.sciencedirect.com/science/article/abs/pii/S0925963511002913

Research, T. M. (2017, December 6). Global Synthetic Diamond Market To Be Worth US$29,150.4 Mn By 2025 . Retrieved from NS Energy : https://www.nsenergybusiness.com/pressreleases/companies/transparency-market-research/pressglobal-synthetic-diamond-market-to-be-worth-us291504-mn-by-2025-transparency-market-research/

Technologies, A. D. (2020, May 1). Frequently Asked Questions about CVD Diamond. Retrieved from Diamond Materials: http://www.cvd-diamond.com/faq_en.htm

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