Chemical vapor deposition (CVD) is a major method for making synthetic diamonds that are grown from a hydrocarbon gas mixture. Microwave power can be used to assist the growing process by generating active radicals, which, on the other hand, set limits on the growth areas.

Qi Liang and Russell J. Hemley, Carnegie Institution of Washington, Washington D.C., USA, along with colleagues have successfully scaled up high-quality diamond production by introducing a 75 kW, 915 MHz microwave plasma-assisted CVD system. Using ultrapure hydrogen and methane gases, the system can grow single-crystal diamonds at a rate of up to 30 μm/h over a 300 mm diameter deposition area.

With an estimated production rate up to 100 grams per day, the researchers have achieved a major breakthrough in terms of growth area, growth rate and quality control, compared to existing CVD systems. They have also identified a growth-annealing co-process that improved the optical quality of CVD diamond.

• Large Area Single-Crystal Diamond Synthesis by 915 MHz Microwave Plasma-Assisted Chemical Vapor Deposition,
  Q. Liang, C.-S. Yan, J. Lai, Y.-F. Meng, S. Krasnicki, H. Shu, H.-K. Mao, R. J. Hemley
  Cryst. Growth Des. 2014.
  DOI: 10.1021/cg500693d