Observation: Trends in CVD Growth Pattern
Nicholas DelRe and Alethea Inns
At GSI we are seeing a changing trend in the typical growth patterning of laboratory-grown diamonds grown by the CVD method. This indicates a change in growth methods to facilitate larger, higher clarity diamonds. This may also impact the ease of detection of undisclosed laboratory-grown diamonds if short-wave fluorescence imaging is used as a primary testing methodology.
With the continued growth of the laboratory-grown diamond market (15%-20% increase in 2019, per Bain & Company’s 2019 Global Diamond Industry Report), Gemological Science International (GSI) is seeing large numbers of laboratory-grown diamonds in our laboratories. As part of our undisclosed laboratory-grown diamonds, we are noticing trends in growth methods.
GSI has been encountering diamonds grown by chemical vapor deposition (CVD) with interesting growth patterns when viewed under deep ultraviolet light, known as UVC light (at about 225 nm). These patterns may make CVD-grown diamonds more difficult to detect if only using growth patterning to separate natural from laboratory-grown diamonds and are appearing more frequently in diamonds submitted to the laboratory.
CVD-grown diamonds are created when carbon ionized from methane gas (using microwaves or other high-energy sources) precipitates on a diamond seed crystal in a sealed chamber. CVD-diamonds grow layer-by-layer on top of the seed crystal. These layers are visible as fine, thin striations when observed in the DiamondView, an imaging device that shows fluorescence by using short-wave ultraviolet light. Striations are typically closely packed and indicate the changes in the growth conditions and uptake of impurities as the conditions in the chamber vary and the crystal grows. These striations visible in the DiamondView are characteristic of CVD-grown diamonds and are often used as indicators in identification.
A CVD laboratory-grown diamond with striae; closely packed parallel lines characteristic of typical CVD-grown diamonds. Image @ GSI
However, lately, GSI is noticing a significant number of diamonds over one (1) carat that show parallel bands in addition and as opposed to thin striations. CVD manufacturers state that this is the result of removing the crystal from the reactor mid-growth, removing any graphitic residues and non-gem polycrystalline diamond, and then returning it back to the reactor for additional growth causing a distinct line in the fluorescence pattern. This "interrupted" growth process aims to achieve better clarity and larger stone sizes.
CVD laboratory-grown diamonds with parallel fluorescent lines indicating the "interrupted" growth process. They are running parallel to the table of the diamond. Blue luminescence is likely caused by structural defects. Image @ GSI
To compound the challenge of identification through fluorescence imaging, some diamonds could be cut to hide the fluorescence bands
"Interrupted growth" banding resembles “step facets” on this cushion modified brilliant cut CVD-grown diamond. It is interesting to note here is that if the fluoresce image on the left is observed on its own, it may appear growth bands are facet junctions instead. Image @ GSI
GSI is noticing an increase in size and quality of CVD laboratory-grown diamonds, and they are still reliably identified by GSI with advanced spectroscopy.
CVD laboratory-grown diamonds have important non-gemological applications from surgical tools, laser and electronic components to medicine delivery. These non-jewelry applications are the driving force behind advances in CVD growth technology, as the need for single-crystal, chemically and structurally pure laboratory-grown diamonds increases. Conversely, there is also a need to engineer optical defects in ultra-pure CVD diamonds to create ultrasensitive sensors for measuring electric and magnetic fields in quantum research.
As the race continues to solve the problems of high growth quality and high growth rate large-area diamonds, the jewelry industry is also impacted. There is no doubt that as advances in CVD growth technology evolve, so will the characteristic growth patterns of the CVD-grown diamonds in gem-quality diamonds. It is up to the gemological laboratories to keep watch on the goods in the market and continue to be prepared as the technology evolves and detection becomes increasingly challenging.
“Although the main objective of Diamond growing technology is for other industries, growers are continually trying to mimic natural diamonds in every possible way,” said, Nick Del Re, GSI’s Chief Information Officer.
GSI stresses the importance of using proper processes, equipment, and expertise when identifying diamonds. GSI’s research department continues to conduct advanced testing on lab-grown and identification.