Letter Gems & Gemology, Fall 2017, Vol. 53, No. 3

Letters: Note on CVD Synthetic Overgrowth

I read with interest the Summer 2017 G&G Lab Note titled “CVD synthetic diamond overgrowth on a natural diamond” (pp. 237–239). The concluding paragraph states, “This synthetic overgrowth on a natural diamond with a Fancy color grade is the first GIA has seen.” However, a Gem News entry published in the Summer 1991 G&G presented color photos of a synthetic bluish gray CVD diamond overgrowth over one rough and two faceted natural near-colorless type Ia diamonds (Koivula and Kammerling, 1991). This Gem News item was more recently reproduced in the G&G In Review: Synthetic Diamonds compilation book, published in 2005. 

The treated gems were documented at the time by myself and other GIA researchers. A scientific article (Fritsch and Phelps, 1993) detailed the work first mentioned in the 1991 Gem News item. It already cautioned the jewelry industry about the availability of such a product and its possible misidentification. The highly doped boron film (approximately 220 ppm B, hence the dark color) was about 0.1 microns thick and deposited by the hot filament method. To everyone’s surprise, the crystallographic orientation of the natural type Ia substrate had no noticeable influence on the quality of the type IIb CVD film. The film could be detected by abrasions on facet edges, infrared spectroscopy (absence of the boron acceptor center), and UV-visible spectroscopy (presence of the N3 center). Of course, no detailed low-temperature photoluminescence was done, as this became common practice on diamonds only around 1999, with the onset on HPHT-treated diamonds. Neither is there a clear influence of the type IIb layer on the infrared spectrum, in part due to its thinness and the difference in efficiency with today’s infrared detectors. 

The three samples were left with GIA Research. I would encourage the authors of the Lab Note to run a full characterization with more up-to-date methods. It is of interest that the stones were submitted to GIA as client stones and followed the normal procedure for blue diamonds at the time, yet this treatment went undetected.

This work predates by two years Yacobi et al. (1993), which the Summer 2017 Lab Note suggests was the first to report deposition of CVD synthetic diamonds on natural type Ia substrates, although not faceted, so less relevant to gemologists’ concerns. (Yacobi’s article, incidentally, was published in the same issue of Diamond and Related Materials as the Fritsch and Phelps article.) The recent Lab Note also states, “Deposition of a boron-doped CVD synthetic film of <10 microns on a natural gem-quality diamond was reported in 2005,” whereas this had already been published almost 15 years prior, in 1991. Furthermore, in contrast with the 2005 article cited, spectroscopic data was presented in the 1993 article.

Emmanuel Fritsch
University of Nantes, CNRS, Team 6502
Institut des Materiaux Jean Rouxel (IMN), Nantes, France

We thank Prof. Fritsch for reading our Summer 2017 Lab Note and writing this letter to Gems & Gemology. In it we mentioned that this synthetic overgrowth diamond was the first GIA had seen, and several factors support this statement. It showed sharp boron peaks at 2455 and 2800 cm–1, and nitrogen aggregates and platelet peaks in the 1000–1500 cm–1 region (figure 1). Therefore, we classified it as mixed type Ia and IIb. In their 1993 Diamond and Related Materials article, Fritsch and Phelps coated natural, near-colorless type Ia diamonds by depositing boron-doped CVD film. They extrapolated the boron concentration of their coated diamonds using electrical conductivity rather than calculating it from the IR spectrum, which did not show any boron peaks. According to diamond type classification (Breeding and Shigley, 2009), the IR spectrum indicates a type Ia diamond, not a mixed type. The diamond we reported on in the last issue is the first CVD-coated mixed-type diamond detected at GIA using FTIR.

Spectra of natural diamonds with CVD coating.
Figure 1. Spectrum A is the IR spectrum of the Fancy blue CVD-coated diamond from Moe et al. (2017). It is a mixed-type diamond with boron peaks at 2455 and 2800 cm–1, along with nitrogen aggregates and a platelet peak between 1000 and 1500 cm–1. Spectrum B, modified from Fritsch and Phelps (1993), represents a CVD-coated bluish gray diamond. It does not show any boron peaks and therefore must be classified as a type Ia diamond.

CVD-coated diamonds previously reported in G&G were not client diamonds (see Fritsch and Phelps, 1993; Eaton-Magaña, 2014). The CVD layer was deposited on natural diamonds for research purposes. In contrast, our diamond was submitted by a client, suggesting CVD-coated natural diamonds have already reached the market. The color has also been improved. Previous CVD-coated diamonds were dark bluish gray (Koivula and Kammerling, 1991; see figure 2) and an initially gray color that altered to Fancy Dark brownish yellowish gray after nine years of wear (Eaton-Magaña, 2014; figure 2, center), whereas ours was graded as Fancy blue (figure 2, right). This was also the first undisclosed client-submitted CVD-coated diamond with blue color identified by GIA. The lack of disclosure and the Fancy blue color grade have significant consequences for the trade. Consequently, our note was translated to Chinese and Japanese on GIA’s website.

A variety of natural diamonds coated with CVD film.
Figure 2. Left: GIA coated three near-colorless natural diamonds with CVD film on pavilion facets in 1991, changing their color to dark bluish gray. Center: In 2005, Dr. Eaton-Magaña coated her own diamond with CVD film, again on the pavilion facets, and achieved a Fancy Dark brownish yellowish gray color. Right: A client submitted a Fancy blue diamond, coated with CVD film on the table facet, for a Colored Diamond Grading report in April 2017. It was the first blue synthetic overgrowth on natural diamond identified by GIA.

The Lab Notes section is intended for new findings at GIA laboratories, especially among client-submitted stones. Unlike research papers, the entries are meant to be short. We try to choose only the most appropriate references. Fritsch and Phelps (1993) described the deposition method of the CVD layer and characterized the CVD-coated diamonds using spectroscopy and gemological methods. That same year, Yacobi et al. (1993) published a paper about growing CVD films on type Ia natural diamonds. They deposited the CVD film on the (001) and (111) planes at various temperatures. They discussed preferential incorporation of defects at different crystallographic planes using cathodoluminescence and Raman spectroscopy. Although Fritsch and Phelps (1993) is an important study, we felt that Yacobi et al. was a more comprehensive reference for our lab note.

Our team respects Prof. Fritsch’s invaluable contributions to gemology, and we thank him for taking time to comment. 

Kyaw Soe Moe
GIA, New York

Breeding C.M., Shigley J.E. (2009) The “type” classification system of diamonds and its importance in gemology. G&G, Vol. 45, No. 2, pp. 96–111.

Eaton-Magaña S. (2014) Lab Notes: Long-term durability of CVD synthetic film on natural diamond. G&G, Vol. 50, No. 2, p. 152.

Fritsch E., Phelps A. (1993) Type IIb diamond thin films deposited onto near-colorless natural gem diamonds. Diamond and Related Materials, Vol. 2, No. 2-4, pp. 70–74.

Koivula J.I., Kammerling R.C. (1991) Gem News: Bluish gray synthetic diamond thin films grown on faceted diamonds. G&G, Vol. 27, No. 2, pp. 118–119.

Yacobi B.G., Lebens J., Vahala K.J., Badzian A.R., Badzian T. (1993) Preferential incorporation of defects in monocrystalline diamond films. Diamond and Related Materials, Vol. 2, No. 2-4, pp. 92–99.