Marking diamond

Details Marking diamond Marking diamond

1998-05-15

2001-02-13

Gulakowski, Randy (Department: 1746)

Etching a substrate: processes

Forming or treating an ornamented article

C216S065000, C216S081000

Reexamination Certificate

active

06187213

ABSTRACT:

BACKGROUND TO THE INVENTION
The present invention relates to a method of producing on a polished facet of a diamond gemstone an information mark which is invisible to the naked eye, comprising using ultraviolet radiation or other radiation to irradiate the surface of the respective portion of the stone. “Invisible to the (naked) eye” means invisible to the (naked) eye of the expert or trained diamond grader. The information mark (which may be called an indicium) may be an identification mark for the diamond but need not identify a particular diamond and in general could give other information such as a quality or trade mark. Normally, the information mark will be a complex mark, not say a simple dot.
Such information marks are discussed in U.S. Pat. No. 5,410,125, from column 1, line 40 to column 2, line 2, but the technology of producing information marks on diamonds is also discussed in U.S. Pat. No. 4,392,476, U.S. Pat. No. 4,467,172, U.S. Pat. No. 5,149,938 and U.S. Pat. No. 5,334,280, and like technology is discussed in U.S. Pat. No. 4,912,298 in relation to spectacle lenses. In EP 0 567 129 A, U.S. Pat. No. 4,478,677, WO 90/03661, a paper by Geis et al in Appl. Phys. Lett. 55(22), pages 2295 to 2297, a paper by Harano et al in Advances in New Diamond Science and Technology, MYU Tokyo 1994, pages 497 to 500, a paper by Rothschild et al in J. Vac. Sci. Technol. B4(1), January/February 1986, pages 310 to 314, a paper by Rothschild et al in Proceedings of the SPIE, 1986, vol 633, Optical Microlithography V (1986), pages 51 to 57, a paper by Sercel et al. in Lasers & Optronics, September 1988, pages 69 to 72, and a paper by Sercel et al in Proceedings of the SPIE, vol 998, pages 76 to 83, there are discussions of similar technology.
There are relatively few published papers on the interaction of good quality gem diamond with intense pulsed ultraviolet lights such as those generated by excimer lasers. If diamond is discussed, most papers are concerned with polycrystalline diamond or “diamond like” films grown by chemical vapour deposition (CVD). The CVD material is often of poor optical quality and may contain significant amounts of carbon bonded in a graphite like (sp
2
) configuration rather than the pure diamond (sp
3
) configuration. Owing to the difference in the structures, these CVD materials are not likely to interact with ultraviolet radiation in the same way as good quality gem diamond material.
It is desirable to be able to produce the information mark in a manner which is not complex, which gives consistent results, which does not take too much time, which causes little pollution, and which gives no risk of damage to the diamond; it is also desirable to produce an even less visible mark which however with suitable magnification and viewing conditions is distinct and readable or identifiable.
The Invention
According to the method of the invention, an information mark which is invisible to the naked eye is produced on a polished facet of a diamond gemstone by irradiating the respective portion of the facet surface with radiation having a wavelength less than about 400 nm, in the presence of a reagent which reacts with the irradiated portion of the facet surface and causes a mark to be formed, the fluence of the radiation being below the level at which substantial darkening is present in the formed mark or below the level at which the formed mark detracts from the clarity grade of the diamond or being below the ablation threshold of the diamond. The invention also provides gemstones having a polished facet marked by the method, and apparatus for carrying out the method, comprising: means for mounting a diamond gemstone; a radiation source and optical means arranged to irradiate the surface of a polished facet of the gemstone with pulsed irradiation having a wavelength less than about 400 nm with a fluence at the location irradiated of not more than about 3 J/cm
2
per pulse and with not fewer than about 100 pulses per location irradiated; and means for having present at the location irradiated a reagent which reacts with the irradiated portion of the facet surface and causes a mark to be formed without there being substantial darkening in the formed mark. In the method of the invention, the conditions suitable for etching are produced by irradiating the desired region or regions of the sample with intense, preferably ultraviolet light, such as the pulsed irradiation produced by ArF excimer lasers. As the irradiation can be selectively applied only to the regions where etching is desired, no etch resist need be applied to the surface.
Ablation
Ablation as used herein is a process in which intense radiation, such as that produced by a pulsed ultraviolet laser, is absorbed in a thin layer at the surface of the diamond, either causing the layer to be transiently heated to a high temperature, or breaking the chemical bonds within that layer, so that a portion of the layer is vaporised or ejected from the material. It essentially involves a physical transformation of the material from a solid to a vapour without the involvement of any other reagents. Once vaporised, the material may react chemically with any reagents present. The hot carbon vaporised during ablation will readily react with an oxygen ambient to produce carbon monoxide and carbon dioxide. However the ablation would still take place in the absence of such a reagent. It is generally thought that ablation will not take place if the fluence of the pulsed irradiation (the energy per pulse per unit area of the irradiated surface) is below a threshold value.
Ablation at anomalously low threshold fluences can be obtained with CVD diamond and diamond-like films. The presence of non-diamond carbon in these materials can be expected to have a detrimental effect on the resistance of the material to the irradiation.
Phase Transformations
Diamond tends to transform to non-diamond forms of carbon when heated to high temperatures. This can lead to a build-up of a partially non-diamond layer in the irradiated region. Once the layer has started to form, it tends to absorb the irradiation more strongly than would be expected of clean diamond. Further energy pulses may then be capable of ablating the modified layer. The apparent ablation threshold for such a modified surface would be lower than for the original diamond. Once ablation is established, the process of forming non-diamond carbon phases continues at the bottom of the mark, so that ablation is sustained.
Darkening
As used herein, “darkening” is the increased optical density caused by the formation of grey or black marks or deposits due to the presence of amorphous carbon or other non-diamond carbon, for instance caused by deposition of vapourised carbon or by phase transformation to form a layer of modified material at or below the diamond surface. Substantial darkening is darkening that is severe enough to make the mark sufficiently visible enough to detract from the value of the stone, normally considered to be darkening that renders the mark visible to an expert using a ×10 loupe (ie to the expert naked eye aided with a ×10 loupe) or (a more stringent test) visible under a ×10 microscope such as a GIA “Gemolite” (trade mark).
Diamonds are graded according to their degree of clarity. Various grading scales are recognised, such as that used by the GIA, but all the scales are in reasonable agreement with each other. A flawless diamond (GIA FL) does not have any inclusions, cracks, or other defects inside the diamond and no defects on the surface of the diamond that would inhibit the free passage of light through the diamond. The test is based on features observable with a ×10 loupe, which is the loupe used by jewellers generally features with a maximum dimension of less than 5 microns are not detectable with a ×10 loupe. If a mark is produced on say the table of such a diamond that is observable with a ×10 loupe, the clarity grade of the diamond, and hence its value, would be reduced and this would not be desirable. Any darkening wi

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