Diamond material

Abstract

The present disclosure relates to a method of making fancy orange synthetic CVD diamond material. Among other things, the method may involve (i) providing a single crystal diamond material that has been grown by CVD and has a [N.sub.s.sup.0] concentration less than 5 ppm; (ii) irradiating the provided CVD diamond material so as to introduce isolated vacancies V into at least part of the provided CVD diamond material such that the total concentration of isolated vacancies [V.sub.T] in the irradiated diamond material is at least the greater of (a) 0.5 ppm and (b) 50% higher than the [N.sub.s.sup.0] concentration in ppm in the provided diamond material; and (iii) annealing the irradiated diamond material to forming vacancy chains from at least some of the introduced isolated vacancies.

Claims

1. A method of making fancy orange synthetic CVD diamond material, the method comprising: (i) irradiating a single crystal diamond material that has been grown by CVD and has a [N.sub.s.sup.0] concentration less than 5 ppm to introduce isolated vacancies V into at least part of the CVD diamond material, the total concentration of isolated vacancies [V.sub.T] in the irradiated diamond material being at least the greater of (a) 0.5 ppm and (b) 50% higher than the [N.sub.s.sup.0] concentration in ppm in the single crystal diamond material, and (ii) annealing the irradiated diamond material to form vacancy chains from at least some of the introduced isolated vacancies.

2. A method according to claim 1, wherein the annealing is carried out at a temperature of at least 700° C. and at most 900° C.

3. A method according to claim 1, wherein the annealing is carried out for a period of at least 2 hours.

4. A method according to claim 1, wherein the annealing steps reduce the concentration of isolated vacancies in the irradiated diamond material, whereby the concentration of isolated vacancies in the irradiated and annealed diamond material is <0.3 ppm.

5. A method according to claim 1, wherein the absorption coefficients at 350 nm and 510 nm for the diamond material prior to irradiation are less than 3 cm.sup.−1 and 1 cm.sup.−1 respectively.

6. A method according to claim 1, wherein the atomic boron concentration [B] in the diamond material is less than 5×10.sup.15 cm.sup.−1.

7. A method according to claim 1, wherein uncompensated boron is present in the diamond material in a concentration of >5×10.sup.15 cm.sup.−3, and the irradiation step (ii) introduces sufficient isolated vacancies into the diamond material so that total concentration of isolated vacancies [V.sub.T] in the irradiated diamond material, after isolated vacancies have been used to compensate the boron, is at least the greater of (a) 0.5 ppm and (b) 50% higher than the [N.sub.s.sup.0] concentration in ppm in the diamond material prior to its irradiation.

8. A method according to claim 1, wherein the diamond material is irradiated from two or more sides.

9. A method according to claim 1, wherein at least 50% of the CVD diamond has been formed from a single growth sector.

10. A method according to claim 1, wherein, after the irradiation and annealing steps (ii) and (iii), the absorption in the 250 nm region of the irradiated and annealed diamond material, when measured at room temperature, is greater than 5 cm.sup.−1.

11. A method according to claim 1, wherein the diamond material prior to irradiation according to step (i) of the method shows a measurable difference in at least one of its absorption characteristics in first and second states, the first state being after exposure to irradiation having an energy of at least 5.5 eV and the second state being after thermal treatment at 798K (525° C.), and wherein after the irradiation and annealing steps of the method the change in color saturation value C* between the diamond material in the said first and second states is reduced by at least 0.5 compared to the change in color saturation value C* between the diamond material in the said first and second states for the diamond material prior to its irradiation.

12. A method according to claim 1, wherein after the irradiation and annealing steps of the method, the change in color saturation C* of the diamond material in first and second states is less than 1, the first state being after exposure to irradiation having an energy of at least 5.5 eV and the second state being after thermal treatment at 798 K (525° C.).

13. A method according to claim 1, wherein the diamond material is annealed in the temperature range 1400° C.-2500° C. prior to the irradiation step.

14. A method according to claim 1, wherein the annealing step (ii) of method claim 1 is carried out after irradiation step (i) of method claim 1 is complete.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1, which has been referred to hereinbefore, is a flow chart which shows routes for methods according to the invention for obtaining orange diamond material;

(2) FIG. 2 are UV visible absorption spectra measured at room temperature for examples 1 and 2, post irradiation and anneal; and

(3) FIG. 3 are UV Visible absorption spectra measured at 77 K for examples 3, 5 and 6 post irradiation and anneal.

EXAMPLES

(4) HPHT diamond substrates suitable for synthesizing single crystal CVD diamond of the invention were laser sawn, lapped into substrates, polished to minimize subsurface defects such that the density of defects is below 5×10.sup.3/mm.sup.2, and generally is below 10.sup.2/mm. Polished HPHT plates 3.6 mm×3.6 mm square by 500 μm thick, with all faces {100} having a surface roughness R.sub.Q at this stage of less than 1 nm were mounted on a refractory metal disk, and introduced into a CVD diamond growing reactor.

(5) Growth Stages 1) The CVD diamond reactor was pre-fitted with point of use purifiers, reducing unintentional contaminant species in the incoming gas stream to below 80 ppb. 2) An in situ oxygen plasma etch was performed using 50/40/3000 sccm (standard cubic centimeter per second) of O.sub.2/Ar/H.sub.2 and a substrate temperature of 760° C. 3) This moved without interruption into a hydrogen etch with the removal of the O.sub.2 from the gas flow. 4) This moved into the growth process by the addition of the carbon source (in this case CH.sub.4) and dopant gases. For these examples the CH.sub.4 flowing at 165 sccm, nitrogen was present in the process gas at different levels for the different samples, provided from a calibrated source for example 100 ppb N.sub.2 either as Air in Ar or N.sub.2 in H.sub.2, and for some examples O.sub.2 was also present in the process gas as shown in Table 3.

(6) TABLE-US-00006 TABLE 3 Nitrogen dopant present in Oxygen flow present in Example the process gas (ppm) the process gas (ppm) 1 and 2 0.7 0 3 1.8 9160 4-6 1.1 13657 5) On completion of the growth period, the substrate was removed from the reactor and the CVD diamond layer removed from the substrate by laser sawing and mechanical polishing techniques. 6) This produced a CVD sample which had typical dimensions ˜3.1×5×5 mm.

(7) This grown CVD diamond is the “provided diamond” that is irradiated by methods of the present specification.

(8) The examples were electron irradiated a 4.5 MeV electron beam at 50% scan width and 20 mA beam current using an electron beam source such as that found at Isotron plc. Diamond samples to be irradiated are mounted in indium on a water cooled copper block to prevent the samples being heated above 350 K. The samples were then annealed in an Elite tube furnace (model THS 16/50/180-2416CG and 27160/T). Typically to make an orange diamond material a dose of 5.8×10.sup.18 e.sup.−/cm.sup.2 (equivalent to 6 hours irradiation with a 4.5 MeV electron beam at 50% scan width and 20 mA beam current) followed by an 8 hour anneal at 800° C. was used.

(9) Table 4 records the CVD growth chemistry, the [N.sub.s.sup.0] concentration in the provided diamond material, the absorption coefficients at 350 nm and 510 nm and the color, of the provided diamond material, the irradiation dose, the vacancy concentration post irradiation, the annealing time and temperature, the color of the diamond material post irradiation and anneal, the color characteristics, the [NV]. [V.sup.0] and [V.sup.−] concentrations and the absorption at 250 nm related to vacancy chains, all post irradiation and anneal. The results table 4 includes not only examples falling within the scope of the present invention, but also a number of comparative examples. For example, if the irradiation dose is not high enough, the number of isolated vacancies available to combine to form chains upon annealing, irrespective of the length of the anneal will not be large enough to form a significant concentration of vacancy chains; this is the case for comparative examples 2 and 6, which fall outside the scope of the present invention as the concentration of isolated vacancies incorporated during the irradiation step is less than the greater of (a) 0.5 ppm and (b) 0.5 ppm more than the [N.sub.s.sup.0] concentration, and the absorption at 250 nm in the treated sample is <5 cm.sup.−1. This is also illustrated with reference to FIG. 2 which is a room temperature UV visible absorption spectrum for examples 1 and 2, post irradiation and anneal. This figure shows strong absorption at 250 nm for example 1, indicating the presence of vacancy chains, whereas in example 2 the absorption in the 250 nm range is less than 5 cm.sup.−1, showing a low concentration of vacancy chains has been formed. Similarly we have found that if the annealing time is not long enough then total concentration of isolated vacancies remaining in the treated sample is >0.3 ppm; this is the case in comparative example 5, which is annealed for only 1 hour and results in a grey colored diamond material as compared with the orange color achieved with example 4, which is an identical diamond material sample to that of example 5 in terms of composition and irradiation, but is annealed for a longer time.

(10) FIG. 3 which shows UV visible spectra taken at 77 K post irradiation and anneal and illustrates for example 3 strong absorption at 250 nm and no peak at 741 nm or 394 nm remaining, showing that substantially all of the isolated vacancies have been annealed out. FIG. 3 also illustrates why comparative example 5 (which has been annealed for an insufficient time) appears grey post irradiation and anneal since there are peaks at 741 nm and 394 nm indicating the presence of isolated vacancies and also at 575 nm and 637 nm showing the presence of NV centers. Similarly FIG. 3 illustrates why comparative example 6 (which has been subjected to insufficient irradiation dose) appears pale pink, since there are peaks at 575 nm and 637 nm, showing the presence of NV centers, a small concentration of isolated vacancies remaining, and weak absorption at 250 nm indicating a low concentration of vacancy chains.

(11) All of the orange diamond samples according to the invention (examples 1, 3 and 4, show strong absorption at around 250 nm. This absorption is believed to be due to the presence of vacancy chains. For example, the measured absorption at 250 nm is >5 cm.sup.−1 for both samples 1 and 3, whereas for comparative sample 2 it is <5 cm.sup.−1.

(12) As noted above an additional benefit of irradiating the CVD diamond material is that typically the color of the material will be more stable to low temperature annealing and exposure to UV light compared to untreated CVD diamond. We found that upon heating example 1 the change in C* between the two states was <1 which illustrates this benefit.

(13) TABLE-US-00007 TABLE 4 N.sub.s.sup.0 conc. Color in the in provided Vacancy Anneal time provided diamond pre- concentration and CVD CVD irradiation Irradiation post temperature Example Growth diamond Abs Abs (Color grade if dose irradiation (hours) Number chemistry (ppm) at 350 nm at 510 nm 0.5 ct RBC) (e/cm.sup.2) (ppm) (° C.) 1  Traditional 0.1 1.09 0.45 Colorless 5.8 × 10.sup.18 V.sup.0 = 1.41 8 hrs at CVD V.sup.− = 0.03 800° C. growth process 2* Traditional 0.1 1.09 0.45 Colorless 2.6 × 10.sup.17 V.sup.0 = 0.17 8 hrs at CVD V.sup.− = 0.033 800° C. growth process 3  Added 0.6 1.85 0.60 Pale yellow 3.9 × 10.sup.18 V.sup.0 = 1.95 8 hrs at oxygen V.sup.− = 0.23 800° C. CVD growth process 4  Added 0.35 1.42 0.63 Pale yellow   2 × 10.sup.18 V.sup.0 = 1.1 8 hrs at oxygen V.sup.− = 0.3 800° C. CVD growth process 5* Added 0.35 1.42 0.63 Pale yellow   2 × 10.sup.18 V.sup.0 = 1.1 1 hr at 800° C. oxygen V.sup.− = 0.3 CVD growth process 6* Added 0.35 1.42 0.63 Pale yellow 2.6 × 10.sup.17 V.sup.0 = 0.06 8 hrs at oxygen V.sup.− = 0.12 800° C. CVD growth process Absorption at 250 nm [V.sup.0] and [V.sup.0] related to Observed Color [NV] concentration vacancy color of characteristics concentration (ppm) chains at RT diamond after L* (ppm) Post Post Example irradiation and C* Post irradiation irradiation and irradiation and Number annealing α and anneal anneal anneal 1  Bright vivid L* = 63.1 NV.sup.0 = 0.035 V.sup.0 = <0.003 22.01 orange C* = 52.6 NV.sup.− = 0.0004 V.sup.− = <0.003 α = 78.2° 2* Dull pinkish L* = 80.2 NV.sup.0 = 0.031 V.sup.0 = 0.046 2.04 brown C* = 5.05 NV.sup.− = 0.0086 V.sup.− = 0.0086 α = 67.7° 3  Bright vivid L* = 59.1 NV.sup.0 = 0.19 V.sup.0 = <0.003 13.74 orange C* = 34.4 NV.sup.− = 0.038 V.sup.− = <0.003 α = 70.7° 4  Orange-pink L* = 70.5 NV.sup.0 = 0.092 V.sup.0 = 0.21 7.8 C* = 17.08 NV.sup.− = 0.019 V.sup.− = 0.034 α = 71.7° 5* Grey L* = 69.3 NV.sup.0 = 0.055 V.sup.0 = 0.45 8.71 C* = 10.8 NV.sup.− = 0.019 V.sup.− = 0.053 α = 83.3° 6* Pale pink L* = 87.4 NV.sup.0 = 0.078 V.sup.0 = 0.041 3.01 C* = 4.26 NV.sup.− = 0.14 V.sup.− = 0.044 α = 44.93°