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High pressure–high temperature growth of diamond crystals using split sphere apparatus
Diamond & Related Materials 14 (2005) 1916 – 1919 www.elsevier.com/locate/diamond
High pressure–high temperature growth of diamond crystals using split sphere apparatus Reza Abbaschian a,*, Henry Zhu b, Carter Clarke b b
a Mechanical Engineering, University of California, Riverside, CA 92521, USA Gemesis Corporation, 7040 Professional Parkway East, Sarasota, FL 34240, USA
Available online 24 October 2005
Abstract An overview of the application of crystal growth fundamentals in the high pressure – high temperature production of diamond by solvent/ catalyst technique is presented. The process, also called temperature gradient process, makes use of a molten catalyst to dissolve carbon from a source (graphite or diamond powder) and transport the dissolved carbon to a growth site where they precipitate on a diamond seed. The pressure and temperature requirements for the process are generally around 5.0 – 6.5 GPa and 1300 – 1700 -C, depending on the chemistry of the solvent used and the desired crystal geometry. In spite of major progress in the science and technology of diamond growth, large scale commercial production of diamonds single crystals for jewelry or electronic applications has not been feasible until recently. This has been mainly due to the substantial cost associated with the presses needed, and the difficulties in controlling the growth parameters and catalyst chemistry. The recent developments in the commercial production of diamond single crystals utilizing the Split Sphere pressurization apparatus are discussed. D 2005 Published by Elsevier B.V. Keywords: Diamond growth; High pressure – high temperature growth; Diamond crystals
1. Introduction Diamond possesses many unique physical and chemical properties. It is the hardest, least compressible and stiffest substance. It also has high dispersion, reflectance and index of dispersion of any transparent materials. In addition, diamond is chemically inert to most acids and alkalis. While diamond has remarkable thermal conductivity, it is also an excellent electrical insulator. Moreover, with a band gap of 5.49 eı´, diamond has better semiconducting properties than silicon for many electronic applications, particularly for high temperature and high power electronics. These unique properties make diamond material of choice for a variety of applications from Jewelry to surgical blades, grinding and polishing to wire drawing dies, and electronic heat sinks to infrared windows. The demand for producing man-made diamonds with tailored properties has been increasing throughout the years. The main challenge in wider produc-
* Corresponding author. E-mail address: [email protected] (R. Abbaschian). 0925-9635/$ - see front matter D 2005 Published by Elsevier B.V. doi:10.1016/j.diamond.2005.09.007
tion, however, remains the high cost of manufacturing, particularly for large monocrystals. Since it was first developed by Bundy et al. at GE in 1955 [1], high pressure –high temperature (HPHT) technology via a temperature gradient process has been widely used to produce type Ib and IIa an IIb single crystals. The pressure and
Fig. 1. Schematic diagram of ‘‘split sphere’’ apparatus; 1—split sphere pressure chamber, 2—safety clamps, 3—large dies, 4—small dies, 5—core, 6—power inlet, 7—rubber membrane, 8—oil inlet, 9—cooling water.
R. Abbaschian et al. / Diamond & Related Materials 14 (2005) 1916 – 1919
1917
must also be controlled properly to allow for an optimum growth rate. Excessive rates cause entrapment of inclusions and morphological instability at the solid – liquid interface. Faster growth rates also cause strains and excessive point or line defects. 2. Split sphere HPHT growth chamber In spite of major progress by the diamond powder growers in the science and technology of diamond growth, large scale commercial production of diamond single crystals for jewelry or electronic applications has not been feasible until recently. This has been mainly due to the substantial cost associated with the capital and operational costs of hydraulic presses to deliver the required growth pressures. The situation has changed recently with the introduction of split sphere, or BARS type, growth apparatus [13,14]. The apparatus, as schematically shown in Fig. 1, consists of two spherical halves held together with steel clamps. Pressurized oil is pumped into the cavity between the inner surface of the spherical chamber and a rubber membrane, which surrounds eight truncated octet shaped anvils. The latter anvils in turn transfer the pressure into the tetragonal growth cell via six pyramid shaped WC – Co anvils. Unlike the belt or other similar presses, the split sphere apparatus is rather compact, as pictured in Fig. 2, and is capable of maintaining pressure for matter of days by using a small mechanical pump. It should be noted that the hydrostatic pressure in the growth cell is intensified by a factor approximately equal to the ratio of the surface area of the membrane to that of the growth cell. As such, approximately 2.5 Kbar of oil pressure in needed to generate 5.0– 6.5 GPa pressure in the growth chamber. Moreover, because of the special design of the gaskets, an active oil pressurization program can be utilized to adjust the pressure within growth cell at a constant level. This is particularly important for growing large crystals, and for compensation of
Fig. 2. Photograph of the split sphere apparatus.
temperature required for the process, generally around 5 –6.5 GPa and 1300 –1700 -C, depend on the chemistry of the solvent used and the desired crystal geometry. The temperature gradient process has been used to grow type Ib and IIa an IIb single crystals. The most commonly used machines for producing diamond have been Belt, cubic, tetrahedral or toroidal machines [2 – 4]. The catalysts used for growing monocrystals involve alloys of Fe, Ni, Co and Mn – C, with other elements such as Ti, Al, B, Cu, and Ge added to getter nitrogen impurities for producing colorless or blue diamonds [4 –10]. Non-metallic solvents have also been used for a limited extent as catalysts [11,12]. However, the growth rates and crystal sizes seem to be more limited. The growth rates using metallic catalysts are in the range of 2 – 15 mg/h, with the largest single crystal grown reported as 34.80 carats [5]. Regardless of the composition of the catalyst used, the most critical requirement for producing quality crystals is the precise control of the temperature and pressure through the entire growth process. Moreover, the temperature difference between the source materials and growth location
Growth region of high-quality type Ib diamond crystal 8.0 7.5 100
100 + 111
Pressure (GPa)
7.0
111
6.5
1
2
3
4
5
Points 3-6: Region for best quality diamonds
6
6.0 5.5 Diamond/Graphite Equilibrium Line
5.0 4.5 4.0 1250
Solvent/Carbon Eutectic Melting Line
1300
1350
1400
1450
1500
Temperature (°C) Fig. 3. Diamond/graphite phase diagram showing growth region for type Ib yellow diamond crystals.
1918
R. Abbaschian et al. / Diamond & Related Materials 14 (2005) 1916 – 1919 3.5
Stone Mass (ct)
3.0 2.5 2.0 1.5 1.0 0.5 0.0 0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
90.0
Time (hr) Fig. 4. Mass vs. time curve for type Ib yellow diamond crystals.
the volume reduction upon conversion of graphite to diamond. 3. Growth of type Ib crystals Diamonds grown using graphite source and binary Fe– Ni catalysts generally contain nitrogen impurity atoms. These diamonds are conventionally classified as type Ib, in that the majority of nitrogen atoms occupy isolated substitutional sites (C –centers). The level of the nitrogen impurity incorporated in diamond strongly depends on the purity of the starting materials. Diamonds produced from high purity starting materials have intense yellow color and contain around 30 ppm nitrogen whereas those produced from low purity materials have higher nitrogen and have yellow-orange coloration. It should noted that type Ia diamonds, which make up around 98% of mined diamonds, may contain up to 3000 ppm of nitrogen. However, the nitrogen atoms in type Ia diamonds occupy, mostly in an agglomerated state of either pairs (A-centers), clusters of four nitrogen atoms (B-centers), or mixtures thereof. Fig. 3 shows the pressure and temperature regions for growing high-quality type Ib diamond crystals using high purity graphite source material and Fe –Ni alloy catalysts in the split sphere apparatus. At 6 GPa pressure, high quality yellow diamonds can be produced in a temperature region from 1350 to 1450 -C. The stable growth range is much broader than those reported for Fe – Co catalysts by Sumiya et al. [15]. The crystal morphology strongly depends on the growth tempera-
Fig. 6. (a) A typical rough type Ib yellow diamond crystal; (b) finished about 1 carat yellow diamonds for jewelry applications.
ture; {100} planes are dominant at lower temperature (points 1– 2 in Fig. 3), while {111} planes are dominant at higher temperature (points 3– 6 in Fig. 3). Also, it was found that higher growth temperatures, i.e., {111} region in diamond/ graphite phase diagram, yield better quality crystals and more intense colors. It should be noted that the quality of the crystals also depends on the atomistic processes (dislocation-assisted versus dislocation-free growth) taking place at the diamond– solvent interface [16]. Variations in local interfacial kinetics and morphology can lead to the entrapment of impurities and particles at the interface. Mass and size versus growth time curves for type Ib diamond crystals are shown in Figs. 4 and 5. It can be seen that in the early stages of growth (less than 40 h), the mass growth rate is about 4 mg/h, while in final stage of the cycle, the mass growth rate can be as high as about 20 mg/h. In contrast, the deposition rate per unit area (mm/h) remains approximately constant during the later stages of growth cycle, while it is much higher in the early stage of growth. Consequently, the increase in the mass accumulation rate is mostly due to the surface area increase of the growing crystal. Based on these findings, high quality yellow diamond crystals with a mass up to 5 carats can be grown in less than 100 h. The grown crystals typically have truncated octahedral shape dominant with {111} planes, frequently modified with minor {110}, {113} and {100} planes [13]. Examples of as grown crystal together with finished diamonds are shown in Fig. 6. Color zoning also exists in these diamonds as the
9 8
Size (mm)
7 6 5 4 3
Width Length Height
2 1 0 0
10
20
30
40
50
60
70
80
90
Time (hr) Fig. 5. Size vs. time curve for type Ib yellow diamond crystals.
Fig. 7. 2.0 carat type IIb blue diamond crystal grown with Fe – Co – Ti alloy catalyst.
R. Abbaschian et al. / Diamond & Related Materials 14 (2005) 1916 – 1919
minor growth sectors look near colorless in yellow and orange-yellow diamonds [13]. The zoning could be attributed to the differences in the incorporation of impurities, particularly nitrogen, in different growth sectors. In general, the nitrogen concentration in minor growth sectors such as {110} and {113} is much lower than that in {111} plane sectors. It should be noted that zoning characteristics also depend on the growth rate and the catalyst chemistry. The recent works by Babich et al. [17,18] and Kiflawi et al. [19] indicate that the growth rate has strong effect on yellow diamond growth when Fe –Ni and Fe –Co solvent catalyst are used. Notwithstanding, the exact nature of the zoning and impurity incorporation are not clearly understood yet. Kiflawi et al. [19] have reported that a faster growth rate causes an increase in the concentration of Ni and Co impurities, which is manifested in growth sector boundaries; when the Ni and Co concentration increases, the N concentration decreases. Babich et al. [17,18] on the other hand, indicate that the difference in concentration of single substitutional nitrogen atoms (Ccenters) and nitrogen pairs (A-centers) throughout the growth sectors result in color zoning. They reported that the concentration of C-centers increases substantially from seed area to the surface of the crystal, which is believed to be due to the annealing and transfer of C-centers to A-centers during the growth cycle. 4. Growth of type IIa and IIb diamond crystals Colorless type IIa diamonds are produced by the elimination of nitrogen impurities with the addition of nitrogen getter materials such as Ti and Al and B. The latter additive also imparts blue color to the crystals, making it type IIb. For both colorless and blue diamond crystals, the growth rates to prevent entrapment of inclusions are found to be appreciably slower than that of yellow diamonds. The rates are typically one quarter of those for yellow diamonds. Moreover, the temperature and pressure windows for growing high quality type IIa and IIb diamonds are much narrower than those for type Ib diamonds. Therefore, more precise control of temperature and pressure throughout the entire growth cycle are required for the production of high quality type IIa and IIb diamond crystals. An example of as-grown 2 carat blue diamond is shown in Fig. 7. The Color intensity is controlled by the amount of B added to the catalyst; varying from 15 ppm for light blue to around 500 ppm for dark blue, and 1000 ppm for black diamonds. For the crystal shown in the Fig. 7, the boron addition was 120 ppm.
1919
5. Summary High quality Type Ib, IIa and IIb diamond crystals have been successfully produced using split sphere apparatus. The apparatus allow for commercial production of high quality crystals at 6 GPa and 1350 to 1450 -C. Better quality crystals are grown in the (111) region in diamond/graphite phase diagram. The growth rate for 5 carat type Ib crystals using Fe – Ni as catalyst reaches as high as about 20 mg/h towards the end of 100 h growth cycle. For type IIa and IIb diamonds, the growth rate necessary for the production of high quality crystals is much lower than that of type Ib. References [1] F.P. Bundy, Science 137 (1962) 1057. [2] F.P. Bundy, H.T. Hall, H.M. Strong, R.H. Wentorf Jr., Nature 176 (1955) 51. [3] H. Tracy Hall, in: A. Weissberger, B. Rossiter (Eds.), Techniques of Chemistry, John Wiley and Sons, 1980, p. 9. [4] O. Zanevskyy, I. Belousov, S. Ivakhnenko, in: J. Lee, N. Novikov (Eds.), Innovative Superhard Materials and Sustainable Coatings for Advanced Manufacturing, Springer, 2005. [5] H. Kanda, J. Gemmol, SOC Japan 20 (1999) 37. [6] R.C. Burns, S. Kessler, M. Sibanda, C.M. Welbourn, D.L. Welch, Advanced Materials ’96, NIRIMp. 105. [7] H. Kanda, T. Ohsawa, O. Fukunaga, I. Sunagawa, Journal of Crystal Growth 94 (1989) 115. [8] H. Sumiya, S. Satoh, Diamond and Related Materials 15 (1996) 1359. [9] Y.N. Palyanov, A.F. Khokhryakov, Y.M. Borzdov, A.G. Sokol, V.A. Gusev, G.M. Rylov, N.V. Sobolev, Russian Geology and Geophysics 38 (1997) 920. [10] H. Sumiya, N. Toda, S. Satoh, New Diamond and Frontier Carbon Technology 10 (2000) 233. [11] S. Yamoka, M.D. Shajikumar, H. Kanda, M. Akaishi, Diamond Related Materials 11 (2002) 1496. [12] Y.N. Palyanov, A.G. Sokol, Y.M. Borzdov, A.F. Khokhrykov, N.V. Sobolev, Nature 400 (1999) 417. [13] J.E. Shigley, R. Abbaschian, C. Clarke, Gem and Gemology 38 (2002) 301. [14] Y.N. Palyanov, Y. Malinovsky, Y.M. Borzdov, A.F. Khokryakov, Doklady Akademii Nauk SSSR 315 (1990) 233. [15] H. Sumiya, N. Toda, S. Satoh, Journal of Crystal Growth 237239 (2002) 1281. [16] R. Abbaschian, C. Clarke, in: J. Lee, N. Novikov (Eds.), Innovative Superhard Materials and Sustainable Coatings for Advanced Manufacturing, Springer, 2005, p. 193. [17] Y.V. Babich, B.N. Feigelson, A.P. Yelisseyev, Diamond and Related Materials 13 (2004) 1802. [18] Y.V. Babich, B.N. Feigelson, D. Fisher, A.P. Yelisseyev, V.A. Nadolinny, J.M. Baker, Diamond and Related Materials 9 (2000) 893. [19] I. Kiflawi, H. Kanda, S.C. Lawson, Diamond and Related Materials 11 (2002) 204.
High pressure–high temperature growth of diamond crystals using split sphere apparatus Reza Abbaschian a,*, Henry Zhu b, Carter Clarke b b
a Mechanical Engineering, University of California, Riverside, CA 92521, USA Gemesis Corporation, 7040 Professional Parkway East, Sarasota, FL 34240, USA
Available online 24 October 2005
Abstract An overview of the application of crystal growth fundamentals in the high pressure – high temperature production of diamond by solvent/ catalyst technique is presented. The process, also called temperature gradient process, makes use of a molten catalyst to dissolve carbon from a source (graphite or diamond powder) and transport the dissolved carbon to a growth site where they precipitate on a diamond seed. The pressure and temperature requirements for the process are generally around 5.0 – 6.5 GPa and 1300 – 1700 -C, depending on the chemistry of the solvent used and the desired crystal geometry. In spite of major progress in the science and technology of diamond growth, large scale commercial production of diamonds single crystals for jewelry or electronic applications has not been feasible until recently. This has been mainly due to the substantial cost associated with the presses needed, and the difficulties in controlling the growth parameters and catalyst chemistry. The recent developments in the commercial production of diamond single crystals utilizing the Split Sphere pressurization apparatus are discussed. D 2005 Published by Elsevier B.V. Keywords: Diamond growth; High pressure – high temperature growth; Diamond crystals
1. Introduction Diamond possesses many unique physical and chemical properties. It is the hardest, least compressible and stiffest substance. It also has high dispersion, reflectance and index of dispersion of any transparent materials. In addition, diamond is chemically inert to most acids and alkalis. While diamond has remarkable thermal conductivity, it is also an excellent electrical insulator. Moreover, with a band gap of 5.49 eı´, diamond has better semiconducting properties than silicon for many electronic applications, particularly for high temperature and high power electronics. These unique properties make diamond material of choice for a variety of applications from Jewelry to surgical blades, grinding and polishing to wire drawing dies, and electronic heat sinks to infrared windows. The demand for producing man-made diamonds with tailored properties has been increasing throughout the years. The main challenge in wider produc-
* Corresponding author. E-mail address: [email protected] (R. Abbaschian). 0925-9635/$ - see front matter D 2005 Published by Elsevier B.V. doi:10.1016/j.diamond.2005.09.007
tion, however, remains the high cost of manufacturing, particularly for large monocrystals. Since it was first developed by Bundy et al. at GE in 1955 [1], high pressure –high temperature (HPHT) technology via a temperature gradient process has been widely used to produce type Ib and IIa an IIb single crystals. The pressure and
Fig. 1. Schematic diagram of ‘‘split sphere’’ apparatus; 1—split sphere pressure chamber, 2—safety clamps, 3—large dies, 4—small dies, 5—core, 6—power inlet, 7—rubber membrane, 8—oil inlet, 9—cooling water.
R. Abbaschian et al. / Diamond & Related Materials 14 (2005) 1916 – 1919
1917
must also be controlled properly to allow for an optimum growth rate. Excessive rates cause entrapment of inclusions and morphological instability at the solid – liquid interface. Faster growth rates also cause strains and excessive point or line defects. 2. Split sphere HPHT growth chamber In spite of major progress by the diamond powder growers in the science and technology of diamond growth, large scale commercial production of diamond single crystals for jewelry or electronic applications has not been feasible until recently. This has been mainly due to the substantial cost associated with the capital and operational costs of hydraulic presses to deliver the required growth pressures. The situation has changed recently with the introduction of split sphere, or BARS type, growth apparatus [13,14]. The apparatus, as schematically shown in Fig. 1, consists of two spherical halves held together with steel clamps. Pressurized oil is pumped into the cavity between the inner surface of the spherical chamber and a rubber membrane, which surrounds eight truncated octet shaped anvils. The latter anvils in turn transfer the pressure into the tetragonal growth cell via six pyramid shaped WC – Co anvils. Unlike the belt or other similar presses, the split sphere apparatus is rather compact, as pictured in Fig. 2, and is capable of maintaining pressure for matter of days by using a small mechanical pump. It should be noted that the hydrostatic pressure in the growth cell is intensified by a factor approximately equal to the ratio of the surface area of the membrane to that of the growth cell. As such, approximately 2.5 Kbar of oil pressure in needed to generate 5.0– 6.5 GPa pressure in the growth chamber. Moreover, because of the special design of the gaskets, an active oil pressurization program can be utilized to adjust the pressure within growth cell at a constant level. This is particularly important for growing large crystals, and for compensation of
Fig. 2. Photograph of the split sphere apparatus.
temperature required for the process, generally around 5 –6.5 GPa and 1300 –1700 -C, depend on the chemistry of the solvent used and the desired crystal geometry. The temperature gradient process has been used to grow type Ib and IIa an IIb single crystals. The most commonly used machines for producing diamond have been Belt, cubic, tetrahedral or toroidal machines [2 – 4]. The catalysts used for growing monocrystals involve alloys of Fe, Ni, Co and Mn – C, with other elements such as Ti, Al, B, Cu, and Ge added to getter nitrogen impurities for producing colorless or blue diamonds [4 –10]. Non-metallic solvents have also been used for a limited extent as catalysts [11,12]. However, the growth rates and crystal sizes seem to be more limited. The growth rates using metallic catalysts are in the range of 2 – 15 mg/h, with the largest single crystal grown reported as 34.80 carats [5]. Regardless of the composition of the catalyst used, the most critical requirement for producing quality crystals is the precise control of the temperature and pressure through the entire growth process. Moreover, the temperature difference between the source materials and growth location
Growth region of high-quality type Ib diamond crystal 8.0 7.5 100
100 + 111
Pressure (GPa)
7.0
111
6.5
1
2
3
4
5
Points 3-6: Region for best quality diamonds
6
6.0 5.5 Diamond/Graphite Equilibrium Line
5.0 4.5 4.0 1250
Solvent/Carbon Eutectic Melting Line
1300
1350
1400
1450
1500
Temperature (°C) Fig. 3. Diamond/graphite phase diagram showing growth region for type Ib yellow diamond crystals.
1918
R. Abbaschian et al. / Diamond & Related Materials 14 (2005) 1916 – 1919 3.5
Stone Mass (ct)
3.0 2.5 2.0 1.5 1.0 0.5 0.0 0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
90.0
Time (hr) Fig. 4. Mass vs. time curve for type Ib yellow diamond crystals.
the volume reduction upon conversion of graphite to diamond. 3. Growth of type Ib crystals Diamonds grown using graphite source and binary Fe– Ni catalysts generally contain nitrogen impurity atoms. These diamonds are conventionally classified as type Ib, in that the majority of nitrogen atoms occupy isolated substitutional sites (C –centers). The level of the nitrogen impurity incorporated in diamond strongly depends on the purity of the starting materials. Diamonds produced from high purity starting materials have intense yellow color and contain around 30 ppm nitrogen whereas those produced from low purity materials have higher nitrogen and have yellow-orange coloration. It should noted that type Ia diamonds, which make up around 98% of mined diamonds, may contain up to 3000 ppm of nitrogen. However, the nitrogen atoms in type Ia diamonds occupy, mostly in an agglomerated state of either pairs (A-centers), clusters of four nitrogen atoms (B-centers), or mixtures thereof. Fig. 3 shows the pressure and temperature regions for growing high-quality type Ib diamond crystals using high purity graphite source material and Fe –Ni alloy catalysts in the split sphere apparatus. At 6 GPa pressure, high quality yellow diamonds can be produced in a temperature region from 1350 to 1450 -C. The stable growth range is much broader than those reported for Fe – Co catalysts by Sumiya et al. [15]. The crystal morphology strongly depends on the growth tempera-
Fig. 6. (a) A typical rough type Ib yellow diamond crystal; (b) finished about 1 carat yellow diamonds for jewelry applications.
ture; {100} planes are dominant at lower temperature (points 1– 2 in Fig. 3), while {111} planes are dominant at higher temperature (points 3– 6 in Fig. 3). Also, it was found that higher growth temperatures, i.e., {111} region in diamond/ graphite phase diagram, yield better quality crystals and more intense colors. It should be noted that the quality of the crystals also depends on the atomistic processes (dislocation-assisted versus dislocation-free growth) taking place at the diamond– solvent interface [16]. Variations in local interfacial kinetics and morphology can lead to the entrapment of impurities and particles at the interface. Mass and size versus growth time curves for type Ib diamond crystals are shown in Figs. 4 and 5. It can be seen that in the early stages of growth (less than 40 h), the mass growth rate is about 4 mg/h, while in final stage of the cycle, the mass growth rate can be as high as about 20 mg/h. In contrast, the deposition rate per unit area (mm/h) remains approximately constant during the later stages of growth cycle, while it is much higher in the early stage of growth. Consequently, the increase in the mass accumulation rate is mostly due to the surface area increase of the growing crystal. Based on these findings, high quality yellow diamond crystals with a mass up to 5 carats can be grown in less than 100 h. The grown crystals typically have truncated octahedral shape dominant with {111} planes, frequently modified with minor {110}, {113} and {100} planes [13]. Examples of as grown crystal together with finished diamonds are shown in Fig. 6. Color zoning also exists in these diamonds as the
9 8
Size (mm)
7 6 5 4 3
Width Length Height
2 1 0 0
10
20
30
40
50
60
70
80
90
Time (hr) Fig. 5. Size vs. time curve for type Ib yellow diamond crystals.
Fig. 7. 2.0 carat type IIb blue diamond crystal grown with Fe – Co – Ti alloy catalyst.
R. Abbaschian et al. / Diamond & Related Materials 14 (2005) 1916 – 1919
minor growth sectors look near colorless in yellow and orange-yellow diamonds [13]. The zoning could be attributed to the differences in the incorporation of impurities, particularly nitrogen, in different growth sectors. In general, the nitrogen concentration in minor growth sectors such as {110} and {113} is much lower than that in {111} plane sectors. It should be noted that zoning characteristics also depend on the growth rate and the catalyst chemistry. The recent works by Babich et al. [17,18] and Kiflawi et al. [19] indicate that the growth rate has strong effect on yellow diamond growth when Fe –Ni and Fe –Co solvent catalyst are used. Notwithstanding, the exact nature of the zoning and impurity incorporation are not clearly understood yet. Kiflawi et al. [19] have reported that a faster growth rate causes an increase in the concentration of Ni and Co impurities, which is manifested in growth sector boundaries; when the Ni and Co concentration increases, the N concentration decreases. Babich et al. [17,18] on the other hand, indicate that the difference in concentration of single substitutional nitrogen atoms (Ccenters) and nitrogen pairs (A-centers) throughout the growth sectors result in color zoning. They reported that the concentration of C-centers increases substantially from seed area to the surface of the crystal, which is believed to be due to the annealing and transfer of C-centers to A-centers during the growth cycle. 4. Growth of type IIa and IIb diamond crystals Colorless type IIa diamonds are produced by the elimination of nitrogen impurities with the addition of nitrogen getter materials such as Ti and Al and B. The latter additive also imparts blue color to the crystals, making it type IIb. For both colorless and blue diamond crystals, the growth rates to prevent entrapment of inclusions are found to be appreciably slower than that of yellow diamonds. The rates are typically one quarter of those for yellow diamonds. Moreover, the temperature and pressure windows for growing high quality type IIa and IIb diamonds are much narrower than those for type Ib diamonds. Therefore, more precise control of temperature and pressure throughout the entire growth cycle are required for the production of high quality type IIa and IIb diamond crystals. An example of as-grown 2 carat blue diamond is shown in Fig. 7. The Color intensity is controlled by the amount of B added to the catalyst; varying from 15 ppm for light blue to around 500 ppm for dark blue, and 1000 ppm for black diamonds. For the crystal shown in the Fig. 7, the boron addition was 120 ppm.
1919
5. Summary High quality Type Ib, IIa and IIb diamond crystals have been successfully produced using split sphere apparatus. The apparatus allow for commercial production of high quality crystals at 6 GPa and 1350 to 1450 -C. Better quality crystals are grown in the (111) region in diamond/graphite phase diagram. The growth rate for 5 carat type Ib crystals using Fe – Ni as catalyst reaches as high as about 20 mg/h towards the end of 100 h growth cycle. For type IIa and IIb diamonds, the growth rate necessary for the production of high quality crystals is much lower than that of type Ib. References [1] F.P. Bundy, Science 137 (1962) 1057. [2] F.P. Bundy, H.T. Hall, H.M. Strong, R.H. Wentorf Jr., Nature 176 (1955) 51. [3] H. Tracy Hall, in: A. Weissberger, B. Rossiter (Eds.), Techniques of Chemistry, John Wiley and Sons, 1980, p. 9. [4] O. Zanevskyy, I. Belousov, S. Ivakhnenko, in: J. Lee, N. Novikov (Eds.), Innovative Superhard Materials and Sustainable Coatings for Advanced Manufacturing, Springer, 2005. [5] H. Kanda, J. Gemmol, SOC Japan 20 (1999) 37. [6] R.C. Burns, S. Kessler, M. Sibanda, C.M. Welbourn, D.L. Welch, Advanced Materials ’96, NIRIMp. 105. [7] H. Kanda, T. Ohsawa, O. Fukunaga, I. Sunagawa, Journal of Crystal Growth 94 (1989) 115. [8] H. Sumiya, S. Satoh, Diamond and Related Materials 15 (1996) 1359. [9] Y.N. Palyanov, A.F. Khokhryakov, Y.M. Borzdov, A.G. Sokol, V.A. Gusev, G.M. Rylov, N.V. Sobolev, Russian Geology and Geophysics 38 (1997) 920. [10] H. Sumiya, N. Toda, S. Satoh, New Diamond and Frontier Carbon Technology 10 (2000) 233. [11] S. Yamoka, M.D. Shajikumar, H. Kanda, M. Akaishi, Diamond Related Materials 11 (2002) 1496. [12] Y.N. Palyanov, A.G. Sokol, Y.M. Borzdov, A.F. Khokhrykov, N.V. Sobolev, Nature 400 (1999) 417. [13] J.E. Shigley, R. Abbaschian, C. Clarke, Gem and Gemology 38 (2002) 301. [14] Y.N. Palyanov, Y. Malinovsky, Y.M. Borzdov, A.F. Khokryakov, Doklady Akademii Nauk SSSR 315 (1990) 233. [15] H. Sumiya, N. Toda, S. Satoh, Journal of Crystal Growth 237239 (2002) 1281. [16] R. Abbaschian, C. Clarke, in: J. Lee, N. Novikov (Eds.), Innovative Superhard Materials and Sustainable Coatings for Advanced Manufacturing, Springer, 2005, p. 193. [17] Y.V. Babich, B.N. Feigelson, A.P. Yelisseyev, Diamond and Related Materials 13 (2004) 1802. [18] Y.V. Babich, B.N. Feigelson, D. Fisher, A.P. Yelisseyev, V.A. Nadolinny, J.M. Baker, Diamond and Related Materials 9 (2000) 893. [19] I. Kiflawi, H. Kanda, S.C. Lawson, Diamond and Related Materials 11 (2002) 204.