ARTICLE pubs.acs.org/crystal
Design an Effective Solution for Commercial Production and Scientific Research on Gem-Quality, Large, Single-Crystal Diamond by High Pressure and High Temperature Qi-Gang Han,† Bao Liu,‡ Mei-hua Hu,‡ Zhan-chang Li,‡ Xiao-Peng Jia,*,‡ Ming-Zhe Li,*,† Hong-An Ma,‡ Shang-Sheng Li,‡ Hong-Yu Xiao,‡ and Yong Li‡ † ‡
Roll-forging Research Institute, Jilin University, Changchun, 130025, China National Lab of Superhard Materials, Jilin University, Changchun 130012, China ABSTRACT: In spite of major progress in the science and technology of diamond growth, large-scale commercial production of gem-quality, large, single-crystal diamonds has not been feasible. Recently, we easily synthesized various types of gemquality, large, single-crystal diamonds (Ib, IIa, and IIb) using a cubic high-pressure apparatus (performance enhanced by new design of double bevel hybrid anvil). Our solution saves the cost associated with the presses need, increases the region of synthesis of gem-quality, large, single-crystal diamonds, and decreases the effects of fluctuations of the pressure or temperature in the cubic sample cell. In addition, the quality and electrical properties of synthetic diamonds have been studied in detail. The synthetic diamonds have been successfully applied as diamond anvils or jewelry. This represents a relatively simple, inexpensive, and effective solution for commercial production and scientific research on gem-quality, large, single-crystal diamonds using a cubic high-pressure apparatus.
1. INTRODUCTION The demands for producing gem-quality, large, single-crystal diamonds have been increasing throughout the years, because diamonds possess many unique physical and chemical properties.1,2 Gem-quality, large, single-crystal diamonds can be grown by low-pressure microwave plasma (MP) chemical vapor deposition (CVD) or temperature gradient growth methods under high pressure and high temperature (HPHT). Recently, diamond growth with CVD has made major progress at the Carnegie Institution of Washington.3,4 However, in most of the world research and commercial organizations, the widespread use of CVD diamonds in many applications has not been successful due to the existence of grain boundaries of polycrystalline diamonds that are produced and slow growth rates.5,6 Thus, until now, the most effective method to grow gem-quality, large, single-crystal diamonds is the temperature gradient growth method. Crystal growers in most of the world's research and commercial organizations involved with HPHT diamond synthesis have efficiently harnessed the solvent/catalyst growth of gem-quality, large, single-crystal diamonds through knowledge of crystal growth mechanisms and engineering of a high-pressure apparatus.7-9 The process, however, was considered too costly to translate into commercial production. 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. Nowadays, the most commonly used apparatuses for producing diamonds are belt, cubic, tetrahedral, or split sphere r 2011 American Chemical Society
apparatuses.10,11 In these apparatuses and systems, the cubic high-pressure apparatus (CHPA) is the most popular apparatus that can accommodate much larger sample volumes than other types of apparatuses and can be adjusted accurately in HPHT. In addition, the pressure of the sample cell in CHPA can rise faster to the pressure of synthesis (only takes 2 min). In the world, about 6000 CHPAs are being used for material synthesis and research, especially in Henan Huanghe Whirlwind Co., Ltd. (the biggest industry diamond producer in the world), which mainly uses the CHPA for synthetic industrial crystal diamonds. However, large-scale commercial production of gem-quality, large, single-crystal diamonds grown using CHPA has not been feasible, because of the big costs of the presses needed (the main cost of WC anvil cracking) and the lower limited pressure (decreases the region of synthesis of gem-quality, large, singlecrystal diamonds). If the effective solution for commercial production of gemquality, large, single-crystal diamond used CHPA can be found, it indeed will be very useful to improve physics, materials science, chemistry, and so on. Scientists and engineers have done their best to resolve the above problems. However, this work has not obtained great progress all the time. Recently, we successfully synthesized various types of gem-quality, large, single-crystal diamonds (Ib, IIa, and IIb) using CHPA (enhanced by the Received: July 16, 2010 Revised: January 22, 2011 Published: March 04, 2011 1000
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Figure 1. Optical photo of the CHPA (a), the cross-section of the multianvils assembly for traditional anvils (b), and the cross-section of the multianvils assembly for hybrid anvils (c). The inset shows the optical photo of anvils.
Fe70Ni30 and Ni70Mn25Co5 alloys were used as the solvent/ catalyst, which generally contained nitrogen impurity atoms. The high-purity Ti/Cu sheet is selected as the nitrogen getter for colorless type IIa diamonds grown. The mixed powder of boron (B) and catalyst for boron-doped, gem-quality, large, singlecrystal diamond (IIb diamond) grown. In addition, small synthetic crystal diamonds for abrasive grits (size about 0.5 mm), grown by the phase difference mechanism (film growth), were used as seed crystals. Figure 2. Schematic diagram of high-pressure cell assembly used in CHPA.
3. RESULTS
new design of a double bevel hybrid-anvil), which can save the cost associated with the presses needed, increase the region of synthesis of gem-quality, large, single-crystal diamonds, and decrease the affected fluctuations of the pressure or temperature in the cubic sample cell.
3.1. Test of CHPA Performance. As shown in Figure 1, we used a steel ring and a steel block to replace the part of the traditional WC anvil and the weight of the WC anvil used in the double bevel hybrid-anvil (1.15 kg), which is much lower than a traditional anvil (4.25 kg). This saves the weight of WC by about 72.94% after the modification of the anvil. In other words, the solution can save the cost of CHPA about by 72.94% after the modification of the anvil. From the view of thermodynamic considerations, the broader growth region of gem-quality, large, single-crystal diamonds is in accordance with the higher synthetic pressure.13 Thus, we design a double bevel in a hybrid-anvil (as shown in inset of Figure 1), which aims to increase the limited pressure of CHPA with the same hydraulic rams.14 The results of the pressure generation test (determined on the basis of room-temperature transitions in Bi, Tl, and Ba) for the new double bevel hybrid-anvil and traditional anvil indicated that the pressure generation by new design of the double bevel hybrid-anvil is increased about 17% (from a 82 MPa decrease to 68 MPa) as compared with the traditional anvil, which can be attributed to the technology of the double bevel and high hardness of the new double bevel hybrid-anvil (enhanced by the supporting rings). When the blowout happens in a highpressure cell, the lifetime of the double bevel hybrid-anvil is longer as compared with that of the traditional anvil, which can be attributed to the bigger cushioning effect and higher sintered quality of the WC anvil as compared with that of the traditional anvil.15 The temperature is determined from a relation between the temperature and the input power, which has been calibrated using a Pt 6% Rh-Pt 30% Rh thermocouple. Our results note
2. EXPERIMENT APPARATUS AND CELL ASSEMBLY In the CHPA, six cubic tungsten carbide (WC) anvils, each with a square anvil tip, are actuated by three pairs of hydraulic rams, forming a cubic cell, within which the sample assembly is compressed (we used “traditional” anvil to denote this geometric dimension of the anvil). Typically, three adjacent anvils are held stationary, while the other three are mobile. Figure 1a shows the optical photo of the CHPA used in our laboratory, Figure 1b shows the schematic diagram of traditional anvil assembly, and Figure 1c shows the schematic diagram of the double bevel hybrid-anvils assembly (a new design as an effect solution for commercial production and research of gem-quality, large, single-crystal diamonds). The double bevel hybrid-anvil has the same geometric shape of the square anvil tip as compared with the traditional anvil (the anvil face is 27.5 27.5 mm2). The gem-quality, large, single-crystal diamonds were synthesized using the CHPA with a new double bevel hybrid-anvil. The schematic diagram of the high-pressure cell assembly is shown in Figure 2. The temperature gradient could be changed freely by adjusting the structure of the assembly.12 Highly pure graphite, which was converted to diamond before the crystals started to grow at diamond seed, was used as the carbon source material.
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Figure 3. Optic micrographs of type Ib yellow diamond (a), near-colorless type IIa diamond (b), and opaque blue-black IIb diamond (c).
Figure 4. Raman spectrum of Ib diamond, IIa diamond, and IIb diamond excited at a wavelength of 228.9 nm (room temperature). The inset shows the full-width half-maximum (fwhm) and the optical micrograph of diamonds measured.
that the temperature generation by the new double bevel hybridanvil is not changed obviously when the cell temperature is about 1000-1350 °C. 3.2. Growth of Gem-Quality, Large, Single-Crystal Diamonds. The synthetic gem-quality diamond crystals have found scientific and commercial uses that are dependent on their size, color, and quality. As shown in Figure 3, we have synthesized various types of gem-quality, large, single-crystal diamonds using CHPA (performance enhanced by the new design of the double bevel hybrid-anvil). At our experiment, yellow Ib diamonds up to 6 mm in size have been grown with a Fe70Ni30 solvent/catalyst, and with the Ni70Mn25Co5 solvent/catalyst, near-colorless IIa diamonds up to 6 mm in size have been grown when the highpurity Ti/Cu sheets (1.8 wt % of solvent/catalyst) have been used as the nitrogen getter. The mixed powder of boron (B) and catalyst has allowed opaque blue-black IIb diamonds up to 5 mm in size to be produced. Synthetic diamond crystals exhibit hexoctahedral shapes mainly, which is determined by the growth temperature. It is well-known that color zoning exists in diamonds as the minor growth sectors, which could be attributed to the differences in the incorporation of nitrogen or boron impurities in different growth sectors. However, in our experiment, color
Figure 5. Optical micrographs of a four-probe arrangement in opaque blue-black IIb diamond (a), {100} cross-section of polished Ib yellow diamond (b), and near-colorless IIa diamond (C) for electrical property measurements.
zoning that exists in yellow Ib diamonds due to nitrogen concentration in the {111} growth sectors can not be observed clearly, because the crystal has a deep yellow tint. No visible color zoning due to nitrogen can be observed in near-colorless IIa diamonds too, because the nitrogen content is about 0.1-1 ppm.16 In IIb diamonds, boron is incorporated in the greatest concentration in the {111} sectors, then in the {110} sectors, and in significantly smaller concentrations in other sectors. The color of IIb diamondd is almost opaque blue-black, because the boron content is a high rate of 1.5 wt.%. Raman microscopy is used as a diagnostic tool for the evaluation of synthetic diamond crystals quality because it is nondestructive, requires little or no specimen preparation, and provides readily distinguishable signatures. The Raman spectra of Ib diamond, IIa diamond, and IIb diamond (seen Figure 4) are dominated by the first-order Raman line at 1331.3 cm-1, which excited at a wavelength of 228.9 nm (room temperature). The observation of a 1331.3 cm-1 line on a flat background with no 1002
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Table 1. Results of the Electrical Resistivity Measurements on Opaque Blue-Black IIb Diamond Using the East Changing ET 9000 Series serial number
direction of current
drive current (A) -5
direction of voltage
value of voltage measure (V)
resistance (Ω)
value of resistance (Ω)
1
I(12)
9.999754 10
V(43)
0.00277715432
R(12,43)
27.77
2 3
I(21) I(23)
-0.0001000049 9.999751 10-5
V(43)V(14)
-0.00277263485 0.00188849657
R(21,43) R(23,14)
27.72 18.89
4
I(32)
-0.0001000048
V(14)-
-0.00188181363
R(32,14)
18.82
0.00277676736
R(34,21)
27.77
-0.00277280645
R(43,21)
27.73
0.00183268881
R(41,32)
18.33
-0.00194008229
R(14,32)
19.40
-5
5
I(34)
9.999752 10
6
I(43)
-0.0001000049
7
I(41)
8
I(14)
9.999757 10-5 -0.0001000049
V(21) V(21)V(32) V(32)-
observable peak in the region 1500-1550 cm-1 can be taken as strong evidence for the production of “pure” diamond. Furthermore, the full-width half-maximums (fwhm) for Ib diamond, IIa diamond, and IIb diamond are 5.57, 5.61, and 5.44 cm-1, respectively. The values of fwhm of synthetic diamond crystals are in accordance with the typical fwhm range of gem-quality diamonds, which can be taken as a measure of the “perfection” of the diamond crystallite.17 From the optic micrographs of the synthetic gem-quality diamond crystals in the Figure 3, we also easily found that the metal inclusions tend to be trapped near the seed and distributed radially, which can be removed by a boiling mixture of H2SO4 and HNO3 (the metal inclusions are not present in the other parts of diamond crystal). The smaller concentration of inclusions can attributed to the stable growth range by the new double bevel hybrid-anvil and is much broader as compared with the traditional anvil (the synthetic region of high quality of diamond crystal under high pressure is broader as compared with low pressure13). 3.3. Electrical Properties of Synthetic Diamonds. The very attractive electrical properties of diamond, coupled with its extremely high thermal conductivity and ruggedness, have potential applications in high-temperature, high-speed, and radiation-hard electronics. The electronic properties of the natural diamond cube after its hydrogenation, the diamond film, and hydrogenated diamond grown by CVD have been studied more extensively, but research rarely studied the electronic properties of gem-quality, large, single-crystal diamonds grown by HPHT.18-22 We use the van der Pauw method for electrical transport measurements on synthetic, gem-quality, single-crystal diamonds, in which the results of resistivity measurements effected by the material of electrodes can been avoided through transform of the direction of current in different Van der Pauw probes.23 Van der Pauw probe arrangements in type Ib diamond, IIa diamond, and IIb diamond for resistance measurements are shown in Figure 5, in which thin copper wires (0.12 mm in diameter) were aligned with square probe arrays via conducting silver on the synthetic diamond at room temperature (21 °C). To get information on intrinsic conductivity, the heating produces a solid-state reaction between the silver and the synthetic diamond is avoided. The electrical characteristic was measured with an electronic transport properties measuring system (East Changing ET 9000 Series). The resistivity measurement was carried out at room temperature (21 °C) and a normal humidity level (40% RH). In the resistivity measurements, a 0.1 mA drive current enters the diamond through probe 1 and leaves it through probe 2.
Then, the voltage drop (V43) was recorded between 4 and 3. We define the resistance R(12, 43) as the potential difference V4-V3 between the contact probe 4 and the contact probe 3 per unit current through the contact probes 1 and 2. Similarly, we define the resistance R(23,14). Then, the bulk electrical resistivity F was obtained by the van der Pauw equation23 1 1 exp - πdRð12, 43Þ þ exp - πdRð23, 14Þ ¼ 1 ð1Þ F F where F is the bulk electrical resistivity, d is the thickness of the sample, R(12,43) = V(43)/I(12),, and R(23,14) = V(14)/I(23). Equation 1 is the basic calculating principle of the intrinsic bulk electrical resistivity by East Changing ET 9000 Series. To get exact information on the intrinsic bulk electrical resistivity (eliminate the effects of contact and lead resistance), similarly, we define the other's resistance in Table 1, which can be used to calculate the intrinsic bulk electrical resistivity by East Changing ET 9000 Series automatically. So, on the basis of the van der Pauw method and the data of Table 1, the intrinsic bulk resistivity of opaque blue-black IIb diamond is calculated to be well in 2.08 101 Ω cm (the thickness of the IIb diamond is 0.2 cm). From eq 2 R ¼F
L S
ð2Þ
where F is the resistivity of material, L is the length of material, and S is the section of material, we can know that the resistance of opaque blue-black IIb diamond is 26 Ω, because the intrinsic bulk resistivity, length, and section of opaque blue-black IIb diamond are 2.08 101 Ω cm, 0.2 cm, and 0.16 cm2, respectively. Furthermore, the hall coefficient, hall mobility, and surface carrier concentration of opaque blue-black IIb diamond are 8.82 101 cm3/c, 4.23 cm2/(V s), and 7.71 1016 cm-3, respectively.23 However, in the same condition, the actual values of voltage measure on yellow Ib diamond and near-colorless IIa diamond surpass the maximum limit on the effective voltage measuring range, which indicated that the resistance of yellow Ib diamond and near-colorless IIa diamond is bigger as compared with that of multimeter 2700 used in East Changing ET 9000 Series (the resistance of multimeter 2700 is 10 MΩ). Thus, the yellow Ib diamond and near-colorless IIa diamond by HPHT are insulators in the tested range, respectively. The opaque blueblack IIb diamond by HPHT is a semiconductor, which may be potential applied in high-temperature, high-speed, and radiationhard electronics. 3.4. Application of Gem-Quality, Large, Single-Crystal Diamonds. Figure 6 shows the synthetic type Ib diamond anvil, 1003
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Figure 6. Optical micrographs of the synthetic gem-quality, single-crystal diamonds for diamond anvils (a) and jewelry (b).
IIb diamond anvil, and gem diamond for diamond anvils and jewelry. The synthetic type Ib diamond anvil contained lower impurities and a lower price than natural diamond anvils. The synthetic IIb diamond anvil has a better electrical performance than the natural diamond anvil. In addition, we are making a machine on synthetic colorless type IIa diamonds, which has a better optical performance than natural diamond anvils. For these reasons, synthetic type diamond crystals are expected to be very useful as diamond anvils and other parts of an apparatus, which can been widely used for high-pressure studies in the fields of material science, condensed matter physics, geochemistry, medical science, and so on.
4. CONCLUSIONS High-quality type Ib yellow diamonds, near-colorless IIa diamonds, and opaque blue-black IIb diamonds have been easily produced using CHPA with double bevel hybrid-anvils. Our solution successfully saves the cost associated with the press needs, increases the region of synthesis of gem-quality, large, single-crystal diamonds, and decreases the effect of fluctuations of the pressure or temperature in the cubic sample cell. In addition, the quality and electrical properties of synthetic diamonds have been studied in detail. The evaluation results indicate that synthetic diamonds are in accordance with the measures of the “perfection” of the diamond crystallite. The yellow Ib diamond and near-colorless IIa diamond by HPHT are insulators in the tested range, respectively. The resistance of the opaque blue-black IIb diamond is confirmed to be well in 26 Ω, which indicates that the opaque blue-black gem-quality, large, single-crystal diamond is a semiconductor. Besides, the synthetic gem-quality, large, single-crystal diamonds have been successfully fabricated as diamond anvils and jewelry. This represents a relatively simple, inexpensive, and effective solution for commercial production and scientific research on gem-quality, large, single-crystal diamonds using CHPA. ’ AUTHOR INFORMATION Corresponding Author
*Tel/Fax: þ86 431 85168858. E-mail:
[email protected] and
[email protected].
’ ACKNOWLEDGMENT We thank Dedi Liu for experimental assistance on Raman microscopy. We thank Xiao-lei Liu for help with English writing. We also thank the reviewers for helpful comments and suggestions. This research was supported by the National Science Foundation of China under Grant Nos. 50572032, 50731006, and 50801030. ’ REFERENCES (1) Burns, R. C.; Davies, G. J. In Properties of Natural and Synthetic Diamond; Field, J. E., Ed.; Academic Press: London, 1992; p 417. (2) Burns, R. C. Science and Technology of New Diamond; Saito, S., Fukunaga, O., and Yoshikawa, M., Eds.; Tokyo, 1990; pp197-201. (3) Meng, Y.-f.; Yan, C.-s.; Lai, J.; Krasnicki, S.; Shu, H.; et al. Enhanced optical properties of chemical vapor deposited single crystal diamond by low-pressure/high-temperature annealing. Proc. Natl. Acad. Sci. U.S.A. 2008, 105, 17620–17625. (4) Yan, C.-s.; Vohra, Y. K; Mao, H.-k.; Hemley, R. J. Very high growth rate chemical vapor deposition of single-crystal diamond. Proc. Natl. Acad. Sci. U.S.A. 2002, 99, 12523–12525. (5) Cao, G. Z.; Schermer, J. J.; van Enckevort, W. J. P. M.; Elst, W. A. L.; Giling, L. J. Growth of {100} textured diamond films by the addition of nitrogen. J. Appl. Phys. 1996, 79, 1357–1364. (6) Afzal, A.; Rego, C. A.; Ahmed, W.; Cherry, R. I. HFCVD diamond grown with added nitrogen: film characterization and gasphase composition studies. Diamond Relat. Mater. 1998, 7, 1033–1038. (7) Burns, R. C.; Hansen, J. O.; Spits, R. A.; Sibanda, M. C.; Welbourn, M.; et al. Growth of high purity large synthetic diamond crystals. Diamond Relat. Mater. 1999, 8, 1433–1437. (8) Sumiya, H.; Satoh, S. High-pressure synthesis of high-purity diamond crystal. Diamond Relat. Mater. 1996, 5, 1359–1365. (9) Hisao, K.; Minoru, A.; Shinobu, Y. New catalysts for diamond growth under high pressure and high temperature. Appl. Phys. Lett. 1994, 65, 784–786. (10) Hall, H. T. High Pressure-Temperature Apparatus; Gschneidner, K. A., Hepworth, M. T., Jr., and Parlee, N. A. D., Eds.; New York, 1964; pp 9-34. (11) Reza, A.; Henry, Z.; Carter, C. High pressure-high temperature growth of diamond crystals using split sphere apparatus. Diamond Relat. Mater. 2005, 14, 1916–1919. (12) Strong, H. M.; Wentorf, R. H., Jr. Growth of large, high-quality diamond crystals at General Electric. Am. J. Phys. 1991, 59, 1005–1008. (13) Sumiya, H.; Toda, N.; Satoh, S. Growth rate of high-quality large diamond crystals. J. Cryst. Growth 2002, 237-239, 1281–1285. 1004
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