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A diamond anvil cell (DAC) is a hand-top device used in scientific experiments. It allows compressing a small (sub-millimeter sized) piece of material to extreme pressures, which can exceed 3,000,000 atmospheres (300 gigapascals).[1]

The device has been used to recreate the pressure existing deep inside planets, creating materials and phases not observed under normal conditions. Notable examples include the non-molecular ice X[2], polymeric nitrogen[3] and MgSiO3 perovskite, thought to be the major component of the Earth's mantle.

A DAC consists of two opposing diamonds with a sample compressed between the culets. Pressure may be monitored using a reference material whose behavior under pressure is known. Common pressure standards include ruby[4] fluorescence, and various structurally simple metals, such as copper or platinum.[5] The uniaxial pressure supplied by the DAC may be transformed into uniform hydrostatic pressure using a pressure transmitting medium, such as argon, xenon, hydrogen, helium, paraffin oil or a mixture of methanol and ethanol[6]. The pressure-transmitting medium is enclosed by a gasket and the two diamond anvils. The sample can be viewed through the diamonds and illuminated by X-rays and visible light. In this way, X-ray diffraction and fluorescence; optical absorption and photoluminescence; Mossbauer, Raman and Brillouin scattering; positron annihilation and other signals can be measured from materials under high pressure. Magnetic and microwave field can be applied externally to the cell allowing nuclear magnetic resonance, electron paramagnetic resonance and other magnetic measurements[7]. Attaching electrodes to the sample allows electrical and magnetoelectrical measurements as well as heating up the sample to a few thousand degrees. Much higher temperatures (up to 7000 K)[8] can be achieved with laser-induced heating, and cooling down to milli-Kelvin has been demonstrated [6].

## Principle Edit

The operation of the diamond anvil cell relies on a simple principle:

$p=\frac{F}{A}$

where p is the pressure, F the applied force, and A the area.

Therefore high pressure can be achieved by applying a moderate force on a sample with a small area, rather than applying a large force on a large area. In order to minimize deformation and failure of the anvils that apply the force, they must be made from a very hard and virtually incompressible material, such as diamond.

## History Edit

Percy Williams Bridgman, the great pioneer of high-pressure research during the first half of the 20th century, developed an opposed anvil device with small flat areas that were pressed one against the other with a lever-arm. The anvils were made of a tungsten-carbon alloy (WC). This device could achieve pressure of a few gigapascals, and was used in electrical resistance and compressibility measurements. The revolution in the field of high pressures came with the development of the diamond anvil cell in the late 1950s in the National Bureau of Standards (NBS) by Weir, Lippincott, Van Valkenburg, and Bunting [9]. The principles of the DAC are similar to the Bridgman anvils but in order to achieve the highest possible pressures without breaking the anvils, they were made of the hardest known material: a single crystal diamond. The first prototypes were limited in their pressure range and there was not a reliable way to calibrate the pressure. During the following decades DACs have been successively refined, the most important innovations being the use of gaskets and the ruby pressure calibration. The DAC evolved to be the most powerful lab device for generating static high pressure.[10] The range of static pressure attainable today extends to the estimated pressures at the Earth’s center (~360 GPa).

## Components Edit

There are many different DAC designs but all have four main components:

1. The force-generating device — relies on the operation of either a lever arm, tightening screws, or pneumatic or hydraulic pressure applied to a membrane. In all cases the force is uniaxial and is applied to the tables (bases) of the two anvils
2. Two opposing diamond anvils — made of high gem quality, flawless diamonds, usually with 16 facets. They typically weigh 1/8 to 1/3 carat (25 to 70 mg). The culet (tip) is ground and polished to a hexadecagonal surface parallel to the table. The culets of the two diamonds face one another, and must be perfectly parallel in order to produce uniform pressure and to prevent dangerous strains. Specially selected anvils are required for specific measurements - for example, low diamond absorption and luminescence is required in corresponding experiments.
3. Gasket — a foil of ~0.2 mm thickness (before compression) that separates the two culets. It has an important role: to contain the sample with a hydrostatic fluid in a cavity between the diamonds, and to prevent anvil failure by supporting the diamond tips, thus reducing stresses at the edges of the culet. Standard gasket materials are hard metals and their alloys, such as stainless steel, Inconel, rhenium, iridium or tungsten carbide. They are not transparent to X-rays, and thus if X-ray illumination through the gasket is required then lighter materials, such as beryllium, boron nitride,[11] boron[12] or diamond[13] are used as a gasket.
4. Pressure-transmitting medium — homogenizes the pressure. Methanol:ethanol 4:1 mixture is rather popular because of ease of handling. However, above ~20 GPa it turns into a glass and thus the pressure becomes nonhydrostatic.[6] Xenon, argon, hydrogen and helium are usable up to the highest pressures, and ingenious techniques have been developed to seal them in the cell.[6]

## Uses Edit

Prior to the invention of the diamond anvil cell, static high-pressure apparatus required large hydraulic presses which weighed several metric tons and required large specialized laboratories. The simplicity and compactness of the DAC meant that it could be accommodated in a wide variety of experiments. Some contemporary DACs can easily fit into a cryostat for low-temperature measurements, and for use with a superconducting electromagnet. In addition to being hard, diamonds have the advantage of being transparent to a wide range of the electromagnetic spectrum from infrared to gamma rays, with the exception of the far ultraviolet and soft X-rays. This makes the DAC a perfect device for spectroscopic experiments and for crystallographic studies using hard X-rays.

A variant of the diamond anvil, the hydrothermal diamond anvil cell (HDAC) is used in experimental petrology/geochemistry for the study of aqueous fluids, silicate melts, immiscible liquids, mineral solubility and aqueous fluid speciation at geologic pressures and temperatures. The HDAC is sometimes used to examine aqueous complexes in solution using the synchrotron light source techniques XANES and EXAFS. The design of HDAC is very similar to that of DAC, but it is optimized for studying liquids.[14]

## References Edit

1. Hemley, Russell J. (1998), "The Revealing Role of Pressure in the Condensed Matter Sciences", Physics Today 51: 26, doi:10.1063/1.882374
2. A.F. Goncharov, V.V. Struzhkin, M.S. Somayazulu, R.J. Hemley and H.K. Mao (1986). "Compression of ice to 210 gigapascals: Infrared evidence for a symmetric hydrogen-bonded phase". Science 273: 218–230. doi:10.1126/science.273.5272.218. PMID 8662500.
3. M. Eremets, R. J. Hemley, H. K. Mao and E. Gregoryanz (2001). "Semiconducting non-molecular nitrogen up to 240 GPa and its low-pressure stability". Nature 411: 170–174. doi:10.1038/35075531.
4. Forman, Richard A.; Piermarini, Gasper J.; Barnett, J. Dean; Block, Stanley (1972), "Pressure Measurement Made by the Utilization of Ruby Sharp-Line Luminescence", Science 176 (4032): 284, doi:10.1126/science.176.4032.284, PMID 17791916
5. Kinslow, Ray; Cable, A. J. (1970). High-velocity impact phenomena. Boston: Academic Press. ISBN 0-12-408950-X.
6. 6.0 6.1 6.2 6.3 A. Jayaraman (1986). "Ultrahigh pressures". Reviews of Scientific Instruments 57: 1013. doi:10.1063/1.1138654.
7. Steven E. Bromberg and I. Y. Chan "Enhanced sensitivity for high-pressure EPR using dielectric resonators" Rev. Sci. Instrum. 63, 3670 (1992)
8. N. V. Chandra Shekar et al. "Laser-heated diamond-anvil cell (LHDAC) in materials science research" J. Mater. Sci. Techn. 19 (2003) 518
9. The Diamond Anvil Pressure Cell
10. S. Block, and G. Piermarini (1976). "The Diamond Cell Stimulates High-Pressure Research". Physics Today 29(9): 44. doi:10.1063/1.3023899.
11. N. Funamori and T. Sato "A cubic boron nitride gasket for diamond-anvil experiments" Rev. Sci. Instrum. 79 (2008) 053903
12. J-F Lin et al. "Amorphous boron gasket in diamond anvil cell research" Rev. Sci. Instrum. 74 (2003) 4732
13. G Zou et al. "A diamond gasket for the laser-heated diamond anvil cell" Rev. Sci. Instrum. 72 (2001) 1298
14. W.A. Bassett et al. "A new diamond anvil cell for hydrothermal studies to 2.5 GPa and from −190 to 1200 °C" Rev. Sci. Instrum. 64 (1993) 2340

## Books and reviews Edit

• M.I. Eremets: "High Pressure Experimental Methods" Oxford Science Publication (1996)
• M. Yousuf Semiconductors and Semimetals: eds. T. Suski and W. Paul, Academic Press, Sun Diego, 1998, 55, 381.
• A. Jayaraman (1983). "Diamond Anvil Cell and High-Pressure Physical Investigations". Reviews of Modern Physics 55: 65–108. doi:10.1103/RevModPhys.55.65.
• A. Jayaraman (1986). "Ultrahigh pressures". Reviews of Scientific Instruments 57: 1013. doi:10.1063/1.1138654.
• D.J. Dunstan, and I.L. Spain (1989). "The Technology of Diamond Anvil High-Pressure Cells". Journal of Physics E: Scientific Instruments 22: 913–933. doi:10.1088/0022-3735/22/11/004.
• N. V. Chandra Shekar et al. "Laser-heated diamond-anvil cell (LHDAC) in materials science research" J. Mater. Sci. Techn. 19 (2003) 518.
• Keith Brister "X-ray diffraction and absorption at extreme pressures" Rev. Sci. Instrum. 68 (1997) 1629