If pressure control must be managed remotely (e.g. It usually involves springs to apply constant force to the diamond anvil seats. In its simplest form the pressurizing mechanism can be a screw or several screws. The pressurizing mechanism is simply a means of adjusting the distance between the diamonds and keeping them in that position. The vast majority of DAC cells can be held in a single hand if not the palm of one's hand, thus DACs are very portable and relatively inexpensive to manufacture. All cells also contain a pressurizing mechanisms. Cell bodies may include circulating gas to cool the diamonds or have ports to allow light, or x-rays etc. The cell keeps diamonds positioned and allows the experiment to be mounted on anything from an optical microscope to a synchrotron beam line. There are cells specialized for room temperature, cryogenic or heated experiments, ultra high pressure, radial or axial diffraction, spectroscopic studies, fluid studies etc. If the anvils are not perfectly aligned very high stresses can occur in the diamonds that will probably cause the anvils to fracture.Ĭell designs are as diverse as the types of experiments that are conducted in them. In some cell designs, the seats may be mounted on half spheres or another mechanism that allows their orientation to be adjusted so that the faces of the opposing anvils are perfectly parallel to each other (figure 2). Depending on the application the seats may also need to be x-ray transparent. If the DAC is heated the seats must be resistant to creep at high temperatures. The diamond anvils sit on "seats." The seats must be made of a strong material as they transmit the load from rest of the cell to the diamonds. Rhenium is commonly used for the gasket, but Kapton, Cu, Be are also used. Gaskets are typically prepared by driving the diamonds into a thin sheet metal and then drilling a tiny hole through the indented portion of the gasket. The steep pressure gradient discussed above is contained in the gasket which spares the sample. The gasket is used to contain the sample, especially if the sample is composed of or surrounded by a fluid. The gasket is a thin sheet of material that has a small hole about ½ diameter of the cutlet face – typically <500 microns. Loading a DAC requires a good binocular scope and a very steady hand. However, if it encounters static charges enroute to the cell, the sample can also suddenly fly off, never to be seen again. Thus samples can be manipulated by adhering to the tip of a fine needle or fiber. At this size, the electrostatic attraction of surfaces is much greater than gravitational attraction. This presents some logistical challenges loading them into the cell. The size of DAC samples is of necessity very small. To alleviate the stress in the sample and to preserve the defect state of sample, gaskets and confining media are now frequently used. Since many physical properties are impacted by defect microstructure and the state of stress, many early studies were marred by this drawback. liquids) or for research questions where a sample needs to be in a quasi hydrostatic stress state or if the defect microstructure is important. This arrangement does not work well for samples that cannot support shear σ (e.g. The pressure at the center of the sample is supported by extreme shear stress within the sample and friction between the sample and the diamond face. However, because the edges of the sample are at 1 atmosphere, there is a tremendous pressure gradient within the sample. The center of the sample will be at high pressure. Once compressed, such a sample will generally become a circular film about 30μm thick. As mentioned above, the simplest sample consists of a powder trapped between the two anvils. Since diamonds are quite inert, a wide range of substances may be examined. Samples that can be examined using the DAC include both solids and liquids and can be virtually anything that won't damage the diamond faces. Image courtesy of Steve Jacobsen at Northwestern University
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