Researchers from the Carnegie Institution have developed an innovative method to improve the properties of diamonds - not only adding luster to gems, but also simplifying the process for making chisel blades, electronic components and even components for quantum computers.
Although a diamond is forever, the same characteristics that make it a superior material for many purposes - its hardness, optical transparency and resistance to chemicals, radiation and electric fields - also make it a material that is not easy to process. Its structural defects can be reduced by a heating process called annealing, but the process can turn a diamond into graphite, the soft, gray form of carbon used in pencil tips. In order to prevent this, diamond treatment previously required high pressures during forging (up to sixty thousand times the atmospheric pressure), a fact that makes the entire process expensive as well as limited when it comes to the sizes and quantities of the treated diamonds.
The research findings were published in October in the scientific journal Proceedings of the National Academies of Science. A number of researchers from the Carnegie Institution's geophysical laboratory used a method called "chemical vapor deposition" (CVD) to prepare synthetic diamonds for their experiments. Unlike the other methods, which imitate the high pressures that exist in the depths of the earth, where the natural diamonds are formed, with this method you get monocrystalline diamonds at low pressure. The diamonds obtained by this method, and quickly, have controlled compositions and a minority of defects.
The research team next performed annealing of these diamonds at a temperature of up to two thousand degrees Celsius using microwave plasma at pressures lower than atmospheric pressure. The crystals, whose original color is yellow-brown, if obtained at very high growth rates, became colorless or pinkish. Despite the absence of stabilizing pressure, minimal graphitization still occurred. Using analytical methods such as photoluminescence and absorption spectroscopy, the researchers were also able to identify the specific defects in the crystal that were responsible for the color changes. In particular, the pink color was obtained by structures called "nitrogen-vacancy" centers, in which a nitrogen atom replaces a carbon atom in the crystal lattice adjacent to a vacant site.
"This annealing, at low pressure and high temperature, increases the optical properties of these diamond crystals," says one of the researchers. "We notice a significant reduction in the amount of absorbed radiation across the spectrum from ultraviolet light to visible and infrared light. We were also able to determine that the reduction is due to changes in the defective structure and is related to hydrogen atoms that intermingle with the crystal lattice during its preparation. It is surprising to see how brown diamonds obtained in this cheap process turn into pink and transparent crystals," says one of the researchers. And because the researchers pinpointed the cause of the color changes in their diamonds, "our research could also help the gem industry distinguish between a natural and a synthetic diamond."
"The most fascinating aspect of this new forging process is the unlimited size of the diamonds that can be treated with it. The breakthrough could allow us to create kilocarat diamonds with high optical quality," notes one of the co-authors of the article. Since the method does not require high pressures, it guarantees a faster processing of diamonds and obtaining a wider variety of diamond types that can go through a de-colored process than the current forging methods required for high pressure.
"The optimal process will make it possible to obtain a higher quality diamond for use in new generation high pressure devices and materials for windows with improved optical properties in the range between the ultraviolet and infrared radiation."
The high-quality single-crystal diamond created by the new process has a wide variety of applications in science and technology, such as its use as an anvil in high-pressure research and optical applications that take advantage of the diamond's extraordinary transparency. Among the more fascinating future applications of the pink diamonds obtained by this method is the application in quantum computing, which will be able to use the free sites of the diamond to store quantum information.
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microwaves!