Development of Giant Diamonds from Chemical Vapor Deposition for High-Pressure Research

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0550040HemleyThis grant provides support for a three year development program aimed at fabrication of large (up to 250 carat) single crystal diamonds by novel chemical vapor deposition (CVD) techniques, the development of "designer" diamond anvils for high pressure/high temperature experimentation in the diamond anvil cell (DAC), and the development of new gaskets and presses for use in large volume DAC experiments at the Geophyscial Lab, Carnegie Institution of Washington. Characterization of the physical, chemical, electrical and mechanical properties of deep earth (lower mantle and core) materials, and properties of gases found within the interiors the giant gas planets (e.g. Jupiter and Saturn) can only be carried out in situ at extreme pressures ( 100-350 GPa) that have been demonstrated in successful DAC experiments. Diamond anvils offer extreme hardness, allowing for megabar pressures to be obtained in pressed cell experiments, high thermal diffusivity that allows for extreme temperature conditions with laser heating, and optical transparency that is ideal for x-ray diffraction and spectroscopic interrogation of high P/T phases in situ. Currently DAC experiments are limited to analysis of the properties of miniscule sample sizes that can be accommodates within flawless natural diamond anvils of limited size (e.g., 0.25 - 2.5 ct). Flawless natural diamonds are very expensive (ca. $1,000 for a 0.25 ct diamond up to $100K for a 2.5 ct diamond) and larger flawless diamond costs increase quadratically with carat weight. Natural flawless diamonds in excess of 25 carats have not been demonstrated to exist in nature. A recently acquired a next generation 6 kW microwave CVD plasma system chamber at CIW-GL is anticvpated to make possible the rapid growth of large ( 10 - 100 ct), flawless, single crystal diamond that could open a new frontier in the study of materials at extremes of pressures and temperatures. Affordable and structurally and optically optimized larger diamonds would afford experimentation with new anvil culet shapes and novel gasket designs. Also, CVD grown diamonds can be manufactured with embedded sensors to make available "designer" anvils for specialized experiments (e.g., magnetic, electrical, and elastic properties characterization of lower mantle and core phases). The goal of this projects is to develop new classes of high-pressure devices that will allow an increase in sample volumes up to 100 to 1000 times that currently available in conventional diamond cells at megabar pressures. The developments will facilitate numerous x-ray based analytical techniques currently unavailable for ultrahigh-pressure research, including those required for the successful utilization of major new neutron (SNS at Oak Ridge) and existing 2nd and 3rd generation synchrotron radiation facilities worldwide (e.g., APS/ANL, BNL, ESRF, SPring-8). Successful development of these new classes of high-pressure cells will allow for novel experiments in high pressure geoscience, planetary and materials science. The project will engage two graduate students in novel instrument design and mineral physics research applications and will prepare them for a diverse range of possible careers in academia, national laboratories, and industry. Beyond geoscience, the study of the electrical, optical and physical properties of materials at extremes of pressure promises novel technological spin offs with profound societal impact (e.g., new classes of CPU chip materials with thermal and electromagnetic properties that can accommodate continued advances in micro-circuitry). ***