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

这项资助为一项为期三年的发展计划提供支持，该计划旨在通过新型化学气相沉积（CVD）技术制造大型（高达250克拉）单晶钻石，在钻石砧室（DAC）中开发用于高压/高温实验的“设计师”钻石砧，以及在华盛顿卡内基研究所地球物理实验室开发用于大体积DAC实验的新垫圈和压力机。深层地球（下地幔和地核）材料的物理、化学、电气和机械特性的表征，以及巨型气体行星（如木星和土星）内部发现的气体特性，只能在已经在DAC实验中成功证明的极端压力（100-350 GPa）下进行。金刚石砧具有极高的硬度，可以在压槽实验中获得兆巴压力，高热扩散率可以在激光加热的极端温度条件下使用，光学透明度是x射线衍射和高P/T相原位光谱分析的理想选择。目前，DAC实验仅限于分析微小样品尺寸的特性，这些样品尺寸可以容纳在有限尺寸（例如，0.25 - 2.5 ct）的完美天然金刚石砧中。无瑕疵的天然钻石非常昂贵（0.25克拉的钻石约为1000美元，2.5克拉的钻石为10万美元），更大的无瑕疵钻石的成本随着克拉重量呈二次增长。没有证据表明自然界中存在超过25克拉的天然无瑕钻石。最近在CIW-GL获得的下一代6kw微波CVD等离子体系统室有望使大型（10 - 100 ct），完美无瑕的单晶金刚石的快速生长成为可能，这可能在极端压力和温度下的材料研究中开辟新的前沿。更大的钻石价格实惠，结构和光学优化，可以进行新的砧榫形状和新型垫圈设计的实验。此外，CVD生长的钻石可以用嵌入式传感器制造，为专门的实验（例如，下地幔和岩心相的磁性、电学和弹性特性表征）提供“设计”砧。该项目的目标是开发新型高压设备，使样品体积增加到目前在兆巴压力下传统金刚石电池的100到1000倍。这一进展将促进许多目前无法用于超高压研究的基于x射线的分析技术，包括成功利用主要新中子（橡树岭的SNS）和全球现有的第二代和第三代同步辐射设施（例如APS/ANL， BNL， ESRF, SPring-8）所需的技术。这些新型高压电池的成功开发将使高压地球科学、行星科学和材料科学的新实验成为可能。该项目将邀请两名研究生参与新仪器设计和矿物物理研究应用，并将为他们在学术界，国家实验室和工业领域的各种可能的职业生涯做好准备。除了地球科学之外，对极端压力下材料的电学、光学和物理特性的研究也有望带来具有深远社会影响的新技术（例如，具有热学和电磁特性的新型CPU芯片材料，可以适应微电路的持续发展）。＊＊＊

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). ***