CAREER: Phase Transformations in Ceramics and Semiconductors Under Contact Loading

9874955 Gogotsi高压下材料中发生的相变对于材料科学和工程中的广泛问题非常重要。 这一领域的大多数结果都是使用各种复杂的高压电池获得的。在这个教师早期职业发展项目中，固态相变和非晶化在高非静水压力下使用硬度压痕测试与拉曼光谱的组合将进行研究。 显微拉曼光谱可能是唯一的方法，允许在几秒钟内进行材料的非破坏性相分析，在材料的未制备表面或表面下的空间分辨率为1微米。 初步的实验已经证明了金属化由于带隙的关闭和随后形成的亚稳相减压后，在Si和Ge。 对于第一次，亚稳相明确观察到的硬度印象，其中一些阶段的拉曼光谱还没有公布。所获得的数据将被用来实验证实，许多脆性材料的硬度水平取决于应力（变形）需要启动相变和提供证据，半导体的金属化是一个变形引起的，而不是一个“压力”引起的现象。TEM与SAD和EELS、micro-XRD和micro-FTIR将被用作相分析的辅助技术。硬度压痕测试与拉曼光谱相结合将被用于分析各种半导体和陶瓷。 这项技术的使用将使PI能够证明金刚石的高压金属化。 该技术还将用于在陶瓷（碳化物和氮化物）和半导体中发现其他新的高压相，这些相在理论上已经预测，但尚未获得。解决这个问题的成功可能会促进高压研究的快速发展，并使其成为几乎每个材料科学家都可以使用的常规技术。 此外，该职业项目的教育部分建立在PI的多学科研究和教育背景之上。 该项目的结构是为了确保在该项目中开发的基础科学将导致实现具有实际意义的长期目标，应用于压痕测试，延性加工，表面纳米图案化，表面质量控制和摩擦学。

9874955GogotsiPhase transformations occurring in materials under high pressures are important for a wide range of problems in materials science and engineering. Most of the results in this area have been obtained using various sophisticated high-pressure cells. In this Faculty Early CAREER Development project, the solid-state phase transformations and amorphization under high non-hydrostatic pressures using a combination of hardness indentation tests with Raman spectroscopy will be studied. Micro-Raman spectroscopy is probably the only method that allows the non-destructive phase analysis of materials to be conducted within seconds with a spatial resolution in the order of 1 micrometer on a non-prepared surface of the material or under the surface. Preliminary experiments have demonstrated metallization due to closing of the band gap and consequent formation of metastable phases upon decompression in Si and Ge. For the first time, metastable phases were unambiguously observed in hardness impressions and for some of these phases Raman spectra have not been published before. The data obtained will be used to confirm experimentally that the hardness level of many brittle materials depends on the stress (deformation) needed to initiate the phase transformation and supply evidence that metallization of semiconductors is a deformation induced, not a 'pressure' induced phenomenon. TEM with SAD and EELS, micro-XRD and micro-FTIR will be used as supplementary techniques for phase analysis.Hardness indentation tests combined with Raman spectroscopy will be used to analyze a variety of semiconductors and ceramics. The use of this technique will allow the PI to demonstrate the high-pressure metallization of diamond. This technique will also be used to find other new high-pressure phases in ceramics (carbides and nitrides) and semiconductors that have been theoretically predicted, but not yet obtained. The success in solving this problem is likely to catalyze rapid advances in high-pressure research, and make it a routine technique which is accessible to almost every material scientist. In addition, the educational component of this CAREER project builds on the PI's multidisciplinary research and educational background. The project is structured in order to ensure that the basic science developed in this project will lead to achievement of long term goals of practical significance with applications in indentation testing, ductile regime machining, nanopatterning of surfaces, surface quality control and tribology.