CAREER: Phase Transformations in Ceramics and Semiconductors Under Contact Loading

材料在高压下发生的相变对于材料科学和工程中的许多问题都很重要。这一领域的大多数结果都是使用各种复杂的高压室获得的。在这个学院早期职业发展项目中，将结合硬度压痕测试和拉曼光谱来研究高非静水压力下的固态相变和非晶化。微拉曼光谱可能是唯一一种能够在几秒钟内以1微米量级的空间分辨率在材料的未制备表面或表面下进行材料的非破坏性物相分析的方法。初步实验表明，在Si和Ge中减压后，由于禁带的闭合和亚稳相的形成，已经实现了金属化。第一次，在硬度印记中明确地观察到亚稳态相，其中一些相的拉曼光谱以前从未发表过。获得的数据将被用来从实验上证实许多脆性材料的硬度水平取决于启动相变所需的应力(变形)，并提供证据表明半导体的金属化是变形诱导的，而不是“压力”诱导的现象。电子显微镜、SAD和EELS、显微X射线衍射仪和显微FTIR将作为物相分析的辅助技术。硬度压痕测试和拉曼光谱将用于各种半导体和陶瓷的分析。这项技术的使用将使PI能够展示钻石的高压金属化。这项技术还将被用来在陶瓷(碳化物和氮化物)和半导体中发现其他新的高压相，这些相已经在理论上预测过，但尚未获得。解决这一问题的成功很可能会促进高压研究的快速发展，并使其成为几乎所有材料科学家都能接触到的常规技术。此外，这个职业项目的教育部分建立在PI的多学科研究和教育背景的基础上。该项目的结构是为了确保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、延展性加工、表面纳米涂层、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.