Phase 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.
