Plasticity, Phase Transformations, and their Interaction under High Pressure in Silicon

晶体相变和材料在高压下的永久塑性变形之间的相互作用广泛存在于几种技术应用中；然而，由于需要专门的设备来观察这种现象，对这种现象的了解很少。该奖项通过支持对硅中这种相互作用的综合实验、理论和计算研究来填补这一空白。硅被选为具有代表性的材料，因为它具有多种类型的相变，广泛应用于电子和微电子机械系统，以及太阳能电池。在高压下相变-塑性相互作用的基本方面所获得的知识也将对脆性半导体和陶瓷的表面过程的定量建模和优化具有更广泛的影响，例如抛光、车削和划痕。作为该项目的一部分，将有机会通过特殊课程和研究来教育和培训研究生和本科生，部分课程和研究将在阿贡国家实验室进行，重点是未被充分代表的学生。这项研究的目的是调查在硅中高压下塑性流动对相变的影响。结合现场高通量实验和模拟，可以定量描述和理解塑性应变如何显著降低相变压力，促进新相的形成，在常压下保留高压相，以及改变不同相间的相变路径。硅样品将在旋转的钻石压腔中被压缩和剪切。同步加速器X射线衍射和吸收、拉曼光谱和位移测量将用于变形和转变过程的现场诊断。发展了耦合相变和局域剪切带(例如位错堆积)的微尺度相场方法，并用于研究单晶和多晶集合体中多个相变之间的相互作用和塑性机制。相变判据，应变控制的动力学方程，以及所有相和相混合物的压力和塑性应变相关的屈服强度将从实验中获得，并纳入宏观唯象模型中。该模型将用于金刚石顶锤变形转变过程的有限元模拟。作为计算框架的应用，还将进行新阶段的搜索。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The interaction between crystalline phase transformations and permanent plastic deformation under high pressure in materials is broadly found in several technological applications; however, knowledge of this phenomenon is scarce because of the specialized equipment needed to observe it. This award fills the gap by supporting an integrated experimental, theoretical, and computational study of this interaction in silicon. Silicon is chosen as a representative material because it exhibits numerous types of phase transformations and is widely used in electronics and micro-electromechanical systems, as well as solar cells. The knowledge gained on the fundamental aspects of phase transformation-plasticity interaction under high pressure will also have broader implications on the quantitative modeling and optimization of surface processes, such as polishing, turning, and scratching, for brittle semiconductors and ceramics. As part of the project, there will be opportunities to educate and train graduate and undergraduate students through special courses and research, parts of which will be conducted at the Argonne National Laboratory, with an emphasis on underrepresented students.The objective of this research is to investigate the effect of plastic flow on phase transformation under high pressure in silicon. Coupled in situ high-throughput experiments and modeling will yield quantitative characterization and understanding of how plastic straining drastically reduces the transformation pressure, promotes the formation of novel phases, retains high-pressure phases at ambient pressure, and changes transformation paths between different phases. Silicon samples will be compressed and sheared in a rotational diamond anvil cell. Synchrotron X-ray diffraction and absorption, Raman spectroscopy, and displacement measurements will be used for in-situ diagnostics of the deformation and transformation processes. A microscale phase field approach for coupled phase transformations and localized shear bands (e.g., due to dislocation pileups) will be developed and used to study the interplay between multiple phase transformations and mechanisms of plasticity in single grains and polycrystalline aggregates. Phase transformation criteria, strain-controlled kinetic equations, and the pressure- and plastic strain-dependent yield strengths of all phases and phase mixtures will be obtained from the experiments and incorporated in a macroscale phenomenological model. This model will be used in the finite element simulations of deformation-transformation processes in diamond anvils. A search for new phases will also be performed as an application of the computational framework.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.