Formation of Micrometer-Sized Textured Hexagonal Silicon Crystals via Nanoindentation

We present a comprehensive study on the formation of micrometer-sized, textured hexagonal silicon (hd-Si) crystals via nanoindentation followed by annealing. Advanced characterization techniques, including polarized Raman spectroscopy, high-resolution transmission electron microscopy (TEM), and electron energy-loss spectroscopy (EELS), reveal the creation of hd-Si with nanometer-sized grains that are slightly misoriented and organized into large, textured domains. First-principles calculations and molecular dynamics simulations confirm the ability of nanoindentation to induce controlled, pressure-driven phase transformations. A critical aspect of this process is the interplay between plastic and elastic deformation during indentation, which competes with phase transformation to influence the final material structure. The balance between these mechanisms determines the uniformity and quality of the hd-Si phase. The high-quality textured hexagonal Si may be a promising material for future applications in semiconductor and optoelectronic devices, particularly for integrated photonics and next-generation transistors. Furthermore, this methodology can be extended to other semiconductor systems, such as SiGe, to create direct-bandgap materials, opening new avenues for the development of advanced on-chip technologies. Funding acknowledgement We acknowledge financial support under the National Recovery and Resilience Plan (NRRP), Mission 4, Component 2, Investment 1.1, Call for tender No. 104 published on 2.2.2022 by the Italian Ministry of University and Research (MUR), funded by the European Union – NextGenerationEU– Project Title "SiGe Hexagonal Diamond Phase by nanoIndenTation (HD‐ PIT)" – CUP H53D23000780001 ‐ Grant Assignment Decree No. 957 adopted on 30.06.2023 by the Italian Ministry of Ministry of University and Research (MUR).