Nanoindentation is a standard technique usually devoted to characterize the mechanical properties of materials. However, the high and localized pressure applied by nanoindentation allows to reach critical condition for phase transition in many materials, thus obtaining metastable phases that often are maintained upon pressure release. Metastable phases can offer different electronic and structural properties with respect to their stable counterpart. This is the case of silicon, indeed its high pressure allotropes are promising for on-chip energy harvesting devices due to the low thermal conductivity and high thermoelectric efficiency. Moreover silicon polymorphs also demonstrate high carrier mobility and superconductivity. Furthermore, some polymorphs have been predicted to exhibit a direct bandgap, enhancing light emission and detection capabilities for use in on-chip photonic circuits. Among these, hexagonal diamond stands out as particularly appealing.
The realization of silicon and silicon-germanium hexagonal crystals is the aim of the “SiGe Hexagonal Diamond Phase by nanoIndenTation (HD-PIT)” project (PRIN 2022) whose Principal Investigator is prof. Scalise (Department of Materials Science).
Recently, the results obtained by the project participants have been published in Small Structure (Wiley, Impact Factor 13.9, Clarivate, 2023). The article is titled “Formation of Micrometer-Sized Textured Hexagonal Silicon Crystals via Nanoindentation”, DOI: 10.1002/sstr.202400552. The synergic collaboration between the theoretical team of researchers working in the department and experimental partners within the project allows for the first time to identify the specific indentation parameters and the subsequent annealing conditions that generate a purely and uniform hexagonal silicon region, micrometric in size.