Mechanical deformation, twinning, and crystallization in engineered micro and nanostructured materials
| PhD ceremony: | H. Wang |
| When: | June 13, 2025 |
| Start: | 12:45 |
| Supervisors: | prof. dr. ir. B.J. (Bart J) Kooi, prof. dr. Y. (Yutao) Pei |
| Where: | Academy building RUG |
| Faculty: | Science and Engineering |
Antimony (Sb) has a unique rhombohedral crystal structure, combining strong covalent-like bonds with weaker van der Waals interactions and exhibiting pronounced Peierls distortion. This gives it excellent electronic, optical, and structural properties, making it ideal for phase-change memory and microelectronics. However, its mechanical behavior at small scales remains largely unexplored. In his thesis, Hui Wang investigates the mechanical performance and deformation mechanisms of Sb- and GaSb-based materials, which are fabricated using pulsed-laser deposition (PLD), across bulk, thin-film, and nanolaminate forms.
First, Wang examines single-crystal Sb through micropillar compression, applying different cooling rates (furnace, air, water, liquid nitrogen). Faster cooling rates refine the grain size and increase the density of rhombohedral twins. Atomic-resolution analysis identifies a specific twinning system (1–104)[–2201]. Wang shows that the deformation strength of Sb strongly depends on both crystal orientation and twin activity.
Next, Wang analyses Sb thin films using nanoindentation and electron microscopy. The results show that PLD-controlled columnar grains and twinning beneath indents improve the material’s hardness without causing delamination. In GaSb films, different annealing processes lead to crystallization and the formation of twin and Lomer-Cottrell locks, which increase hardness and modulus but reduce fracture toughness—illustrating the crucial trade-off between plasticity and toughness for phase-change device reliability.
Finally, Wang investigates GaSb–Al₂O₃ nanolaminates, showing that reducing bilayer thickness and optimizing annealing lead to enhanced hardness and toughness via Hall–Petch strengthening and complex dislocation dynamics. Overall, this work demonstrates how PLD-engineered microstructures can optimize the mechanical properties of Sb-based materials for next-generation microelectronics.