This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: A research team led by Yang Lu from the Department of Mechanical Engineering at the Faculty of Engineering, The University of Hong Kong (HKU), has uncovered the microscopic physical nature of ultralarge elasticity in covalent semiconductors such as silicon and diamond. The discovery provides quantitative guidance for deep elastic strain engineering (DESE), paving the way for the development of next-generation electronic, optoelectronic and quantum devices.
Despite the potential of DESE, the underlying deformation mechanisms of these covalent crystals have long remained elusive. The research team was the first to directly observe the pure lattice evolution of single-crystal silicon and diamond under tension at the atomic scale. By precisely quantifying the resulting lattice strains, the researchers bridged macroscopic mechanical strain with microscopic lattice strain, establishing a physical foundation for the design of advanced semiconductor devices.
The research team also includes PhD student Jiayi Li and postdoctoral fellow Dr. Bulk covalent crystals have been widely considered "hard and brittle" materials, often undergoing brittle fracture during mechanical loading. In recent years, Lu first demonstrated that covalent semiconductor materials such as silicon and diamond can achieve ultralarge elastic strains approaching their theoretical limits at the micro- and nanoscale.
Subsequently, the team further proved that this extreme elastic deformation can produce new physical properties, enabling dynamic, continuous and reversible modulation of physical properties such as band gap and optics. However, the underlying deformation mechanisms have remained elusive: Does this ultralarge reversible deformation arise from pure atomic lattice displacements or from atomic rearrangements (such as defects, phase changes or superelasticity)? Direct, lattice-resolved measurements of deep elastic strain remain scarce.
To uncover its physical nature, the research team developed advanced in situ high-resolution transmission electron microscopy (in situ HRTEM) and in situ four-dimensional scanning transmission electron microscopy (in situ 4D-STEM) techniques for this study. At room temperature, they conducted uniaxial tensile testing on microfabricated single-crystal silicon and single-crystal diamond microbridges along the [100] and [110] directions. They tracked the distribution of deep-strained atomic coordinates in real time and extracted lattice-resolved strain maps.
They also mapped high-precision elastic lattice strains across the entire sample with nanoscale spatial resolution and a wide field of view for both semiconductor crystals. The study found that the ultralarge tensile strains in silicon and diamond originate completely from reversible atomic lattice displacements. Experiments confirmed that, without any extended defects or phase changes, the crystal lattices of diamond and silicon can achieve sample-wide uniform elastic elongation of up to 8.9% and 11.3%, respectively.
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