Nanoscale 3D Imaging of Defects

Bragg Coherent Diffractive Imaging (BCDI) is at the forefront of defect characterization, offering a revolutionary approach to studying the three-dimensional nature of materials. Traditional state-of-the-art techniques, such as 4D Scanning Transmission Electron Microscopy and surface probe methods, are inherently two-dimensional and fall short in capturing the full 3D complexity of defects like dislocations, stacking faults, inversion boundaries, grain boundaries, and multiferroic topological defects.

While it is possible to obtain 3D information from these techniques through destructive sample preparation methods—such as milling to create sample slices or removing surface layers—these approaches inherently alter the material. This alteration prevents accurate characterization of the sample in its as-grown state, as the destructive processes change the material’s original structure. Although these changes are often considered insignificant, this assumption cannot be critically evaluated without direct measurement of the as-grown 3D defects.

BCDI overcomes these limitations, allowing us to fully leverage the unique opportunities presented by these defects and advancing our understanding of material properties in their true, unaltered state.

BCDI leverages the intricate nature of diffraction to access the full strain tensor of distortions within a crystal. This sensitivity to 3D strain enables the analysis of buried defects without the need for destructive sample preparation. Defects play a crucial role in influencing the mechanical, optical, and electronic properties of materials. Consequently, controlling defects—including their creation, elimination, and density—is vital in materials engineering.

Our group is at the forefront of developing and utilizing BCDI to uncover the complex 3D nature of defects within real materials. By exploiting the topological characteristics of defects such as dislocations and ferroelectric forces, we create comprehensive models of individual nanoparticles. Our sensitivity encompasses a wide range of defects in systems ranging from fabricated semiconductors to photocatalysts and ferroelectric insulators. This 3D approach reveals how defects in crystals, such as those illustrated, introduce long-range structures that cannot be fully understood through 2D analysis. The image on the right showcases the long-range behavior induced by 3D defects within a crystal. Further investigation reveals that these structures originate from dislocations—defects that could only be partially characterized using traditional 2D methods.

We apply these advanced techniques to increasingly complex systems, incorporating a diverse array of defects. Our research particularly focuses on systems with multiple interacting defects, such as dislocations and stacking faults, or ferroelectric domains and vortices. When these defects interact, they can produce unique behaviors not observed in isolated defects, including strain relaxation, altered transport properties, and enhanced electronic properties.

Understanding the nature of these defects in 3D enhances our ability to grow high-quality samples with a low density of undesirable defects, such as inversion domain boundaries and misfit dislocations. By deepening our understanding of defect tolerance and interaction in diverse systems, we can ultimately develop new and innovative devices.