Bragg Coherent X-ray Diffraction Imaging (BCDI) is an emerging technique in the field of lensless imaging and provides an amazing insight into the world of nanocrystals. If we take a crystal and illuminate it with a coherent X-ray beam, we can measure the resulting diffraction pattern on a detector. This diffraction pattern contains information about the shape and internal structure of the crystal. More technically, it is a slice through the Fourier transform of the projected complex electron density of the crystal, also known as a Bragg peak. By rotating or rocking the crystal, we can sample 2D slices through the Bragg peak, as shown in figure a). If we put these diffraction pattern slices into a computer phase retrieval algorithm, we can reconstruct a 3D image of the crystal, shown in figure b), as well as probe the lattice displacement within this crystalline volume.
BCDI is typically performed on as-grown nanocrystals, but unfortunately many of the systems we wish to investigate form much larger crystals. Recently we have developed a protocol for fabricating BCDI strain microscopy samples from bulk samples, whereby it is possible to extract a specific feature of interest from a bulk sample and map the full lattice strain and rotation tensors with a typical voxel size of 5 nm and a strain sensitivity of 0.0001. Accessing these length scales and columns is challenging, if not impossible, via any other technique, thus BCDI is a critically important tool in the study of crystal defects.
We apply BCDI to many novel applications including the imaging of strain within nano indented tungsten and gold micro-crystals damaged by focussed ion beam, the investigation of irradiation damage within future fusion reactor components and more generally defect microstructure, dislocation networks and defect engineering. To support the investigation of increasingly complex materials we are developing new computational tools and novel phase retrieval processes. With these studies, we gain an understanding of how crystal defects affect the properties of materials, filling the information gap between atomistic simulations and observations within bulk materials.