Almost-impossible Materials Science by 3D Diffraction Microscopy
Ian McNulty
Advanced Photon Source, Argonne National Laboratory
The capability to image structure in three dimensions at the molecular scale and beyond is essential to solve manifold problems in materials, condensed matter, and biological science. Examples of current materials interest include nanostructure synthesis and self-assembly, magnetic and ferroelectric domain growth and evolution, and defects and strain in low-dimensional structures such as quantum wires. Most microscopes with the necessary resolution can only image surfaces or require many identical copies of the structure to be imaged. Electron and scanning probe methods such as atomic force microscopy are superb tools for studying surfaces and thin films; x-ray crystallography has enjoyed tremendous success in structural biology but depend on highly ordered samples. Coherent x-ray diffraction microscopy offers the tantalizing possibility of molecular-scale 3D imaging of individual non-crystalline structures without the resolution limitations of lenses and multiple scattering of electrons. Paradoxically, the weak interaction of x-rays with matter that makes 3D diffraction microscopy possible also makes it technically daunting. Diffraction tomography, which uses many views projected through the sample to obtain good depth resolution, is one solution. But if multiple copies of the sample are unavailable or many measurements on the sample are impractical due to radiation damage, the only avenue is to obtain all the data in a single measurement. Near-simultaneous acquisition of 3D data could also enable time-resolved studies currently out of reach of today's methods. We examine various schemes to achieve this utilizing the unprecedented coherent flux provided by the proposed ERL in combination with holography to aid phase retrieval from the tremendous quantity of data needed for 3D imaging.
