Three-dimensional electron density mapping of shape-controlled nanoparticle by focused hard X-ray diffraction microscopy.

Coherent diffraction microscopy using highly focused hard X-ray beams allows us to three-dimensionally observe thick objects with a high spatial resolution, also providing us with unique structural information, i.e., electron density distribution, not obtained by X-ray tomography with lenses, atom probe microscopy, or electron tomography. We measured high-contrast coherent X-ray diffraction patterns of a shape-controlled Au/Ag nanoparticle and successfully reconstructed a projection and a three-dimensional image of the nanoparticle with a single pixel (or a voxel) size of 4.2 nm in each dimension. The small pits on the surface and a hollow interior were clearly visible. The Au-rich regions were identified based on the electron density distribution, which provided insight into the formation of Au/Ag nanoboxes.