Application of ptychography to visualization of dislocations in silicon single crystal

Professor Y. Takahashi (Osaka University, Japan) and his colleagues have recently reported that coherent X-ray imaging using Bragg diffraction can aid the observation of nanoscale dislocation strain fields in a silicon single crystal. The experiments were done with 11.8 keV micro-focused X-ray photons, around 1 μm in both directions, using KB mirrors at BL-29XUL, SPring-8, Japan. In this research, a 1 μm thick silicon (100) single crystal was placed in the X-ray path so that X-rays could pass through it and the 220 Bragg reflection spot was observed by a CCD camera 2 m behind the sample. The sample was scanned in XY directions as well. The research team found phase singularities, i.e., two pairs of vortices with opposite directions in the phase map, that corresponded to the locally dark positions in the intensity map. It was concluded that this corresponded to the projection of the {111} dislocation loops. For more information, see the paper, "Bragg x-ray ptychography of a silicon crystal: Visualization of the dislocation strain field and the production of a vortex beam", Y. Takahashi et al., Phys. Rev. B87, 121201(R) (2013).