Sample Preparation for Lensless Strain Imaging at Twin Grain Boundaries

We seek to use Bragg coherent diffraction imaging (BCDI) to study how metals begin to damage at the nanometer scale. BCDI has previously been shown to have near wavelength-limited resolution. We use BCDI data from coherent x-rays scattered from crystalline metal samples at Argonne National Laboratory's Advanced Photon Source. We then use a program, Cohere, to create 3D strain maps of single metal grains during past beam times. We wish to eventually develop a method allowing joint reconstruction of multiple Bragg peaks. This would allow us to better study how defects in a polycrystalline metal are transmitted through a grain boundary under strain. The constraints necessary for 3D complex image retrieval via an iterative phase-retrieval technique will be explained with the aid of computer simulations utilizing fast Fourier transforms. Because a priori information results in more quickly converging iterative solution, twin grain boundaries were identified as prime sites for testing our technique. To identify samples with the necessary properties, we used scanning electron microscopy. The analysis and preparation of samples for our beamline experiments will be discussed.