X-ray vision of nano-materials Eric E Fullerton, University of California-San Diego, DMR 0906957

1. X-ray vision of nano-materialsEric E Fullerton, University of California-San Diego, DMR 0906957 • Researcher at University of California, San Diego and Argonne National Laboratory have demonstrated three-dimensional structural imaging of individual Ni nanowires. By exploiting the powerful x-ray beams available at Argonne's Advanced Photon Source (APS) they performed coherent x-ray diffraction imaging. The x-ray diffraction patterns are numerically inverted to reveal important nanoscale characteristics of the nanowires including the wire shape, density variations and internal stresses and strains. • This imaging approach provides a new way to non-destructively probe inside nanomaterials and understand their elastic and mechanical properties. The approach further opens the door to strain engineering nanoscale systems and provides a gateway to developing and imaging novel nanowire-based device functionalities under external stimuli such as pressure, electric or magnetic fields. • For details see Fohtung et al., “Probing the three-dimensional strain inhomogeneity and equilibrium elastic properties of single crystal Ni nanowires”, Appl. Phys. Lett. 101, 033107 (2012). (above) Coherent x-ray scatting pattern from a single nanowire. (below) Reconstructed (a) shape, (b) density and (c) lattice strain obtained from multiple diffraction patterns

2. New twist on magnetism in nanowiresEric E Fullerton, University of California-San Diego, DMR 0906957 • Researcher at University of California, San Diego and the Lawrence Berkeley National Laboratory have determined the magnetic structure of individual Ni nanowires. By combining synthesis of single-crystal nanowires, high-resolution x-ray magnetic imaging and micromagnetic modeling they uncovered a new periodic chiral state. The magnetic structure consists of chiral magnetic arrangement where the handedness alternates between right and left handedness periodically down the nanowire. • This new periodic structure arises from the competition between the shape of the nanowires and the well-defined crystalline anisotropies. While handedness is common in nature, it is quite unusual to find systems that mix left and right handedness. This novel structure may lead to new interactions of magnetism with current or light 120nm 0nm 20nm 40nm 60nm 80nm 100nm 120nm

3. Controlled growth of Ni nanostructuresEric E Fullerton, University of California-San Diego, DMR 0906957 • Researcher at University of California, San Diego have developed a general chemical vapor deposition process that leads to controlled growth of distinct nanostructured Ni products. These nanostructures include core-shell Ni-NiO nanowires, horizontally and vertically oriented single-crystal nanowires, and fully isometric single-crystal cubes. The different structures are all obtained upon an amorphous SiO2||Si and controlled by obtained by subtle changes in temperature and humidity. This approach of non-epitaxial growth of single crystal nanostructures may be extended to other material systems. • Due to their high surface-to-volume ratio, transition metal Ni nanostructures such as nanowires could potentially be used in a broad range of applications in catalysis, sensors, batteries, fuel cells, and magnetic devices • For more details see Chan et al. Philosophical Magazine 92, 2173 (2012).