WHAT DO WE REALLY KNOW ABOUT THE ATOMIC-SCALE STRUCTURES OF NANOPHASEMATERIALS

Robert W. Balluffi has spent a rich research lifetime critically inves tigating and elucidating the atomic-scale defect structures of materia ls. Now, a new class of ultrafine-grained materials has been created i n which such defects exercise a dominant role. The structures of these new nanophase materials, both metals and ceramics, have been investig ated over the past several years by a wide range of experimental metho ds. These studies have included observations by X-ray and neutron scat tering, transmission and scanning electron microscopy, Mossbauer, Rama n and poistron annihilation spectroscopy and, most recently, scanning tunneling and atomic force microscopy and nuclear magnetic resonance. While the experiments have yielded considerable useful information abo ut the structures of nanophase materials on a Variety of length scales , much about the local atomic arrangements in the grains and interface s of these materials remains to be elucidated. The present status of o ur knowledge of these structures is reviewed and some future research needs and opportunities are considered.