Direct Sub-Angstrom Imaging of a Crystal Lattice
P.D. Nellist1, M.F. Chisholm2, N. Dellby1, O.L. Krivanek1, M.F. Murfitt1, Z.S. Szilagyi1, A.R. Lupini2, A. Borisevich2, W.H. Sides2 Jr., S. J Pennycook2.
Science 305, 1741 (2004)
Direct, sub-Angstrom imaging of a crystal lattice has been achieved for the first time at Oak Ridge National Laboratory using a scanning transmission electron microscope (STEM) equipped with an aberration corrector from Nion Co, Kirkland, Washington. The image shows pairs of silicon atom columns just 0.78 Angstroms apart that are clearly resolved. Analysis of the image reveals that the microscope resolution is actually 0.6 Angstroms, a new world record for a direct image. The image was recorded by scanning a 0.6-Angstrom beam across a thin specimen and recording the electrons scattered onto a ring-shaped detector surrounding the transmitted beam. This mode of imaging provides a direct image of the crystal, in which atoms contribute according to their atomic number (Z). Oak Ridge National Laboratory has been a pioneer in this Z-contrast mode of imaging for the last 15 years.
Higher resolution allows the atomic structure of materials to be seen more clearly. It allows light elements to be seen in the presence of heavy atoms, for example, oxygen is now visible in superconductors and colossal magnetoresistant manganites where it plays a dominant role in determining properties. The smaller beam provides greatly improved sensitivity to single atoms, either lying on a materials surface or inside the bulk. Single atoms can determine the performance of electronic and structural materials. Single impurity atoms in the active region of a computer chip can be disastrous, however, at the core of a dislocation in an alloy they may be the key to high temperature stability. This advance in direct imaging is expected to benefit a broad range of materials, chemical and nanosciences. It should enable the development of new catalysts for energy production, chemical manufacture, polymers and plastics, of new corrosion resistant, lightweight alloys for transportation, of improved electronic and photonic devices for communications and information technology, and a new understanding of atomistic mechanisms in the nanosciences.
1. Nion Co, 1102 8th St. Kirkland, Washington 98033
2. Condensed Matter Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA