Imaging Single, Individual Macromolecules
A new imaging technique that uses electron diffraction waves to improve both image resolution and sensitivity to small structures has been developed. The technique works on the same principle as X-ray diffraction, but uses a laser-like collimated and coherent electron beam of a few tens of nanometers in diameter. The small beam size and electron coherence allows the recording of interference patterns from a single nanostructure or macromolecule. The laser-like electron beam is formed by using a fine aperture and adjustments to the settings of the existing lenses in a state-of-the-art analytical microscope with a field emission gun, based on a detailed understanding of electron optics and electron probe formation. For an electron beam of 50 nm in diameter, the divergence angle is less than 0.05 mrad. This represents a level of performance from a conventional electron microscope never achieved before. The coherence of the beam allows analysis of the hologram-like diffraction patterns and interpretation of the structure of objects as small as a single molecule. To demonstrate the effectiveness of the imaging technique, the diffraction pattern from a double-wall carbon nanotube was recorded. An iterative process was then used to retrieve phase information from the diffracted beams and construct to an image with a resolution of 0.1 nm.
Determining the structure of materials — such as protein crystals — is currently performed using X-ray diffraction. However, many small structures used in nanotechnology do not crystallize into a lattice and have not been accessible to crystallography, so their structures remain unknown. The ability to generate images from nanoscale diffraction patterns offers a way to determine the structure of nonperiodic objects, from inorganic nanostructures to biological macromolecules, much like X-ray diffraction does for crystals. This opens a door to examining the structure of individual and highly irregular molecules and nanostructures like clusters and wires. The technique described is being used currently in structure determination of Carbon and Boron Nitride nanotubes, alloy nanoclusters, early stage of structural transformation and crystallization of amorphous alloys.
Senior FS-MRL PI: J.M. Zuo