Researchers at IBM’s Almaden Research Center in California’s Silicon Valley have demonstrated two-dimensional imaging of objects as small as 90 nanometres with magnetic resonance techniques (MRI).
The ultimate goal is to use MRI to study individual atoms in three dimensions. While this remains some way off, Dan Rugar and his IBM colleagues say that 50 nanometre resolution in 2-D may be possible within the next year or two using modest improvements to the techniques presented in their recently-published Nature Nano paper. Fully three-dimensional MRI should then follow within a few years.
Magnetic Resonance Force Microscopy (MRFM) offers imaging sensitivity some 60,000 times better than the conventional MRI technology used in medical scanners. Combining elements of atomic force microscopy with MRI, MRFM employs a sharp magnetic tip attached to a sensitive micromechanical cantilever which bends in response to tiny magnetic force variations, including those due to the spins of atomic nuclei in the sample.
“Ideally, we would like to have the sensitivity to detect individual nuclear spins, and use this sensitivity to map the 3-D coordinates of atoms in a macromolecule (like a protein) with atomic (sub-nanometre) resolution,” says Rugar. “To get the required 1000 times improvement in sensitivity, we need to further improve the magnetic tip technology in order to generate much larger magnetic field gradients.”
Rugar and his colleagues also need to reduce measurement noise, using better cantilevers and by going to lower temperatures, in order to detect smaller, sub-attonewton forces.
IBM Research has pioneered the development of microscopes for nanoscale imaging. Gerd Binnig and Heinrich Rohrer of IBM’s Zürich Research Laboratory received the 1986 Nobel Prize in Physics for their invention of the scanning tunnelling microscope.
Achieving 3-D imaging at the atomic scale will have a major impact on the study of materials – ranging from proteins and pharmaceuticals to integrated circuits – for which a detailed understanding of atomic structure is essential.
Reference: Nuclear magnetic resonance imaging with 90-nm resolution, Mamin et al., Nature Nano 2, 301 (2007).
Article first published in Nanomaterials News.