When Dan Rugar first heard about an idea for a new microscope that could peer beneath the surface of molecules and pick out individual atoms, he was skeptical. Scientists had dreamed of having such a device to help them unravel the complex structures of proteins, spot the defects in semiconductors, and solve a thousand other mysteries. But so far nobody had come up with a way of building a microscope powerful enough to produce a three-dimensional image showing the precise location of each and every atom--without destroying or changing the structure of the material.
Rugar knew the problem as well as anybody. As a physicist at IBM, he had helped develop the atomic force microscope (AFM), which uses a tiny mechanical cantilever to feel individual atoms on the surface of a sample--or more precisely, to feel the electrostatic repulsion exerted by the atoms’ electrons. Indeed, the proposal Rugar was listening to that day in 1991 sounded remarkably familiar.
In the new microscope, as in the AFM, a cantilever would be moved across a sample like a microscopic phonograph needle. But instead of responding only to surface atoms, this cantilever would pick up the far feebler magnetic force exerted by resonating atoms below the surface. That technique is known as magnetic resonance imaging, or MRI; hospitals already use it every day, in a much cruder form, to image internal organs.