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 b