STM Tip Builds Golden Mounds
Langreth, Robert N., Science News
STM tip builds golden mounds
Physicists have devised a simple and speedy method for creating microscopic images and characters. Their new technique -- using a scanning tunneling microscope (STM) to deposit tiny gold mounds onto gold or platinum surfaces -- brings scientists one step closer to making near-molecular-scale electronic devices.
In recent years, many groups have sought to manipulate increasingly small clusters of atoms, with the ultimate goal of making tiny circuits and data storage devices. The STM has proved a helpful tool. Invented in 1981, the instrument works by positioning a tiny metal tip within a few atomic diameters of a surface, close enough to allow electrons to leap, or "tunnel," across the air gap to the surface. The resultant current varies with the width of the gap, allowing scientists to chart surface bumps and grooves as small as individual atoms (SN: 4/1/89, p.200).
Dan Rugar, H. Jonathon Mamin and Peter H. Guethner at the IBM Almaden Research Center in San Jose, Calif., wondered whether they could somehow release clusters of atoms from an STM tip and deposit them onto a surface. "I had the idea the if we could apply [an external] voltage to the tip, we could get some atoms to be emitted," says Rugar.
Scientists have long known that a strong electric field can ionize and eject atoms from a surface, but no one had tried this approach with a solid STM tip. The IBM team chose gold as the tip material because it holds its atoms loosely and does not react in air, disrupting the STM. …