NASA Jet Propulsion Laboratory, California Institute of Technology

The second international workshop on Ballistic Electron Emission Microscopy (BEEM) is scheduled for Jan. 28 at NASA's Jet Propulsion Laboratory in Pasadena, Calif.

BEEM is a technique, based on scanning tunneling microscopy, that permits examination of interfaces. Interfaces are the boundaries between different materials below the surfaces of semiconductors and metals.

The technique was invented at JPL in 1988 by Drs. William Kaiser and L. Douglas Bell and is currently in use at many laboratories worldwide.

The Second BEEM Workshop will be held immediately preceding the 1991 Physics & Chemistry of Semiconductor Interfaces (PSCI) conference Jan. 29-Feb.1 in Long Beach, Calif.

The program is to include one tutorial designed to introduce new people to the field of BEEM and to provide background for the main portion of the meeting, which will consist of contributed papers.

Other tutorials will include experiment and theory. There also will be oral presentations and poster sessions.

BEEM is based on scanning tunneling microscopy, or STM, which won its creators the Nobel Prize in Physics in 1986. STM permits the imaging of metal and semiconductor surfaces at the resolution of an atom.

STM uses electron tunneling across a vacuum gap between an atom-sized probe tip and a target surface. This tunneling process only occurs when the tip is within about one nanometer (one billionth of a meter) of the surface. By holding the tunneling current constant and scanning the tip across the surface, the tip follows the surface without actually touching it, and an image at the resolution of an atom may be obtained.

BEEM uses an STM tip to inject a highly localized electron beam into a sample structure which has an interface below the surface. Electrons entering the structure propagate "ballistically," or without undergoing scattering or loss of energy, into the material a distance of 10 nanometers or more.

By scanning the tip across the surface, not only is a surface image obtained as in conventional STM, but also an image of the electron transmission across the buried interface. The resolution of the probe is on the order of one nanometer.

The day-long workshop is presented jointly by JPL, the American Vacuum Society, the Strategic Defense Initiative Organization/Innovative Science and Technology Office, and the Office of Naval Research. Conference chairman is Dr. Leo Schowalter of Rensselaer Polytechnic Institute, Troy, N.Y.

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