Dahmen Named Director of LBL's National Center for Electron Microscopy

November 19, 1993

By Lynn Yarris, [email protected]

Uli Dahmen is a man with a mission. He wants to re- establish LBL's National Center for Electron Microscopy (NCEM) as the premier facility of its kind in the world. He is now in a position to make his dream come true.

Dahmen has been named the new director of NCEM. Previously, those duties were split between Gareth Thomas, who was NCEM's founder and scientific director, and Ken Westmacott, who was NCEM's managing director. Both Thomas and Westmacott retired from their respective director duties and Dahmen has been the acting NCEM director since 1991.

"Gareth Thomas provided the vision that got NCEM started in 1983 and Ken Westmacott established the infrastructure that made it an effective user facility," says Dahmen. "In recent years, however, there has been an erosion of our operating funds that has crippled us. For the past two years, I have fought to return us to the scientific forefront."

Dahmen is a recognized leader in the crystallographic study of microstructures with more than 100 scientific publications and more than 50 invited lectures to his credit. German-born, he came to LBL in 1979 after getting his Ph.D. in materials science and engineering from UC Berkeley. In 1988, he became a principal investigator for what is now the Materials Sciences Division.

For the past two years, as part of his revitalization effort, Dahmen has led the drive to acquire two new microscopes for NCEM. The first, which should be in place within the next two years, is the One Angstrom Microscope. As the name says, this device will resolve images to a single angstrom using an electron beam at an energy of only 300,000 electron volts. By comparison, NCEM's Atomic Resolution Microscope provides a resolution of 1.6 angstroms using an electron beam at an energy of one million electron volts.

"This reduction in energy greatly reduces the radiation damage to the specimen," Dahmen says. "The One Angstrom Microscope will be used as a tool for discovery and as a tool for measurement and characterization."

The second new addition planned for NCEM is a Magnetic Materials Microscope, an electron microscope with a "field-free" objective lens. Electron microscopes use electromagnetic fields as the objective lens that focus their electron beams onto a sample. When the sample being imaged is itself magnetic, this poses a major problem.

Explains Dahmen, "It is like shining a flashlight onto a piece of photographic film. You wipe out the magnetic field of the sample."

With the Magnetic Materials Microscope, the electromagnetic objective lens is split in half. The magnetic fields of each lens half flow in opposite directions. This leaves the magnetic field of a sample untouched when it is sandwiched in between the two halves.

"With this technique we can obtain nanometer scale resolution of magnetic materials and study the interplay between magnetism and structural defects," says Dahmen. "No other facility can offer this capability."

Dahmen sees the two new microscopes in combination with additional new laboratory space as crucial to NCEM's future. He also believes that the NCEM needs to make its facilities easier to use for all investigators -- inside LBL as well as outside the Laboratory.

"Having spent much of the past two years raising funds for NCEM's revitalization, it is nice to reach the point where I can be optimistic," says Dahmen.