Seeing atoms in action: CU electron microscope to make huge advance

By David Brand

An early look at Cornell's next major advance in microscopy was provided on April 4 at the 20th annual Cornell Society of Engineers (CSE) conference on campus. The new scanning transmission electron microscope (STEM) will be installed in the nearly completed Duffield Hall when the machine arrives early next year.

The microscope, which will be part of a larger instrumental development in Duffield, was termed "a paradigm shift of huge proportions" by Philip Batson '70, Ph.D. '76, of IBM Research Labs. Said Batson's long-time collaborator, John Silcox, Cornell vice provost for physical sciences, "This is going to be a very exciting instrument."

The introduction to the new STEM, which will be able to image single atoms and the structures around them with extraordinary clarity, was an appropriate subject for the conference, which had as its theme, "Breaking the Size Barrier: Engineering at the Smallest Dimensions."

The CSE conference was held April 3 to 5 in a number of locations on campus. Also sponsored by Cornell's College of Engineering, the conference provided an overview of current research and applications of nanoscience, or engineering at the molecular level -- and smaller. CSE has been the engineering college's official alumni association since 1905.

Engineering Dean W. Kent Fuchs opens the CSE conference April 4. Nicola Kountoupes/University Photography

Opening the conference in Barnes Hall, W. Kent Fuchs, the Joseph Silbert Dean of Engineering at Cornell, noted that "nanotechnology, nanoscience and nanoengineering are really at the heart of Cornell's expertise, and its future." The investment in Duffield, the new nanoscience building, "will pay great rewards in the education of our students and also the discoveries and research that faculty will accomplish," he said.

Also opening the conference in his role as a Frank H.T. Rhodes Class of '56 University Professor, Bill Nye, television's "Science Guy," noted: "I travel a great deal and visit many universities. The thing about Cornell is that there is an openness here and an inclusion of undergraduates that we really need to nourish, because undergraduates are the future."

Describing the STEM in a talk in B17 Upson Hall, Silcox, the David E. Burr Professor of Engineering, Applied and Engineering Physics, said the new $2 million microscope, funded by the National Science Foundation and Cornell, with key equipment from Gatan Inc., Lucent Technologies Bell Laboratories and Sandia National Laboratories, will operate at 100 kilovolts (kV).

Thanks to new lens designs pioneered by Ondrej Krivanek and Niklas Dellby at Nion Co., Kirkland, Wash., the very tiny electron probe produced by the new instrument is targeted to be one angstrom (one hundred-millionth of a centimeter), the size of an atom. This incredibly small probe will make possible a resolution at 20 times the diameter of the wavelength of the electrons, exceeding previous performance levels, which were 50 times the wavelength. To give some idea of the resolution that will be possible with the new microscope, features in a silicon structure only 1.5 angstroms across will be clearly visible for the first time, said Silcox, allowing "exquisite control over the growth process."

The new STEM will be installed on the first floor of Duffield in the characterization lab, or electron microscopy suite, which Silcox will direct. The microscope is being designed and built by Nion.

Silcox and Batson have been working on a program to exploit the atomic-size electron beam, coupled with electron spectroscopy, to image electronic-structural features on an atomic scale. Batson, who was Silcox's student, both as an undergraduate and as a doctoral candidate, noted in the CSE talk that the STEM is a giant advance over previous electron microscopes not only because of its size -- it fits into a regular lab -- but also because of the clarity of atomic detail it exposes.

For the past five years Batson has been researching and building a prototype of the STEM, which, for the first time, corrects the spherical aberrations that have distorted images from previous electron microscopes. This is achieved by adding corrective, magnetic "lenses," called quadrupoles and octupoles, to the microscope's original three-lens system. These lenses are computer-adjusted in much the same way as adaptive optics are used to operate advanced astronomical telescopes. Batson likened the use of the magnetic lenses to correcting the distortions produced when looking through a wineglass. "We have been living with distortions in electron microscopy for the past 60 years," he said.

A video camera was added to the STEM to aid in the computer-controlled adjustment of the microscope's 35 coils, or power supplies. Without video controls, said Batson, "we don't know which knob to twist." Cornell's new instrument will be engineered to improve the caliber of the rest of the electron optical system.

One of the striking results of the long research was shown by Batson in a video film produced with the STEM prototype: two gold atoms moving on a carbon surface, with one bumping against a ledge, an imperfection in the material. "You are seeing the dynamics of the interaction of two atoms in real time," said Batson.