Just as the Hubble space telescope is discovering giant galaxies at the edges of the universe, a revolution in electron microscopy at Lehigh promises to shed light on the atoms of the nano-world that play a disproportionate role in the efficiency and safety of everyday materials.
Next spring, with support from the National Science Foundation, Lehigh will become the first and only university in the world to have two aberration-corrected electron microscopes. The NSF funding will enable the university to acquire a new, aberration-corrected transmission electron microscope and an aberration corrector for its existing scanning transmission electron microscope.
An improved understanding of the microscopic behaviors of atoms and molecules has led to advances in materials used in semiconductor chips, airplane wings, VCRs, cell phones, and many other modern devices.
It also has given metallurgists new diagnostic capabilities. The Titanic
, scientists now believe, may have been doomed while it was being built, when a handful of sulfur atoms slipped unseen into the grains of iron in the ship’s hull, rendering it brittle.
“Electron microscopy helps us understand the microstructure and microchemistry of materials,” says David Williams, vice provost for research and one of the principal investigators on the microscope proposal. “Once we know those things, then we can learn how to control the physical, mechanical, electronic, and chemical properties of a material.” ”A new pair of reading glasses”
The new instruments will give scientists an ability they have long sought: to simultaneously locate and identify individual atoms in crystalline materials.
The microscopes achieve this improved resolution by correcting an imbalance in the lenses that focus the electron beam on the specimen being examined. The outer extremities of the lenses tend to focus more strongly than their centers, limiting the beam width to 1 or 2 nanometers—or about the width of five to six atoms. (One nm is equal to one one-billionth of a meter.)
An aberration corrector, aided by a sophisticated feedback mechanism, measures the amount of “over-focus” and adjusts the outermost of the lenses, known as the objective lens.
The resulting beam measures .1 nm in width, or about half the width of an atom.
“This is like fitting a microscope with a new pair of reading glasses, giving it 20:20 vision,” says Chris Kiely, professor of materials science and engineering and director of the Nanoscale Characterization Laboratory in the Center for Advanced Materials and Nanotechnology.
The aberration-corrected microscopes will offer previously unobtainable insights into the nature of a variety of phenomena. These include the segregation of impurity atoms that control brittle fracture of steels in nuclear reactors, the chemistry of catalytic nanoparticles used for to oxidate carbon monoxide and remove organic pollutants from groundwater, and the microstructure of new ion-containing polymers that could provide protection against chemical warfare.
The aberration corrector will permit the electron microscope to detect the presence of a single impurity atom. “This is extremely important, for example, in trying to understand the embrittlement of steel,” Williams says.
The new instruments will play a key role in the Lehigh Microscopy School, the largest short courses of their kind, which attract 150 to 200 participants from academia and industry to Lehigh every June.
“The new discoveries that will inevitably be made using these new microscopes will undoubtedly raise the research profile of Lehigh University,” Williams says. “Our goal is to keep Lehigh as one of the leading electron microscopy centers in the world and now, with the help of the NSF, we will have an unparalleled suite of instruments to offer students and faculty colleagues.” --Carol Kiely For more information, contact Kurt Pfitzer in University Relations.