Volume 16 - 2006

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Microscopes

are in Demand at

UNT Microscopy Laboratory

By James Naples

Metals characterization

In addition to Brian Gorman, two UNT scientists using the Electron and Ion Microscopy Laboratory's microscopes to develop new techniques for characterizing materials are Rajarshi Banerjee and Michael J. Kaufman. Both are conducting metallurgical research.

Banerjee, an associate professor in the Department of Materials Science and Engineering, studies the effects of reduced system dimensions on the crystal structure and properties of metallic thin films and multilayers. Examples of thin films include the top metallic layer on a microchip and the coating on a magnetic disk. Multilayers are made up of a "stack" of thin films.

Kaufman, professor and chair of the department, is studying the relationship of structures, properties and processing abilities in metallic materials. The microscopes enable him to look at microstructural changes in metals and how these affect the metals' characteristics after processing.

A new array of high-powered microscopes at the University of North Texas affords researchers a combination of tools nearly unique in the world.

The microscopes were acquired by UNT's Electron and Ion Microscopy Laboratory through the university's research initiative known as the Advanced Research and Technology Institute. Through the institute, UNT is able to bring in large-ticket research equipment, says Brian Gorman, an assistant professor in the Department of Materials Science and Engineering and the lab's director. Established in 2005 within the department, the lab is located at the UNT Research Park about four miles north of the main campus.


World-Class Instruments

The three brightest stars in this stellar array of world-class instruments are a dual-beam focused ion beam/scanning electron microscope (FIB/SEM), an analytical high-resolution transmission electron microscope (HRTEM) and a local electrode atom probe (LEAP). Only Oak Ridge National Laboratory in Tennessee offers the same lineup of instruments.

Brian Gorman</strong>, director of UNT's Electron and Ion Microscopy Laboratory, is pictured with the lab's laser-pulsed local electrode atom probe.

Brian Gorman, director of UNT's Electron and Ion Microscopy Laboratory, is pictured with the lab's laser-pulsed local electrode atom probe. The LEAP system can map the positions of a sample's atoms in three dimensions.

The LEAP, made by Imago Scientific Instruments, is described as a three-dimensional atom probe capable of tomographic characterization (or, imaging by sections of a specimen) at the atomic scale. In other words, the LEAP can map the positions of atoms in a sample in three dimensions. The resulting images, says Gorman, "tell us what the atoms are, what the atoms are made of and exactly where they are."

"The LEAP can tell us the ultimate composition of a material," he continues. "We may already know what the structure looks like, but the LEAP can lead us to exactly what it's made of - even if we're looking for parts per million and almost parts per billion."

The HRTEM, made by FEI Co., delivers a resolution of one angstrom, one-tenth of a nanometer. (A nanometer is one-billionth of a meter.)

"With the HRTEM, we can see individual columns of atoms," explains Gorman. "It gives us images of where the atoms are sitting, what the structure looks like and, if it's made of layers, how big the layers are."

The FIB/SEM, also made by FEI, combines a dual-column focused ion beam and a scanning electron microscope. The SEM measures surface topography with resolutions of a nanometer by bringing electrons down to the sample and enabling the user to see what "reflects" off the sample. The FIB images with gallium ions, which can also cut open a large structure to help explain undesirable results. The FIB is also capable of "machining" or cutting into the surface of a sample. Gorman demonstrates the FIB's ability by showing how he milled the UNT logo onto the surface of a silicon wafer.

Doctoral student Oscar Olea-Mejia (left) works with the microscopy lab's high-resolution transmission electron microscope.

Doctoral student Oscar Olea-Mejia (left) works with the microscopy lab's high-resolution transmission electron microscope. With resolutions of one-tenth of a nanometer, the HRTEM allows researchers to look at individual columns of atoms. Doctoral student Junyeon Hwang (right) demonstrates the dual-beam focused ion beam/scanning electron microscope. The SEM measures surface topography with resolutions of a nanometer, and the FIB can cut open a structure or cut into the surface of a sample.

"Ten of these logos would fit across the diameter of one of your hairs," he says.

Each of the instruments has its own capabilities and limitations, Gorman says. For instance, while all three are capable of resolutions at the "nano" level, only the LEAP and the HRTEM can do atomic-scale imaging. The FIB and the HRTEM can also work at the "micro" (one-millionth of a meter) level, but the HRTEM is lacking low-level chemistry information. The combination of the instruments overcomes the limitations of each, says Gorman.


Solar Cells and Fuel Cells

Of course, the ability to etch the UNT logo onto a surface seven-millionths of a meter wide doesn't justify the purchase of these instruments. Rather, it's their promise in research outside of the strictly microscopic realm that excites Gorman and his colleagues and graduate students.

A small sampling of the areas in which they are conducting research includes photovoltaics, fuel cells, computer chips and even medicine.

Photovoltaics, also known as solar cells, convert sunlight into electricity. Given the desire to lessen our dependence on nonrenewable and polluting energy sources such as oil and coal, researchers are naturally attracted to this renewable and clean source of energy.

"Most solar cells are grown as big single crystals such as silicon wafers," Gorman explains. "But we are working in collaboration with researchers at the National Renewable Energy Lab with polycrystalline structures made of copper, indium and selenium. The boundaries between the crystals have been shown to be very conductive, which is a good thing. We can use the FIB to pull out a boundary and look at it to see why it conducts better. That's something nobody else in the world is trying.

"We apply what we know about materials science and physics to make solar cells more efficient, so the cost of electricity comes down," says Gorman.

He finds current research into fuel cells particularly exciting.

"What better way to reduce our dependence on foreign oil," he asks, "than to run a fuel cell off landfill gas?"

While the most common fuel cells these days are polymer cells, which conduct hydrogen, Gorman is concentrating on oxide fuel cells. Here, power is produced by the chemical difference between having oxygen on one side of a ceramic fuel cell and a fuel such as trash-produced methane on the other.

He uses the microscopes to examine the interactions between the different layers of the fuel cell and to help determine what metals might serve as the best catalysts to enhance these interactions. His goal is to make fuel cells mainstream. Widespread use by individual homeowners is probably not in the immediate future, Gorman says, but electricity could be generated at local landfills to supply power to the electrical grid.

"Composting trash would offset individual users' power consumption," he says, "similar to the way wind and solar generators currently feed power from the home back onto the grid."


The lab will not only attract more corporations and federal research facilities to join with UNT, it will also bring in more graduate students.

Computers and Medicine

Another "huge area for us," says Gorman, is computer chips. He and his fellow researchers can use the FIB to pull out a single transistor from a chip. (A transistor is a small electronic device that contains a semiconductor. An Intel Pentium chip has approximately one billion transistors.) The researchers then put the transistor into the HRTEM and take high-resolution images to learn about the chemistry of the transistor's 10-atom-thick layer.

"We want to find out where every atom is in this transistor," Gorman says. "If we can show the depth of atoms within a device, the thickness of insulators and the width of the electrical contacts, we can design our device processing to get the most out of the structures.

"There's no way to get this information except by what we're doing," says Gorman. "Thanks to the advances in microscopy, manufacturers will be able to pack more transistors on a chip, allowing for more calculations to be done more quickly, using less power."

In the medical realm, Gorman describes a recent undertaking on behalf of Chris Gilpin and fellow researchers at the University of Texas Southwestern Medical Center at Dallas.

"The folks at UT Southwestern wanted to find out where the waste goes in the glomerulus," he explains. Each human kidney contains about a million glomeruli - small, ball-shaped structures that make up the nephron, the functional unit of the kidney. The glomerulus is composed of capillary blood vessels that filter the blood to form urine.

"We used the FIB to cut open a section of a glomerulus," explains Gorman, "and then we used the SEM to make a map of it. We can help figure out how the kidney functions and how disease occurs. We have even taken a single red blood cell and cut it open."


Growing Attraction

Not surprisingly, reservations to use the microscopes book quickly, Gorman says.

"Our LEAP system is one of only eight in the world and the only one at a public university in the U.S.," he explains, "so there's a lot of interest by people wanting to use it."

Fortunately, Gorman's collaborators in the UNT computer science department have written an online system that makes scheduling easy.

"It's a very nice program and a fine example of interdepartmental cooperation," says Gorman.

The establishment of the microscopy laboratory is sure to boost the already growing reputation of UNT as a research institution. The lab will not only attract more corporations and federal research facilities to join with UNT, it will also bring in more graduate students to the university's master's and doctoral programs in materials science and engineering.

"Having a university that can attract students to engineering and science is key to making us a top research institution," says Gorman.

"I feel blessed to have all these high-tech tools at our disposal," he says. "We're doing things that nobody else in the world is doing - not even close."



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Web Extrasvideo file

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Brian Gorman describes how the FIB/SEM and LEAP are helping determine solar cell efficiency.

You will need to download the latest Macromedia Flash Player for your system to view this webextra.


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