Materials Science and Engineering

microwave effect discovered by Materials Science & Engineering Professor Reid Cooper (left), Electrical and Computer Engineering Professor John Booske (right) and recent materials science PhD recipient Sam Freeman may help researchers process materials more quickly and at lower temperatures than they could using conventional furnaces.

The standard way of heating solids is through convective or radiative transfer to the surface and subsequent conduction into the material--similar to roasting a turkey. But this standard method heats and cooks the outside of the turkey faster than the inside. In materials such as ceramics, heating rapidly can lead to underprocessed interiors, thermal stressing and cracking.

Microwave energy heats surface and interior equally. Using microwaves to process materials, some researchers observed unusually fast processing rates, which many peers attributed to faulty temperature-measurement methods.

Intrigued, Cooper and Booske designed experiments free of questions about temperature measurement. "Reaction rates in ceramics are typically a product of a 'mobility' and a 'driving' force," says Cooper. Initially they thought microwaves might cause materials' atoms to diffuse more easily than those in materials heated conventionally. With Freeman, they discovered their hypothesis was wrong. Instead, they learned that microwaves' electromagnetic fields produce an additional--and entirely unexpected--driving force for transport that can stimulate a reaction rate faster than the rate generated by heat alone. The breakthrough is important, says Cooper, because it means industry can heat materials uniformly and quickly at high temperatures, yet use less power.

Recently Cooper and Booske shifted their focus from ceramics to semiconductors. Collaborating with Electrical and Computer Engineering Assistant Professor Yogesh Gianchandanii, they hope to learn more about applying the microwave effect to semiconductor processing.

From razor blades to turbine blades: Students apply materials science

Each semester, an ephemeral rainbow of colorful 3-by-4-foot posters lines the second-floor hallways of the Materials Science & Engineering Building, evidence of undergraduates' curiosity about the properties and microstructure of such varied products as guitar strings, door locks, turbine blades and coins. The posters, plus oral presentations, culminate Grainger and L.V. Shubnikov Professor David Larbalestier's one-credit MS&E 360 (Materials Lab I) course, which students take in their second or third semester of study. Students learn simple metallurgical techniques: preparing samples, viewing them through a microscope and measuring their properties. They analyze brass and steel, and learn to keep lab books, organize their data and write reports. For their final projects, however, Larbalestier encourages them to research objects that interest them. Among recent results, students learned that "platinum-quality" razor blades don't contain platinum, pricey kitchen knives don't necessarily have better-quality blades, and fancy guitar strings are just like inexpensive strings.

Larbalestier says the hands-on class reinforces the idea that students can learn thinking and research skills as freshmen. "One of the most important things is we can do is teach the students that they are capable of much more than they thought they were," he says. Additionally, the course gives students the chance to apply materials science early in their education.

Semiconductors: making the right contacts

The most advanced semiconductor devices in the world are useless if the metal contacts, which connect semiconductors with the outside electrical world, aren't reliable. "Electrical contacts to wide-bandgap semiconducting materials attract a lot of active research due to the tremendous interest in light-emitting and high-power and high-temperature devices," says Wisconsin Distinguished Professor Y. Austin Chang.

Manufacturers employ wide-bandgap semiconductors in many products we encounter daily. They use infrared light-emitting diodes in TV remote controls and auto-focus cameras, and CD players will use nitride-based blue lasers that increase a CD's storage capacity by about 300 percent. By selecting compositions based on their thermodynamic and kinetic properties, Chang's group is attempting to understand, predict and control the interfaces between such metal conductors as nickel aluminide, titanium aluminide and nickel indide, and various nitride semiconductors. With investigators at Hewlett-Packard Co., they identify ideal properties of contacts based on the semiconductor device function and then try to achieve those properties by controlling the interface. Once they select a materials system, Chang's group fabricates samples, then measures and characterizes them to determine if the interfaces behave in the manner their modeling has predicted. Ultimately, they hope their work will improve semiconductor device operation.

Sindo Kou, Chair
276 Materials Science and Engineering Building
1509 University Avenue
Madison, WI 53706-1595

Tel: 608/262-3732
Fax: 608/262-8353
E-mail: msaedept@engr.wisc.edu
www.engr.wisc.edu/mse