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Focus On Materials

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Faculty Spotlight

 

Suzanne Mohney

 

MahoneyProfessor of Materials Science and Engineering
Website - http://www.esm.psu.edu/mohney/

 

Steidle Building, at the heart of the University Park campus, is the home of Materials Science and Engineering (MatSE), one of the world’s top materials departments. Long echoing halls and high-ceilinged unpretentious offices indicate its industrial origins as the Mineral Industries Building, dating from the early 1930s. With the light flooding through tall, narrow windows, Steidle shows the hard use of generations of students, but its labs are brightly lit and full of shiny modern technology, the latest equipment, and some futuristic research that is at the leading edge of materials engineering.

 

In her lab on the second floor of Steidle building, Professor Suzanne Mohney shows off her latest acquisition, a new multipurpose physical vapor deposition system. Purchased with a research grant from the Department of Defense, the equipment can make multiple samples at once to help speed up the testing of contacts and interconnects, the main focus of her research.

 

"Three-quarters of my group’s research focuses on the problem of electrical contacts in semiconductors," Mohney remarks. Uncontrolled chemical reactions between metal contacts and the semiconductor material can result in poor electrical connections and thermal instability. "We work on the processing and characterization of electronic materials."

 

Electrical contacts can play active or passive roles in devices such as transistors, photodetectors, optoelectric devices or laser diodes, she explains. In their passive role, they allow current in with a minimum of resistance. Active contacts turn transistors on or off when they are used as Schottky barriers, the energy barriers at the interface between metal and a semiconductor.

 

Some of her contacts are designed to function on the nanoscale, a few atoms in diameter. As devices shrink in size to what will soon be a molecular level, there are some difficult questions Prof. Mohney would like to find answers for: "How do you get current into nanowires that are only tens of nanometers thick? How do you prepare the contacts? Some require real innovation. Then, how do you measure the current? How is the current transport altered by the very small geometry?"

 

Mohney’s group looks at electrical contacts from multiple viewpoints, using phase diagrams, reaction kinetics, current transport and device physics to understand both the physics of the materials as well as the engineering applications. "Sometimes we’ll work very closely with companies that have already commercialized their products, and we are trying to improve them. We want to make their devices last longer under harsh conditions. Or, in some cases, a company may want to make a transistor even smaller, but the device fails because the metal reacts too strongly and consumes a layer of semiconductor."

 

For the Air Force, Mohney is working on electrical contacts that can survive in flight turbulence at 350 degrees C. On one DARPA (Defense Advanced Research Projects Agency) project, they work with industry on high speed devices that have low power consumption, with applications for communications for the Department of Defense. Her group studied indium phosphide and indium arsenide based semiconductors, called III-V semiconductors.

 

Her group is also working on nanowires, which are of interest, she says, because they could be used in very high speed transistors. "There are some people who believe, based on theoretical predictions, that they could be used," she says. "And there are some preliminary measurements in the literature that suggest they might be used." On the nanowire project, Mohney has worked with professors Joan Redwing, Theresa Mayer and Beth Dickey, colleagues at Penn State with other areas of expertise. Their future research may help determine if those theoretical predictions for nanowires are correct.

 

Of more immediate utility is her research with Chris Muhlstein, a professor in Materials Science and Engineering, on electrical interconnects. Interconnects are a problem area for some electronics companies who need to be able to make contacts between devices such as LED displays or transistors, she says. Mohney and Muhlstein use patterned thin films created by vapor deposition using her new vapor deposition system. The thin film acts like tiny wires to make electrical connections. As well as the multipurpose physical vapor deposition system, her lab also contains electrical characterization stations, probe stations, sample preparation equipment for electron transmission microscopy, and annealing furnaces. "Eighty to ninety percent of our work is experimental," she remarks.

 

The Mohney research group currently numbers eleven members, made up primarily of grad students and post docs, but including a couple of undergraduates as well. In the last two years, five of her students have finished their Ph.D.’s and one of her post-docs recently accepted a research position with computer giant Intel.

 

Asked how she feels Penn State compares to other research universities, Dr. Mohney pauses before replying carefully that Penn State gives her students an exposure to a much broader range of topics in materials science than they might get elsewhere. "My students makes extensive use of user facilities on campus, such as the Materials Characterization Lab. We use their transmission electron microscopes, scanner Auger microprobe, x-ray photoelectron microscopy and scanning electron microscope. We have great hands-on facilities on campus, and most of the users are grad students."

 

Beyond that, she adds, "There are more seminars on campus than you could ever find time to hear. There are a lot of faculty in research groups that you can call upon for expertise when you start moving out of something you know. The opportunities for collaboration are really good, and the number of courses available to graduate students is high compared to many universities."

 

Dr. Mohney’s cross-campus collaborations are not unique, especially in an emerging field such as nanoscience where new areas of research find scientists exploring territories of physics and chemistry largely unknown to the researchers who worked in the labs of the old Minerals Industries Building. These days, the advance of knowledge requires new types of interconnections, of both the human and the electronic kind.

 

Education:
Dr. Mohney received her M.S. and Ph.D. degrees in Materials Science from the University of Wisconsin-Madison, and her undergraduate degree in Chemical Engineering from Washington University in St. Louis.

 

Recent Publications:

 

By Walt Mills,Validate to view address, 814-865-0285