The science of controlling individual atoms to manipulate their behavior, cuts across engineering disciplines and aligns squarely with CIT's multidisciplinary strengths.
Controlling and predicting the behavior of nanoparticles has its challenges. When working at the nanoscale with particles that are 1-100 nanometers in size, quantum physics takes effect and materials behave differently, and here's where the fun begins. Chemical, electrical and magnetic properties change, giving engineers a new toolbox full of novel materials whose unique phenomena have yet to be discovered. The opportunities for exploiting nanoparticles and creating devices are immeasurable.
Reaching this point was all part of the plan outlined by the National Nanotechnology Initiative (NNI). Launched by the U.S. Federal Government in 2001, the NNI set out to establish the U.S as a worldwide pacesetter in nanotechnology innovation, and its success is evident. Today nanoparticles are used in a variety of consumer products, ranging from lightweight sporting equipment to ceramic coatings for solar cells. Conservative estimates reveal that more than 800 nanotech products are publicly available. Our understanding of nanoscience has swelled, but the fact remains: we are just starting to realize the full potential of nanotechnology.
For over a decade the National Science Foundation (NSF) has boosted funding for nanotechnology because "they want to exploit emerging research areas that alter materials or some feature at the nanoscale in order to create new properties that otherwise would not exist," says Gary Fedder, the director of CIT's Institute for Complex Engineered Systems (ICES). Found within ICES are multidisciplinary centers, such as the Center for Nano-enabled Devices and Energy Technologies (CNXT) that explore the use of nano science, systems and devices to solve problems.
Fedder explains that one distinguishing feature of nanoparticles is that they have far more surface area per volume than larger-scale particles, and this is important. "If a material reacts with the environment, then it has chemical properties that can be enhanced through nanotechnology by creating more surface area," he says. Greater surface area allows larger portions of a material to connect with other materials and react.
Platinum, for example, is a catalytic material commonly used in chemical reactions. "If more surface area is created while volume is kept fixed, then a more efficient reaction results," continues Fedder. To create vast surfaces and improve reactivity, researchers seek ways to texture materials while simultaneously making them stay stable over time. Fedder cites batteries as one application where this concept plays out. "If one wants to make a small-volume battery that fits into a cell phone, nano is good for this application." In larger batteries, texturing electrodes increases surface area while material interactions at the nanoscale keep everything intact over long-term cycling. As he sums it up, "The smaller you can texture, the bigger the win."
Nanotechnology has broad applications, and because of the latitude, "if you pick one stakeholder, whether it's industry or a government agency, usually it focuses on one specific problem where nanotechnology can provide a solution." However, in CIT our research is as diverse as the challenges we face. We intend to use nanotechnology to transform fields where we have established centers of excellence: biomedical engineering, the environment, energy and electronics.
Engineering Better Health
Nanotechnology is bringing about significant advances in the diagnosis and treatment of diseases. For example, CIT's Chris Bettinger, an expert in biomedical engineering and materials, is developing "soft" materials that can be used inside of the body without being rejected. The potential applications for these materials range from retinal implants to IV catheters.
On a different front, the pharmaceutical industry has much to gain from emerging nano research. Nisha Shukla, a research faculty member in the Institute for Complex Engineered Systems (ICES), is fabricating gold nanoparticles that have chiral surfaces. This work is of great interest because chiral drugs account for more than half of the drugs sold worldwide and have a market share worth over $200 billion per year.
Many biochemicals exist in both left- and right-handed forms. When biochemicals are synthesized, attention must be paid to their "handedness" or chirality, because one form can be therapeutic, while its counterpart of opposite handedness may be harmful. Thalidomide, which caused serious birth defects in the 1950s and early 1960s, exemplifies what can happen when the wrong chiral form of a drug is used.
"When pharmaceutical companies make chiral drugs, they separate the right and left forms," says Shukla. "Presently, they use columns [High-performance liquid chromatography] to separate these drugs. This process is working well, but what would happen if nanomaterials that have really large surface areas were used instead? Can we use small amounts of nanomaterials to efficiently separate these drugs?"
To test if her idea was plausible, she used chemical synthesis techniques to modify gold nanoparticles. She made the particles chiral and then used them to separate the left- and right-handed forms of a small chiral molecule. This gave her "proof of concept," and opened the door for exciting new research. For example, gold is very expensive, and Shukla is exploring if other metals can be used for chiral separations. "Right now we are learning a lot about the science of doing separations with nanoparticles," says Shukla. Eventually, testing will be performed with chiral drugs.
After Shukla published her initial findings, interest in using nanoparticles for drug separations swelled and "even the gold people got excited about it. We received a lot of attention for this work," she says. However, one important aspect of Shukla's research that most people aren't aware of is that her research team is comprised entirely of undergraduate students. "All the research I do involves undergraduates, and they have done remarkably well," she said. One of Shukla's former students earned a National Science Foundation fellowship for early work on this project. Today, Shukla and three of her students, Nathan Khosla (junior, ChemE), Abigail Ondeck (senior, ChemE, BME) and Abigail's brother Nathaniel Ondeck (junior, ChemE, BME), are applying for a patent pertaining to this research.
"Introducing undergraduate students to research is important to me," says Shukla. She explains that when undergraduates are provided with meaningful research exposure, they are more likely to enter graduate school, and this enhances CIT's reputation.
"In my lab, the students learn research and how to be responsible. The undergraduates work like Ph.D. students, and they work hard. By the time they graduate, they have four or five papers published. When they enter Ph.D. programs, they are ahead of other students. The education that this research gives to students is amazing," states Shukla.
Engineered nanoparticles can be comprised of several materials or they may have protective coatings. In energy production, for example, coatings prevent nanoparticles from clumping together and hindering reactions; whereas in biomedical applications, the coatings bind with specific proteins. These coatings become an integral part of the particle. But what happens when the coatings degrade? If waste water containing silver nanoparticles is rinsed down the drain, what happens when the particles enter the sewer?
Understanding the complex relationships between nanomaterials and environmental and human health risks is the goal of CEINT@Carnegie Mellon—the Center for the Environmental Implications of Nanotechnology. In this center, researchers study the fate of and transport of nanoparticles and their toxicity in the environment. Greg Lowry, CEINT's director and a professor in Civil and Environmental Engineering, works with colleagues throughout CIT, examining factors that alter the behavior and chemistry of nanoparticles. The manner in which these particles move through or aggregate in different environments, say water as opposed to soil, generates environmental questions. Do the particles pose risks to our health? What will happen when plants and animals take up these particles? Can we determine which nanoparticles will become harmful so we can avoid problems in the future? These are the questions that CEINT explores.
Training engineers to remain cognizant of the impacts of engineered nanomaterials is critical. Water-quality expert Jeanne VanBriesen is leading a doctoral program focusing on the technological and policy implications of nanotechnology.
"All the microprocessors made today are made from semiconductors, and there are two things you need to know about them," starts Jimmy Zhu, ABB Professor of ECE and director of the Data Storage Systems Center. First, semiconductors are expensive to make. The price tag on a semiconductor fabrication facility ranges from $5 to $10 billion, and global competition is ferocious. The U.S. struggles to preserve its share of an industry that's dominated by Taiwan, Korea and Singapore.
Another issue with semiconductors is that they need to operate at certain voltage level. Power consumption is directly proportional to operating voltage. "Low voltage, low power devices are the name of the game today in many applications, especially for handheld devices, such as the iPhone," says Zhu.
To take processors to the next level and circumvent the challenges inherent to semiconductors would take a transformational change that would fundamentally alter the way we create these devices. Zhu and his colleague Larry Pileggi, Tanoto Professor and director of the FCRP Center for Circuit and System Solutions, may have very well figured out how to do this. "We are trying to make a processor that is made entirely of metal and without any semiconductors," say Zhu. They call their creation mLogic.
"In mLogic, the "m" can stand for metallic or magnetic—you can use either," explains Zhu. The basic idea is to apply a very small current to move a magnetic domain wall that is trapped in a tiny magnetic device, utilizing a quantum effect called spin transfer torque. The researchers can change the magnetic resistance state of the device by pulsing the current, which changes the spin of the electrons.
And the significance of this? "This tiny device can be made smaller than the size of a transistor today. We have developed novel methods to connect them together so that they can perform the exact same functions as today's microprocessors," replies Zhu.
Working with metals instead of semiconductors posits major advantages. First, the researchers believe they can keep manufacturing costs low. Metallic fabrication will ballpark around $300 million, which is far cheaper than semiconductor fabrication. Another revolutionary advantage is that the metal devices will operate at low voltages; they'll require less power and be nonvolatile. For example, with current microprocessors, if the power goes out, the devices lose what they've computed. But with mLogic, if you lose power, the computation continues when the power returns. Zhu says, "You don't need power to maintain memory states, and you only need a pulse to do a computation." This encourages military and space applications. The novel metallic chips would be "rad hard," or unsusceptible to electromagnetic radiation. Zhu explains that in space, electronic devices won't work if they are exposed to too much radiation. Today, processors used in space are entombed in heavy, lead boxes to protect them. Leaving the lead boxes on Earth would certainly lighten the payload.
While actual devices have yet to be built, the researchers modeled the magnetic behavior, simulated cells that performed signal processing tasks, and compared the results to traditional CMOS technology. "At low operating voltage, we are over one million times faster than CMOS," says Zhu. He and Pileggi have received approximately $1 million from government agencies to produce a prototype. Two of their ECE Ph.D. students, David Bromberg and Dan Morris, won a $100,000 fellowship from Qualcomm for their work on the project.
"This project is a result of joint thinking. Nobody has ever been able to design something like this that is metal based. I'm a magnetics guy, and integrated circuits are Larry's expertise. Neither of us could do this individually. Nanotechnology is interdisciplinary. It is on the edges of different subjects, and that is where new things come from," concludes Zhu.
Making Solar Energy Work
The Department of Energy (DOE) wants to harvest solar energy and transfer it to the grid. To do this efficiently, "lightweight, solid-state, medium voltage (>13 kV) energy conversion is needed for megawatt-scale power applications in utility-scale inverter circuits," states Michael McHenry, a professor of Materials Science and Engineering.
"The cores in power convertors are made of magnetic materials. We can switch their magnetization back and forth. And if we can make the magnetic components switch at higher frequencies, we can reduce the size of these power convertors and their cost," says McHenry. The implications of this are profound, and that is why the DOE awarded him $1.7 million to develop magnetic nanomaterials for use in smaller convertors. These novel systems will improve the control of renewable energy that's inserted into the power grid, and ultimately lower the price of energy.
"Typically, distribution transformers in the power grid are switching at 60 hertz. We are developing new materials for convertor cores that aim to switch at 100 kilohertz. This can lead to a large reduction in power convertor size," he explains.
In a brief history lesson, McHenry explains that "back in the days of Edison, when the power grid was created, there was debate if we were going to use AC or DC. They decided to use AC at a low frequency of 60 hertz because of materials limitations. At this time, the main materials were steels and iron." Since then materials have evolved considerably.
For two decades, McHenry has been developing the amorphous metallic magnetic materials that are being used in this project. To test his alloys, McHenry collaborates with a Pittsburgh-based company called Magnetics, a division of Spang Inc., which is a world leader in producing magnetic cores. After testing, the promising materials will go to Los Alamos National Laboratories, where they will be used to build a DC convertor. "This convertor will hit power levels of 100 kilowatts. At Los Alamos, they have techniques where they can take these convertors in parallel and achieve power levels exceeding a megawatt, and that is what the DOE is interested in," says McHenry. He predicts that the researchers will deliver convertor cores that switch at 20 kilohertz within the next three years, while demonstrating materials in the laboratory that switch at 100 kilohertz.
While smaller power convertors will enhance the way power is generated, the production of these systems could have other positive effects on our economy. "To build these components, we need lots of materials and you have to employ people to make them," says McHenry, adding that he and other researchers are developing new technologies, and with this comes opportunities for new applications and even new markets for novel materials and systems.
The College of Engineering has identified nanotechnology as an area of strategic focus. Nanoscale research is pervasive throughout CIT's departments, and the initiatives mentioned in this article are examples of the pioneering nanoscale work that is underway in our research centers and laboratories.
by Sherry Stokes
Share this story: