Superconducting Nanowires Assist in Quantum Phase Transitions Study

By creating superconducting nanowires using carbon nanotube molecules, researchers at the University of Illinois are investigating just how small a wire can become and remain a superconductor. The answer could prove useful in applications such as supercomputing, where short superconducting wires can connect circuit elements.

"The phenomenon of superconductivity depends upon the phase coherence of the condensate," said Alexey Bezryadin, a professor of physics. "But for small systems, such as ultrathin wires, the phase is a quantum variable which may or may not have a definite value, corresponding to both superconducting and insulating states."

To study these quantum effects, Bezryadin and colleagues at Harvard University developed a technique that creates tiny superconducting wires from carbon nanotubes. The nanotubes serve as scaffolds. Uniform superconducting films of molybdenum-germanium alloy are deposited on these scaffolds. When the nanowires are placed across a narrow slit etched in a silicon chip, the researchers can apply a voltage and measure the resulting current.

"The molybdenum-germanium films have a sharp superconducting transition and show no signs of granularity down to a thickness of about one nanometer," Bezryadin said. "By changing how much material is deposited, we can make wires of different diameters and study important phase transitions between superconducting and insulating states."

Recent measurements by Bezryadin and U of I graduate research assistant Anthony Bollinger are shedding new light on superconducting phase transitions while also clarifying earlier findings.

The researchers fabricated superconducting nanowires from specially prepared, fluorinated carbon nanotubes prepared by chemist John Margrave at Rice University. Unlike typical carbon nanotubes, Margrave’s fluorinated nanotubes are insulators.

Bezryadin said, "With these nonconducting nanotubes, we have no doubt that the current we measure is flowing through the molybdenum-germanium film and not through the carbon scaffold. The fluorotubes also appear to allow the fabrication of even thinner nanowires."

The National Science Foundation supported the work.

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Medical Microspheres Provide Precision-Release Drug Delivery

The elusive goal of controlling the release rate of encapsulated compounds for the precise delivery of drugs over a prolonged period is finally within reach.

At the University of Illinois, professor of electrical and computer engineering Kyekyoon (Kevin) Kim, professor of chemical engineering Daniel Pack, and graduate student Cory Berkland have developed a method for making drug-encapsulated, biodegradable polymer microspheres that provides precise control over sphere size and shell thickness.

With their precise microspheres, the researchers have the ability to control the drug delivery kinetics–the rate at which a drug is released to the body–and also to create single-shot vaccines that could improve patient comfort and compliance.

To create uniform microspheres, the researchers begin by spraying a solution of biodegradable polymer, organic solvent, and the drug to be encapsulated through a small nozzle. "Left alone, the resulting stream would naturally break up into droplets, like water spraying from a garden hose," Kim said. "But the droplets would form in random sizes."

To produce uniform droplets, the researchers vibrate the nozzle with a piezoelectric transducer. "This launches a wave of acoustic energy along the thin liquid jet, which develops bulges–resembling sausage links–that snap off as droplets at a controlled rate," Kim said. "Shaking the nozzle at a defined rate is what makes the spheres all the same size."

To make even smaller droplets, the researchers use a coaxial nozzle to surround the polymer jet with a faster moving carrier stream. The carrier stream pulls on the polymer solution, stretching it into an even narrower stream that creates tinier droplets. By varying the flow rate and the frequency of the vibration, the researchers can precisely control the size of the resulting spheres.

By combining the acoustic activation and carrier stream techniques, the researchers have fabricated uniform microspheres with diameters ranging from 5 to 500 microns (by comparison, a human hair is about 100 microns in diameter). With a more sophisticated nozzle assembly, they have also created similarly sized microcapsules that consist of a drug core surrounded by a biodegradable polymer shell. By varying the shell size and thickness, the researchers can control the time delay for drug release.

"For many drug delivery applications, you would like to have the drug released at a constant rate," Pack said. "This is very difficult to achieve with conventional microspheres. But by mixing microcapsules of different sizes, we can generate a constant rate of release over a relatively long period of time."

The researchers demonstrated their constant-release kinetics with both a model drug compound (rhodamine B) and with piroxicam, a nonsteroidal anti-inflammatory drug used to treat inflammation associated with arthritis.

Such controlled-release drug delivery would be especially useful for drugs that require multiple daily injections and for vaccinations that require additional booster shots at timely intervals. "Single-shot vaccinations could increase both patient comfort and compliance," Pack said. "They would also dramatically reduce the number of injections required when inoculating people of Third World nations against infectious diseases or inoculating large populations against a bioterror attack."

While the researchers have focused their efforts on drug delivery, the technology has other potential applications, from producing tiny uniform balls of solder for packaging integrated circuits to creating hollow, lightweight ball bearings for aircraft, spacecraft, and satellites. They have applied for a patent.

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Tool Pinpoints Acceptable Pricing of Combination Vaccines

Four infant vaccines. One injection. How much will the industry charge? How much is a parent willing to pay? How much will government and insurance cover? Such issues are becoming real, says a University of Illinois researcher who has developed a mathematically based analysis tool to help pinpoint acceptable pricing.

"If you look around the world right now, combination vaccines are being used in Canada and Europe with tremendous success," said Sheldon H. Jacobson, a professor of mechanical and industrial engineering. "We initially analyzed the value of four particular combination vaccines, but our tool is really applicable to any combination, and there are several now on the horizon of reaching the FDA for approval."

His analysis tool incorporates a Monte Carlo simulation and an integer programming model, allowing re-searchers to study the various relationships of vaccine costs and any number of individual factors, including individual and societal benefits. The tool computes an optimum price for a combination vaccine to meet a manufacturer’s targeted market share.

A pilot study by Jacobson, in which he weighed the economic value of combining vaccines to reduce the number of injections or clinical visits, was published in 1998. Since then, he has increased the model’s capabilities to encompass any number of considerations. Edward C. Sewell of Southern Illinois University was co-author of the new study.

The new study focused on four combination vaccines, with each combination configured with the 12 licensed vaccines now being used for six childhood diseases in the Recommended Childhood Immunization Schedule. Rather than finding a single price, the tool considers any number of cost-associated factors and finds a distribution of prices that match a manufacturer's target market percentages and what consumers will pay.

A new way to assemble complex, three-dimensional structures from specially formulated colloidal inks could find use in advanced ceramics, sensors, composites, catalyst supports, tissue engineering scaffolds, and photonic materials.

Scientists have developed colloidal, gel-based inks that form self-supporting features through a robotic deposition process called robocasting. For this research process, a computer-controlled robot squeezes the ink out of a syringe, almost like a cake decorator, building the desired structure layer by layer.

"Our goal is to make designer materials that can’t be made by conventional forming techniques," said Jennifer Lewis, a professor of materials science and engineering and of chemical engineering at the University of Illinois. The work is a collaboration involving Lewis, U of I graduate student James May, and Joseph Cesarano, a staff scientist at the U.S. Department of Energy’s Sandia National Laboratories in Albuquerque, N.M.

Cesarano pioneered the new concept of robocasting several years ago and implemented it as an alternative "rapid prototyping" method for producing ceramic components. The Illinois-Sandia group is advancing the technique to finer scales and designing special inks that can form self-supporting features.

"The directed assembly of fine-scale, three-dimensional structures containing spanning elements required the development of concentrated colloidal, gel-based inks," Lewis said. "These inks must first flow through a very fine deposition nozzle and then quickly ‘set’ to maintain their shape while simultaneously bonding to the underlying layer."

The researchers have created structures with features as small as 100 microns (about the diameter of a human hair). They have spanned gaps as large as 2 millimeters.

The elastic properties and the viscous response of the ink can be "tuned" by tailoring the strength of the interparticle attractions, Lewis said. Because of the dynamic nature of the resulting gel, the particle network forms very quickly after the ink is pushed through the syringe, providing the desired shape retention.

Through careful control of colloidal forces, the researchers not only can produce complex shapes that can’t be made by conventional molding or extrusion processes, they also can build in complexity with respect to chemical composition.

"The robotic deposition equipment has the capability of handling multiple inks and dispensing them simultaneously," Lewis said. "As the relative rates of deposited ink are regulated, structures can be built that have compositional variations in them."

Inks are housed in separate syringes mounted on the robotic deposition apparatus and can be mixed or deposited independently. The ink exits the nozzle as a continuous, rod-like filament that is deposited onto a moving platform, yielding a two-dimensional pattern. After each layer is generated, the stage is raised and another layer is deposited.

The machine’s motion is controlled by a computer program called RoboCAD, developed by May. The software allows users to rapidly design and build complex, three-dimensional structures by simply designing layers as two-dimensional drawings.

"Ink can be made from nearly any particulate material that can be suspended in solution, as long as the interparticle forces can be tuned to yield the desired viscoelastic response," Lewis said. "We have made inks out of silica, alumina, lead zirconate titanate, and hydroxyapatite (the basic inorganic constituent of bone) colloidal particles. We also can deposit polymeric, metallic, and semiconducting colloidal inks."

The National Science Foundation and the Department of Energy funded this research.

As telecommunications and information systems become commonplace in society, a more secure means of encrypting and transmitting data is required. Underlying nearly all forms of encryption is the necessity for a truly secret key, which can be distributed without the threat of an undetected eavesdropper. Several protocols have demonstrated the potential effectiveness of quantum cryptography in meeting this need.

Now, researchers at the University of Illinois and the Los Alamos National Laboratory have implemented a six-state protocol using polarization-entangled photons that could enhance the versatility of quantum cryptography.

Quantum cryptography uses quantum states of photons to transfer cryptographic key material. In a typical protocol, the sender "Alice" uses single photons (or entangled photons) to transmit secret random bits to the receiver "Bob." Alice encodes each random bit value using one of several polarization states. Bob randomly measures each photon’s polarization and records the results. Then, by conventional communications, Alice and Bob reveal their basis choice for each bit and sift out the set for which they used the same basis. If an eavesdropper were present, detectable errors would be introduced into the key.

"Although the six-state protocol can make an eavesdropper substantially more visible, the protocol is technically harder to perform, and more data is lost," said Paul Kwiat, the John Bardeen Professor of Electrical and Computer Engineering and Physics at the University of Illinois. "Despite these drawbacks, the new protocol could prove useful in certain applications," he added.

To investigate the six-state protocol, Kwiat and his Los Alamos colleagues, Daphna Enzer (now at the Jet Propulsion Laboratory), Phillip Hadley, Richard Hughes, and Charles Peterson, created pairs of polarization-entangled photons by passing a laser pulse through two adjacent nonlinear crystals.

The photons were directed to Alice and Bob, who analyzed them in one of three randomly chosen bases: horizontal or vertical, diagonal or antidiagonal, and right or left circularly polarized. Whenever Alice and Bob chose the same basis, they obtained correlated results, which comprised their sifted cryptographic key material. The researchers also simulated the effects of different eavesdropping strategies.

"While the six-state protocol has enhanced eavesdropper sensitivity, it significantly reduces the number of key-producing events," Kwiat said. "For systems with low error rates–less than about 8 percent–the efficiency for secret key generation is higher when using a simpler protocol. However, as the error rate increases, the six-state protocol becomes beneficial."

With their enhanced signal-to-noise ratio, entangled photons should permit secure key distribution over longer distances–particularly in fiber-based systems. Entangled photons also allow automatic source verification, Kwiat said.

Microelectronics researchers at the University of Illinois have developed a low-loss, wide-bandwidth microelectromechanical systems (MEMS) switch that can be integrated with existing technologies for high-speed electronics.

The new low-voltage switch could be used in switching networks for phased-array radars, multibeam satellite communications systems, and wireless applications.

"The switch has a tiny metal pad that can move up or down in less than 25 microseconds," said Milton Feng, the Nick Holonyak, Jr., Professor of Electrical and Computer Engineering. "This simple configuration provides a very low insertion loss of less than 0.1 dB, and the metal-to-metal contact has the inherently wide-band response of a larger, more typical mechanical switch."

The switches are fabricated in the Micro and Nanotechnology Laboratory using standard MEMS processing techniques. To create the unique metal pull-down pad, Feng and graduate students David Becher, Richard Chan, and Shyh-Chiang Shen first deposit a thin layer of gold on a sacrificial layer of photosensitive material. Then they dissolve the substrate, pick up the pad, and place it in position on the switch.

The metal pad–about 150 microns wide and 200 microns long–is supported at the four corners by serpentine cantilevers, which allow mechanical movement up and down.

"When in the ‘up’ position, the metal pad forms a bridge that spans a segment of the coplanar waveguide and allows the signal to pass through," Feng said. "But an applied voltage will pull the pad down into contact with the signal line, creating a short circuit that blocks the signal transmission."

In reliability tests, the switches have demonstrated lifetimes in excess of 780 million switching cycles. To further enhance the reliability, the researchers are attempting to lower the actuation voltage to less than 10 volts.

"For any device to be used in a practical application it must be reliable," Feng said. "Our results show that good reliability is possible with low voltage operation."

The Defense Advanced Research Projects Agency funded the work.

Laura Schmitt & Tina Prow

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Ahn Sang-Gyeun’s "Freewill"–a bicycle-scooter hybrid that transforms itself from one human-powered vehicle to another with a simple 90-degree rotation of the frame–could move from prototype to the production line as early as year’s end.

While finishing up his graduate degree in industrial design at the University of Illinois last year, Ahn won the $15,000 grand-prize in the Sixth International Bicycle Design Competition. The competition was sponsored by the Department of Industrial Technology, Ministry of Economic Affairs of the Republic of China, and organized by the Taiwan Bicycle Industry R&D Center. Endorsed by the International Council of Societies of Industrial Design, the competition received 1,131 entries from 58 countries.

As a designer, "I am interested in cultural differences–using the same object for different purposes," he said. "In my country (South Korea), the bicycle is used mainly for transportation; here, it is used for exercise."

Ahn said he got the idea for the novel "convertible" after noticing the proliferation of foot-powered scooters on campus sidewalks and streets the past couple of years. As a cash-strapped graduate student, "I thought, how about designing just one model, so people could buy one instead of two? It’s too expensive to have both. So, I thought, why not?"

The one-speed hybrid features a front T-bar construction, similar to most scooters. When the base is flipped to function as a scooter platform, the pedals and seat retract, and a rear wheel flips into place.

If his design goes into production, the scooter-bike will be marketed first in Southeast Asian markets, he said. If successful there, it could be manufactured and marketed in the United States sometime down the road.

Ahn (pictured below) now is a faculty member in industrial design at Auburn University.

Stephen A. Boppart, a professor of electrical and computer engineering and of bioengineering at the University of Illinois, was chosen as one of the world’s 100 Top Young Innovators (TR100) by Technology Review. The world’s oldest magazine on technology, Technology Review is published by the Massachusetts Institute of Technology.

The TR100 consists of people under age 35 whose innovative work in technology and business has a profound impact on today’s world. Nominees are recognized for their contribution in transforming the nature of technology in such industries as biotechnology, computing, energy, manufacturing, medicine, nanotechnology, telecommunications, and transportation.

Boppart has helped to dramatically improve the resolution of optical coherence tomography (OCT), an imaging technique useful for medical diagnostics–such as the detection and removal of tumors at the cellular level. Similar in operation to ultrasound, OCT works by focusing a beam of near-infrared light (like that used in CD players) into tissue and measuring the intensity and position of the resulting reflections.

Boppart also converted the imaging hardware into a handheld probe that looks like a laser pointer. A version of this device is being used by surgeons at Brigham and Women’s Hospital in Boston to see through a patient’s skin and through internal tissue before making an incision.

Seichi "Bud" Konzo’s 1992 book, The Quiet Indoor Revolution, was on reading lists this year as the nation marked the centennial of the first industrial air conditioner system. Although Willis Haviland Carrier is regarded as "the father of air conditioning," air conditioning was still a rare commodity in 1936, when the Dust Bowl swirled in the Plains states.

In his book, Konzo noted that the temperature in Central Illinois that summer surpassed 100 degrees Fahrenheit for 17 consecutive days. But as people struggled to cope with the heat and humidity, Konzo managed to keep his cool in one of the first air-cooled houses in North America.

Konzo, along with his wife and daughter, were tenants of University of Illinois Research Residence No. 1, a two-story Colonial-style home used for heating and cooling studies. A professor of mechanical engineering, Konzo supervised some of the earliest ongoing experiments for residential central air conditioning strategies and systems.

"In retrospect the early start in residential cooling was bold and reckless," Konzo wrote in his book. "We were treading new ground, and because we had no preconceived ideas of what might work, we tried almost every conceivable form of cooling that showed some sign of being practical."

Some of those ideas were downright "absurd" by today’s standards, he noted. They included placing a unit the size of a refrigerator–equipped with fans and filled with ice–in the middle of the living room. Another test involved dumping two tons of ice daily into a basement storage chamber; cooled air was then distributed by means of a separate unit installed in the return-air duct of the home’s forced-air furnace system.

Konzo died in 1992. Researchers at the university’s Building Research Council still use his work as a foundation for current research focusing on indoor air quality and humidity and moisture control.

Steve Sullivan (MSEE ‘91, PhD ‘97) took home an Oscar for his computer vision work in Pearl Harbor. A principal engineer at Industrial Light + Magic (ILM) in San Rafael, Calif., Sullivan co-invented the matchmoving and tracking software used to create realistic shots of the Japanese aerial attack in the movie.

After filmmakers flew over Pearl Harbor shooting footage of the landscape below, a team of specialists known as matchmovers used the Motion and Structure Recovery System (MARS) to digitally remove the modern buildings and replace them with buildings that were there on December 7, 1941. The result: accurate and authentic-looking footage.

Employing sophisticated algorithms, MARS has a rich set of user-interface tools that enable animators to automatically reconstruct detailed geometric models (such as terrain). They can also use MARS to figure out the camera position and where objects are in a shot. MARS also enables animators to manually manipulate a computer scene directly.

MARS has been used on eight other pictures, including The Mummy Returns, A.I. Artificial Intelligence, Jurassic Park III, Planet of the Apes, Harry Potter and the Sorcerer’s Stone, E.T. The Extra-Terrestrial re-release, Star Wars: Episode II Attack of the Clones, and Minority Report.

Sullivan and his MARS co-creator received a 2001 Academy Award for Technical Achievement for their innovative software system from the Academy of Motion Picture Arts and Sciences. These awards recognize accomplishments that contribute to the progress of the industry.

The research and development work that Sullivan does has direct ties to his electrical engineering doctoral research. For his thesis, Sullivan focused on automatically building models of real-world objects using just a few pictures–understanding what surface representations were helpful and developing procedures to calibrate the pictures to build the models.

Article and photo provided by Laura Schmitt. Read more about Steve Sullivan in the ECE Alumni News, Summer 2002, at www.ece.uiuc.edu/news/pubindex.html.