Superconducting Amplifier Designed to Study the Universe

July 18, 2012

Technology

The new amplifier consists of a superconducting material (niobium titanium nitride) coiled into a double spiral 16 millimeters in diameter. Image credit: NASA/JPL-Caltech

Designed by scientists at the California Institute of Technology and at NASA’s Jet Propulsion Laboratory, a new amplifier using titanium nitride and niobium titanium nitride will help researchers study the universe.

Researchers at NASA’s Jet Propulsion Laboratory and the California Institute of Technology, both in Pasadena, have developed a new type of amplifier for boosting electrical signals. The device can be used for everything from studying stars, galaxies and black holes to exploring the quantum world and developing quantum computers.

“This amplifier will redefine what it is possible to measure,” said Jonas Zmuidzinas, chief technologist at JPL, who is Caltech’s Merle Kingsley Professor of Physics and a member of the research team.

An amplifier is a device that increases the strength of a weak signal. “Amplifiers play a basic role in a wide range of scientific measurements and in electronics in general,” said Peter Day, a principal scientist at JPL and a visiting associate in physics at Caltech. “For many tasks, current amplifiers are good enough. But for the most demanding applications, the shortcomings of the available technologies limit us.”

One of the key features of the new amplifier is that it incorporates superconductors-materials that allow an electric current to flow with zero resistance when lowered to certain temperatures. For their amplifier, the researchers are using titanium nitride and niobium titanium nitride, which have just the right properties to allow the pump signal to amplify the weak signal.

Although the amplifier has a host of potential applications, the reason the researchers built the device was to help them study the universe. The team built the instrument to boost microwave signals, but the new design can be used to build amplifiers that help astronomers observe in a wide range of wavelengths, from radio waves to X-rays.

“It’s hard to predict what all of the applications are going to end up being, but a nearly perfect amplifier is a pretty handy thing to have in your bag of tricks,” Zmuidzinas said. And by creating their new device, the researchers have shown that it is indeed possible to build an essentially perfect amplifier. “Our instrument still has a few rough edges that need polishing before we would call it perfect, but we think our results so far show that we can get there.”

The team recently described the new instrument in the journal Nature Physics.

In addition to Zmuidzinas and Day, the other authors of the paper are Byeong Ho Eom of Caltech, and Henry LeDuc of JPL. This research was supported by NASA, the Keck Institute for Space Studies, and the JPL Research and Technology Development program. JPL is managed by Caltech for NASA.

Source: Priscilla Vega, Jet Propulsion Laboratory

Image: NASA/JPL-Caltech

Macroporous Silicon and Pyrolyzed Polyacrylonitrile form High Performance Anodes

July 18, 2012

Technology

Micronwide pores in silicon give the material room to expand when soaking in lithium ions in a rechargeable battery, according to researchers at Rice University and Lockheed Martin. The scientists are developing the material to replace graphite as the anode in common batteries for commercial electronics and perhaps even electric vehicles. (Credit: Madhuri Thakur/Rice University)

By detaching a freestanding macroporous silicon film from the underlying bulk silicon and combining it with pyrolyzed polyacrylonitrile, researchers have found a way to make multiple high-performance anodes from a single silicon wafer.

Researchers at Rice University and Lockheed Martin reported this month that they’ve found a way to make multiple high-performance anodes from a single silicon wafer. The process uses simple silicon to replace graphite as an element in rechargeable lithium-ion batteries, laying the groundwork for longer-lasting, more powerful batteries for such applications as commercial electronics and electric vehicles.

The work led by Sibani Lisa Biswal, an assistant professor of chemical and biomolecular engineering at Rice, and lead author Madhuri Thakur, a Rice research scientist, details the process by which Swiss cheese-like silicon “sponges” that store more than four times their weight in lithium can be electrochemically lifted off of wafers.

The research was reported online this month in the American Chemical Society journal Chemistry of Materials.

Silicon – one of the most common elements on Earth – is a candidate to replace graphite as the anode in batteries. In a previous advance by Biswal and her team, porous silicon was found to soak up 10 times more lithium than graphite.

Because silicon expands as it absorbs lithium ions, the sponge-like configuration gives it room to grow internally without degrading the battery’s performance, the researchers reported. The promise that silicon sponges, with pores a micron wide and 12 microns deep, held for batteries was revealed in 2010 at Rice’s Buckyball Discovery Conference by Thakur, Biswal, their Rice colleague Michael Wong, a professor of chemical and biomolecular engineering and of chemistry, and Steven Sinsabaugh, a Lockheed Martin Fellow. But even then Thakur saw room for improvement as the solid silicon substrate served no purpose in absorbing lithium.

A Swiss cheese-like silicon sponge lifts off from a wafer in a process developed by researchers at Rice University and Lockheed Martin who hope to replace graphite anodes in lithium-ion batteries with a material that has a larger capacity for lithium. (Credit: Madhuri Thakur/Rice University)

In the new work, they discovered the electrochemical etching process used to create the pores can also separate the sponge from the substrate, which is then reused to make more sponges. The team noted that at least four films can be drawn from a standard 250-micron-thick wafer. Removing the sponge from the silicon substrate also eliminates a limiting factor to the amount of lithium that can be stored.

The team also found a way to make the pores 50 microns deep. Once lifted from the wafer, the sponges, now open at the top and bottom, were enhanced for conductivity by soaking them in a conductive polymer binder, pyrolyzed polyacrylonitrile (PAN).

The product was a tough film that could be attached to a current collector (in this case, a thin layer of titanium on copper) and placed in a battery configuration. The result was a working lithium-ion battery with a discharge capacity of 1,260 milliamp-hours per gram, a capability that should lead to batteries that last longer between charges.

A sponge formed from a solid wafer of silicon helps the material realize its potential to hold 10 times the amount of lithium ions than current materials used in rechargeable batteries. The material was developed by Rice University and Lockheed Martin. (Credit: Madhuri Thakur/Rice University)

The researchers compared batteries using their film before and after the PAN-and-bake treatment. Before, the batteries started with a discharge capacity of 757 milliamp-hours per gram, dropped rapidly after the second charge-discharge cycle and failed completely by cycle 15. The treated film increased in discharge capacity over the first four cycles – typical for porous silicon, the researchers said – and the capacity remained consistent through 20 cycles.

The researchers are investigating techniques that promise to vastly increase the number of charge-discharge cycles, a critical feature for commercial applications in which rechargeable batteries are expected to last for years.

Co-authors of the paper are postdoctoral researcher Roderick Pernites, alumnus Naoki Nitta and Lockheed Martin researcher Mark Isaacson.

The work was supported by the Lockheed Martin Advanced Nanotechnology Center of Excellence at Rice.

Source: Mike Williams, Rice University News

Images: Madhuri Thakur/Rice University

Self-Assembling Polymer Molecules Create Complex Microchip Structures

July 19, 2012

Technology

An artist’s representation of the structures produced by this self-assembly method shows a top-down view, with the posts produced by electron-beam lithography shown in blue, and the resulting self-assembled shapes shown in white. Image: Yan Liang

Using tiny posts to guide the patterning of self-assembling polymer molecules, researchers at MIT developed a new technique to create perfect square and rectangular patterns of tiny polymer wires on microchips.

Researchers at MIT have developed a new approach to creating the complex array of wires and connections on microchips, using a system of self-assembling polymers. The work could eventually lead to a way of making more densely packed components on memory chips and other devices.

The new method — developed by MIT visiting doctoral student Amir Tavakkoli of the National University of Singapore, along with two other graduate students and three professors in MIT’s departments of Electrical Engineering and Computer Science (EECS) and Materials Science and Engineering (DMSE) — is described in a paper published in the journal Advanced Materials.

The process is closely related to a method the same team described last month in a paper in Science, which makes it possible to produce three-dimensional configurations of wires and connections using a similar system of self-assembling polymers.

In the new paper, the researchers describe a system for producing arrays of wires that meet at right angles, forming squares and rectangles. While these shapes are the basis for most microchip circuit layouts, they are quite difficult to produce through self-assembly. When molecules self-assemble, explains Caroline Ross, the Toyota Professor of Materials Science and Engineering and a co-author of the papers, they have a natural tendency to create hexagonal shapes — as in a honeycomb or an array of soap bubbles between sheets of glass.

For example, an array of tiny ball bearings in a box “tends to give a hexagonal symmetry, even though it’s in a square box,” Ross says. “But that’s not what circuit designers want. They want patterns with 90-degree angles” — so overcoming that natural tendency was essential to producing a useful self-assembling system, she says.

The team’s solution creates an array of tiny posts on the surface that guides the patterning of the self-assembling polymer molecules. This turns out to have other advantages as well: In addition to producing perfect square and rectangular patterns of tiny polymer wires, the system also enables the creation of a variety of shapes of the material itself, including cylinders, spheres, ellipsoids and double cylinders. “You can generate this astounding array of features,” Ross says, “with a very simple template.”

Karl Berggren, an associate professor of electrical engineering at MIT and a co-author of the paper, explains that these complex shapes are possible because “the template, which is coated so as to repel one of the polymer components, causes a lot of local strain on the pattern. The polymer then twists and turns to try to avoid this strain, and in so doing rearranges on the surface. So we can defeat the polymer’s natural inclinations, and make it create much more interesting patterns.”

This system can also produce features, such as arrays of holes in the material, whose spacing is much closer than what can be achieved using conventional chip-making methods. That means it can produce much more closely packed features on the chip than today’s methods can create — an important step in the ongoing efforts to pack more and more electronic components onto a given microchip.

“This new technique can produce multiple [shapes or patterns] simultaneously,” Tavakkoli says. It can also make “complex patterns, which is an objective for nanodevice fabrication,” with fewer steps than current processes. Fabricating a large area of complex circuitry on a chip using electron-beam lithography “could take several months,” he says. By contrast, using the self-assembling polymer method would take only a few days.

That’s still far too long for manufacturing a commercial product, but Ross explains that this step needs to be done only once to create a master pattern, which can then be used to stamp a coating on other chips in a very rapid fabrication process.

The technique could extend beyond microchip fabrication as well, Ross says. For example, one approach to the quest to pack ever-greater amounts of data onto magnetic media such as computer hard disks is to use a magnetic coating with a very fine pattern stamped into it, precisely defining the areas where each bit of data is to be stored. Such fine patterning could potentially be created using this self-assembly method, she says, and then stamped onto the disks.

Craig Hawker, a professor of chemistry and biochemistry at the University of California at Santa Barbara who was not involved in this work, says, “There is a growing need and requirement for industry to find an alternative to traditional photolithography for the fabrication of cutting-edge microelectronic devices. This work represents a pivotal achievement in this area and clearly demonstrates that structures once considered impossible to achieve by a self-assembly strategy can now be prepared with a high degree of fidelity.”

Tavakkoli and Ross’ colleagues in this work are DMSE doctoral students Adam Hannon and Kevin Gotrik, DMSE professor Alfredo Alexander-Katz and EECS professor Karl Berggren. The research, which included work at MIT’s Nanostructures Laboratory and Scanning-Electron-Beam Lithography facility, was funded by the Semiconductor Research Corporation, the Center on Functional Engineered Nano Architectonics, the National Resources Institute, the Singapore-MIT Alliance, the National Science Foundation, the Taiwan Semiconductor Manufacturing Company and Tokyo Electron.

Source: David L. Chandler, MIT News Office

Image: Yan Liang

Engineers to Develop a Smart Suit That Improves Physical Endurance

July 20, 2012

Technology

The new wearable system would be made from soft, stretchable, assistive devices, which would help improve physical endurance for soldiers in the field. Courtesy of the Wyss Institute

Engineers at the Wyss Institute are working on a smart suit that helps improve physical endurance for soldiers in the field, delaying the onset of fatigue and potentially improving the body’s resistance to injuries when carrying heavy loads.

The Wyss Institute for Biologically Inspired Engineering at Harvard University today announced that it has received a $2.6 million contract from the Defense Advanced Research Projects Agency (DARPA) to develop a smart suit that helps improve physical endurance for soldiers in the field.

The novel wearable system would potentially delay the onset of fatigue, enabling soldiers to walk longer distances, and also potentially improve the body’s resistance to injuries when carrying heavy loads.

Lightweight, efficient, and nonrestrictive, the proposed suit will be made from soft wearable assistive devices that integrate several novel Wyss technologies. One is a stretchable sensor that would monitor the body’s biomechanics without the need for the typical rigid components that often interfere with motion. The system could potentially detect the onset of fatigue. Additionally, one of the technologies in the suit may help the wearer maintain balance by providing low-level mechanical vibrations that boost the body’s sensory functions.

The new smart suit will be designed to overcome several of the problems typically associated with current wearable systems, including their large power requirements and rigid overall structures, which restrict normal movement and can be uncomfortable.

Although the DARPA project is focused on assisting and protecting soldiers in the field, the technologies being developed could have many other applications as well. For instance, similar soft-wearable devices hold the potential to increase endurance in the elderly and help improve mobility for people with physical disabilities.

Conor Walsh, assistant professor of mechanical and biomedical engineering at the Harvard School of Engineering and Applied Sciences (SEAS) and Wyss core faculty member, will lead this interdisciplinary program. The program will include collaborations with core faculty member Rob Wood and Wyss Technology Development Fellow Yong-Lae Park, for developing soft sensor technologies, and with core faculty member George Whitesides, for developing novel soft interfaces between the device and the wearer. Wood is also the Gordon McKay Professor of Electrical Engineering at the SEAS, and Whitesides is also the Woodford L. and Ann A. Flowers University Professor at Harvard. Sang-bae Kim, assistant professor of mechanical engineering at the Massachusetts Institute of Technology, and Ken Holt, associate professor at Boston University’s College of Health and Rehabilitation Sciences, will also play key roles on the project.

Also working on the project will be several members of the Wyss Advanced Technology Team who will oversee the testing of prototypes in the Wyss Institute’s biomechanics lab, using motion-capture capabilities that can measure the impact of the suit on specific muscles and joints.

“This project is a excellent example of how Wyss researchers from different disciplines work side by side with experts in product development to develop solutions to difficult problems that might not otherwise be possible,” said Donald Ingber, Wyss founding director and the Judah Folkman Professor of Vascular Biology in the Department of Pathology.

Source: Twig Mowatt, Wyss Institute Communications; Harvard Gazette

Image: Wyss Institute