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Nano News & Events
Next Big FutureNanofabrication of a silicon chip with all quantum info processorNext Big Future"We can make a lot of these nanodevices easily by copying our design hundreds or thousands of times, without much additional effort or cost," said Carsten Schuck, post-doctoral researcher and lead author of the paper. "It's similar to what people in ...New chip unlocks computer potentialYale Daily News (blog)all 2 news articles »
The News JournalUD invests big in science of the very smallThe News JournalUniversity of Delaware's new 8,500-square-foot Nanofabrication Facility, or UDNF, is one of about 30 academic labs of its caliber in the country and features some of the most advanced equipment in the Mid-Atlantic. Yet the facility will be accessible ...
Since the 1960s, computer chips have been built using a process called photolithography. But in the past five years, chip features have gotten smaller than the wavelength of light, which has required some ingenious modifications of photolithographic processes. Keeping up the rate of circuit miniaturization that we’ve come to expect — as predicted by Moore’s Law — will eventually require new manufacturing techniques. Block copolymers, molecules that spontaneously self-assemble into useful shapes, are one promising alternative to photolithography. In a new paper in the journal Nature Communications, MIT researchers describe the first technique for stacking layers of block-copolymer wires such that the wires in one layer naturally orient themselves perpendicularly to those in the layer below. The ability to easily produce such “mesh structures” could make self-assembly a much more practical way to manufacture memory, optical chips, and even future generations of computer processors. “There is previous work on fabricating a mesh structure — for example our work,” says Amir Tavakkoli, a postdoc in MIT’s Research Laboratory of Electronics and one of three first authors on the new paper. “We used posts that we had fabricated by electron-beam lithography, which is time consuming. But here, we don’t use the electron-beam lithography. We use the first layer of block copolymer as a template to self-assemble another layer of block copolymer on top of it.” Tavakkoli’s co-first-authors on the paper are Sam Nicaise, a graduate student in electrical engineering, and Karim Gadelrab, a graduate student in materials science and engineering. The senior authors are Alfredo Alexander-Katz, the Walter Henry Gale Associate Professor of Materials Science and Engineering; Caroline Ross, the Toyota Professor of Materials Science and Engineering; and Karl Berggren, a professor of electrical engineering. Unhappy couples Polymers are long molecules made from basic molecular units strung into chains. Plastics are polymers, and so are biological molecules like DNA and proteins. A copolymer is a polymer made by joining two different polymers. In a block copolymer, the constituent polymers are chosen so that they’re chemically incompatible with each other. It’s their attempts to push away from each other — both within a single polymer chain and within a polymer film — that causes them to self-organize. In the MIT researchers’ case, one of the constituent polymers is carbon-based, the other silicon-based. In their efforts to escape the carbon-based polymer, the silicon-based polymers fold in on themselves, forming cylinders with loops of silicon-based polymer on the inside and the other polymer bristling on the outside. When the cylinders are exposed to an oxygen plasma, the carbon-based polymer burns away and the silicon oxidizes, leaving glass-like cylinders attached to a base. To assemble a second layer of cylinders, the researchers simply repeat the process, albeit using copolymers with slightly different chain lengths. The cylinders in the new layer naturally orient themselves perpendicularly to those in the first. Chemically treating the surface on which the first group of cylinders are formed will cause them to line up in parallel rows. In that case, the second layer of cylinders will also form parallel rows, perpendicular to those in the first. But if the cylinders in the bottom layer are allowed to form haphazardly, snaking out into elaborate, looping patterns, the cylinders in the second layer will maintain their relative orientation, creating their own elaborate, but perpendicular, patterns. The orderly mesh structure is the one that has the most obvious applications, but the disorderly one is perhaps the more impressive technical feat. “That’s the one the materials scientists are excited about,” Nicaise says. Whys and wherefores Glass-like wires are not directly useful for electronic applications, but it might be possible to seed them with other types of molecules, which would make them electronically active, or to use them as a template for depositing other materials. The researchers hope that they can reproduce their results with more functional polymers. To that end, they had to theoretically characterize the process that yielded their results. “We use computer simulations to understand the key parameters controlling the polymer orientation,” Gadelrab says. What they found was that the geometry of the cylinders in the bottom layer limited the possible orientations of the cylinders in the upper layer. If the walls of the lower cylinders are too steep to permit the upper cylinders from fitting in comfortably, the upper cylinders will try to find a different orientation. It’s also important that the upper and lower layers have only weak chemical interactions. Otherwise, the upper cylinders will try to stack themselves on top of the lower ones like logs on a pile. Both of these properties — cylinder geometry and chemical interaction — can be predicted from the physics of polymer molecules. So it should be possible to identify other polymers that will exhibit the same behavior. According to Patrick Theofanis, an engineer at the chip manufacturer Intel, the nanocylinders themselves are less interesting than the spaces between them. “In general, the ability to pattern square holes is very useful for us,” he says. “If you think of the back end of our chips, we have the back-end wiring, and then you have the interconnect layers between those back-end metal layers, and that’s where you’d like to be able to punch through holes and connect one layer to the next one. It’s an attractive technology because the aspect ratio is very tunable in the way that they’ve done their scheme.” The research was funded by the National Science Foundation and the Taiwan Semiconductor Manufacturing Corporation.
FLEXcon Shares Insights on Developments and Safety Guidelines in Nanotechnology - Business Wire (press release)
FLEXcon Shares Insights on Developments and Safety Guidelines in NanotechnologyBusiness Wire (press release)The event brought together members of NENA, an association committed to sharing information, energy, and ideas for fostering nanotechnology innovation, commercialization and economic prosperity to benefit both the people and environment of New ...and more »
Two MIT researchers have developed a thin-film material whose phase and electrical properties can be switched between metallic and semiconducting simply by applying a small voltage. The material then stays in its new configuration until switched back by another voltage. The discovery could pave the way for a new kind of “nonvolatile” computer memory chip that retains information when the power is switched off, and for energy conversion and catalytic applications. The findings, reported in the journal Nano Letters in a paper by MIT materials science graduate student Qiyang Lu and associate professor Bilge Yildiz, involve a thin-film material called a strontium cobaltite, or SrCoOx. Usually, Yildiz says, the structural phase of a material is controlled by its composition, temperature, and pressure. “Here for the first time,” she says, “we demonstrate that electrical bias can induce a phase transition in the material. And in fact we achieved this by changing the oxygen content in SrCoOx.” “It has two different structures that depend on how many oxygen atoms per unit cell it contains, and these two structures have quite different properties,” Lu explains. One of these configurations of the molecular structure is called perovskite, and the other is called brownmillerite. When more oxygen is present, it forms the tightly-enclosed, cage-like crystal structure of perovskite, whereas a lower concentration of oxygen produces the more open structure of brownmillerite. The two forms have very different chemical, electrical, magnetic, and physical properties, and Lu and Yildiz found that the material can be flipped between the two forms with the application of a very tiny amount of voltage — just 30 millivolts (0.03 volts). And, once changed, the new configuration remains stable until it is flipped back by a second application of voltage. Strontium cobaltites are just one example of a class of materials known as transition metal oxides, which is considered promising for a variety of applications including electrodes in fuel cells, membranes that allow oxygen to pass through for gas separation, and electronic devices such as memristors — a form of nonvolatile, ultrafast, and energy-efficient memory device. The ability to trigger such a phase change through the use of just a tiny voltage could open up many uses for these materials, the researchers say. Previous work with strontium cobaltites relied on changes in the oxygen concentration in the surrounding gas atmosphere to control which of the two forms the material would take, but that is inherently a much slower and more difficult process to control, Lu says. “So our idea was, don’t change the atmosphere, just apply a voltage.” “Voltage modifies the effective oxygen pressure that the material faces,” Yildiz adds. To make that possible, the researchers deposited a very thin film of the material (the brownmillerite phase) onto a substrate, for which they used yttrium-stabilized zirconia. In that setup, applying a voltage drives oxygen atoms into the material. Applying the opposite voltage has the reverse effect. To observe and demonstrate that the material did indeed go through this phase transition when the voltage was applied, the team used a technique called in-situ X-ray diffraction at MIT’s Center for Materials Science and Engineering. The basic principle of switching this material between the two phases by altering the gas pressure and temperature in the environment was developed within the last year by scientists at Oak Ridge National Laboratory. “While interesting, this is not a practical means for controlling device properties in use,” says Yildiz. With their current work, the MIT researchers have enabled the control of the phase and electrical properties of this class of materials in a practical way, by applying an electrical charge. In addition to memory devices, the material could ultimately find applications in fuel cells and electrodes for lithium ion batteries, Lu says. “Our work has fundamental contributions by introducing electrical bias as a way to control the phase of an active material, and by laying the basic scientific groundwork for such novel energy and information processing devices,” Yildiz adds. In ongoing research, the team is working to better understand the electronic properties of the material in its different structures, and to extend this approach to other oxides of interest for memory and energy applications, in collaboration with MIT professor Harry Tuller. José Santiso, the nanomaterials growth division leader at the Catalan Institute of Nanoscience and Nanotechnology in Barcelona, Spain, who was not involved in this research, calls it “a very significant contribution” to the study of this interesting class of materials, and says “it paves the way for the application of these materials both in solid state electrochemical devices for the efficient conversion of energy or oxygen storage, as well as in possible applications in a new kind of memory devices.” The work was supported by the National Science Foundation.
Two simple room-temperature and solution-based chemical processes are used to realize a new class of silver nano-network-based devices.
Nature Nanotechnology, an online manual, has published a report outlining the concept of combining nanoparticles with molecular and photodynamic therapies in order to deliver anticancer treatment, and...
A research team from the University of Amsterdam's Van’t Hoff Institute for Molecular Sciences (HIMS) has discovered a new method to achieve improved catalytic performance. In this method,...
Developing novel materials from the atoms up goes faster when some of the trial and error is eliminated. A new Rice University and Montreal Polytechnic study aims to do that for graphene and boron nitride hybrids.