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Madīnat Sittah Uktūbar, Egypt

News Article
Site: http://news.mit.edu/topic/mitmaterials-science-rss.xml

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 SrCoO . 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 SrCoO .” “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.


News Article
Site: http://phys.org/nanotech-news/

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 SrCoO . 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 SrCoO ." "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." Explore further: Transistor made from vanadium dioxide could function as smart window for blocking infrared light More information: Qiyang Lu et al. Voltage-Controlled Topotactic Phase Transition in Thin-Film SrCoO Monitored by In Situ X-ray Diffraction , Nano Letters (2016). DOI: 10.1021/acs.nanolett.5b04492


News Article
Site: http://www.nature.com/nature/current_issue/

Questions are swirling over the future of Egypt’s first science city, after the death of the Nobel laureate who made the project his legacy. The Zewail City of Science and Technology, a campus outside Cairo comprising a non-profit university and several research institutes, is named for the man who spearheaded it: Egyptian-born US chemist Ahmed Zewail, the first Arab to win a science Nobel. But Zewail’s death at the age of 70 last week raises fresh doubts about the research hub's already precarious finances. The institute had relied heavily on Zewail’s star name and contacts to attract the support of scientific luminaries and millions of dollars in donations and government loans. It is now running out of money, has not yet raised enough cash to support a planned move to a new campus and will probably have to rely on more state support, say researchers working there. “Fundraising has always been a challenge, and I think it is likely to be affected by the loss of Dr Zewail in the short term,” says Sherif El-Khamisy, a molecular biologist at the University of Sheffield, UK, who is also director of Zewail City’s Center for Genomics. “But the logistical support envisaged from the state is expected to override the initial fear or uncertainty.” Uncertainty has plagued Zewail City since its inception. While working at the California Institute of Technology in Pasadena, Zewail proposed in 1999 to found the university and technology hub near Cairo as a flagship science project, essential for Egypt’s research development. But it was not until 2011 that the institute launched — a delay that Zewail has ascribed to political instability and bureaucracy. The young university was quickly plunged into controversy, after Egypt's first not-for-profit private research institution, Nile University — also outside Cairo — argued that it owned some of the buildings gifted to the science city. Nile University ultimately won the legal dispute — although it has allowed researchers from Zewail City to stay on in its buildings until a new campus is complete. Zewail City began accepting students in 2013; it currently has more 500 students and 150 academic professors and researchers. The first class of students will graduate next year, many of whom have received scholarships to cover their tuition fees. The project’s new campus is expected to be finished in 2019, at a cost of at least US$450 million; a first phase should be complete by July 2017, when many faculty and students are to move there. But Zewail City hasn’t raised enough money to finish even its first phase, says Sherif Fouad, a spokesperson for the institute. To pay for scholarships and campus construction, it has almost used up the 700 million Egyptian pounds (around US$80 million) raised from donors; its other funding comes in the form of a 1-billion-Egyptian-pound loan from the ministry of defence, which ultimately must be paid back. A shaky economy and the widely expected devaluation of Egypt’s currency is not helping matters. El-Khamisy and others affiliated with the institute say they are hopeful that it will survive — not least because it has the verbal backing of Egypt’s president, Abdel Fattah el-Sisi. In a speech on 6 August after Zewail’s death, el-Sisi asked Egyptians to continue to donate to the city, but vowed that Egypt’s armed forces — whose engineers are building the new campus — would finish construction even if no more money comes through. “The president’s speech was very reassuring for us all that Zewail City remains a priority for the government and is considered one of Egypt’s national projects,” says Fouad. It is likely that Egypt’s government will ultimately need to step in with support, says Salah Obayya, a physicist who is currently acting chairman of Zewail City until a replacement for Zewail is elected. How the state deals with that intervention could affect whether the institute can maintain the support of scientists whom Zewail sought to attract, says Ibrahim el-Sherbiny, joint director of the institute’s Center for Materials Science. “If they feel the reassurance on the ground, they will remain and attract others because they loved Dr Zewail, and I am sure they would love to support him after his death,” he says. Zewail City enjoys an unusual autonomy: unlike other Egyptian state-sponsored institutions, it has been granted a decree that allows the campus to outline its own structure and governance, guaranteeing its independence from the education ministry. Obayya says that he does not expect such autonomy to be affected by closer government intervention. At a meeting on 8 August, Zewail City’s board of directors vowed that their pioneer’s “national mission” would carry on. British-Egyptian cardiac surgeon Magdi Yacoub of Imperial College London is widely tipped to take Zewail’s place at the head of the project, says Fouad. “If Sir Magdi Yacoub is chosen to run the city, it will give the project the needed stability to soldier on,” says Sherif Sedky, a physicist and former academic president of Zewail City, who is now provost of the American University in Cairo.


News Article
Site: http://phys.org/nanotech-news/

Materials Processing Center (MPC)-Center for Materials Science and Engineering (CMSE) Summer Scholar Justin Cheng worked this summer in MIT professor of electrical engineering Karl K. Berggren's Quantum Nanostructures and Nanofabrication Group to develop specialized techniques for forming these patterns in gold on silicon. "Ideally, we'd want to be able to get arrays of gold nanoparticles to be completely ordered," says Cheng, a rising senior at Rutgers University. "My work deals with the fundamentals of how to write a pattern using electron-beam lithography, how to deposit the gold, and how to heat up the substrate so we can get completely regular arrays of particles," Cheng explains. In MIT's NanoStructures Laboratory, Cheng wrote code to produce a pattern that will guide the dewetting of a thin gold film into nanoparticles, examined partially ordered grids with an electron microscope, and worked in a clean room to develop a polymer resist, spin coat the resist onto samples, and plasma clean the samples. He is part of a team that includes graduate student Sarah Goodman and postdoctoral associate Mostafa Bedewy. He was also assisted by the NanoStructures Lab manager James Daley. "Plasmons are collective oscillations of the free-electron density at the surface of a material, and they give metal nanostructures amazing properties that are very useful in applications like sensing, optics and various devices," Goodman explained in a presentation to Summer Scholars in June. "Plasmonic arrays are very good for visible displays, for example, because their color can be tuned based on size and geometry." This multi-step fabrication process begins with spin coating hydrogen silsesquioxane (HSQ), which is a special electron-beam resist, or mask, onto a silicon substrate. Cheng worked on software used to write a pattern onto the resist through electron-beam lithography. Unlike some resists, HSQ becomes more chemically resistant as you expose it to electron beams, he says. The entire substrate is about 1 centimeter by 1 centimeter, he notes, and the write area is about 100 microns (or 0.0001 centimeter) wide. After the electron-beam lithography step, the resist is put through an aqueous (water-based) developer solution of sodium hydroxide and sodium chloride, which leaves behind an ordered array of posts on top of the silicon layer. "When we put the sample in the developer solution, all of the less chemically resistant areas of the HSQ mask come off, and only the posts remain," Cheng says. Then, Daley deposits a gold layer on top of the posts with physical vapor deposition. Next, the sample is heat treated until the gold layer decomposes into droplets that self-assemble into nanoparticles guided by the posts. A key underlying materials science phenomenon at work in this self-assembly, Cheng says, is known as solid-state dewetting. "Self-assembly is a process where you apply certain conditions to a material that allow it to undergo a transformation over a large area. So it's a very efficient patterning technique," Goodman explains. Because of repulsive interaction between the silicon and gold layers, the gold tends to form droplets, which can be coaxed into patterns around the posts. The Berggren group is working collaboratively with Carl V. Thompson, the Stavros Salapatas Professor of Materials Science and Engineering and the director of the Materials Processing Center, who is an expert in solid-state dewetting. Using a scanning electron microscope, Cheng examines these patterns to determine their quality and consistency. "The gold naturally forms droplets because there is a driving force for it to decrease the surface area it shares with the silicon. It doesn't look completely ordered but you can see beginnings of some order in the dewetting," he says, while showing an SEM image on a computer. "[In] other pictures you can clearly see the beginnings of patterning." "When we take the posts and we make them closer together, you can see that the gold likes to dewet into somewhat regular patterns. These aren't completely regular in all cases, but for certain post sizes and spacings, we start to see regular arrays. Our goal is to successfully fabricate a plasmonic array of ordered, monodisperse [equally sized] gold nanoparticles," Cheng says. Goodman notes that Thompson's group has demonstrated exquisite control over dewetting in single crystalline films at the micron scale, but the Berggren group hopes to extend this control down to the nanoscale. "This will be a really key result if we're able to bring this dewetting that's beautifully controlled on the micro scale and enable that on the nanoscale," Goodman says. Cheng says that during his summer internship in Berggren's lab, he learned to operate the scanning electron microscope and learned about nanofabrication processes. "I have learned a lot. Aside from the lab work that I'm doing, I've been scripting for the [LayoutEditor] CAD program that I use, and I've been using Matlab, too," he says. "I actually learned a lot about image analysis because there are a lot of steps that go into image analysis. Since we have so much data and so many images to analyze, I'm doing it quantitatively and automatically to make sure I have repeatability." Explore further: Another tool in the nano toolbox: Scientists use electron beam to manipulate nanoparticles


News Article
Site: http://news.mit.edu/topic/mitnanotech-rss.xml

MIT Materials Processing Center (MPC)-Center for Materials Science and Engineering (CMSE) Summer Scholar Grant Smith is working in the lab of MIT assistant professor of electrical engineering and computer science Luqiao Liu, to create special thin film materials suitable for spin-based devices such as magnetic tunnel junctions used in computer memory. For his summer project, Smith is operating a sputter deposition chamber, where he grows ultrathin films from 2 to 10 nanometers thick. He is making devices that are precursors to a memory device and measuring their properties. Magnetic tunnel junctions used in spin-based systems for computer memory got their start with a key breakthrough in 1994 at MIT by research scientist Jagadeesh S. Moodera and colleagues. They are especially valued because they retain information even when the power is off. A magnetic tunnel junction pairs two thin film materials, each with a special property called ferromagnetism. “Those ferromagnetic layers can either have their magnetizations aligned or anti-aligned,” Smith explains. If they are aligned, that is their magnetic fields both point in the same direction, the electrons in one layer will have more states available for them in the other layer, but if they are anti-aligned [with magnetic fields pointing in opposite directions], there will be fewer states for electrons available in that other layer. “When you’re trying to push a current through and the magnetizations are aligned, the resistance is much lower. So if you fix one of the magnetic layers and flip the other one based on whether you want it to be a zero or a one or if you’re just trying to detect the existence of a magnetic field, you’ll be able to see something on the order of a 100 to 300 percent change in the resistance of that device,” Smith says. This is about 10 to 30 times greater that the approximately 10 percent shift in resistance in the first such devices. Smith is working with a dual-layer of an antiferromagnet called iridium manganese and a ferromagnet called cobalt iron boron. “Those two in conjunction, when you condition them in a specific way, they pin the magnetization of the one ferromagnet in that one specific direction. So that is your fixed layer,” he explains. For his summer project, Smith seeks to establish that ability to grow these magnetic tunnel junctions in Liu’s lab, and if that is a success, to try to manipulate that magnetization with the spin texture of a topological semimetal in order to do switching. “I’m just happy to learn anything about this field basically,” says Smith, a rising senior at Penn State University majoring in physics, who hopes to pursue a doctorate in the sciences. “I’m glad to be learning how to manufacture these magnetic tunnel junctions. That’s a really important skill. They’re used everywhere as far as doing experiments in this field. They’re useful in industry. It’s actually a very nice spot to be in.” Liu, who joined the MIT faculty in September 2015, says, “So far I have been very glad with Grant Smith's performance. Having a summer intern working in our lab does provide a good advantage to our research as it allows us to look into directions that we were not able to previously due to a shortage of manpower. Moreover, Mr. Smith is really diligent and smart. It is a very nice experience so far to work with such a motivated undergraduate student.” For Smith, working in Liu’s lab on materials at room temperature is a change of pace from his work at Penn State on materials at extremely low temperatures in the range of 4 kelvins (-452.47 degrees Fahrenheit). “When you’re working with these sort of things you can learn about new behaviors, new scientific phenomenon,” he says. “Here everything is very room temperature focused working much closer towards, working much more closely with the place industry is at right now,” Smith says. ‪MPC‬‬‬‬‬‬‬‪ and CMSE sponsor the nine-week National Science Foundation (NSF) Research Experience for Undergraduates internships with support from NSF’s Materials Research Science and Engineering Centers program. The program runs from June 7 through Aug. 6. ‬‬‬‬‬‬‬

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