Center for Nanoscale Systems

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Center for Nanoscale Systems

Ithaca, NY, United States
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Novel fabrication of diamond nanophotonics coupled to single-photon detectors Diamond nanophotonics is a rapidly evolving platform in which non-classical light—emitted by defect centers in diamond—can be generated, manipulated, and detected in a single monolithic device (e.g., for quantum information processing applications).1–3 Indeed, novel diamond fabrication techniques make it possible to engineer unique nanostructures in which diamond's extraordinary material properties (e.g., high refractive index, wide band gap, and large optical transmission window) can be exploited.4, 5 The relatively large Kerr non-linearity6 of diamond also makes it an attractive platform for on-chip nonlinear optics at visible and IR wavelengths.7 This nonlinearity could be used for frequency conversion of photons generated by color centers in diamond (i.e., from their typical visible wavelengths to telecom wavelengths).8 In turn, this would enable transmission of quantum information and distribution of quantum entanglement9, 10 over long distances. Such integrated diamond–quantum photonics platforms would benefit from the use (and realization) of high-performance single-photon detectors that have broadband photon sensitivity and are integrated on the same diamond chip. Superconducting nanowire single-photon detectors (SNSPDs) are a class of cutting-edge photon detectors that outperform other technologies in terms of detection efficiency, dark counts, timing jitter, and maximum count rates.11–13 SNSPDs typically consist of narrow nanowires that are patterned into an ultrathin (4–8nm) superconducting film.14 The nanowires are biased close to the critical current of the superconductor material so that when an incident photon is absorbed by the wire, a small resistive hotspot forms and generates a voltage pulse, which is amplified and measured.15 In our work,16,17 we have developed a novel fabrication procedure with which we can etch freestanding diamond nanostructures directly from a bulk substrate. We use these freestanding diamond waveguides to guide the emission from diamond color centers—nitrogen18 or silicon vacancies (NVs or SiVs), see Figure 1, that we implant within the waveguides—to evanescently coupled niobium titanium nitride SNSPDs. The evanescently coupled SNSPDs can thus be used to detect the color center fluorescence, while filtering out the pump laser that scatters into the waveguide. A scanning electron microscope image of several freestanding diamond waveguides (with triangular cross sections) is shown in Figure 2(a). We etched these waveguides from single-crystal diamond with the use of our angled-etching fabrication method.4 The waveguides are supported periodically by thin support structures underneath the waveguide that are created by slightly increasing the width of the waveguide at the support locations. This allows long segments of the waveguide to remain freestanding (while not perturbing the waveguide mode).19 In addition, single meander SNSPDs—see Figure 2(b)—are located on both ends of the waveguide. The SNSPDs are then connected to titanium/gold contact pads for electrical readout. Finite-difference time-domain simulations of the diamond waveguide SNSPD device are shown in Figure 3. The normalized field distribution of the optical mode in the diamond waveguide is shown in Figure 3(a), which illustrates the capacity for single-mode waveguide operation in the triangular cross section diamond waveguide. In addition, the absorption characteristics of the device—Figure 3(b)—indicate that more than 99% of the optical power has been absorbed by the SNSPD after a propagation distance of 15μm. The photon-counting performance of an SNSPD on one of the freestanding diamond waveguides (at 4.2K)—when illuminated with vertically incident 705nm photons—is depicted by the blue curve in Figure 4, and the red curve indicates the dark count response of the detector. The temperature (4.2K) and superconductor thickness (10.5nm) of the device limit the SNSPD from reaching a fully saturated photon count rate. However, we do observe a wide photon-counting operational range (i.e., the region where the device count rate begins to level off and approach an ideal saturated regime) that is still far from the detector's intrinsic dark counts. In summary, we have developed a platform with which SNSPDs can be fabricated on freestanding waveguides that are etched from single-crystal diamond (which can host quantum emitters with good spectral properties).20 We have also characterized the photon-counting performance of our fabricated detectors. With our approach it is possible to achieve monolithic and scalable integration of diamond quantum optical circuits that are based on defect color centers. In the next stages of our work, we plan to improve the filtering of the pump beam (i.e., that is used to excite the color centers) so that the SNSPDs are no longer saturated by pump photons. This work was performed in part at the Center for Nanoscale Systems (CNS), a member of the National Nanotechnology Infrastructure Network, which is supported by the National Science Foundation (NSF) award ECS-0335765. CNS is part of Harvard University. We also acknowledge the financial support of the Ontario Centres of Excellence, the Natural Sciences and Engineering Research Council of Canada, and the Institute for Quantum Computing. This work was also partly supported by the Science and Technology Center (STC) for Integrated Quantum Materials (by NSF grant DMR-1231319) and the Harvard Quantum Optics Center. Robert Westervelt was supported by the STC for Integrated Quantum Materials by NSF grant DMR-1231319.


Montemore M.M.,Harvard University | Montessori A.,Third University of Rome | Succi S.,Harvard University | Succi S.,CNR Institute of Neuroscience | And 6 more authors.
Journal of Chemical Physics | Year: 2017

The surface structure and composition of a multi-component catalyst are critical factors in determining its catalytic performance. The surface composition can depend on the local pressure of the reacting species, leading to the possibility that the flow through a nanoporous catalyst can affect its structure and reactivity. Here, we explore this possibility for oxidation reactions on nanoporous gold, an AgAu bimetallic catalyst. We use microscopy and digital reconstruction to obtain the morphology of a two-dimensional slice of a nanoporous gold sample. Using lattice Boltzmann fluid dynamics simulations along with thermodynamic models based on first-principles total-energy calculations, we show that some sections of this sample have low local O2 partial pressures when exposed to reaction conditions, which leads to a pure Au surface in these regions, instead of the active bimetallic AgAu phase. We also explore the effect of temperature on the surface structure and find that moderate temperatures (≈300-450 K) should result in the highest intrinsic catalytic performance, in apparent agreement with experimental results. © 2017 Author(s).


Lin P.T.,Massachusetts Institute of Technology | Singh V.,Massachusetts Institute of Technology | Lin H.-Y.G.,Center for Nanoscale Systems | Tiwald T.,J. A. Woollam Co. Inc. | And 2 more authors.
Optics InfoBase Conference Papers | Year: 2014

We experimentally demonstrate a sophisticated mid-IR microphotonics platform adopting engineered Si-rich and low-stress silicon nitride (SiNx) thin films where an extensive infrared transparency up to λ = 8.5 μm is achieved. Furthermore, because of the designed lowstress property, the SiNx deposition is able to reach a thickness > 2 μm that significantly reduces mid-IR waveguide loss to less than 0.2 dB/cm. We show directional couplers functioning over a broad infrared spectrum, thus enabling monolithic mid-IR multiplexing schemes for integrated linear and nonlinear photonics leading to sophisticated label-free sensing technologies. CLEO:2014 © 2014 OSA.


Lin P.T.,Massachusetts Institute of Technology | Singh V.,Massachusetts Institute of Technology | Lin H.-Y.G.,Center for Nanoscale Systems | Tiwald T.,J. A. Woollam Co. Inc. | And 3 more authors.
Frontiers in Optics, FiO 2014 | Year: 2014

We experimentally demonstrate a sophisticated mid-IR microphotonics platform adopting engineered Si-rich and low-stress silicon nitride (SiNx) thin films where an extensive infrared transparency up to λ = 8.5 μm is achieved. Furthermore, because of the designed lowstress property, the SiNx deposition is able to reach a thickness > 2 μm that significantly reduces mid-IR waveguide loss to less than 0.2 dB/cm. We show directional couplers functioning over a broad infrared spectrum, thus enabling monolithic mid-IR multiplexing schemes for integrated linear and nonlinear photonics leading to sophisticated label-free sensing technologies. © OSA 2014.


News Article | March 16, 2016
Site: news.mit.edu

Behaviors in complex systems are often more than the sum of their parts, whether in the brain where neurons enable expression of personality, or in fast data storage devices enabled by magnetic interactions. Physicists call these distinctive collective behaviors “emergent” properties. MIT assistant professor of physics Joseph G. Checkelsky is working at the intersection of materials synthesis and quantum physics to discover new materials that host these emergent phenomena, which in turn may foster new technologies. “In the context of solid state physics, emergent behavior often takes the form of collective behavior of electrons,” Checkelsky explains. “For example, looking at an individual electron, one would not imagine that it could form a coherent superconducting condensate by partnering with other electrons in a solid. Nor would one expect that different crystalline solids could give rise to the dynamic family of superconductors we know from experiment. Our goal is to look at materials where the quantum mechanical nature of the underlying electrons is brought out in new types of such collective properties.” Checkelsky recently won a National Science Foundation (NSF) CAREER award to pursue research into particular kinds of quantum materials that combine so-called frustrated atomic lattices and mobile electrons. An ordinary magnet gets its magnetism from the quantum mechanical property that electrons are indistinguishable and may lower their energy by aligning their magnetic moments. In some magnetic materials, known as antiferromagnets, magnetic moments of ions alternate in a repeating up/down pattern to lower their energy. The notion of a frustrated lattice, Checkelsky explains, is to create a repeating structure in the arrangement of atoms that confuses this ordering with competing interactions so that the system is unable to find a suitable way to orient itself. It is expected that this will lead to electrons with stronger quantum mechanical interactions that promote collective behavior. “By using these atomic arrangements one can force the electrons to have to deal with each other,” Checkelsky says. In Checkelsky’s lab, graduate student Linda Ye and postdoc Takehito Suzuki are studying an example of this with various arrangements of iron and tin atoms on the Kagome lattice structure, a series of overlapping triangles and hexagons. This work was inspired by theoretical work from 2011 by Cecil and Ida Green Professor of Physics Xiao-Gang Wen, Checkelsky notes. Many frustrated systems are electrically insulating. Whereas the study of those types of frustrated materials is established (including seminal contributions from MIT), in these new experiments the researchers are adding free electrons to these systems and studying how they behave. Ye explains that theorists proposed that ferromagnetic electrons on this Kagome lattice with strong spin-orbit coupling might give rise to topological bands with fractional excitations. “Generally this is a combination of strong spin-orbit interaction, magnetism, and the lattice degree of freedom,” she says. “It turns out to be a very interesting electronic system.” It differs from much of the low-temperature work in the lab because it displays interesting properties at room temperature. “It has strong ferromagnetism even at room temperature,” she says. The crystal lattice, in a ratio of three iron to two tin atoms, is made with the chemical vapor transport method. The obtained single crystals are hexagonally shaped plates with dimensions of about 1 millimeter (about four one-hundreths of an inch), Ye says. “There is one trick about growing this crystal. It’s not a stable phase at room temperature,” she says. Her approach is to cool down the crystals rapidly from high temperature in cold water so the lattice doesn’t change its phase. It can take up to a full month in the furnace to grow these single-crystal compounds. Ye is studying the mechanism underlying a phenomenon known as the anomalous Hall effect by measuring voltage made in the direction transverse (perpendicular) to a current flowing through a crystal of this material. Ye  presented a report on the work today an American Physical Society meeting in Baltimore. Ye, 26, grew up in the city of Chengdu in Sichuan, China, and earned her bachelor’s degree at Tsinghua University in Beijing. She has a master’s in engineering (applied physics) from the University of Tokyo. Checkelsky was named a Moore Foundation Fellow in Materials Synthesis in August 2013. The award helped him to establish a lab that combines the growth of new materials with analyzing their properties and creating new devices that exploit their unique behavior. “The Moore Foundation has allowed our laboratory the capabilities to both synthesize and study materials. This ranges from thin film growth by molecular beam epitaxy to cryogenic measurements. Because of their support at the inception of our lab, we have been able to make fast progress towards realizing exotic quantum materials and studying their properties,” Checkelsky explains. The lab features a synthesis side with furnaces for growing materials and an analysis side with equipment such as cryogenic refrigerators and superconducting magnets for testing them. “It’s one room, but it has two distinct halves,” he says. “Every day the students are walking across the line between the two sides — we are trying to make this border disappear.” The group includes postdoc Takehito Suzuki, graduate students Linda Ye and Aravind Devarakonda and undergraduate Christina Wicker. A second postdoc is expected to join the group this summer, and Checkelsky plans to add more graduate and undergraduate students. “It’s very exciting to have seen all the big equipment come one by one, and put [it] together,” Ye says. “Many of the things in the lab we design and make by ourselves.” She is making a high vacuum probe for the thermal measurements inside the cryogenic refrigerator. Accurate measurements require using modern tools of nanoscience to probe the electronic properties of materials, Checkelsky says. “One type of life cycle for a project begins with an idea for physics of interest that we have in the office or learn through discussions with our theory colleagues. We then consider what materials systems are most likely to support such behavior and try to synthesize them. With the characterized material in hand we then design ways to incisively probe the physics of interest, which can involve high magnetic field, scattering, or making and measuring nanodevices from the material.” Checkelsky adds, “Accidental discoveries more interesting than our original targets also happen in the lab — which we are more than happy to embrace.” Besides equipment in his own lab, Checkelsky and his research team use facilities on the MIT campus at the Microsystems Technology Lab (MTL), as well as tools at the Harvard Center for Nanoscale Systems, the NIST Center for Neutron Research, and the National High Magnetic Field Laboratory in Tallahassee. The Florida lab features the world’s largest static magnet. “When we finally have our best materials, we bring them down to the magnet lab. They have been very supportive of our projects,” he adds. Checkelsky says he is looking forward to completion of MIT.nano, where he hopes to make use of the state-of-the-art facilities. “Then we will be able to go from thinking of projects to combining the powders to making the crystals to walking them next door to MIT.nano for the next step. It will be a really key facility for our projects,” he says. Checkelsky also is part of the Center for Integrated Quantum Materials. He works closely with MIT experimentalists Nuh Gedik, Ray Ashoori, and Pablo Jarillo-Herrero and theorists Patrick Lee, Liang Fu, Senthil Todadri, Leonid Levitov, and Xiao-Gang Wen. Graduate student Aravind Devarakonda is studying magnetic behavior of heavy metal compounds where static magnetism provides a source of correlation for the electrons. “The basic idea is that certain spinel compounds have a fixed level of magnetic order which can persist even with changing composition of other lattice constituents. By going from lighter to heavier elements surrounding these magnetic atoms, we can introduce topological electronic features into the material,” Devarakonda says. “If we want to combine electronic correlation with the physics of topological insulators and related materials we have to make progress on several fronts,” Checkelsky explains. “In addition to following theoretical predictions, an experimental voyage into material systems is a key component of this. And indeed thus far the work has been experimentally driven. In this sense the theme has been to look at systems where the presence of non-trivial electronic topology is not well-resolved from theory due to the complications of electronic correlation but which we can grow and examine experimentally.” Devarakonda, who earned his bachelor’s in applied science (physics) at Rutgers University, has become expert in the techniques of crystal growth, cryogenics, electrical measurements, nanofabrication, metal work, and first principles calculations — “the full tool belt,” Checkelsky says. Checkelsky received his BS in physics at Harvey Mudd College and PhD in physics at Princeton University in 2010. Before joining the faculty at MIT in January 2014, Checkelsky was a postdoc at Japan’s Institute for Physical and Chemical Research (RIKEN) and a lecturer at the University of Tokyo. His work and continued collaboration there includes studies of the surface properties of topological insulators and more recently unusual electronic properties of a compound material with layers of three elements — bismuth, tellurium, and iodine. “The atoms line up in the same stacking sequence through the whole material,” Checkelsky explains. “So, the system breaks a spatial symmetry and has a direction associated with it.” “This type of compound is called polar because of this directionality. That structural difference has profound implications for the electronic behavior,” he says. In particular this polarity changes the spin degree of freedom of the electron so that the way electrons move in the solid very strictly depends on the spin direction. Experiments published in a 2015 paper demonstrated a spin up channel and a spin down channel with different energy levels in measurement of their electrical resistance under a magnetic field. This work could have implications for future spintronic devices. Checkelsky is in his third term of teaching  8.02 (Electromagnetism) in the Department of Physics. With a typical class size of 100 students, 8.02 is taught in a Technology Enabled Active Learning (TEAL) classroom with students around the teacher. “It gives you not only face-to-face communication with the students, but a technological link as well. They have a clicker with which they can respond to questions, which can offer a view into what they’re thinking,” Checkelsky explains. “I had the good fortune of starting my teaching in 8.02 with Peter Dourmashkin, who is a constant source of insight into how to approach the class. I really enjoy working with the students and trying to convey not only my enthusiasm for physics but also practical, effective ways for them to tackle the course material.” Checkelsky’s lab has a partnership with the Wilson Creek Elementary School located in Johns Creek, Georgia, near his hometown north of Atlanta. With the help of their teachers, students there submit questions about science, and Checkelsky’s team comes up with the best answers they can. Analysis of student submissions showed that the most frequently occurring word in the students’ questions is “possible.” “They’re really at a very young age interested in what is possible for human beings and technology,” Checkelsky says. “We approach their questions as seriously as any kind of scientific question that comes up in our research. We have to read papers and discuss with colleagues; we really try to come up with a complete answer for students.” In addition to the support of the teachers and Principal Andrea Cushing, it is no doubt a great benefit that Checkelsky’s mom, Eileen Checkelsky, is the current principal’s secretary at Wilson Creek Elementary School. Checkelsky’s office windows are lined with towering plants inherited from Tom Greytak, retired professor of physics, who previously had the office. “At first I had to figure out what the names of the plants were. But taking care of them has become a serious hobby of mine.” This dovetails with his interest in cooking. “I think it’s curious that what I do at MIT is synthesizing and studying inorganic materials and my hobbies are basically synthesizing and processing organic ones. It all revolves around finding the right recipe,” he says.


Abstract: A research team of physicists from Harvard University has developed new hand-held spectrometers capable of the same performance as large, benchtop instruments. The researchers' innovation explained this week in APL Photonics, from AIP Publishing, derives from their groundbreaking work in meta-lenses. The hand-held spectrometers offer real promise for applications ranging from health care diagnostics to environmental and food monitoring. Spectrometers are instruments that are widely used to quantify the presence of various biological or chemical compounds based on their interaction with light. However, to be a practical tool for users, such as physicians at the bedside or food-safety inspectors out in the field, spectrometers have to be portable, low-cost and easy to use without specialized equipment or training. Typically, however, there is an inherent trade-off between the size and performance of the spectrometer. To maintain performance while reducing spectrometer size, this team of researchers has developed a spectrometer incorporating meta-lenses that combine the functionalities of a traditional grating and focusing mirror into a single component, as well as having much greater ability to spatially separate wavelengths (the so-called dispersion). In all, the overall size of the spectrometer is significantly reduced without sacrificing performance. "This research has its roots all the way back to 2011, when we were investigating the fundamental properties of light as it interacts with two dimensional metamaterials (metasurfaces) and discovered generalized laws for the refraction and reflection of light for metasurface, which are powerful generalizations of the textbook laws valid for ordinary surfaces," explained Federico Capasso of Harvard. Unlike traditional refractory lenses that are millimeters thick and have a characteristic curved surface, a meta-lens is a completely flat or planar lens made up of millions of nanostructures. Using lithographic techniques, proper placement and fabrication of these nanostructures enables similar or better functionalities compared to traditional lenses. These meta-lenses can be customized to a user's specifications, and mass-produced using the same foundries that produce computer chips. "For these reasons, we believe meta-lenses to be game-changers," Capasso said. "In fact, our work on metalenses in the visible, published last year, was hailed by Science magazine as one of the top breakthroughs of the year in 2016." "The potential applications of these new smaller spectrometers are significant for portable monitoring of biological and chemical compounds" said Alex Zhu, lead author of the paper. "For example, physicians could bring hospital-level diagnostic capabilities to patients in the field where sophisticated equipment and highly trained personnel are not available, providing data on a timescale of minutes to hours, as opposed to days or weeks from usual chemistry-based methods." The same is true for environmental monitoring: Data about pollutants, or toxic chemicals could be collected and processed in real time on site at various locations with ultra-compact, high performance spectrometers. The next step toward realizing the full potential of these meta-spectrometers is to improve the performance of the prototype for both the working wavelength range and spectral resolution. This would allow it to be used for a wide variety of analyses, including highly specialized ones to identify proteins or gene markers (Raman spectroscopy), which typically involve onerous processes with sophisticated equipment in a full-size laboratory. "The goal is to be able to achieve comparable levels of performance with a simple 'plug-and-play' two-component device, i.e., a meta-lens and a detector, which together function as a meta-spectrometer," Zhu said. "The potential for this already exists in the meta-lens technology; it is simply a question of finding the right configurations and making it work." ### The research was partially funded by the Air Force Office of Scientific Research (AFOSR). This work was performed in part at the Center for Nanoscale Systems (CNS), a member of the National Nanotechnology Coordinated Infrastructure Network (NNCI), which is supported by the National Science Foundation under NSF award no. 1541959. CNS is part of Harvard University. About American Institute of Physics APL Photonics is the dedicated home for open access multidisciplinary research from and for the photonics community. The journal publishes fundamental and applied results that significantly advance the knowledge in photonics across physics, chemistry, biology and materials science. See scitation.aip.org/content/aip/journal/app. For more information, please click If you have a comment, please us. Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.


Xu X.,Center for Nanoscale Systems | Gabor N.M.,Center for Nanoscale Systems | Gabor N.M.,Cornell University | Alden J.S.,Cornell University | And 3 more authors.
Nano Letters | Year: 2010

We investigate the optoelectronic response of a graphene single-bilayer interface junction using photocurrent (PC) microscopy. We measure the polarity and amplitude of the PC while varying the Fermi level by tuning a gate voltage. These measurements show that the generation of PC is by a photothermoelectric effect. The PC displays a factor of ∼10 increase at the cryogenic temperature as compared to room temperature. Assuming the thermoelectric power has a linear dependence on the temperature, the inferred graphene thermal conductivity from temperature dependent measurements has a T1.5 dependence below ∼100 K, which agrees with recent theoretical predictions. © 2010 American Chemical Society.


Lin P.T.,Massachusetts Institute of Technology | Kwok S.W.,Harvard University | Lin H.-Y.G.,Center for Nanoscale Systems | Singh V.,Massachusetts Institute of Technology | And 3 more authors.
Nano Letters | Year: 2014

A mid-infrared (mid-IR) spectrometer for label-free on-chip chemical sensing was developed using an engineered nanofluidic channel consisting of a Si-liquid-Si slot-structure. Utilizing the large refractive index contrast (Δn ∼ 2) between the liquid core of the waveguide and the Si cladding, a broadband mid-IR lightwave can be efficiently guided and confined within a nanofluidic capillary (≤100 nm wide). The optical-field enhancement, together with the direct interaction between the probe light and the analyte, increased the sensitivity for chemical detection by 50 times when compared to evanescent-wave sensing. This spectrometer distinguished several common organic liquids (e.g., n-bromohexane, toluene, isopropanol) accurately and could determine the ratio of chemical species (e.g., acetonitrile and ethanol) at low concentration (<5 μL/mL) in a mixture through spectral scanning over their characteristic absorption peaks in the mid-IR regime. The combination of CMOS-compatible planar mid-IR microphotonics, and a high-throughput nanofluidic sensor system, provides a unique platform for chemical detection. © 2013 American Chemical Society.


News Article | February 15, 2017
Site: www.eurekalert.org

WASHINGTON, D.C., Feb. 9, 2017 -- A research team of physicists from Harvard University has developed new hand-held spectrometers capable of the same performance as large, benchtop instruments. The researchers' innovation explained this week in APL Photonics, from AIP Publishing, derives from their groundbreaking work in meta-lenses. The hand-held spectrometers offer real promise for applications ranging from health care diagnostics to environmental and food monitoring. Spectrometers are instruments that are widely used to quantify the presence of various biological or chemical compounds based on their interaction with light. However, to be a practical tool for users, such as physicians at the bedside or food-safety inspectors out in the field, spectrometers have to be portable, low-cost and easy to use without specialized equipment or training. Typically, however, there is an inherent trade-off between the size and performance of the spectrometer. To maintain performance while reducing spectrometer size, this team of researchers has developed a spectrometer incorporating meta-lenses that combine the functionalities of a traditional grating and focusing mirror into a single component, as well as having much greater ability to spatially separate wavelengths (the so-called dispersion). In all, the overall size of the spectrometer is significantly reduced without sacrificing performance. "This research has its roots all the way back to 2011, when we were investigating the fundamental properties of light as it interacts with two dimensional metamaterials (metasurfaces) and discovered generalized laws for the refraction and reflection of light for metasurface, which are powerful generalizations of the textbook laws valid for ordinary surfaces," explained Federico Capasso of Harvard. Unlike traditional refractory lenses that are millimeters thick and have a characteristic curved surface, a meta-lens is a completely flat or planar lens made up of millions of nanostructures. Using lithographic techniques, proper placement and fabrication of these nanostructures enables similar or better functionalities compared to traditional lenses. These meta-lenses can be customized to a user's specifications, and mass-produced using the same foundries that produce computer chips. "For these reasons, we believe meta-lenses to be game-changers," Capasso said. "In fact, our work on metalenses in the visible, published last year, was hailed by Science magazine as one of the top breakthroughs of the year in 2016." "The potential applications of these new smaller spectrometers are significant for portable monitoring of biological and chemical compounds" said Alex Zhu, lead author of the paper. "For example, physicians could bring hospital-level diagnostic capabilities to patients in the field where sophisticated equipment and highly trained personnel are not available, providing data on a timescale of minutes to hours, as opposed to days or weeks from usual chemistry-based methods." The same is true for environmental monitoring: Data about pollutants, or toxic chemicals could be collected and processed in real time on site at various locations with ultra-compact, high performance spectrometers. The next step toward realizing the full potential of these meta-spectrometers is to improve the performance of the prototype for both the working wavelength range and spectral resolution. This would allow it to be used for a wide variety of analyses, including highly specialized ones to identify proteins or gene markers (Raman spectroscopy), which typically involve onerous processes with sophisticated equipment in a full-size laboratory. "The goal is to be able to achieve comparable levels of performance with a simple 'plug-and-play' two-component device, i.e., a meta-lens and a detector, which together function as a meta-spectrometer," Zhu said. "The potential for this already exists in the meta-lens technology; it is simply a question of finding the right configurations and making it work." The research was partially funded by the Air Force Office of Scientific Research (AFOSR). This work was performed in part at the Center for Nanoscale Systems (CNS), a member of the National Nanotechnology Coordinated Infrastructure Network (NNCI), which is supported by the National Science Foundation under NSF award no. 1541959. CNS is part of Harvard University. The article, "Ultra-compact visible chiral spectrometer with meta-lenses," is authored by A. Y. Zhu, W. T. Chen, M. Khorasaninejad, J. Oh, Aun Zaidi, Ishan Mishra, R. C. Devlin and F. Capasso. The article will appeared in the journal APL Photonics Feb. 7, 2017 (DOI: 10.1063/1.494259) and can be accessed at http://aip. . APL Photonics is the dedicated home for open access multidisciplinary research from and for the photonics community. The journal publishes fundamental and applied results that significantly advance the knowledge in photonics across physics, chemistry, biology and materials science. See http://scitation. .


News Article | April 26, 2016
Site: www.cemag.us

Martin Thuo likes to look for new, affordable and clean ways to put science and technology to work in the world. His lab is dedicated to an idea called frugal innovation: "How do you do very high-level science or engineering with very little?" said Thuo, an assistant professor of materials science and engineering at Iowa State University and an associate of the U.S. Department of Energy's Ames Laboratory. "How can you solve a problem with the least amount of resources?" That goal has Thuo and his research group using their materials expertise to study soft matter, single-molecule electronics and renewable energy production. A guiding principle is that, whenever possible, nature should do part of the work. "Nature has a beautiful way of working for us," he said. "Self-assembly and ambient oxidation are great tools in our designs." One of the latest innovations from Thuo's lab is finding a way to make micro-scale, liquid-metal particles that can be used for heat-free soldering plus the fabricating, repairing and processing of metals - all at room temperature. The discovery was recently reported online in the journal Scientific Reports. Thuo's co-authors all have Iowa State ties: Simge Cinar, a postdoctoral research associate; Ian Tevis, a former postdoctoral researcher who's now chief technical officer at an Ames startup called SAFI-Tech; and Jiahao Chen, a doctoral student. Ask about the discovery and Thuo says Iowa State is just the place for a new development in soldering technology. Back in 1996, a research team led by Iver Anderson of the Ames Laboratory and Iowa State's department of materials science and engineering patented lead-free solder. That patent expired in 2013. But at its peak, the technology was licensed by more than 50 companies in 13 countries. Thuo is hoping his heat-free soldering technology is just as useful. To try to help make that happen, he's worked with Tevis to launch SAFI-Tech. Thuo said the company plans to locate to the Iowa State Economic Development StartUp Factory when it opens in the ISU Research Park later this year. The project started as a search for a way to stop liquid metal from returning to a solid - even below the metal's melting point. That's something called undercooling and it has been widely studied for insights into metal structure and metal processing. But it had been a challenge to produce large and stable quantities of undercooled metals. Thuo's research team thought if tiny droplets of liquid metal could be covered with a thin, uniform coating, they could form stable particles of undercooled liquid metal. The engineers experimented with a new technique that uses a high-speed rotary tool to sheer liquid metal into droplets within an acidic liquid. And then nature lends a hand: The particles are exposed to oxygen and then an oxidation layer is allowed to cover the particles, essentially creating a capsule containing the liquid metal. That layer is then polished until it is thin and smooth. Thuo's research group proved the concept by creating liquid-metal particles containing Field's metal (an alloy of bismuth, indium and tin) and particles containing an alloy of bismuth and tin. The particles are 10 micrometers in diameter, about the size of a red blood cell. "We wanted to make sure the metals don't turn into solids," Thuo said. "And so we engineered the surface of the particles so there is no pathway for liquid metal to turn to a solid. We've trapped it in a state it doesn't want to be in." Those liquid metal particles could have significant implications for manufacturing. "We demonstrated healing of damaged surfaces and soldering/joining of metals at room temperature without requiring high-tech instrumentation, complex material preparation or a high-temperature process," the engineers wrote in their paper. Thuo and the Iowa State Research Foundation Inc. have filed for a patent on the technology. Thuo supported the project with faculty startup funds from Iowa State and funds from a Black and Veatch faculty fellowship. The project also included imaging work at the Center for Nanoscale Systems at Harvard University in Cambridge, Massachusetts. Tevis, of the SAFI-Tech startup, said the company is still testing the liquid-metal technology for electrical conductivity and mechanical reliability. He said the company is also developing the technology for product demonstrations. Thuo said the project is a good example of his frugal approach to science: it should be practical, sustainable, inexpensive and all about innovating and solving problems.

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