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Some laws are made to be broken, or at least challenged. A research team led by faculty scientist Ali Javey at the Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) has done just that by creating a transistor with a working 1-nanometer gate. For comparison, a strand of human hair is about 50,000 nanometers thick. "We made the smallest transistor reported to date," said Javey, a lead principal investigator of the Electronic Materials program in Berkeley Lab's Materials Science Division. "The gate length is considered a defining dimension of the transistor. We demonstrated a 1-nanometer-gate transistor, showing that with the choice of proper materials, there is a lot more room to shrink our electronics." The key was to use carbon nanotubes and molybdenum disulfide (MoS ), an engine lubricant commonly sold in auto parts shops. MoS is part of a family of materials with immense potential for applications in LEDs, lasers, nanoscale transistors, solar cells, and more. The findings will appear in the Oct. 7 issue of the journal Science. Other investigators on this paper include Jeff Bokor, a faculty senior scientist at Berkeley Lab and a professor at UC Berkeley; Chenming Hu, a professor at UC Berkeley; Moon Kim, a professor at the University of Texas at Dallas; and H.S. Philip Wong, a professor at Stanford University. The development could be key to keeping alive Intel co-founder Gordon Moore's prediction that the density of transistors on integrated circuits would double every two years, enabling the increased performance of our laptops, mobile phones, televisions, and other electronics. "The semiconductor industry has long assumed that any gate below 5 nanometers wouldn't work, so anything below that was not even considered," said study lead author Sujay Desai, a graduate student in Javey's lab. "This research shows that sub-5-nanometer gates should not be discounted. Industry has been squeezing every last bit of capability out of silicon. By changing the material from silicon to MoS2, we can make a transistor with a gate that is just 1 nanometer in length, and operate it like a switch." When 'electrons are out of control' Transistors consist of three terminals: a source, a drain, and a gate. Current flows from the source to the drain, and that flow is controlled by the gate, which switches on and off in response to the voltage applied. Both silicon and MoS2 have a crystalline lattice structure, but electrons flowing through silicon are lighter and encounter less resistance compared with MoS2. That is a boon when the gate is 5 nanometers or longer. But below that length, a quantum mechanical phenomenon called tunneling kicks in, and the gate barrier is no longer able to keep the electrons from barging through from the source to the drain terminals. "This means we can't turn off the transistors," said Desai. "The electrons are out of control." Because electrons flowing through MoS are heavier, their flow can be controlled with smaller gate lengths. MoS can also be scaled down to atomically thin sheets, about 0.65 nanometers thick, with a lower dielectric constant, a measure reflecting the ability of a material to store energy in an electric field. Both of these properties, in addition to the mass of the electron, help improve the control of the flow of current inside the transistor when the gate length is reduced to 1 nanometer. Once they settled on MoS as the semiconductor material, it was time to construct the gate. Making a 1-nanometer structure, it turns out, is no small feat. Conventional lithography techniques don't work well at that scale, so the researchers turned to carbon nanotubes, hollow cylindrical tubes with diameters as small as 1 nanometer. They then measured the electrical properties of the devices to show that the MoS2 transistor with the carbon nanotube gate effectively controlled the flow of electrons. "This work demonstrated the shortest transistor ever," said Javey, who is also a UC Berkeley professor of electrical engineering and computer sciences. "However, it's a proof of concept. We have not yet packed these transistors onto a chip, and we haven't done this billions of times over. We also have not developed self-aligned fabrication schemes for reducing parasitic resistances in the device. But this work is important to show that we are no longer limited to a 5-nanometer gate for our transistors. Moore's Law can continue a while longer by proper engineering of the semiconductor material and device architecture." Explore further: Breakthrough paves way for post-silicon future with carbon nanotube electronics


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

From the SPIE Photonics West Show Daily : Three plenary speakers at LASE 2017 discussed the LIGO discovery of gravitational waves in space, laser-based direct-write methods, and high-power EUV light sources for lithography. For more than a quarter of a century, Karsten Danzmann has dedicated his career to developing technology that could expand our understanding of the universe by detecting gravitational waves emanating from exotic objects in space. On September 14, 2015, the Laser Interferometer Gravitational-wave Observatory (LIGO) finally did just that. For the first time, US LIGO detectors in Livingston, LA, and Hanford, WA, heard the first "peep" from an event in the distant universe — in this case the collision of two black holes. The event confirmed a major prediction of Albert Einstein's 1915 general theory of relativity and opened a new window into the cosmos. It was such a major breakthrough that it took several days for the LIGO team to accept that it might actually be real, according to Danzmann, director of the Max Planck Institute for Gravitational Physics, a member of the LIGO Scientific Collaboration. And it was another five months before they made their findings public. "I've been chasing this for 27 years, and when it finally happened it was unbelievable," said Danzmann, who noted that a second, similar event, the detection of gravitational waves produced by two black holes colliding 1.4 billion light years away, was captured in June 2016 at the same two observatories. "We've been looking at the universe with our eyes for thousands of years, and we know it looks very different depending on whether we look at it with visible light, infrared light, gamma rays, xrays, ... but we haven't been able to hear it. And suddenly now we can. And we have hope that the dark side of the universe, which makes up 99% of the universe, is now accessible to us." During the LASE plenary session at SPIE Photonics West 2017 in February, Danzmann's enthusiasm was contagious as he described the developments leading up to that historic moment, from the physics and technology to the thousands of people involved worldwide for decades (the first published paper, in Physics Review Letters, listed 1004 authors from 133 institutions). For Danzmann, one of the key turning points came when Advanced LIGO, a $200 million upgrade to LIGO, was unveiled in mid-2015. With the upgrade, which took five years to complete, the observatories are now 10 times more sensitive than their predecessors, thanks to advances in the optical layout, new high-power (165W) stabilized laser systems, advanced mirror suspension, and improved pre-isolation for detecting very low frequencies, according to Danzmann. "The upgrade to Advanced LIGO was drastic," Danzmann said. "The building is still the same, and the stainless steel of vacuum tubes are the same, but everything else has changed." Danzmann is equally excited about a more recent development: LISA Pathfinder, a satellite mission launched in December 2015 whose payload includes the first laser interferometer in space. "On the ground we are listening to the high frequencies of the universe, but if we want to listen to low frequencies, we have to go into space," said Danzmann, who is co-principal investigator on the LISA technology package. "Some of the most interesting things in the universe are supermassive black holes. When galaxies collide, which happens all the time, these super black holes merge and emit a huge signal, and that is what we want to listen to in space." Another LASE plenary talk featured an overview of the current state-of-the-art in using laser-based direct-write (LDW) methods to print hybrid electronics. The talk was given by Alberto Pique, acting head of the Materials and Sensor Branch of the Materials Science Division at the US Naval Research Laboratory. "The goal is very simple: can we go from a design to a printed part that is not faithful in a structural sense but in a functional sense?" Pique posited. "To do that, we need a substrate, we need to wire it up, place the devices, then connect the wires and devices. If you do it right, you end up with a functional circuit." This is where additive manufacturing (AM) comes in. AM is considered a game changer for design and fabrication of 3D parts by reducing the number of steps from concept to part, while direct-write processes make it possible to fabricate custom electronics in less time and at lower cost than other techniques. Combining the two paves the way for more efficient and cost-effective printing of hybrid electronics. The ability of LDW to deposit functional materials over a wide viscosity range onto many diverse surfaces makes it unique among direct write processes, Pique noted. For example, when manufacturing inkjet nozzles, "you have to be careful about the material you put on the nozzle and you have to worry about the nature of the fluid. But when you use the LDW forward transfer technique, the nature of material is not that critical." Advances in lasers, materials, and positioning have spurred the development of LDW in AM, he added. In particular, the availability of high-repetition rate solid-state UV lasers with stable, moderate energies has allowed LDW to deposit materials rapidly in all three dimensions. By comparison, low-rep rate UV lasers with more uniform beam profiles have enabled printing larger area voxels, which also speeds up the LDW process. "Over the years, we have shown that with LDW we can both add and remove material, and this gives the laser technique an edge (over other direct-write techniques) because you can do two things with the same set up," Pique said. "The same system performs both additive and subtractive processes." In the final LASE plenary talk, Hakaru Mizoguchi, executive vice president of Gigaphoton, provided an update on the company's efforts to develop high-power EUV light sources for high-volume manufacturing (HVM) lithography. In July 2016, Gigaphoton demonstrated 250W light output at 4% conversion efficiency with a laser-produced plasma (LPP) light source prototype for EUV scanners. Since then, Gigaphoton has continued to test and refine its EUV light sources, with a goal of eventually reaching 500W, according to Mizoguchi. Photolithography equipment manufacturers are keen for a 250W power EUV source to deliver the kind of wafer productivity throughput their customers demand. To achieve these powers, Gigaphoton uses a dual-laser "priming" pulse from a yv04 (vanadate) laser ahead of a nanosecond-duration carbon dioxide blast, plus sub 20 μm micro droplet supply technology, proprietary energy control technology, and magnetic field-enabled debris mitigation technology. In anticipation of introducing these systems to the commercial market, the company is preparing to move into a new headquarters in Japan that doubles its office space and provides 1.5 times the production space, Mizoguchi noted. Symposium chairs for LASE 2017 were SPIE Fellows Koji Sugioka of RIKEN (Japan) and Reinhart Poprawe of Fraunhofer-Institut für Lasertechnik (Germany). Cochairs were SPIE Fellow Yongfeng Lu of University of Nebraska, Lincoln (USA), and Guido Hennig of Daetwyler Graphics (Switzerland). Photonics West 2017, 28 January through 2 February at the Moscone Center in San Francisco, CA (USA), encompassed more than 4700 presentations on light-based technologies across more than 95 conferences. It was also the venue for dozens of technical courses for professional development, the Prism Awards for Photonics Innovation, the SPIE Startup Challenge, a two-day job fair, two major exhibitions, and a diverse business program with more than 25 events. SPIE Photonics West 2018 will run 27 January through 1 February at Moscone Center.


News Article | January 21, 2016
Site: www.rdmag.com

Lawrence Livermore National Laboratory researchers have created a library of nanoporous gold structures on a single chip that has direct applications for high-capacity lithium ion batteries as well as neural interfaces. Nanoporous gold (np-Au), a porous metal used in energy and biomedical research, is produced through an alloy corrosion process known as dealloying that generates a characteristic three-dimensional nanoscale network of pores and ligaments. In the cover article in the Jan. 14 issue of Nanoscale(link is external), a journal published by the Royal Society of Chemistry, LLNL researchers and their University of California, Davis(link is external) collaborators describe a method for creating a library of varying np-Au morphologies on a single chip via precise delivery of tunable laser energy. UC Davis professor Erkin Seker served as the principal investigator (PI) of the UC Fees project that primarily funded the work, along with co-PI Monika Biener of LLNL’s Materials Science Division. Laser microprocessing (e.g. micromachining) provides spatial and temporal control while imposing energy near the surface of the material. “Traditional heat application techniques for the modification of np-Au are bulk processes that cannot be used to generate a library of different pore sizes on a single chip,” said LLNL staff scientist Ibo Matthews, co-author of the paper. “Laser microprocessing offers an attractive solution to this problem by providing a means to apply energy with high spatial and temporal resolution.” The researchers used multiphysics simulations to predict the effects of continuous wave vs. pulsed laser mode and varying thermal conductivity of the supporting substrate on the local np-Au film temperatures during photothermal annealing. They were then able to fabricate an on-chip material library consisting of 81 np-Au samples of nine different morphologies for use in the parallel study of structure–property relationships. “These libraries have the potential to drastically increase the throughput of morphology interaction studies for np-Au, specifically in applications such as high capacity lithium ion batteries, cell-material interaction studies for neural interfaces, analytical biosensors, as well as nanoscale material science studies,” said Biener, co-author of the paper. This work sets the foundation for understanding laser-based annealing of porous thin film materials. The fabrication of single chip material libraries has the potential to increase the throughput of material interaction testing in many disciplines through easy single-chip material screening libraries. LLNL’s Juergen Biener of the Material Sciences Division collaborated on the work along with UC Davis researchers Christopher Chapman (lead author) and Ling Wang. This work was funded by UC Lab Fees, National Science Foundation and National Institutes of Health.


News Article | January 21, 2016
Site: www.cemag.us

Lawrence Livermore National Laboratory researchers have created a library of nanoporous gold structures on a single chip that has direct applications for high-capacity lithium ion batteries as well as neural interfaces. Nanoporous gold (np-Au), a porous metal used in energy and biomedical research, is produced through an alloy corrosion process known as dealloying that generates a characteristic three-dimensional nanoscale network of pores and ligaments. In the cover article in a recent issue of Nanoscale, a journal published by the Royal Society of Chemistry, LLNL researchers and their University of California, Davis collaborators describe a method for creating a library of varying np-Au morphologies on a single chip via precise delivery of tunable laser energy. UC Davis professor Erkin Seker served as the principal investigator (PI) of the UC Fees project that primarily funded the work, along with co-PI Monika Biener of LLNL’s Materials Science Division. Laser microprocessing (e.g. micromachining) provides spatial and temporal control while imposing energy near the surface of the material. “Traditional heat application techniques for the modification of np-Au are bulk processes that cannot be used to generate a library of different pore sizes on a single chip,” says LLNL staff scientist Ibo Matthews, co-author of the paper. “Laser microprocessing offers an attractive solution to this problem by providing a means to apply energy with high spatial and temporal resolution.” The researchers used multiphysics simulations to predict the effects of continuous wave vs. pulsed laser mode and varying thermal conductivity of the supporting substrate on the local np-Au film temperatures during photothermal annealing. They were then able to fabricate an on-chip material library consisting of 81 np-Au samples of nine different morphologies for use in the parallel study of structure-property relationships. “These libraries have the potential to drastically increase the throughput of morphology interaction studies for np-Au, specifically in applications such as high capacity lithium ion batteries, cell-material interaction studies for neural interfaces, analytical biosensors, as well as nanoscale material science studies,” says Biener, co-author of the paper. This work sets the foundation for understanding laser-based annealing of porous thin film materials. The fabrication of single chip material libraries has the potential to increase the throughput of material interaction testing in many disciplines through easy single-chip material screening libraries. LLNL’s Juergen Biener of the Material Sciences Division collaborated on the work along with UC Davis researchers Christopher Chapman (lead author) and Ling Wang. This work was funded by UC Lab Fees, National Science Foundation, and National Institutes of Health. Release Date: January 20, 2016 Source: Lawrence Livermore National Laboratory


News Article | September 19, 2016
Site: www.rdmag.com

Graphene is the stuff of the future. For years, researchers and technologists have been predicting the utility of the one-atom-thick sheets of pure carbon in everything from advanced touch screens and semiconductors to long-lasting batteries and next-generation solar cells. But graphene's unique intrinsic properties – supreme electrical and thermal conductivities and remarkable electron mobility, to name just a few – can only be fully realized if it is grown free from defects that disrupt the honeycomb pattern of the bound carbon atoms. A team led by Materials Scientist Anirudha Sumant with the U.S. Department of Energy's (DOE) Argonne National Laboratory's Center for Nanoscale Materials (CNM) and Materials Science Division, along with collaborators at the University of California-Riverside, has developed a method to grow graphene that contains relatively few impurities and costs less to make, in a shorter time and at lower temperatures compared to the processes widely used to make graphene today. Theoretical work led by Argonne nanoscientist Subramanian Sankaranarayanan at the CNM helped researchers understand the molecular-level processes underlying the graphene growth. "I'd been dealing with all these different techniques of growing graphene, and you never see such a uniform, smooth surface." The new technology taps ultrananocrystalline diamond (UNCD), a synthetic type of diamond that Argonne researchers have pioneered through years of research. UNCD serves as a physical substrate, or surface on which the graphene grows, and the source for the carbon atoms that make up a rapidly produced graphene sheet. "When I first looked at the [scanning electron micrograph] and saw this nice uniform, very complete layer, it was amazing," said Diana Berman, the first author of the study and former postdoctoral research associate who worked with Sumant and is now an Assistant Professor at the University of North Texas. "I'd been dealing with all these different techniques of growing graphene, and you never see such a uniform, smooth surface." Current graphene fabrication protocols introduce impurities during the etching process itself, which involves adding acid and extra polymers, and when they are transferred to a different substrate for use in electronics. "The impurities introduced during this etching and the transferring step negatively affect the electronic properties of the graphene," Sumant said. "So you do not get the intrinsic properties of the graphene when you actually do this transfer." The team found that the single-layer, single-domain graphene can be grown over micron-size holes laterally, making them completely free-standing (that is, detached from the underlying substrate). This makes it possible to exploit the intrinsic properties of graphene by fabricating devices directly over free-standing graphene. The new process is also much more cost-effective than conventional methods based on using silicon carbide as a substrate. Sumant says that the 3- to 4-inch silicon carbide wafers used in these types of growth methods cost about $1,200, while UNCD films on silicon wafers cost less than $500 to make. The diamond method also takes less than a minute to grow a sheet of graphene, where the conventional method takes on the order of hours. The high quality of graphene was confirmed by the UC Riverside co-authors Zhong Yan and Alexander Balandin by fabricating top-gate field-effect transistors from this material and measuring its electron mobility and charge carrier concentration. "It is well known that certain metals, such as nickel and iron, dissolve diamond at elevated temperatures, and the same process has been used for many years to polish diamond," said Sumant. He and his team used this property to employ nickel in converting the top layer of diamond into amorphous carbon, but it was not clear how these freed carbon atoms converted instantly into high-quality graphene. After Sumant's and Berman's initial breakthrough of growing graphene directly on UNCD, Sankaranarayanan and his postdocs Badri Narayanan and Sanket Deshmukh, computational material scientists at the CNM used resources at the Argonne Leadership Computing Facility (ALCF) to help the team better understand the mechanism of the growth process underlying this interesting phenomenon using reactive molecular dynamic simulations. Computer simulations developed by Narayanan, Deshmukh and Sankaranarayanan showed that certain crystallographic orientation of nickel-111 highly favor nucleation, and subsequent rapid growth of graphene; this was then confirmed experimentally. These large-scale simulations also showed how graphene forms. The nickel atoms diffuse into the diamond and destroy its crystalline order, while carbon atoms from this amorphous solid move to the nickel surface and rapidly form honeycomb-like structures, resulting in mostly defect-free graphene. The nickel then percolated through the fine crystalline grains of the UNCD, sinking out of the way and removing the need for acid to dissolve away excess metal atoms from the top surface. "It is like meeting a good Samaritan at an unknown place who helps you, does his job and leaves quietly without a trace," said Sumant. "The proven predictive power of our simulations places us in a position of advantage to enable rapid discovery of new catalytic alloys that mediate growth of high-quality graphene on dielectrics and move away on their own when the growth is completed," added Narayanan. In addition to the utility in making minimally defective, application-ready graphene for things like low-frequency vibration sensors, radio frequency transistors and better electrodes for water purification, Berman and Sumant say that the Argonne team has already secured three patents arising from their new graphene growth method. The researchers have already struck a collaboration with Swedish Institute of Space Physics involving the European Space Agency for their Jupiter Icy Moons Explorer (JUICE) program to develop graphene-coated probes that may help exploratory vehicles sense the properties of plasma surrounding the moons of Jupiter. Closer to home, the team has also crafted diamond and graphene needles for researchers at North Carolina University to use in biosensing applications. The Argonne researchers are now fine-tuning the process – tweaking the temperature used to catalyze the reaction and adjusting the thickness of the diamond substrate and the composition of the metal film that facilitates the graphene growth – to both optimize the reaction and to better study the physics at the graphene-diamond interface. "We're trying to tune this more carefully to have a better understanding of which conditions lead to what quality of graphene we're seeing," Berman said. Other Argonne authors involved in the study were Alexander Zinovev and Daniel Rosenmann. The paper, "Metal-induced rapid transformation of diamond into single and multilayer graphene on wafer scale," is published inNature Communications.


News Article | September 19, 2016
Site: www.cemag.us

Graphene is the stuff of the future. For years, researchers and technologists have been predicting the utility of the one-atom-thick sheets of pure carbon in everything from advanced touch screens and semiconductors to long-lasting batteries and next-generation solar cells. But graphene’s unique intrinsic properties — supreme electrical and thermal conductivities and remarkable electron mobility, to name just a few — can only be fully realized if it is grown free from defects that disrupt the honeycomb pattern of the bound carbon atoms. A team led by Materials Scientist Anirudha Sumant with the U.S. Department of Energy’s (DOE) Argonne National Laboratory’s Center for Nanoscale Materials (CNM) and Materials Science Division, along with collaborators at the University of California-Riverside, has developed a method to grow graphene that contains relatively few impurities and costs less to make, in a shorter time and at lower temperatures compared to the processes widely used to make graphene today. Theoretical work led by Argonne nanoscientist Subramanian Sankaranarayanan at the CNM helped researchers understand the molecular-level processes underlying the graphene growth. The new technology taps ultrananocrystalline diamond (UNCD), a synthetic type of diamond that Argonne researchers have pioneered through years of research. UNCD serves as a physical substrate, or surface on which the graphene grows, and the source for the carbon atoms that make up a rapidly produced graphene sheet. “When I first looked at the [scanning electron micrograph] and saw this nice uniform, very complete layer, it was amazing,” says Diana Berman, the first author of the study and former postdoctoral research associate who worked with Sumant and is now an Assistant Professor at the University of North Texas. “I’d been dealing with all these different techniques of growing graphene, and you never see such a uniform, smooth surface.” Current graphene fabrication protocols introduce impurities during the etching process itself, which involves adding acid and extra polymers, and when they are transferred to a different substrate for use in electronics. “The impurities introduced during this etching and the transferring step negatively affect the electronic properties of the graphene,” Sumant says. “So you do not get the intrinsic properties of the graphene when you actually do this transfer.” The team found that the single-layer, single-domain graphene can be grown over micron-size holes laterally, making them completely free-standing (that is, detached from the underlying substrate). This makes it possible to exploit the intrinsic properties of graphene by fabricating devices directly over free-standing graphene. The new process is also much more cost-effective than conventional methods based on using silicon carbide as a substrate. Sumant says that the 3- to 4-inch silicon carbide wafers used in these types of growth methods cost about $1,200, while UNCD films on silicon wafers cost less than $500 to make. The diamond method also takes less than a minute to grow a sheet of graphene, where the conventional method takes on the order of hours. The high quality of graphene was confirmed by the UC Riverside co-authors Zhong Yan and Alexander Balandin by fabricating top-gate field-effect transistors from this material and measuring its electron mobility and charge carrier concentration. “It is well known that certain metals, such as nickel and iron, dissolve diamond at elevated temperatures, and the same process has been used for many years to polish diamond,” says Sumant. He and his team used this property to employ nickel in converting the top layer of diamond into amorphous carbon, but it was not clear how these freed carbon atoms converted instantly into high-quality graphene. After Sumant’s and Berman’s initial breakthrough of growing graphene directly on UNCD, Sankaranarayanan and his postdocs Badri Narayanan and Sanket Deshmukh, computational material scientists at the CNM used resources at the Argonne Leadership Computing Facility (ALCF) to help the team better understand the mechanism of the growth process underlying this interesting phenomenon using reactive molecular dynamic simulations. Computer simulations developed by Narayanan, Deshmukh and Sankaranarayanan showed that certain crystallographic orientation of nickel-111 highly favor nucleation, and subsequent rapid growth of graphene; this was then confirmed experimentally. These large-scale simulations also showed how graphene forms. The nickel atoms diffuse into the diamond and destroy its crystalline order, while carbon atoms from this amorphous solid move to the nickel surface and rapidly form honeycomb-like structures, resulting in mostly defect-free graphene. The nickel then percolated through the fine crystalline grains of the UNCD, sinking out of the way and removing the need for acid to dissolve away excess metal atoms from the top surface. “It is like meeting a good Samaritan at an unknown place who helps you, does his job and leaves quietly without a trace,” says Sumant. “The proven predictive power of our simulations places us in a position of advantage to enable rapid discovery of new catalytic alloys that mediate growth of high-quality graphene on dielectrics and move away on their own when the growth is completed,” adds Narayanan. In addition to the utility in making minimally defective, application-ready graphene for things like low-frequency vibration sensors, radio frequency transistors and better electrodes for water purification, Berman and Sumant say that the Argonne team has already secured three patents arising from their new graphene growth method. The researchers have already struck a collaboration with Swedish Institute of Space Physics involving the European Space Agency for their Jupiter Icy Moons Explorer (JUICE) program to develop graphene-coated probes that may help exploratory vehicles sense the properties of plasma surrounding the moons of Jupiter. Closer to home, the team has also crafted diamond and graphene needles for researchers at North Carolina University to use in biosensing applications. The Argonne researchers are now fine-tuning the process — tweaking the temperature used to catalyze the reaction and adjusting the thickness of the diamond substrate and the composition of the metal film that facilitates the graphene growth — to both optimize the reaction and to better study the physics at the graphene-diamond interface. “We’re trying to tune this more carefully to have a better understanding of which conditions lead to what quality of graphene we’re seeing,” Berman says. Other Argonne authors involved in the study were Alexander Zinovev and Daniel Rosenmann. The paper, “Metal-induced rapid transformation of diamond into single and multilayer graphene on wafer scale,” is published in Nature Communications. The study used resources of the CNM and the ALCF as well as the National Energy Research Scientific Computing Center at Lawrence Berkeley National Laboratory, all DOE Office of Science User Facilities. Additional support was provided by the U.S. Department of Energy’s Office of Science.


News Article | January 21, 2016
Site: phys.org

Nanoporous gold (np-Au), a porous metal used in energy and biomedical research, is produced through an alloy corrosion process known as dealloying that generates a characteristic three-dimensional nanoscale network of pores and ligaments. In the cover article in the Jan. 14 issue of Nanoscale, a journal published by the Royal Society of Chemistry, LLNL researchers and their University of California, Davis (link is external) collaborators describe a method for creating a library of varying np-Au morphologies on a single chip via precise delivery of tunable laser energy. UC Davis professor Erkin Seker served as the principal investigator (PI) of the UC Fees project that primarily funded the work, along with co-PI Monika Biener of LLNL's Materials Science Division. Laser microprocessing (e.g. micromachining) provides spatial and temporal control while imposing energy near the surface of the material. "Traditional heat application techniques for the modification of np-Au are bulk processes that cannot be used to generate a library of different pore sizes on a single chip," said LLNL staff scientist Ibo Matthews, co-author of the paper. "Laser microprocessing offers an attractive solution to this problem by providing a means to apply energy with high spatial and temporal resolution." The researchers used multiphysics simulations to predict the effects of continuous wave vs. pulsed laser mode and varying thermal conductivity of the supporting substrate on the local np-Au film temperatures during photothermal annealing. They were then able to fabricate an on-chip material library consisting of 81 np-Au samples of nine different morphologies for use in the parallel study of structure–property relationships. "These libraries have the potential to drastically increase the throughput of morphology interaction studies for np-Au, specifically in applications such as high capacity lithium ion batteries, cell-material interaction studies for neural interfaces, analytical biosensors, as well as nanoscale material science studies," said Biener, co-author of the paper. This work sets the foundation for understanding laser-based annealing of porous thin film materials. The fabrication of single chip material libraries has the potential to increase the throughput of material interaction testing in many disciplines through easy single-chip material screening libraries. Explore further: Visualization of gold nanoparticle self-assembly via TEM More information: Christopher A. R. Chapman et al. Engineering on-chip nanoporous gold material libraries via precision photothermal treatment, Nanoscale (2016). DOI: 10.1039/C5NR04580K


Lawrence Livermore National Laboratory, Livermore, Calif., reports that its researchers have created a library of nanoporous gold structures on a single chip that has direct applications for high-capacity lithium ion batteries as well as neural interfaces. Nanoporous gold (np-Au), a porous metal used in energy and biomedical research, is produced through an alloy corrosion process known as dealloying that generates a characteristic three-dimensional nanoscale network of pores and ligaments. In the cover article in the Jan. 14 issue of Nanoscale, a journal published by the Royal Society of Chemistry, LLNL researchers and their University of California, Davis collaborators describe a method for creating a library of varying np-Au morphologies on a single chip via precise delivery of tunable laser energy. UC Davis professor Erkin Seker served as the principal investigator of the UC Fees project that primarily funded the work, along with Monika Biener of LLNL's Materials Science Division. Laser micromachining provides spatial and temporal control while imposing energy near the surface of the material. "Traditional heat application techniques for the modification of np-Au are bulk processes that cannot be used to generate a library of different pore sizes on a single chip," said LLNL staff scientist Ibo Matthews, co-author of the paper. "Laser microprocessing offers an attractive solution to this problem by providing a means to apply energy with high spatial and temporal resolution." The researchers used multiphysics simulations to predict the effects of continuous wave vs. pulsed laser mode and varying thermal conductivity of the supporting substrate on the local np-Au film temperatures during photothermal annealing. They were then able to fabricate an on-chip material library consisting of 81 np-Au samples of nine different morphologies for use in the parallel study of structure–property relationships. "These libraries have the potential to drastically increase the throughput of morphology interaction studies for np-Au, specifically in applications such as high capacity lithium ion batteries, cell-material interaction studies for neural interfaces, analytical biosensors, as well as nanoscale material science studies," said Dr. Biener, co-author of the paper. This work sets the foundation for understanding laser-based annealing of porous thin film materials. The fabrication of single chip material libraries has the potential to increase the throughput of material interaction testing in many disciplines through easy single-chip material screening libraries. LLNL's Juergen Biener of the Material Sciences Division collaborated on the work along with UC Davis researchers Christopher Chapman (lead author) and Ling Wang. www.llnl.gov


News Article | November 9, 2015
Site: www.materialstoday.com

Lawrence Livermore National Laboratory scientists have found that lithium ion batteries operate longer and faster when their electrodes are treated with hydrogen. Lithium ion batteries (LIBs) are a class of rechargeable battery types in which lithium ions move from the negative electrode to the positive electrode during discharge and back when charging. The growing demand for energy storage emphasizes the urgent need for higher-performance batteries. Several key characteristics of lithium ion battery performance -- capacity, voltage and energy density -- are ultimately determined by the binding between lithium ions and the electrode material. Subtle changes in the structure, chemistry and shape of an electrode can significantly affect how strongly lithium ions bond to it. Through experiments and calculations, the Livermore team discovered that hydrogen-treated graphene nanofoam electrodes in the LIBs show higher capacity and faster transport. “These findings provide qualitative insights in helping the design of graphene-based materials for high-power electrodes,” said Morris Wang, an LLNL materials scientist and co-author of a paper (link is external) appearing in Nov. 5 edition of Nature Scientific Reports. Lithium ion batteries are growing in popularity for electric vehicle and aerospace applications. For example, lithium ion batteries are becoming a common replacement for the lead acid batteries that have been used historically for golf carts and utility vehicles. Instead of heavy lead plates and acid electrolytes, the trend is to use lightweight lithium ion battery packs that can provide the same voltage as lead-acid batteries without requiring modification of the vehicle's drive system. Commercial applications of graphene materials for energy storage devices, including lithium ion batteries and supercapacitors, hinge critically on the ability to produce these materials in large quantities and at low cost. However, the chemical synthesis methods frequently used leave behind significant amounts of atomic hydrogen, whose effect on the electrochemical performance of graphene derivatives is difficult to determine. Yet Livermore scientists did just that. Their experiments and multiscale calculations reveal that deliberate low-temperature treatment of defect-rich graphene with hydrogen can actually improve rate capacity. Hydrogen interacts with the defects in the graphene and opens small gaps to facilitate easier lithium penetration, which improves the transport. Additional reversible capacity is provided by enhanced lithium binding near edges, where hydrogen is most likely to bind. “The performance improvement we’ve seen in the electrodes is a breakthrough that has real world applications,” said Jianchao Ye, who is a postdoc staff scientist at the Lab’s Materials Science Division, and the leading author of the paper. To study the involvement of hydrogen and hydrogenated defects in the lithium storage ability of graphene, the team applied various heat treatment conditions combined with hydrogen exposure and looked into the electrochemical performance of 3-D graphene nanofoam (GNF) electrodes, which are comprised chiefly of defective graphene. The team used 3-D graphene nanofoams due to their numerous potential applications, including hydrogen storage, catalysis, filtration, insulation, energy sorbents, capacitive desalination, supercapacitors and LIBs. The binder-free nature of graphene 3-D foam makes them ideal for mechanistic studies without the complications caused by additives. “We found a drastically improved rate capacity in graphene nanofoam electrodes after hydrogen treatment. By combining the experimental results with detailed simulations, we were able to trace the improvements to subtle interactions between defects and dissociated hydrogen. This results in some small changes to the graphene chemistry and morphology that turn out to have a surprisingly huge effect on performance,” said LLNL scientist Brandon Wood, another co-author of the paper. The research suggests that controlled hydrogen treatment may be used as a strategy for optimizing lithium transport and reversible storage in other graphene-based anode materials. This story is reprinted from material from Lawrence Livermore National Laboratory, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.


News Article | February 20, 2017
Site: phys.org

The process of electrophoretic deposition (EPD) uses an electric field to drive colloidal particles suspended in a liquid from a solution onto a conductive substrate. Commonly used to apply paint to cars, EPD also is utilized to coat ceramics, metals and polymers with a range of materials and for 3-D printing objects. Developed using a particle dynamics framework and run on the Vulcan supercomputing system at LLNL, the newly published model tracks every single particle during the entire EPD process—each particle is about 200 nanometers wide, roughly the diameter of the smallest bacteria. The research is published in the Dec. 20 issue of the journal Langmuir . "This gives us more information than any model before and fresh insights that were previously inaccessible," said the study's LLNL postdoctoral researcher Brian Giera. "Within this particle dynamics framework we were able to get really detailed information. In terms of understanding the EPD process in detail, this is a first-of-its kind." Over a period of two years, the team, led by principal investigator Todd Weisgraber, a researcher from LLNL's Materials Engineering Division, developed the model and ran several dozens of different simulations, changing the strength of the electrical field and the concentration of salt in the system. Not only does the strength of the electrical field affect the development of crystals, Giera said, but salt concentration, surprisingly, also plays a key role. Giera said the model could be used to better understand deposition kinetics, determine how fast to build and anticipate resulting crystallinity, which could impact how armor is produced, and how coatings are applied using the EPD process. "The model is poised to take on a lot of questions," Giera said. "It gives us more predictive information to optimize the system." Luis Zepeda-Ruiz, a scientist in the Lab's Materials Science Division, built the initial model containing all the essential mechanisms before Giera took over the work. He said the model can be augmented to allow for virtually any type of material, extending the science to a broad range of applications. "Our computational model can access details that are extremely difficult to observe in real experiments," Zepeda-Ruiz said. "It also can be used when experiments fail to reproduce results, when the solution ages and changes its chemistry. Now we have a pure, reproducible means for doing EPD, and that's a benefit." The model has been so well received by the scientific community that it was selected to be presented in a keynote speech by Giera at the international Electrophoretic Deposition Conferences Series held in South Korea in October. LLNL researcher Andy Pascall, an expert in EPD, helped define the model's initial parameter choices and is working on validating it for future implementation. Pascall said the model will be particularly useful to the field of photonics science, which requires precise control over crystallization. "Photonic crystallization is interesting to the scientific community in general. The way this has been done before in the lab has been through trial and error," Pascall said. "It's fair to say this is the only particle-based EPD model out there. Having a model that can be predictive allows you to run hundreds of virtual experiments that would take us months to do in the lab." Next, Giera will study how the colloidal particles re-suspend and, more importantly, tailor the model to account for particles of different sizes. Explore further: Theoretical model reveals how droplets grow around tiny particles on a surface More information: Brian Giera et al. Mesoscale Particle-Based Model of Electrophoretic Deposition, Langmuir (2017). DOI: 10.1021/acs.langmuir.6b04010

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