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  • richardmitnick 4:59 pm on September 26, 2016 Permalink | Reply
    Tags: Nanotechnology, , , ,   

    From BNL: “Crystalline Fault Lines Provide Pathway for Solar Cell Current” 

    Brookhaven Lab

    September 26, 2016
    Karen McNulty Walsh
    kmcnulty@bnl.gov
    (631) 344-8350
    Peter Genzer
    genzer@bnl.gov
    (631) 344-3174

    New tomographic AFM imaging technique reveals that microstructural defects, generally thought to be detrimental, actually improve conductivity in cadmium telluride solar cells.

    1
    CFN staff scientist Lihua Zhang places a sample in the transmission electron microscope.

    A team of scientists studying solar cells made from cadmium telluride, a promising alternative to silicon, has discovered that microscopic “fault lines” within and between crystals of the material act as conductive pathways that ease the flow of electric current. This research—conducted at the University of Connecticut and the U.S. Department of Energy’s Brookhaven National Laboratory, and described in the journal Nature Energy—may help explain how a common processing technique turns cadmium telluride into an excellent material for transforming sunlight into electricity, and suggests a strategy for engineering more efficient solar devices that surpass the performance of silicon.

    “If you look at semiconductors like silicon, defects in the crystals are usually bad,” said co-author Eric Stach, a physicist at Brookhaven Lab’s Center for Functional Nanomaterials (CFN). As Stach explained, misplaced atoms or slight shifts in their alignment often act as traps for the particles that carry electric current—negatively charged electrons or the positively charged “holes” left behind when electrons are knocked loose by photons of sunlight, making them more mobile. The idea behind solar cells is to separate the positive and negative charges and run them through a circuit so the current can be used to power houses, satellites, or even cities. Defects interrupt this flow of charges and keep the solar cell from being as efficient as it could be.

    But in the case of cadmium telluride, the scientists found that boundaries between individual crystals and “planar defects”—fault-like misalignments in the arrangement of atoms—create pathways for conductivity, not traps.

    2
    These CTAFM images show a cadmium telluride solar cell from the top (above) and side profile (bottom) with bright spots representing areas of higher electron conductivity. The images reveal that the conductive pathways coincide with crystal grain boundaries. Credit: University of Connecticut.

    Members of Bryan Huey’s group at the Institute of Materials Science at the University of Connecticut were the first to notice the surprising connection. In an effort to understand the effects of a chloride solution treatment that greatly enhances cadmium telluride’s conductive properties, Justin Luria and Yasemin Kutes studied solar cells before and after treatment. But they did so in a unique way.

    Several groups around the world had looked at the surfaces of such solar cells before, often with a tool known as a conducting atomic force microscope. The microscope has a fine probe many times sharper than the head of a pin that scans across the material’s surface to track the topographic features—the hills and valleys of the surface structure—while simultaneously measuring location-specific conductivity. Scientists use this technique to explore how the surface features relate to solar cell performance at the nanoscale.

    But no one had devised a way to make measurements beneath the surface, the most important part of the solar cell. This is where the UConn team made an important breakthrough. They used an approach developed and perfected by Kutes and Luria over the last two years to acquire hundreds of sequential images, each time intentionally removing a nanoscale layer of the material, so they could scan through the entire thickness of the sample. They then used these layer-by-layer images to build up a three-dimensional, high-resolution ‘tomographic’ map of the solar cell—somewhat like a computed tomography (CT) brain scan.


    Assembling the layer-by-layer CTAFM scans into a side-profile video file reveals the relationship between conductivity and planar defects throughout the entire thickness of the cadmium telluride crystal, including how the defects appear to line up to form continuous pathways of conductivity.Credit: University of Connecticut.

    “Everyone using these microscopes basically takes pictures of the ‘ground,’ and interprets what is beneath,” Huey said. “It may look like there’s a cave, or a rock shelf, or a building foundation down there. But we can only really know once we carefully dig, like archeologists, keeping track of exactly what we find every step of the way—though, of course, at a much, much smaller scale.”

    The resulting CT-AFM maps uniquely revealed current flowing most freely along the crystal boundaries and fault-like defects in the cadmium telluride solar cells. The samples that had been treated with the chloride solution had more defects overall, a higher density of these defects, and what appeared to be a high degree of connectivity among them, while the untreated samples had few defects, no evidence of connectivity, and much lower conductivity.

    Huey’s team suspected that the defects were so-called planar defects, usually caused by shifts in atomic alignments or stacking arrangements within the crystals. But the CTAFM system is not designed to reveal such atomic-scale structural details. To get that information, the UConn team turned to Stach, head of the electron microscopy group at the CFN, a DOE Office of Science User Facility.

    “Having previously shared ideas with Eric, it was a natural extension of our discovery to work with his group,” Huey said.

    Said Stach, “This is the exact type of problem the CFN is set up to handle, providing expertise and equipment that university researchers may not have to help drive science from hypothesis to discovery.”

    CFN staff physicist Lihua Zhang used a transmission electron microscope (TEM) and UConn’s results as a guide to meticulously study how atomic scale features of chloride-treated cadmium telluride related to the conductivity maps. The TEM images revealed the atomic structure of the defects, confirming that they were due to specific changes in the stacking sequence of atoms in the material. The images also showed clearly that these planar defects connected different grains in the crystal, leading to high-conductivity pathways for the movement of electrons and holes.

    “When we looked at the regions with good conductivity, the planar defects linked from one crystal grain to another, forming continuous pathways of conductance through the entire thickness of the material,” said Zhang. “So the regions that had the best conductivity were the ones that had a high degree of connectivity among these defects.”

    3
    These transmission electron microscopy images taken at Brookhaven’s CFN reveals how the stacking pattern of individual atoms (bright spots) shifts. The images confirmed that the bright spots of high conductivity observed with CTAFM imaging at UConn occurred at the interfaces between two different atomic alignments (left) and that these “planar defects” were continuous between individual crystals, creating pathways of conductivity (right). The labels WZ and ZB refer to the two atomic stacking sequences “wurtzite” and “zinc blende,” which are the two types of crystal structures cadmium telluride can form. No image credit.

    The authors say it’s possible that the chloride treatment helps to create the connectivity, not just more defects, but that more research is needed to definitively determine the most significant effects of the chloride solution treatment.

    In any case, Stach says that combining the CTAFM technique and electron microscopy, yields a “clear winner” in the search for more efficient, cost-competitive alternatives to silicon solar cells, which have nearly reached their limit for efficiency.

    “There is already a billion-dollar-a-year industry making cadmium telluride solar cells, and lots of work exploring other alternatives to silicon. But all of these alternatives, because of their crystal structure, have a higher tendency to form defects,” he said. “This work gives us a systematic method we can use to understand if the defects are good or bad in terms of conductivity. It can also be used to explore the effects of different processing methods or chemicals to control how defects form. In the case of cadmium telluride, we may want to find ways to make more of these defects, or look for other materials in which defects improve performance.”

    This research was supported by the DOE Office of Energy Efficiency and Renewable Energy (EERE)—including its Sunshot Program—and the DOE Office of Science. The cadmium telluride samples were provided by Andrew Moore of Colorado State University.

    The University of Connecticut’s Institute of Materials Science serves as the heart of materials science research at the University of Connecticut, with a mission of supporting materials research and industry throughout Connecticut and the Northeast. It houses the research labs of more than 30 core faculty, with an overall membership of 120 UConn faculty whose work benefits from the available facilities and expertise.

    See the full article here .

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    One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. The Laboratory’s almost 3,000 scientists, engineers, and support staff are joined each year by more than 5,000 visiting researchers from around the world.Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.
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  • richardmitnick 8:41 am on September 26, 2016 Permalink | Reply
    Tags: , Nanotechnology, , Tokyo Tech, Controllable light-emitting materials to advance light sensing and nano-medicine   

    From Tokyo Tech: “Controllable light-emitting materials to advance light sensing and nano-medicine” 

    tokyo-tech-bloc

    Tokyo Institute of Technology

    September 26, 2016
    No writer credit found

    Luminous bismuth: controllable light-emitting materials having the potential to advance high-intensity, light sensing and nano-medicine

    Scientists at Tokyo Tech have developed an approach to control the photoluminescence and solid-state emission of bismuth complexes by complexation with phenylazomethine dendrimers. This research
    [journal: Angewandte Chemie International Edition] not only sheds light on the structure of a rare, luminescent bismuth complex, but will also be used to advance the potential applications of luminous dendrimers, especially in light harvesting, sensing, electronics, photonics, and nano-medicine.

    Precise control of the photoluminescence, or light emission from matter after the absorption of photons, plays a considerable role in the advancement of various optical materials. Modification of the emission intensity, rather than the wavelength, presents a challenge for materials scientists, and simple strategies that can be used to control the intensity of phosphors are desired.

    The assembly of photoluminescent components within dendrimers, a class of synthetic polymers with branching, tree-like structures, may be a suitable method for controlling the emission intensity. However, the use of dendrimers as nano-capsules suffers from several drawbacks such as quenched luminescence due to high local concentrations of the phosphors, and controlling the number of phosphors within the dendrimer skeleton is difficult.

    To address these challenges, a group of scientists led by Kimihisa Yamamoto from the Laboratory for Chemistry and Life Science at Tokyo Institute of Technology developed luminous dendrimers with finely tunable optical properties using dendritic polyphenylazomethines (DPAs). Due to the electron donating ability of the phenylazomethines, the assembly of the metal ions could be controlled in a radial and stepwise fashion. The semi-rigid structure of the DPAs also allowed for the optical properties of the metal complexes to be maintained by preventing intermolecular electronic interactions. Thus, by careful selection of the ligand, the typical issues encountered with encapsulation of phosphors by dendrimers were overcome, and a new method to control emission intensity was achieved. In addition, the luminescence of the bismuth complexes could be switched on and off by the addition of a Lewis base or by redox control, owing to the reversible coordination bonds within the complexes. As such, Prof. Yamamoto and co-workers showed that the phenylazomethine-bismuth complexes are a new class of stimuli-responsive materials.

    Prof. Yamamoto and co-workers formed rare and functional photoluminescent dendrimers containing specific numbers of bismuth ions. The stimuli-responsive optical properties of the bismuth complexes, including the tunable emission intensity, are expected to be useful for the generation of novel sensors and optical standards. The results not only shed light on the structures of the novel bismuth complexes, but will also facilitate the future design of novel functional phosphors, which may have far-reaching applications in a variety of fields.

    1
    Figure. Luminous phenylazomethine-bismuth complexes were precisely assembled in the dendrimer. The emission intensity of one molecular dendrimer could be controlled by the number of bismuth units. The dendrimer skeleton enabled solid-state emission and optical switching induced by chemical and electronic stimuli. No image credit.

    See the full article here .

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    tokyo-tech-campus

    Tokyo Tech is the top national university for science and technology in Japan with a history spanning more than 130 years. Of the approximately 10,000 students at the Ookayama, Suzukakedai, and Tamachi Campuses, half are in their bachelor’s degree program while the other half are in master’s and doctoral degree programs. International students number 1,200. There are 1,200 faculty and 600 administrative and technical staff members.

    In the 21st century, the role of science and technology universities has become increasingly important. Tokyo Tech continues to develop global leaders in the fields of science and technology, and contributes to the betterment of society through its research, focusing on solutions to global issues. The Institute’s long-term goal is to become the world’s leading science and technology university.

     
  • richardmitnick 1:14 pm on September 22, 2016 Permalink | Reply
    Tags: , Nanotechnology, , Copper nanowires   

    From LLNL: “Livermore scientists purify copper nanowires” 


    Lawrence Livermore National Laboratory

    Sep. 22, 2016
    Anne M Stark
    stark8@llnl.gov
    925-422-9799

    1
    An illustration of the separation process from a mixture of various copper nanocrystal shapes (two tubes to the left) to pure nanowires and nanoparticles (two tubes to the right). No image credit.

    Cell phones and Apple watches could last a little longer due to a new method to create copper nanowires.

    A team of Lawrence Livermore National Laboratory (LLNL) scientists have created a new method to purify copper nanowires with a near-100 percent yield. These nanowires are often used in nanoelectronic applications.

    The research, which appears in the online edition of Chemical Communications and on the cover of the hardcopy issue, shows how the method can yield large quantities of long, uniform, high-purity copper nanowires. High-purity copper nanowires meet the requirements of nanoelectronic applications as well as provide an avenue for purifying industrial-scale synthesis of copper nanowires, a key step for commercialization and application.

    Metal nanowires (NWs) hold promise for commercial applications such as flexible displays, solar cells, catalysts and heat dissipators.

    The most common approach to create nanowires not only yield nanowires but also other low-aspect ratio shapes such as nanoparticles (NPs) and nanorods. These undesired byproducts are almost always produced due to difficulties in controlling the non-instantaneous nucleation of the seed particles as well as seed types, which causes the particles to grow in multiple pathways.

    “We created the purest form of copper nanowires with no byproducts that would affect the shape and purity of the nanowires,” said LLNL’s Fang Qian, lead author of the paper.

    The team demonstrated that copper nanowires, synthesized at a liter-scale, can be purified to near 100 percent yield from their nanoparticle side-products with a few simple steps.

    Functional nanomaterials are notoriously difficult to produce in large volumes with highly controlled composition, shapes and sizes. This difficulty has limited adoption of nanomaterials in many manufacturing technologies.

    “This work is important because it enables production of large quantities of copper nanomaterials with a very facile and elegant approach to rapidly separate nanowires from nanoparticles with extremely high efficiency,” said Eric Duoss, a principal investigator on the project. “We envision employing these purified nanomaterials for a wide variety of novel fabrication approaches, including additive manufacturing.”

    The key to success is the use of a hydrophobic surfactant in aqueous solution, together with an immiscible water organic solvent system to create a hydrophobic-distinct interface, allowing nanowires to crossover spontaneously due to their different crystal structure and total surface area from those of nanoparticles.

    “The principles developed from this particular case of copper nanowires may be applied to a variety of nanowire applications,” Qian said. “This purification method will open up new possibilities in producing high quality nanomaterials with low cost and in large quantities.”

    Other Livermore researchers include: Pui Ching Lan, Tammy Olson, Cheng Zhu and Christopher Spadaccini.

    “We also are developing high surface area foams as well as printable inks for additive manufacturing processes, such as direct-ink writing using the NWs,” said LLNL’s Yong Han, a corresponding author of the paper.

    The work was funded by the Laboratory Directed Research and Development program.

    See the full article here .

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  • richardmitnick 4:22 pm on September 19, 2016 Permalink | Reply
    Tags: , , Nanoscale Tetrapods Could Provide Early Warning of a Material’s Failure, Nanotechnology   

    From LBNL: “Nanoscale Tetrapods Could Provide Early Warning of a Material’s Failure” 

    Berkeley Logo

    Berkeley Lab

    September 19, 2016
    Dan Krotz
    dakrotz@lbl.gov
    510-486-4019

    1
    These atom-scale computer simulations of tetrapods show how they sense compression (left) and tension along one axis (right), both of which are crucial to detecting nanoscale crack formation. The color bar indicates the percent change of the tetrapods’ volume. (Credit: Berkeley Lab)

    Light-emitting, four-armed nanocrystals could someday form the basis of an early warning system in structural materials by revealing microscopic cracks that portend failure, thanks to recent research by scientists from the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) and UC Berkeley.

    The researchers embedded tetrapod-shaped quantum dots, which are nanosized semiconducting particles, in a polymer film. The tetrapods’ cores emit fluorescent light when their arms are twisted or bent out of shape. This indicates the polymer is undergoing a degree of tensile or compressive strain, from which stress over sub-micron-scale regions of the material can be detected. Such stress can cause nanoscale cracks to develop into macroscopic failure. Initial tests show the tetrapods can cycle more than 20 times without losing their ability to sense stress, and they don’t degrade the strength of the polymer in which they’re matrixed.

    So far the scientists have tested their approach in the lab, but in practice, all that would be needed to detect the tetrapods’ fluorescent warning is an off-the-shelf, portable spectrometer. A person could point a spectrometer at a steel beam, airplane wing, or any material that has the tetrapods embedded inside, and the spectrometer could potentially detect incipient cracks that are only 100 nanometers long.

    “This is the length scale at which cracks develop, which is when you want to catch them, well before the material fails,” says Shilpa Raja, who conducted the research while she was an affiliate in Berkeley Lab’s Materials Sciences Division and a PhD student at UC Berkeley. Raja is now a postdoctoral scholar at Stanford University. Robert Ritchie and Paul Alivisatos, also of the Materials Sciences Division and UC Berkeley, are the co-corresponding authors of a paper on this research published online in the journal Nano Letters (2016, vol. 16, issue 8, pgs. 5060-5067).

    “Our approach could also be a big step toward self-healing smart materials. The tetrapods could be coupled with nanosized repair particles to form a material that senses local stress and then repairs itself,” adds Raja.

    2
    This schematic shows a tetrapod-polymer film before and after it is stretched length-wise. The orange areas are clusters of tetrapods. The scientists found the color of light emitted by the tetrapods changed when the polymer was stretched. (Credit: Berkeley Lab)

    In addition to materials applications, the tetrapods could potentially be used to detect the presence of cancerous cells in tissue samples because cancerous cells have different mechanical properties than healthy cells, such as an increased stiffness.

    To develop the technique, the scientists started with a polymer widely used in airframes and other structures. They mixed tetrapod nanocrystals into the polymer and cast slabs of the mixture in petri dishes. The slabs were then mounted in a tensile tester and exposed to a laser. This allowed the researchers to simultaneously measure the slab’s fluorescence and mechanical stress.

    “This is a low-cost fabrication technique, and it resulted in the best optomechanical agreement between fluorescence and mechanical tests sensed by a nanocrystal in a film,” says Raja.

    Raja says the tetrapods’ shape makes them very sensitive to stress. Their four arms act as antennae that take stress from their immediate environment, amplify the stress, and transfer it to the core. The color of light emitted by the core indicates the degree of stress (and strain) felt by the arms.

    Their approach promises to be a big improvement over current ways to detect nanoscale stress in materials, particularly in the field. This can be done in the lab with techniques like atomic force microscopy and nano-indentation techniques, but these require a very controlled environment. Over the past five years, scientists have developed ways to matrix other stress-sensing nanoparticles into materials, but these methods have a very low signal-to-noise ratio and don’t use visible light detection. In addition, some of these approaches degrade the mechanical properties of the material they’re embedded in, or they can’t cycle back and forth, meaning they can only give a warning signal once.

    Atom-scale computer simulations of the tetrapod were conducted at the National Energy Research Scientific Computing Center (NERSC). And electron tomography of the tetrapods under stress was conducted at the Molecular Foundry. Both facilities are DOE Office of Science User Facilities located at Berkeley Lab.

    The research was funded in part by the Department of Energy’s Office of Science.

    See the full article here .

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  • richardmitnick 8:52 am on September 15, 2016 Permalink | Reply
    Tags: , Nanotechnology,   

    From UCLA: “UCLA chemists report new insights about properties of matter at the nanoscale” 

    UCLA bloc

    UCLA

    September 13, 2016
    Stuart Wolpert

    1
    A fluid with a viscosity like water enters UCLA-R3, where its viscosity at the nanoscale becomes like honey. Xing Jiang, Miguel García-Garibay/UCLA Chemistry and Biochemistry

    UCLA nanoscience researchers have determined that a fluid that behaves similarly to water in our day-to-day lives becomes as heavy as honey when trapped in a nanocage of a porous solid, offering new insights into how matter behaves in the nanoscale world.

    “We are learning more and more about the properties of matter at the nanoscale so that we can design machines with specific functions,” said senior author Miguel García-Garibay, dean of the UCLA Division of Physical Sciences and professor of chemistry and biochemistry.

    The research is published in the journal ACS Central Science.

    Just how small is the nanoscale? A nanometer is less than 1/1,000 the size of a red blood cell and about 1/20,000 the diameter of a human hair. Despite years of research by scientists around the world, the extraordinarily small size of matter at the nanoscale has made it challenging to learn how motion works at this scale.

    “This exciting research, supported by the National Science Foundation, represents a seminal advance in the field of molecular machines,” said Eugene Zubarev, a program director at the NSF. “It will certainly stimulate further work, both in basic research and real-life applications of molecular electronics and miniaturized devices. Miguel Garcia-Garibay is among the pioneers of this field and has a very strong record of high-impact work and ground-breaking discoveries.”

    Possible uses for complex nanomachines that could be much smaller than a cell include placing a pharmaceutical in a nanocage and releasing the cargo inside a cell, to kill a cancer cell, for example; transporting molecules for medical reasons; designing molecular computers that potentially could be placed inside your body to detect disease before you are aware of any symptoms; or perhaps even to design new forms of matter.

    To gain this new understanding into the behavior of matter at the nanoscale, García-Garibay’s research group designed three rotating nanomaterials known as MOFs, or metal-organic frameworks, which they call UCLA-R1, UCLA-R2 and UCLA-R3 (the “r” stands for rotor). MOFs, sometimes described as crystal sponges, have pores — openings which can store gases, or in this case, liquid.

    Studying the motion of the rotors allowed the researchers to isolate the role a fluid’s viscosity plays at the nanoscale. With UCLA-R1 and UCLA-R2 the molecular rotors occupy a very small space and hinder one another’s motion. But in the case of UCLA-R3, nothing slowed down the rotors inside the nanocage except molecules of liquid.

    García-Garibay’s research group measured how fast molecules rotated in the crystals. Each crystal has quadrillions of molecules rotating inside a nanocage, and the chemists know the position of each molecule.

    UCLA-R3 was built with large molecular rotors that move under the influence of the viscous forces exerted by 10 molecules of liquid trapped in their nanoscale surroundings.

    “It is very common when you have a group of rotating molecules that the rotors are hindered by something within the structure with which they interact — but not in UCLA-R3,” said García-Garibay, a member of the California NanoSystems Institute at UCLA. “The design of UCLA-R3 was successful. We want to be able to control the viscosity to make the rotors interact with one another; we want to understand the viscosity and the thermal energy to design molecules that display particular actions. We want to control the interactions among molecules so they can interact with one another and with external electric fields.”

    García-Garibay’s research team has been working for 10 years on motion in crystals and designing molecular motors in crystals. Why is this so important?

    “I can get a precise picture of the molecules in the crystals, the precise arrangement of atoms, with no uncertainty,” García-Garibay said. “This provides a large level of control, which enables us to learn the different principles governing molecular functions at the nanoscale.”

    García-Garibay hopes to design crystals that take advantage of properties of light, and whose applications could include advances in communications technology, optical computing, sensing and the field of photonics, which takes advantage of the properties of light; light can have enough energy to break and make bonds in molecules.

    “If we are able to convert light, which is electromagnetic energy, into motion, or convert motion into electrical energy, then we have the potential to make molecular devices much smaller,” he said. “There will be many, many possibilities for what we can do with molecular machines. We don’t yet fully understand what the potential of molecular machinery is, but there are many applications that can be developed once we develop a deep understanding of how motion takes place in solids.”

    Co-authors are lead author Xing Jiang, a UCLA graduate student in García-Garibay’s laboratory, who this year completed his Ph.D.; Hai-Bao Duan, a visiting scholar from China’s Nanjing Xiao Zhuang University who spent a year conducting research in García-Garibay’s laboratory; and Saeed Khan, a UCLA crystallographer in the department of chemistry and biochemistry.

    The research was funded by the National Science Foundation (grant DMR140268).

    García-Garibay will continue his research on molecular motion in crystals and green chemistry during his tenure as dean.

    See the full article here .

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    For nearly 100 years, UCLA has been a pioneer, persevering through impossibility, turning the futile into the attainable.

    We doubt the critics, reject the status quo and see opportunity in dissatisfaction. Our campus, faculty and students are driven by optimism. It is not naïve; it is essential. And it has fueled every accomplishment, allowing us to redefine what’s possible, time after time.

    This can-do perspective has brought us 12 Nobel Prizes, 12 Rhodes Scholarships, more NCAA titles than any university and more Olympic medals than most nations. Our faculty and alumni helped create the Internet and pioneered reverse osmosis. And more than 100 companies have been created based on technology developed at UCLA.

     
  • richardmitnick 5:44 am on September 10, 2016 Permalink | Reply
    Tags: , Electron beam microscope directly writes nanoscale features in liquid with metal ink, Nanotechnology,   

    From ORNL: “Electron beam microscope directly writes nanoscale features in liquid with metal ink” 

    i1

    Oak Ridge National Laboratory

    September 9, 2016
    Dawn Levy, Communications
    levyd@ornl.gov
    865.576.6448

    1
    To direct-write the logo of the Department of Energy’s Oak Ridge National Laboratory, scientists started with a gray-scale image. They used the electron beam of an aberration-corrected scanning transmission electron microscope to induce palladium from a solution to deposit as nanocrystals. Image credit: Oak Ridge National Laboratory, U.S. Dept. of Energy.

    Scientists at the Department of Energy’s Oak Ridge National Laboratory are the first to harness a scanning transmission electron microscope (STEM) to directly write tiny patterns in metallic “ink,” forming features in liquid that are finer than half the width of a human hair.

    The automated process is controlled by weaving a STEM instrument’s electron beam through a liquid-filled cell to spur deposition of metal onto a silicon microchip. The patterns created are “nanoscale,” or on the size scale of atoms or molecules.

    Usually fabrication of nanoscale patterns requires lithography, which employs masks to prevent material from accumulating on protected areas. ORNL’s new direct-write technology is like lithography without the mask.

    Details of this unique capability are published online in Nanoscale, a journal of the Royal Society of Chemistry, and researchers are applying for a patent. The technique may provide a new way to tailor devices for electronics and other applications.

    “We can now deposit high-purity metals at specific sites to build structures, with tailored material properties for a specific application,” said lead author Raymond Unocic of the Center for Nanophase Materials Sciences (CNMS), a DOE Office of Science User Facility at ORNL. “We can customize architectures and chemistries. We’re only limited by systems that are dissolvable in the liquid and can undergo chemical reactions.”

    The experimenters used grayscale images to create nanoscale templates. Then they beamed electrons into a cell filled with a solution containing palladium chloride. Pure palladium separated out and deposited wherever the electron beam passed.

    Liquid environments are a must for chemistry. Researchers first needed a way to encapsulate the liquid so the extreme dryness of the vacuum inside the microscope would not evaporate the liquid. The researchers started with a cell made of microchips with a silicon nitride membrane to serve as a window through which the electron beam could pass.

    Then they needed to elicit a new capability from a STEM instrument. “It’s one thing to utilize a microscope for imaging and spectroscopy. It’s another to take control of that microscope to perform controlled and site-specific nanoscale chemical reactions,” Unocic said. “With other techniques for electron-beam lithography, there are ways to interface that microscope where you can control the beam. But this isn’t the way that aberration-corrected scanning transmission electron microscopes are set up.”

    Enter Stephen Jesse, leader of CNMS’s Directed Nanoscale Transformations theme. This group looks at tools that scientists use to see and understand matter and its nanoscale properties in a new light, and explores whether those tools can also transform matter one atom at a time and build structures with specified functions. “Think of what we are doing as working in nanoscale laboratories,” Jesse said. “This means being able to induce and stop reactions at will, as well as monitor them while they are happening.”

    Jesse had recently developed a system that serves as an interface between a nanolithography pattern and a STEM’s scan coils, and ORNL researchers had already used it to selectively transform solids. The microscope focuses the electron beam to a fine point, which microscopists could move just by taking control of the scan coils. Unocic with Andrew Lupini, Albina Borisevich and Sergei Kalinin integrated Jesse’s scan control/nanolithography system within the microscope so that they could control the beam entering the liquid cell. David Cullen performed subsequent chemical analysis.

    “This beam-induced nanolithography relies critically on controlling chemical reactions in nanoscale volumes with a beam of energetic electrons,” said Jesse. The system controls electron-beam position, speed and dose. The dose—how many electrons are being pumped into the system—governs how fast chemicals are transformed.

    This nanoscale technology is similar to larger-scale activities, such as using electron beams to transform materials for 3D printing at ORNL’s Manufacturing Demonstration Facility. In that case, an electron beam melts powder so that it solidifies, layer by layer, to create an object.

    “We’re essentially doing the same thing, but within a liquid,” Unocic said. “Now we can create structures from a liquid-phase precursor solution in the shape that we want and the chemistry that we want, tuning the physiochemical properties for a given application.”

    Precise control of the beam position and the electron dose produces tailored architectures. Encapsulating different liquids and sequentially flowing them during patterning customizes the chemistry too.

    The current resolution of metallic “pixels” the liquid ink can direct-write is 40 nanometers, or twice the width of an influenza virus. In future work, Unocic and colleagues would like to push the resolution down to approach the state of the art of conventional nanolithography, 10 nanometers. They would also like to fabricate multi-component structures.

    The title of the paper is “Direct-write liquid phase transformations with a scanning transmission electron microscope.”

    This research was conducted at the Center for Nanophase Materials Sciences, a DOE Office of Science User Facility at ORNL. The DOE Office of Science supported the work. ORNL Laboratory Directed Research and Development funds supported a portion of the work.

    See the full article here .

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    ORNL is managed by UT-Battelle for the Department of Energy’s Office of Science. DOE’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time.

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  • richardmitnick 11:59 am on September 9, 2016 Permalink | Reply
    Tags: , , , Catalytically active gold nanoparticles, Nanotechnology   

    From BNL: “Collaboration Strikes Gold Pioneering a New Method for Catalyst Production” 

    Brookhaven Lab

    September 7, 2016
    Alexander Orlov
    Karen McNulty Walsh

    1
    Stony Brook University graduate student Qiyuan Wu and Brookhaven Lab Center for Functional Nanomaterials (CFN) staff scientist Dmitri Zakharov studying samples at the Titan Environmental Transmission Electron Microscope at the CFN. No image credit.

    An ultra-high-vacuum chamber with temperatures approaching absolute zero—the coldest anything can get—may be the last place you would expect to find gold. But a group of researchers from Stony Brook University (SBU) in collaboration with scientists at the Air Force Research Lab (AFRL) and the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory have just demonstrated that such a desolate place is ideal for producing catalytically active gold nanoparticles. A paper describing the first catalyst ever produced using their new method, called Helium Nanodroplet Deposition (HND), was recently published in the Journal of Physical Chemistry Letters.

    As lead researcher Alexander Orlov of SBU explains, HND works by boiling gold atoms in a vacuum to produce a vapor. The vaporized gold is then “picked up” by an extremely cold jet stream of liquid helium droplets that act to literally strike gold clusters against a solid collector downstream. Upon striking the collector, the liquid helium droplets instantly evaporate releasing helium gas and leaving behind unprecedentedly pure and stable gold nanoparticles.

    2
    This atomic-resolution image shows how single-nanometer-scale gold particles (round features at the top of the image), created by a “helium nandroplet deposition” method, sit on top of a single-crystal titanium dioxide support substrate (bottom portion of the image). The image was made using a scanning transmission electron microscope at the Center for Functional Nanomaterials at Brookhaven National Laboratory. No image credit.

    “This new method to produce active nanoparticles offers unique opportunities to create materials with unprecedented properties to solve energy and environmental problems,” Orlov said. “Our Brookhaven and AFRL collaborators made it possible for our students to access the most unique facilities in the world, which made all the difference in our research.”

    Qiyuan Wu, a graduate student working in Orlov’s laboratory and first author on the paper, performed much of the work to develop the method. Michael Lindsay and Claron Ridge of AFRL provided state-of-the-art facilities at Eglin Air Force Base, one of only a few places in the world with the capabilities required to generate the gold nanoparticles using the new technique. And a team at the Center for Functional Nanomaterials (CFN), a DOE Office of Science User Facility at Brookhaven Lab, used advanced imaging and characterization tools to study the nanoparticles’ catalytic activity.

    Specifically, Brookhaven scientists Eric Stach and Dmitri Zakharov of the CFN and Shen Zhao, then a postdoctoral fellow working under Stach, developed a method to deposit the gold nanoparticles onto a “catalyst support” structure they use for characterizing the stability of other nanomaterials. They then studied the characteristics of the nanoparticles, including their stability under reaction conditions, using the Titan Environmental Transmission Electron Microscope at the CFN. Further characterization by Zhao and CFN staff member Dong Su using aberration-corrected Scanning Transmission Electron Microscopy allowed the SBU researchers to understand how the droplets form.

    “This was part of a User project, that morphed into a collaboration,” said Stach, who leads the electron microscopy group at CFN. “It was a very nice study”—and an example of how the Office of Science User Facilities offer not just unique scientific equipment but also scientific expertise that can be essential to the success of a research project.

    Nanoparticles are of high research interest due to their improved properties compared to bulk materials. They have revolutionized technologies aimed at improving sustainability such as fuel cells, photocatalysts, and solar panels. The gold nanoparticle catalysts produced in this study are capable of converting poisonous carbon monoxide gas into carbon dioxide gas, an essential reaction that occurs in the catalytic converters of cars to reduce pollution and lower impacts on the environment.

    According to Orlov, the HND method is not limited to the production of gold nanoparticles, but can be applied to nearly all metals and can even produce challenging multi-metallic nanoparticles. The technique’s versatility and ability to produce clean and well-defined samples make it a powerful tool for the discovery of new catalysts and studying factors that affect catalyst performance.

    3
    Schematic of the Helium Nanodroplet Deposition method: A temperature-controlled nozzle produces an extremely cold jet stream of liquid helium droplets (blue bubbles) that pick up vaporized gold atoms (produced by boiling gold in a vacuum chamber). When the liquid helium droplets containing the gold vapor strike a solid collector downstream, the helium evaporates leaving behind unprecedentedly pure and stable gold nanoparticles. No image credit.

    The collaboration is currently researching how the parameters of HND can be adjusted to control catalyst performance.

    This research was funded by the Division of Materials Research at the National Science Foundation and the Air Force Office of Scientific Research. The work at CFN was funded by the DOE Office of Science.

    See the full article here .

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    One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. The Laboratory’s almost 3,000 scientists, engineers, and support staff are joined each year by more than 5,000 visiting researchers from around the world.Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.
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  • richardmitnick 10:13 am on September 9, 2016 Permalink | Reply
    Tags: , Nanotechnology, ,   

    From Physics Today: “Water flows freely through carbon nanotubes” 

    Physics Today bloc

    Physics Today

    08 September 2016
    Andrew Grant

    A new experiment confirms the slipperiness of the minuscule carbon cylinders but not their boron nitride counterparts.

    Despite the frenzy of research into carbon nanotubes (CNTs) over the past few decades (see, for example, Physics Today, June 1996, page 26), there isn’t much experimental evidence for one of the tiny structures’ most talked-about superpower­s: the ability to funnel water with nearly zero friction. The problem has been achieving the sensitivity to measure water transport rates as feeble as a femtoliter a second. Now Lydéric Bocquet and his colleagues at École Normale Supérieure in Paris have confirmed the slipperiness of CNTs by directly measuring water flow through individual nanotubes whose bores ranged from 15 nm to 50 nm. The researchers stuck a multiwalled CNT inside a small pipette and essentially turned the nanotube into the needle of a syringe. Pressure applied inside the pipette caused water to flow through the CNT and into a tank of water. Rather than tracking the water as it flowed through the tube, Bocquet and his team analyzed the motion of suspended polystyrene nanobeads in the tank to deduce the strength of the jet emerging from the CNT (see image below, which shows the response at various pressures). The results verify that CNTs allow water to flow extremely efficiently. Bocquet’s team also confirmed its 2010 prediction that the flow rate would increase as the tube’s radius decreased, although the dependence turned out to be roughly quadratic rather than quartic. The biggest surprise came when the researchers replaced the CNTs with nanotubes of boron nitride. Although the BN tubes are nearly structurally identical to their carbon counterparts (see Physics Today, November 2010, page 34), they proved far more resistant to water flow. The finding seems to suggest that electronic properties—CNTs are conductors; boron nitride nanotubes are insulators—play a role in hydrodynamics at very small scales. Bocquet and his team plan to investigate that possibility as they explore the nanotubes’ potential for applications such as water distillation and filtration. (E. Secchi et al., Nature 537, 210, 2016.)

    1

    See the full article here .

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    “Our mission

    The mission of Physics Today is to be a unifying influence for the diverse areas of physics and the physics-related sciences.

    It does that in three ways:

    • by providing authoritative, engaging coverage of physical science research and its applications without regard to disciplinary boundaries;
    • by providing authoritative, engaging coverage of the often complex interactions of the physical sciences with each other and with other spheres of human endeavor; and
    • by providing a forum for the exchange of ideas within the scientific community.”

     
  • richardmitnick 7:46 am on September 9, 2016 Permalink | Reply
    Tags: , , Nanotechnology, Rohit Karnik   

    From MIT: “Rohit Karnik seeks sustainable solutions through nanotechnology” 

    MIT News
    MIT News
    MIT Widget

    September 1, 2016
    Jennifer Chu | MIT News Office

    1
    “I try to guide my research by … asking myself the question, ‘What can we do today that will have a lasting impact and be conducive to a sustainable human civilization?’” says Rohit Karnik, an associate professor in MIT’s Department of Mechanical Engineering. Photo: Ken Richardson

    Engineer’s designs may help purify water, diagnose disease in remote regions of world.

    In Rohit Karnik’s lab, researchers are searching for tiny solutions to some of the world’s biggest challenges.

    In one of his many projects, Karnik, an associate professor in MIT’s Department of Mechanical Engineering, is developing a new microfluidic technology that can quickly and simply sort cells from small samples of blood. The surface of a microfluidic channel is patterned to direct certain cells to roll toward a reservoir for further analysis, while allowing the rest of the blood sample to pass through. With this design, Karnik envisions developing portable, disposable devices that doctors may use, even in remote regions of the world, to quickly diagnose conditions ranging from malaria to sepsis.

    Karnik’s group is also tackling issues of water purification. The researchers are designing filters from single layers of graphene, which are atom-thin sheets of carbon known for their exceptional strength. Karnik has devised a way to control the size and concentration of pores in graphene, and is tailoring single layers to filter out miniscule and otherwise evasive contaminants. The group has also successfully filtered salts using the technique and hopes to develop efficient graphene filters for water purification and other applications.

    In looking for water-purifying solutions, Karnik’s group also identified a surprisingly low-tech option: the simple tree branch. Karnik found that the pores within a pine branch that normally help to transport water up the plant are ideal for filtering bacteria from water. The group has shown that a peeled pine branch can filter out up to 99.00 percent of E. coli from contaminated water. Karnik’s group is building up on this work to explore the potential for simple and affordable wood-based water purification systems.

    “I try to guide my research by long-term sustainability, in a specific sense, by asking myself the question, ‘What can we do today that will have a lasting impact and be conducive to a sustainable human civilization?’ Karnik says. “I try to align myself with that goal.”

    From stargazer to tinkerer

    Karnik was born and raised in Pune, India, which was then a relatively quiet city 100 miles east of Mumbai. Karnik describes himself while growing up as shy, yet curious about the way the world worked. He would often set up simple experiments in his backyard, seeing, for instance, how transplanting ants from one colony to another would change the ants’ behavior. (The short answer: They fought, sometimes to the death.) He developed an interest in astronomy early on and often explored the night sky with a small telescope, from the roof of his family’s home.

    “I used to take my telescope up to the terrace in the middle of the night, which required three different trips up six or seven flights of stairs,” Karnik says. “I’d set the alarm for 3 a.m., go up, and do quite a bit of stargazing.”

    That telescope would soon serve another use, as Karnik eventually found that, by inverting it and adding another lens, he could repurpose the telescope as a microscope.

    “I built a little setup so I could look at different things, and I used to collect stuff from around the house, like onion peels or fungus growing on trees, to look at their cells,” Karnik says.

    When it came time to decide on a path of study, Karnik was inspired by his uncle, a mechanical engineer who built custom machines “that did all kinds of things, from making concrete bricks, to winding up springs,” Karnik says. “What I saw in mechanical engineering was the ability to building something that integrates across different disciplines.”

    Seeking balance and insight

    As an entering student at the Indian Institute of Technology Bombay, Karnik chose to study mechanical engineering over electrical engineering, which was the more popular choice among students at the time. For his thesis, he looked for new ways to model three-dimensional cracks in materials such as steel beams.

    Casting around for a direction after graduating, Karnik landed on the fast-growing field of nanotechnology. Arun Majumdar, an IIT alum and professor at the University of California at Berkeley, was studying energy conversion and biosensing in nanoscale systems. Karnik joined the professor’s lab as a graduate student, moving to California in 2002. For his graduate work, Karnik helped to develop a microfluidic platform to rapidly mix the contents of and test reactions occurring within droplets. He followed this work up with a PhD thesis in which he explored how fluid, flowing through tiny, nanometer-sized channels, can be controlled to sense and direct ions and molecules.

    Toward the end of his graduate work, Karnik interviewed for and ultimately accepted a faculty position at MIT. However, he was still completing his PhD thesis at Berkeley and had less than 4 years of experience beyond his bachelor’s degree. To help ease the transition, MIT offered Karnik an interim postdoc position in the lab of Robert Langer, the David H. Koch Institute Professor and a member of the Koch Institute for Integrative Cancer Research.

    “It was an insightful experience,” Karnik remembers. “For a mechanical engineer who’s never been outside mechanical engineering, I basically had little experience how to do things in biology. It opened up possibilities for working with the biomedical community.”

    When Karnik finally assumed his position as assistant professor of mechanical engineering in 2007, he experienced a tidal wave of deadlines, demands, and responsibilities — a common initiation for first-time faculty.

    “By its nature the job is overwhelming,” Karnik says. “The trick is how to maintain balance and sanity and do the things you like, without being distracted by the busyness around you, in some sense.”

    He says several things have helped him to handle and even do away with stress: walks, which he takes each day to work and around campus, as well as yoga and meditation.

    “If you can see things the way they are, by clearing away the filters your mind puts in place, you can get a clear perspective, and there are a lot of insights that come through,” Karnik says.

    See the full article here .

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    The mission of MIT is to advance knowledge and educate students in science, technology, and other areas of scholarship that will best serve the nation and the world in the twenty-first century. We seek to develop in each member of the MIT community the ability and passion to work wisely, creatively, and effectively for the betterment of humankind.

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  • richardmitnick 6:52 am on September 6, 2016 Permalink | Reply
    Tags: , , Nanodiamonds in an instant, Nanotechnology,   

    From Rice: “Nanodiamonds in an instant” 

    Rice U bloc

    Rice University

    September 6, 2016

    David Ruth
    713-348-6327
    david@rice.edu

    Mike Williams
    713-348-6728
    mikewilliams@rice.edu

    Rice University-led team morphs nanotubes into tougher carbon for spacecraft, satellites

    1
    Experiments at Rice University showed nanodiamonds and other forms of carbon were created when carbon nanotube pellets were fired at a target at hypervelocity. (Credit: Illustration by Pedro Alves da Silva Autreto)

    Superman can famously make a diamond by crushing a chunk of coal in his hand, but Rice University scientists are employing a different tactic.

    Rice materials scientists are making nanodiamonds and other forms of carbon by smashing nanotubes against a target at high speeds. Nanodiamonds won’t make anyone rich, but the process of making them will enrich the knowledge of engineers who design structures that resist damage from high-speed impacts.

    The diamonds are the result of a detailed study on the ballistic fracturing of carbon nanotubes at different velocities. The results showed that such high-energy impacts caused atomic bonds in the nanotubes to break and sometimes recombine into different structures.

    The work led by the labs of materials scientists Pulickel Ajayan at Rice and Douglas Galvao at the State University of Campinas, Brazil, is intended to help aerospace engineers design ultralight materials for spacecraft and satellites that can withstand impacts from high-velocity projectiles like micrometeorites.

    The research appears in the American Chemical Society journal ACS Applied Materials and Interfaces.

    Knowing how the atomic bonds of nanotubes can be recombined will give scientists clues to develop lightweight materials by rearranging those bonds, said co-lead author and Rice graduate student Sehmus Ozden.

    “Satellites and spacecraft are at risk of various destructive projectiles, such as micrometeorites and orbital debris,” Ozden said. “To avoid this kind of destructive damage, we need lightweight, flexible materials with extraordinary mechanical properties. Carbon nanotubes can offer a real solution.”

    The researchers packed multiwalled carbon nanotubes into spherical pellets and fired them at an aluminum target in a two-stage light-gas gun at Rice, and then analyzed the results from impacts at three different speeds.

    At what the researchers considered a low velocity of 3.9 kilometers per second, a large number of nanotubes were found to remain intact. Some even survived higher velocity impacts of 5.2 kilometers per second. But very few were found among samples smashed at a hypervelocity of 6.9 kilometers per second. The researchers found that many, if not all, of the nanotubes split into nanoribbons, confirming earlier experiments.

    Co-author Chandra Sekhar Tiwary, a Rice postdoctoral researcher, noted the few nanotubes and nanoribbons that survived the impact were often welded together, as observed in transmission electron microscope images.

    “In our previous report, we showed that carbon nanotubes form graphene nanoribbons at hypervelocity impact,” Tiwary said. “We were expecting to get welded carbon nanostructures, but we were surprised to observe nanodiamond as well.”

    The orientation of nanotubes both to each other and in relation to the target and the number of tube walls were as important to the final structures as the velocity, Ajayan said.

    “The current work opens a new way to make nanosize materials using high-velocity impact,” said co-lead author Leonardo Machado of the Brazil team.

    Machado is a graduate student at the State University of Campinas, Brazil, and the Federal University of Rio Grande do Norte, Brazil. Co-authors are Rice’s Robert Vajtai, an associate research professor, and Enrique Barrera, a professor of materials science and nanoengineering, and Pedro Alves da Silva of the State University of Campinas and the Federal University of ABC, Santo Andre, Brazil. Ajayan is chair of Rice’s Department of Materials Science and NanoEngineering, the Benjamin M. and Mary Greenwood Anderson Professor in Engineering and a professor of chemistry.

    The research was supported by the Department of Defense, the U.S. Air Force Office of Scientific Research and its Multidisciplinary University Research Initiative, NASA’s Johnson Space Center, the Sao Paulo Research Foundation, the Center for Computational Engineering and Sciences at Unicamp, Brazil, and the Brazilian Federal Agency for Support and Evaluation of Graduate Education.

    See the full article here .

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    Rice U campus

    In his 1912 inaugural address, Rice University president Edgar Odell Lovett set forth an ambitious vision for a great research university in Houston, Texas; one dedicated to excellence across the range of human endeavor. With this bold beginning in mind, and with Rice’s centennial approaching, it is time to ask again what we aspire to in a dynamic and shrinking world in which education and the production of knowledge will play an even greater role. What shall our vision be for Rice as we prepare for its second century, and how ought we to advance over the next decade?

    This was the fundamental question posed in the Call to Conversation, a document released to the Rice community in summer 2005. The Call to Conversation asked us to reexamine many aspects of our enterprise, from our fundamental mission and aspirations to the manner in which we define and achieve excellence. It identified the pressures of a constantly changing and increasingly competitive landscape; it asked us to assess honestly Rice’s comparative strengths and weaknesses; and it called on us to define strategic priorities for the future, an effort that will be a focus of the next phase of this process.

     
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