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Suganuma K.,Tokyo University of Agriculture and Technology | Suganuma K.,Teijin Ltd | Matsuda H.,Teijin Ltd | Cheng H.N.,Southern Regional Research Center | And 4 more authors.
Polymer Testing | Year: 2014

Poly(lactic acid), (PLA), is a well known bioplastic derived from agri-based renewable materials. Because PLA's material properties depend largely on its tacticity, an improved test method for PLA tacticity would be useful. NMR analysis of PLA tacticity is revisited in this work, especially the assignments of NMR peaks from CH carbon and CH3 proton at the tetrad level in deuterated pyridine. The methyl protons are better resolved in pyridine due to solvent effects such as ring current shielding of the aromatic ring and electric field effect from the nitrogen lone pair. As an aid for the tacticity assignments, two-dimensional NMR spectra of poly(DL-lactic acid) (L/D = 50/50) and relative intensities of PLA samples have been used. The new assignments provide more detailed understanding of the 1H and 13C NMR spectra of PLA. © 2014 Elsevier Ltd. All rights reserved. Source


News Article | August 30, 2016
Site: http://www.cemag.us/rss-feeds/all/rss.xml/all

A device made of bilayer graphene, an atomically thin hexagonal arrangement of carbon atoms, provides experimental proof of the ability to control the momentum of electrons and offers a path to electronics that could require less energy and give off less heat than standard CMOS transistors. It is one step forward in a new field of physics called valleytronics. “Current silicon-based transistor devices rely on the charge of electrons to turn the device on or off, but many labs are looking at new ways to manipulate electrons based on other variables, called degrees of freedom,” says Jun Zhu, associate professor of physics at Penn State, who directed the research. “Charge is one degree of freedom. Electron spin is another, and the ability to build transistors based on spin, called spintronics, is still in the development stage. A third electronic degree of freedom is the valley state of electrons, which is based on their energy in relation to their momentum.” Think of electrons as cars and the valley states as blue and red colors, Zhu suggests, just as a way to differentiate them. Inside a sheet of bilayer graphene, electrons will normally occupy both red and blue valley states and travel in all directions. The device her Ph.D. student, Jing Li, has been working on can make the red cars go in one direction and the blue cars in the opposite direction. “The system that Jing created puts a pair of gates above and below a bilayer graphene sheet. Then he adds an electric field perpendicular to the plane,” Zhu says. “By applying a positive voltage on one side and a negative voltage on the other, a bandgap opens in bilayer graphene, which it doesn’t normally have. In the middle, between the two sides, we leave a physical gap of about 70 nanometers,” Li explains. Inside this gap lives one-dimensional metallic states, or wires, that are color-coded freeways for electrons. The red cars travel in one direction and the blue cars travel in the opposite direction. In theory, colored electrons could travel unhindered along the wires for a long distance with very little resistance. Smaller resistance means power consumption is lower in electronic devices and less heat is generated. Both power consumption and thermal management are challenges in current miniaturized devices. Zhu adds, “It’s quite remarkable that such states can be created in the interior of an insulating bilayer graphene sheet, using just a few gates. They are not yet resistance-free, and we are doing more experiments to understand where resistance might come from. We are also trying to build valves that control the electron flow based on the color of the electrons. That’s a new concept of electronics called valleytronics.” Li worked closely with the technical staff of Penn State’s nanofabrication facility to turn the theoretical framework into a working device. "The alignment of the top and bottom gates was crucial and not a trivial challenge. The state of the art electron beam lithography capabilities at the Penn State Nanofabrication Laboratory allowed Jing to create this novel device with nanoscale features," says Chad Eichfeld, Nanolithography Engineer. Their paper, titled “Gate-controlled topological conducting channels in bilayer graphene,” appears online in the journal Nature Nanotechnology. Additional authors include Ke Wang and Yafei Ren and their advisor Zenhua Qiao of University of Science and Technology of China, who performed numerical studies to model the behavior of the wires. The high-quality hexagonal Boron Nitride crystals used in the experiment came from Kenji Watanabe and Takashi Taniguchi of National Institute for Material Science, Japan. Two undergraduate students, Kenton McFaul and Zachary Zern, contributed to the research. Funding was provided by the U.S. Office of Naval Research, the National Science Foundation and funding agencies in China and Japan. Kenton McFaul, a visiting student from Grove City College, was supported by a Research Experience for Undergraduates grant from the NSF NNIN. Jun Zhu is a member of the Center for 2-Dimensional and Layered Materials in Penn State’s Materials Research Institute.


Home > Press > Device to control 'color' of electrons in graphene provides path to future electronics Abstract: A device made of bilayer graphene, an atomically thin hexagonal arrangement of carbon atoms, provides experimental proof of the ability to control the momentum of electrons and offers a path to electronics that could require less energy and give off less heat than standard silicon-based transistors. It is one step forward in a new field of physics called valleytronics. "Current silicon-based transistor devices rely on the charge of electrons to turn the device on or off, but many labs are looking at new ways to manipulate electrons based on other variables, called degrees of freedom," said Jun Zhu, associate professor of physics, Penn State, who directed the research. "Charge is one degree of freedom. Electron spin is another, and the ability to build transistors based on spin, called spintronics, is still in the development stage. A third electronic degree of freedom is the valley state of electrons, which is based on their energy in relation to their momentum." Think of electrons as cars and the valley states as blue and red colors, Zhu suggested, just as a way to differentiate them. Inside a sheet of bilayer graphene, electrons will normally occupy both red and blue valley states and travel in all directions. The device her Ph.D. student, Jing Li, has been working on can make the red cars go in one direction and the blue cars in the opposite direction. "The system that Jing created puts a pair of gates above and below a bilayer graphene sheet. Then he adds an electric field perpendicular to the plane," Zhu said. "By applying a positive voltage on one side and a negative voltage on the other, a bandgap opens in bilayer graphene, which it doesn't normally have," Li explained. "In the middle, between the two sides, we leave a physical gap of about 70 nanometers." Inside this gap live one-dimensional metallic states, or wires, that are color-coded freeways for electrons. The red cars travel in one direction and the blue cars travel in the opposite direction. In theory, colored electrons could travel unhindered along the wires for a long distance with very little resistance. Smaller resistance means power consumption is lower in electronic devices and less heat is generated. Both power consumption and thermal management are challenges in current miniaturized devices. "Our experiments show that the metallic wires can be created," Li said. "Although we are still a long way from applications." Zhu added, "It's quite remarkable that such states can be created in the interior of an insulating bilayer graphene sheet, using just a few gates. They are not yet resistance-free, and we are doing more experiments to understand where resistance might come from. We are also trying to build valves that control the electron flow based on the color of the electrons. That's a new concept of electronics called valleytronics." Li worked closely with the technical staff of Penn State's nanofabrication facility to turn the theoretical framework into a working device. "The alignment of the top and bottom gates was crucial and not a trivial challenge," said Chad Eichfeld, nanolithography engineer. "The state-of-the-art electron beam lithography capabilities at the Penn State Nanofabrication Laboratory allowed Jing to create this novel device with nanoscale features." ### Their paper, "Gate-controlled topological conducting channels in bilayer graphene," appears online today (Aug 29) in the journal Nature Nanotechnology. Additional authors include Ke Wang and Yafei Ren and their advisor Zenhua Qiao of University of Science and Technology of China, who performed numerical studies to model the behavior of the wires. The high-quality hexagonal Boron Nitride crystals used in the experiment came from Kenji Watanabe and Takashi Taniguchi of National Institute for Material Science, Japan. Two undergraduate students, Kenton McFaul and Zachary Zern, contributed to the research. The U.S. Office of Naval Research, the National Science Foundation and funding agencies in China and Japan funded this project. Kenton McFaul, a visiting student from Grove City College, was supported by a Research Experience for Undergraduates grant from the NSF NNIN. Jun Zhu is a member of the Center for 2-Dimensional and Layered Materials in Penn State's Materials Research Institute. For more information, please click If you have a comment, please us. Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.


Huang Z.D.,University of Kiel | Bensch W.,University of Kiel | Lotnyk A.,Institute for Material Science | Kienle L.,Institute for Material Science | And 4 more authors.
Journal of Molecular Catalysis A: Chemical | Year: 2010

Ex situ and in situ decomposition of the sulfur-containing precursors ammonium thiomolybdate (ATM) and nickel diethyldithiocarbamate (NiDETC) was applied for the preparation of SBA-15-supported NiMo catalysts. The catalysts were characterized with X-ray diffraction (XRD), N2-physisorption and high-resolution transmission electron microscopy (HRTEM). The in situ activation performed in the presence of hydrocarbon solvent during the HDS of dibenzothiophene is more beneficial for the preparation of NiMo catalysts with a high HDS performance compared to the ex situ activation mode using a N2/H2 (10% H2) gas flow at 773 K. Low MoS2 stacking, small MoS2 slabs and a less pronounced pore blocking present in the in situ activated NiMo/SBA-15 materials might be mainly responsible for the high HDS performance. In addition, the in situ decomposition mode is a "softer" reducing atmosphere and represents a beneficial condition for the generation of the catalytic active "NiMoS" phase. © 2010 Elsevier B.V. All rights reserved. Source


Konig J.D.,Fraunhofer Institute for Physical Measurement Techniques | Winkler M.,Fraunhofer Institute for Physical Measurement Techniques | Buller S.,Institute for Inorganic Chemistry | Bensch W.,Institute for Inorganic Chemistry | And 3 more authors.
Journal of Electronic Materials | Year: 2011

In this work, Bi 2Te 3-Sb 2Te 3 superlattices were prepared by the nanoalloying approach. Very thin layers of Bi, Sb, and Te were deposited on cold substrates, rebuilding the crystal structure of V 2VI 3 compounds. Nanoalloyed super- lattices consisting of alternating Bi 2Te 3 and Sb 2Te 3 layers were grown with a thickness of 9 nm for the individual layers. The as-grown layers were annealed under different conditions to optimize the thermoelectric parameters. The obtained layers were investigated in their as-grown and annealed states using x-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive x-ray (EDX) spectroscopy, transmission electron microscopy (TEM), and electrical measurements. A lower limit of the elemental layer thickness was found to have c-orientation. Pure nanoalloyed Sb 2Te 3 layers were p-type as expected; however, it was impossible to synthesize p-type Bi 2Te 3 layers. Hence the Bi 2Te 3-Sb 2Te 3 superlattices consisting of alternating n- and p-type layers showed poor thermoelectric properties. © 2011 TMS. Source

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