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Edge-Stress-Induced Warping of Graphene Sheets and Nanoribbons

Physical Review Letters 2008年第24期101卷 245501-245501页

作者： V. B. Shenoy C. D. Reddy A. Ramasubramaniam Y. W. Zhang Division of Engineering Brown University Providence Rhode Island 02912 USA Institute of High Performance Computing Singapore 138632 Program in Applied and Computational Mathematics Princeton University Princeton New Jersey 08544 USA Department of Materials Science and Engineering National University of Singapore Singapore 119260

We show that edge stresses introduce intrinsic ripples in freestanding graphene sheets even in the absence of any thermal effects. Compressive edge stresses along zigzag and armchair edges of the sheet cause out-of-plane warping to attain several degenerate mode shapes. Based on elastic plate theory, we identify scaling laws for the amplitude and penetration depth of edge ripples as a function of wavelength. We also demonstrate that edge stresses can lead to twisting and scrolling of nanoribbons as seen in experiments. Our results underscore the importance of accounting for edge stresses in thermal theories and electronic structure calculations for freestanding graphene sheets.

关键词： Nanoribbons

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Epitaxial piezoelectric thin films on flexible substrates

Epitaxial piezoelectric thin films on flexible substrates

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IEEE International Symposium on Applications of Ferroelectrics (ISAF)

作者： C.T. Shelton C. Dandeneau V. Matias B.J. Gibbons Materials Science Program Department of Mechanical Engineering Oregon State University Corvallis OR USA Superconductivity Technology Center Los Alamos National Laboratory Los Alamos NM USA

It is well known that the piezoelectric properties of a thin film can be influenced by crystallographic texture. At the extreme case, epitaxial thin films can be deposited on single crystal substrates (with appropriate lattice matching) to effectively achieve a single crystal thin film. Here, the maximum advantage of orientation dependence is found. Typically this has required small, expensive single crystalline substrates. In the past 10 years however, the technique of Ion Beam Assisted Deposition (IBAD) has been developed for applying a biaxial textured template to an arbitrary smooth surface. That is, biaxially textured MgO (~10 nm thick) can be deposited on a flexible, polycrystalline or amorphous substrate. This has opened up a new realm of materials integration possibilities, with the prime example being high-temperature superconducting wires. Here, the same template is utilized for deposition of epitaxial piezoelectric thin films onto flexible substrates.

关键词： Piezoelectric films Substrates Crystallization Sputtering Crystallography Lattices Ion beams Surface texture Amorphous materials Superconducting materials

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Moisture Absorption Phenomena in Green Composite Printed Circuit Board Prototypes

Moisture Absorption Phenomena in Green Composite Printed Cir...

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Pulsed Power Conference, 2005 IEEE;San Francisco,CA,USA

作者： John D. Lincoln Andrew A. Shapiro Jean-Daniel M. Saphores Oladele A. Ogunseitan Department of Chemical Engineering and Materials Science University of California Irvine CA USA Department of Electrical Engineering and Computer Science University of California Irvine CA USA Departments of Civil and Environmental Engineering Economics and Planning Policy and Design University of California Irvine CA USA Public Health Program College of Health Sciences and the Program in Industrial Ecology Department of Environmental Health Science and Policy University of California Irvine CA USA

ISBN: (纸本)9781424422722

This research developed the moisture-resistance of printed circuit board (PCB) laminate prototypes based on the non-toxic composite materials made from epoxidized linseed oil, melamine polyphosphate, and flax fibers. One of the key issues associated with using renewable base materials in composites is their sensitivity to moisture. A characterization of the properties of the 'green' printed circuit boards developed in the present study showed that moisture absorption for untreated fiber laminates (4.87% vs. established limit <0.8% for FR4 boards over a 24 hour submersion period) compromised electrical resistance and decreased dielectric breakdown to an unacceptable level. A theoretical model was used to target methods for reducing moisture absorption. Based on this model, we found that reductions in fiber diffusivity and fiber volume fraction substantially reduce composite diffusivity. Through the use of chemical treatment, moisture absorption over a 24 hour time period was reduced from 4.87% to 1.15%, which improved electrical properties. At the end of this study, 15 of 18 PCB property requirements were met, while 3 moisture-critical property targets were narrowly missed.

关键词： Printed Circuit Board Design for Environment Green Composite Moisture Absorption Natural Fiber

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Material analysis and characterization of cesium iodide (CsI) coated C fibers for field emission applications

Material analysis and characterization of cesium iodide (CsI...

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IEEE International Conference on Plasma science (ICOPS)

作者： Vasilios Vlahos Dane Morgan John H. Booske Interdisciplinary Materials Science Program Madison WI USA University of Wisconsin Madison Madison WI US Department of Electrical and Computer Engineering University of Wisconsin Madison Madison WI USA

Field emission cathodes consisting of cesium iodide (CsI) coated graphite fibers have been investigated as promising electron sources for high power microwave (HPM) devices. After conditioning for removing adsorbed water vapor, these cathodes have operated stably for more than one million pulses and release little or no plasma. One of the most useful properties of the Csl coatings appears to be a significant reduction in turn-on electric fields compared to un-coated graphite fiber cathodes. Computational investigations of the modification of the electronic properties of a C surface upon adsorption of both isolated and crystalline thin layers of Csl have been performed, indicating that these adsorbed layers are capable of significantly improving the emission properties of the C fibers by forming surface dipole layers . These layers are predicted to alter the electrostatic potential barrier for electron emission of the surface and lower the overall work function of the system from ~4.5 eV (pure graphite) down to ~1.2 - 1.4 eV. In order to further correlate the microscopic properties of the material system with the computational results obtained and the macroscopic performance characteristics of these cathodes, a series of materials characterizations are being carried out on the cathodes. These studies will facilitate the determination of both bulk and surface elemental composition of the cathodes, provide the value of the surface work function, determine the micro-morphological characteristics of the cathode's surface as well as the micro-structural characteristics of the bulk, and identify the role of any interface regions on the emission properties of the cathode. A more complete understanding of the mechanism(s) responsible for the superior emission characteristics of Csl coated C fibers and the nano-physics of the system will be obtained.

关键词： Cathodes Surface morphology materials Optical fiber devices Plasmas Coatings Surface treatment

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Monolithic integration of a p-n junction and porous silicon host matrix for next generation photovoltaics

Monolithic integration of a p-n junction and porous silicon ...

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2008 33rd IEEE Photovoltaic Specialists Conference

作者： J.P. Clarkson G. See B. Veeramachaneni L.L. Gadeken K.D. Hirschman P.M. Fauchet BetaBatt Inc. Houston TX USA Microelectronic Engineering Department Rochester Institute of Technology Rochester NY USA Department of Electrical and Computer Engineering University of Rochester Rochester NY USA Materials Science Program University of Rochester Rochester NY USA

We report on a novel three-dimensional Si p-n junction that is capable of performing photovoltaic energy conversion. Vertically aligned pores with a very high aspect ratio of ≫ 100 were formed into a p-type Si substrate through an electrochemical etching process. A conformal p-n junction was then created in the etched porous silicon region by introducing phosphorous dopants through proximity rapid thermal diffusion. Al electrodes were subsequently evaporated on the front and back sides of the diode to establish electrical contact to the n-type and p-type regions respectively. Typical device structures resulted in highly three-dimensional diodes with pores extending up to 100 μm deep into the bulk Si. Porous films this thick correspond to an effective internal surface area of ∼ 5150 cm 2 /cm 3 . This ultimately makes the device applicable to both inorganic and organic next generation photovoltaics where it is desirable to maximize the amount of interfacing surface to a given photoactive compound. Dark box and illuminated I–V measurements of the device demonstrated successful monolithic integration of a p-n diode and a high internal surface area host matrix.

关键词： Monolithic integrated circuits P-n junctions Silicon Photovoltaic cells Diodes Etching Energy conversion Rapid thermal processing Electrodes Contacts

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Nanoscale porous silicon waveguides for biosensing applications

Nanoscale porous silicon waveguides for biosensing applicati...

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IEEE Photonics Conference (IPC)

作者： G. Rong X. Wei C. Kang M. Liscidini J. E. Sipe R. L. Mernaugh S. M. Weiss Department of Electrical Engineering and Computer Science Vanderbilt University Nashville TN USA Interdisciplinary Graduate Program in Materials Science Vanderbilt University Nashville TN USA Department of Physics and Institute for Optical Sciences University of Toronto Toronto ONT Canada Department of Biochemistry Vanderbilt University Nashville TN USA

Nanoscale porous silicon waveguides, both on silicon substrates and free-standing membranes, are explored for biosensing applications. Measured detection limits in the nanomolar range are reported for DNA sensing.

关键词： Silicon Biosensors Optical waveguides Gratings Biomembranes Resonance DNA Biological materials Optical materials Optical surface waves

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Phonon engineered silicon - diamond nanoscale heterostructures with enhanced carrier mobility

Phonon engineered silicon - diamond nanoscale heterostructur...

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IEEE Silicon Nanoelectronics Workshop (SNW)

作者： D.L. Nikal E.P. Pokatilov A.A. Balandin University of California Riverside Riverside CA US Department of Electrical Engineering University of California - Riverside Riverside California USA Department of Theoretical Physics State University of Moldova Chisinau Chisinau Republic of Moldova Materials Science and Engineering Program University of California - Riverside Riverside California USA

ISBN: (纸本)9781424420711

Maintaining high electron mobility in Si channels as the transistor feature sizes continue to decrease is important for the development of Si nanoelectronics. Here we propose a novel way for the enhancement of the phonon-limited electron mobility in Si ultra-thin films. The method works over the wide range of temperatures and does not require SiGe alloy under layers which deteriorate heat removal. Our calculations show that the modification of the acoustic phonon spectrum in Si thin films embedded within ¿acoustically hard¿ barriers results in the suppression of the electron - phonon scattering rates and corresponding increase in mobility.

关键词： Phonons Electron mobility Maintenance engineering HEMTs MODFETs Nanoelectronics Semiconductor films Temperature distribution Silicon germanium Germanium silicon alloys

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Plasma induced damage of aggressively scaled gate dielectric (EOT less than or equal 1.0nm) in metal gate/high-k dielectric CMOSFETs

Plasma induced damage of aggressively scaled gate dielectric...

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46th Annual 2008 IEEE International Reliability Physics Symposium, IRPS

作者： Min, Kyung Seok Kang, Chang Yong Yoo, Ook Sang Park, Byoung Jae Kim, Sung Woo Young, Chadwin D. Heh, Dawei Bersuker, Gennadi Lee, Byoung Hun Yeom, Geun Young SEMATECH 2706 Montopolis Drive Austin TX 78741 United States Department of Advanced Materials Science and Engineering Sungkyunkwan University Suwon. 440-746 Korea Republic of University of Texas Austin TX 78758 United States Dept. of Electronics Engineering Chungnam National Univ. Korea Republic of National Program for Tera-Level Nanodevice Hawolgok-dong Sungbuk-ku Seoul 136-791 Korea Republic of

No abstract available

ISBN: (纸本)9781424420506

No abstract available

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Microstructural development of porous β-Si3N4 ceramics prepared by pressureless-sintering compositions in the Si-Re-O-N quaternary systems (Re=La, Nd, Sm, Y, Yb)

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31st International Conference on Advanced Ceramics and Composites

作者： Quinlan, Mervin Heard, D. Plucknett, Kevin P. Garrido, Liliana Genova, Luis Materials Engineering Program Department of Process Engineering and Applied Science Dalhousie University 1360 Barrington Street Halifax NS B3J 1Z1 Canada M.B. Gonnet. Pcia De Buenos Aires Argentina IPEN Instituto de Pesquisas Energéticas e Nucleares CCTM Centro de Ciência e Technologia de Materiais Cidade Universitária Travessa R 400 05508-900 São Paulo Brazil

ISBN: (纸本)9780470196403

It has recently been demonstrated that porous β-Si3N 4 can be engineered to provide similar mechanical properties to dense β-Si3N4, with the additional benefits of reduced mass. Porous p-Si3N4 applications could potentially include filtration media, thermal shock resistant components and high-strength, lightweight structural components. Prior work in Japan has shown that flexural strengths exceeding 1 GPa can be achieved by tailoring the microstructure of the β-Si3N4 grains, such that moderately high aspect ratios are obtained after sintering (up to 10:1) with considerable anisotropic grain alignment, while maintaining porosity levels of ∼10-15 %. In the present study, β-Si3N4 ceramics containing higher porosity levels are generated via pressureless sintering in a nitrogen atmosphere, with the addition of single rare earth oxide sintering aids. The oxide additives have been chosen from both the lanthanide (La, Nd, Sm, Yb) and Group IIIB (Y) elements. In each case, the compositions were milled for 24 hours, cold isostatically pressed and then sintered in nitrogen (0.1 MPa) at temperatures ranging from 1500 to 1750°C. Post sinter microstructural characterization was performed using scanning electron microscopy and x-ray diffraction. It is noted that densification and phase transformation kinetics are both strongly influenced by the oxide chosen.

关键词： X ray diffraction

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Fluid-filled tunable mold for polymer lenses

Fluid-filled tunable mold for polymer lenses

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Conference on Lasers and Electro-Optics (CLEO)

作者： Sung Hwan Cho Frank S. Tsai Robert Vasko Jeff Vasko Yu-Hwa Lo Materials Science and Engineering Program Jacobs School of Engineering University of California San Diego La Jolla CA USA ECE Department Jacobs School of Engineering University of California San Diego La Jolla CA USA Rhevision Technology Inc. San Diego CA USA

Polymer lenses were fabricated using a fluid-filled tunable molding process providing a simple and cost-effective way to control lens curvature and shape. This approach enables fast prototyping and shortens the design... 详细信息

ISBN: (纸本)9781557528599

关键词： Lenses Biomembranes Shape control Optical design Rough surfaces Surface roughness Jacobian matrices Optical polymers Optical interferometry Distortion measurement

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