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São Miguel dos Campos, Brazil

News Article | April 23, 2014
Site: http://www.techtimes.com/rss/sections/energy.xml

U.S. researchers say they've used carbon structures just one atom thick to develop high-performance, low-cost energy-storing ultracapacitors. Combining two different carbon nanostructures possessing complementary properties -- single-walled nanotubes and graphene flakes -- yielded capacitors capable of containing large quantities of energy that can be quickly released to provide a power surge, the researchers at George Washington University say. Such ultracapacitors may provide increased performance in handheld electronics like smartphones and tablets, in electric vehicles, audio systems and other applications, they say. Excellent electronic, mechanical and thermal properties make both graphene and single-walled nanotubes attractive candidates for ultracapacitors, lead researcher Jian Li says; the trick was in bringing them together. Although both materials had been studied singly, few efforts had been made to combine them, Li's colleague Michael Keidar says. "In our lab we developed an approach by which we can obtain both single-walled carbon nanotubes and graphene, so we came up with the idea to take advantage of the two promising carbon nanomaterials together," he says. Writing in the Journal of Applied Physics, the researchers describe how they combine the two different nanostructures to create ink capable of being rolled onto paper, a normal separator used in current capacitor designs. The resulting specific capacitance -- defined as the energy performance of the capacitor compared with its weight -- was as much as three times that of a capacitor made from the carbon nanotubes by themselves, they reported. While the graphene flakes contribute good conductivity and a large surface area, the nanotubes hold the structure tougher in a uniformly spaced network, Li explained. The carbon nanotubes act as reinforcing bars, making the single-atom graphene flakes much easier work with. The resulting capacitor is inexpensive, since the desirable mix of nanostructures is simple to create in large amounts. The researchers said they were able to synthesize the graphene flakes and nanotubes simultaneously by vaporizing a hollow graphite rod filled with metallic catalyst powder with an electric arc. In addition to being cheap to produce, because the ultracapacitor is light and small it will lead to ever smaller and more efficient electronic devices, they researchers said. The research was conducted in the Micro-propulsion and Nanotechnology Laboratory at George Washington University.

Lee J.-C.,Nanotechnology Laboratory | Lee D.-W.,Nanotechnology Laboratory
Microelectronic Engineering

This paper presents a novel design of tactile sensing arrays with integrated strain gauges for the measurement of contact force. Surface stress or strain changes on the sensor area due to applied force are measured by the encapsulated Au gauges. The fabricated tactile sensors are highly flexible and durable so that they can conform to more complex surfaces without damaging the skin structure and the metal interconnects on the sensing array. The experimental results show the output characteristics are linear with contact force from 0 to 700 gf and a sensitivity of 3%/100 gf within the full scale range of 700 gf. The effect of electrode structure and position on the enhancement of sensitivity are also numerically simulated by a finite element method and verified experimentally. The measured tactile sensors are robust enough for direct contact with human and contaminants without undue care. © 2009 Elsevier B.V. All rights reserved. Source

Vadivelan V.,Bharathiar University | Chandar Shekar B.,Nanotechnology Laboratory
Springer Proceedings in Physics

Visible spectrum of solar light concentration on wavelength depended solar cell is to enhance the diffraction efficiency of the solar cell is our prime aim. Initial step of successful recording of high diffraction efficiency and good visible transmission holographic optical element were recorded. For this, we used ultra fine grain visible wavelength responsive silver halide holographic emulsion from Ultimate holography. The novelty of this work is three different laser sources of 442, 532 and 633 nm were used to record a single holographic transmission lens by using multiplex technique. The detail study of the holographic optical element recording is explained. © Springer India 2015. Source

Varadarajan V.,Bharathiar University | Bellan C.S.,Nanotechnology Laboratory
2015 2nd International Conference on Opto-Electronics and Applied Optics: Advances in Optical Sciences and Engineering II, IEM OPTRONIX 2015

Holography has been utilized for fabrication of optical elements in Silver halide photosensitive emulsion. The main drawback of transmission phase holograms in silver halide emulsion is getting darkens or discolor over the period of time, whenexposed to the ambient light, known as print-out effect. Hence this is unsuitable for out-door applications. In this study, holographic optical elements were fabricated in commercially available silver halide fine grain emulsion, almost completely controlled the darkening or discoloring effect by new chemical technique and it is practically examined by three different testing methods. Fabricated transmission phase holographic lenses have unique property of diffracting, focusing and concentrating of particularwavelength solar spectrumon wavelength dependable solar cells. © 2015 IEEE. Source

Yan J.,Nanotechnology Laboratory | Yan J.,State University of New York at Buffalo | Liu X.,State University of New York at Buffalo | Yao M.,State University of New York at Buffalo | And 4 more authors.
Chemistry of Materials

Lithium-sulfur (Li-S) batteries suffer from major problems including poor cycle performance and low efficiency, mainly due to the high solubility of intermediate polysulfides and their side-reactions with the Li-anode. Here, we report the development of advanced, multilayered, sulfur cathodes composed of alternately arranged, negatively charged S-carbon nanotube layers and positively charged S-polyaniline layers that effectively immobilize polysulfides and reduce polysulfide migration onto the Li-anode. The use of a layer-by-layer nanoassembly technique leads to a binder-free, three-dimensional porous cathode via electrostatic attraction and enables the fabrication of Li-S cells with remarkably improved performance including a long cycle life exceeding 600 cycles and a high Coulombic efficiency of 97.5% at the 1 C rate. Moreover, these Li-S cells have presented a high-rate response up to 2.5 C with high sulfur utilization (a reversible capacity of 1100 mAhg-1, 900 mAhg-1, 700 mAhg-1, and 450 mAhg-1 of sulfur at 0.3, 0.6, 1, and 2.5 C rates, respectively). The results provide important progress toward the understanding of the role of multilayered cathodes and the realization of high-efficiency and long-term service life for Li-S batteries. © 2015 American Chemical Society. Source

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