New Laser Technology Could Kill Viruses and Improve DVDs

New Laser Technology Could Kill Viruses and Improve DVDs

  10:16:00 AM    Science Lover

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A team led by a professor at the University of California, Riverside Bourns College of Engineering has made a discovery in semiconductor nanowire laser technology that could potentially do everything from kill viruses to increase storage capacity of DVDs.

From left, Guoping Wang, a graduate student, Jianlin Liu, a professor of electrical engineering, and Sheng Chu, a graduate student. (Credit: Image courtesy of University of California - Riverside)

Ultraviolet semiconductor diode lasers are widely used in data processing, information storage and biology. Their applications have been limited, however, by size, cost and power. The current generation of ultraviolet lasers is based on a material called gallium nitride, but Jianlin Liu, a professor of electrical engineering, and his colleagues have made a breakthrough in zinc oxide nanowire waveguide lasers, which can offer smaller sizes, lower costs, higher powers and shorter wavelengths.

Until now, zinc oxide nanowires couldn't be used in real world light emission applications because of the lack of p-type, or positive type, material needed by all semiconductors. Liu solved that problem by doping the zinc oxide nanowires with antimony, a metalloid element, to create the p-type material.

The p-type zinc oxide nanowires were connected with n-type, or negative type, zinc oxide material to form a device called p-n junction diode. Powered by a battery, highly directional laser light emits only from the ends of the nanowires.

"People in the zinc oxide research community throughout the world have been trying hard to achieve this for the past decade," Liu said. "This discovery is likely to stimulate the whole field to push the technology further."

Liu's findings have been published in the July issue of Nature Nanotechnology. Co-authors are: Sheng Chu, Guoping Wang, Jieying Kong, Lin Li and Jingjian Ren, all graduate students at UC Riverside; Weihang Zhou, a student at Fudan University in China; Leonid Chernyak, a professor of physics at the University of Central Florida; Yuqing Lin, a graduate student at the University of Central Florida; and Jianze Zhao, a visiting student from Dalian University of Technology in China.

The discovery could have a wide-range of impacts.



For information storage, the zinc oxide nanowire lasers could be used to read and process much denser data on storage media such as DVDs because the ultraviolet has shorter wavelength than other lights, such as red. For example, a DVD that would store two hours of music could store four or six hours using the new type of laser.

For biology and medical therapeutics, the ultra-small laser light beam from a nanowire laser can penetrate a living cell, or excite or change its function from a bad cell to a good cell. The light could also be used to purify drinking water.

For photonics, the ultraviolet light could provide superfast data processing and transmission. Reliable small ultraviolet semiconductor diode lasers may help develop ultraviolet wireless communication technology, which is potentially better than state-of-the-art infrared communication technologies used in various electronic information systems.

While Liu and the students in his laboratory have demonstrated the p-type doping of zinc oxide and electrically powered nanowire waveguide lasing in the ultraviolet range, he said more work still needs to be done with the stability and reliability of the p-type material.

The work on the ZnO device was in part supported by Army Research Office Young Investigator Program and the National Science Foundation. The work on p-type ZnO was supported by the Department of Energy.

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First self-powered device with wireless data transmission

First self-powered device with wireless data transmission

  9:55:00 AM    Science Lover

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Scientists are reporting development of the first self-powered nano-device that can transmit data wirelessly over long distances. In a study in ACS's journal Nano Letters, they say it proves the feasibility of a futuristic genre of tiny implantable medical sensors, airborne and stationary surveillance cameras and sensors, wearable personal electronics, and other devices that operate independently without batteries on energy collected from the environment.

Zhong Lin Wang and colleagues explain that advances in electronics have opened the door to developing tiny devices that operate battery-free on minute amounts of electricity that can be harvested from the pulse of a blood vessel, a gentle breeze, or the motions of a person walking. "It is entirely possible to drive the devices by scavenging energy from sources in the environment such as gentle airflow, vibration, sonic wave, solar, chemical, and/or thermal energy," the scientists explain.

The device consists of a nanogenerator that produces electricity from mechanical vibration/triggering, a capacitor to store the energy, and electronics that include a sensor and a radio transmitter similar to those in Bluetooth mobile phone headsets. Their device transmitted wireless signals that could be detected by an ordinary commercial radio at distances of more than 30 feet.

More information: “Self-Powered System with Wireless Data Transmission” Nano Lett., 2011, 11 (6), pp 2572–2577 DOI: 10.1021/nl201505c

Abstract

We demonstrate the first self-powered system driven by a nanogenerator (NG) that works wirelessly and independently for long-distance data transmission. The NG was made of a free cantilever beam that consisted of a five-layer structure: a flexible polymer substrate, ZnO nanowire textured films on its top and bottom surfaces, and electrodes on the surfaces. When it was strained to 0.12% at a strain rate of 3.56% S–1, the measured output voltage reached 10 V, and the output current exceeded 0.6 μA (corresponding power density 10 mW/cm3). A system was built up by integrating a NG, rectification circuit, capacitor for energy storage, sensor, and RF data transmitter. Wireless signals sent out by the system were detected by a commercial radio at a distance of 5–10 m. This study proves the feasibility of using ZnO nanowire NGs for building self-powered systems, and its potential application in wireless biosensing, environmental/infrastructure monitoring, sensor networks, personal electronics, and even national security.

Provided by American Chemical Society

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New Solar Cell Technology Greatly Boosts Efficiency

New Solar Cell Technology Greatly Boosts Efficiency

  7:17:00 PM    Science Lover

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With the creation of a 3-D nanocone-based solar cell platform, a team led by Oak Ridge National Laboratory's Jun Xu has boosted the light-to-power conversion efficiency of photovoltaics by nearly 80 percent.

Nanocone-based solar cell consisting of n-type 
nanocones, p-type matrix, transparent conductive 
oxide (TCO) and glass substrate. (Credit: Image 
courtesy of DOE/Oak Ridge National Laboratory)

The technology substantially overcomes the problem of poor transport of charges generated by solar photons. These charges -- negative electrons and positive holes -- typically become trapped by defects in bulk materials and their interfaces and degrade performance.

"To solve the entrapment problems that reduce solar cell efficiency, we created a nanocone-based solar cell, invented methods to synthesize these cells and demonstrated improved charge collection efficiency," said Xu, a member of ORNL's Chemical Sciences Division.

The new solar structure consists of n-type nanocones surrounded by a p-type semiconductor. The n-type nanoncones are made of zinc oxide and serve as the junction framework and the electron conductor. The p-type matrix is made of polycrystalline cadmium telluride and serves as the primary photon absorber medium and hole conductor.

With this approach at the laboratory scale, Xu and colleagues were able to obtain a light-to-power conversion efficiency of 3.2 percent compared to 1.8 percent efficiency of conventional planar structure of the same materials.

"We designed the three-dimensional structure to provide an intrinsic electric field distribution that promotes efficient charge transport and high efficiency in converting energy from sunlight into electricity," Xu said.

Key features of the solar material include its unique electric field distribution that achieves efficient charge transport; the synthesis of nanocones using inexpensive proprietary methods; and the minimization of defects and voids in semiconductors. The latter provides enhanced electric and optical properties for conversion of solar photons to electricity.

Because of efficient charge transport, the new solar cell can tolerate defective materials and reduce cost in fabricating next-generation solar cells.

"The important concept behind our invention is that the nanocone shape generates a high electric field in the vicinity of the tip junction, effectively separating, injecting and collecting minority carriers, resulting in a higher efficiency than that of a conventional planar cell made with the same materials," Xu said.

Research that forms the foundation of this technology was accepted by this year's Institute of Electrical and Electronics Engineers photovoltaic specialist conference and will be published in the IEEE Proceedings. The papers are titled "Efficient Charge Transport in Nanocone Tip-Film Solar Cells" and "Nanojunction solar cells based on polycrystalline CdTe films grown on ZnO nanocones."

The research was supported by the Laboratory Directed Research and Development program and the Department of Energy's Office of Nonproliferation Research and Engineering.

Other contributors to this technology are Sang Hyun Lee, X-G Zhang, Chad Parish, Barton Smith, Yongning He, Chad Duty and Ho Nyung Lee.

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New Nanogenerator May Charge IPods And Cell Phones With A Wave Of The Hand

New Nanogenerator May Charge IPods And Cell Phones With A Wave Of The Hand

  3:18:00 AM    Science Lover

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Pictured is a schematic illustration shows the microfiber-nanowire hybrid nanogenerator, which is the basis of using fabrics for generating electricity. (Credit: Professor. Z. L. Wang and Dr. X. D. Wang, Georgia Institute of Technology.)

Imagine if all you had to do to charge your iPod or your BlackBerry was to wave your hand, or stretch your arm, or take a walk? You could say goodbye to batteries and never have to plug those devices into a power source again.

In research presented at the American Chemical Society's 237th National Meeting in Salt Lake City, Utah on March 26, scientists from Georgia describe technology that converts mechanical energy from body movements or even the flow of blood in the body into electric energy that can be used to power a broad range of electronic devices without using batteries.

"This research will have a major impact on defense technology, environmental monitoring, biomedical sciences and even personal electronics," says lead researcher Zhong Lin Wang, Regents' Professor, School of Material Science and Engineering at the Georgia Institute of Technology. The new "nanogenerator" could have countless applications, among them a way to run electronic devices used by the military when troops are far in the field.

The researchers describe harvesting energy from the environment by converting low-frequency vibrations, like simple body movements, the beating of the heart or movement of the wind, into electricity, using zinc oxide (ZnO) nanowires that conduct the electricity. The ZnO nanowires are piezoelectric — they generate an electric current when subjected to mechanical stress. The diameter and length of the wire are 1/5,000th and 1/25th the diameter of a human hair.

In generating energy from movement, Wang says his team concluded that it was most effective to develop a method that worked at low frequencies and was based on flexible materials. The ZnO nanowires met these requirements. At the same time, he says a real advantage of this technology is that the nanowires can be grown easily on a wide variety of surfaces, and the nanogenerators will operate in the air or in liquids once properly packaged. Among the surfaces on which the nanowires can be grown are metals, ceramics, polymers, clothing and even tents.

"Quite simply, this technology can be used to generate energy under any circumstances as long as there is movement," according to Wang.

To date, he says that there have been limited methods created to produce nanopower despite the growing need by the military and defense agencies for nanoscale sensing devices used to detect bioterror agents. The nanogenerator would be particularly critical to troops in the field, where they are far from energy sources and need to use sensors or communication devices. In addition, having a sensor which doesn't need batteries could be extremely useful to the military and police sampling air for potential bioterrorism attacks in the United States, Wang says.

While biosensors have been miniaturized and can be implanted under the skin, he points out that these devices still require batteries, and the new nanogenerator would offer much more flexibility. A major advantage of this new technology is that many nanogenerators can produce electricity continuously and simultaneously. On the other hand, the greatest challenge in developing these nanogenerators is to improve the output voltage and power, he says. Last year Wang's group presented a study on nanogenerators driven by ultrasound. Today's research represents a much broader application of nanogenerators as driven by low-frequency body movement.

The study was funded by the Defense Advanced Research Projects Agency, the Department of Energy, the National Institutes of Health and the National Science Foundation.

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Adapted from materials provided by American Chemical Society, via EurekAlert!, a service of AAAS.

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