July 29, 2011
Physics News Highlights of the American Institute of Physics summarizes select papers accepted for publication. This service for journalists covers the latest research and findings across the physical sciences. Copies of papers are available to journalists upon request.
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Topics in this issue:
- "Wonder material" graphene tapped for electronic memory devices: Hailed as the new "wonder material," graphene is being tapped by an international research team to help overcome issues associated with increasing the storage density and speed of electronic memory devices.
- Solar cells get a boost from bouncing light: A new twist on an old solar cell design sends light ricocheting through layers of microscopic spheres, increasing its electricity-generating potential by 26 percent.
- Motorcycle helmets hard on hearing: Motorcycle helmets, while protecting bikers' brains, may also be contributing to hearing loss. Scientists mapped the airflow and noise patterns to find out why.
- Warmed-up organic memory transistor has larger memory capacity: Scientists show that non-volatile memory made from a sandwich of silver nanoparticle-laced plastic retains its on/off state over a wider voltage range when operating at toasty temperatures.
- "Wonder material" graphene tapped for electronic memory devices
Electronic memory devices, which store information, are increasingly expected to provide not only greater storage density, but also faster access to information. As storage density increases, however, power consumption and unwanted heat generation also increase, and the fidelity of accessing the memory is frequently diminished. Various platforms exist to overcome these hurdles, according to a team led by University of California at Los Angeles researchers, which they describe in detail in the AIP's Applied Physics Letters. A spin-transfer-torque device, for example, relies on a clever technique for storing and accessing information in a magnetic dipole moment, which is similar to a hard drive. Information can be stored in a ferroelectric material in the form of an electric dipole moment in a class of devices known as "ferroelectric-field-effect-transistors" or more commonly as FFETs. For this research, graphene is used to write and read the electric dipole moments of an underlying ferroelectric material. And the very good news, the researchers report, is that this graphene-FFET has a high fidelity and low operating voltage. Future work will focus on improving the speed of the device's performance.
Article: "Robust bi-stable memory operation in single-layer graphene ferroelectric memory," is accepted for publication in Applied Physics Letters.
Authors: Emil Beom Song (1), Bob Lian (1), Sung Min Kim (1), Sejoon Lee (1), Tien-Kan Chung (2), Minsheng Wang (1), Caifu Zeng (1), Guangya Xu (1), Kin Wong (1), Yi Zhou (1), Haider I. Rasool (1), David H. Seo (3), Hyun-Jong Chung (3), Jinseong Heo (3), Sunae Seo (4), and Kang L. Wang (1)
- University of California, Los Angeles
- National Chiao Tung University
- Samsung Advanced Institute of Technology
- Sejong University
- Solar cells get a boost from bouncing light
By engineering alternating layers of nanometer and micrometer particles, a team of engineers from the University of Minnesota has improved the efficiency of a type of solar cell by as much as 26 percent. These cells, known as dye-sensitized solar cells (DSSC), are made of titanium dioxide (TiO2), a photosensitive material that is less expensive than the more traditional silicon solar cells, which are rapidly approaching the theoretical limit of their efficiency. Current DSSC designs, however, are only about 10 percent efficient. One reason for this low efficiency is that light from the infrared portion of the spectrum is not easily absorbed in the solar cell. The new layered design, as described in the AIP's Journal of Renewable and Sustainable Energy, increases the path of the light through the solar cell and converts more of the electromagnetic spectrum into electricity. The cells consist of micrometer-scale spheres with nanometer pores sandwiched between layers of nanoscale particles. The spheres, which are made of TiO2, act like tightly packed bumpers on a pinball machine, causing photons to bounce around before eventually making their way through the cell. Each time the photon interacts with one of the spheres, a small charge is produced. The interfaces between the layers also help enhance the efficiency by acting like mirrors and keeping the light inside the solar cell where it can be converted to electricity. This strategy to increase light-harvesting efficiency can be easily integrated into current commercial DSSCs.
Article: "Layered mesoporous nanostructures for enhanced light harvesting in dye-sensitized solar cells," is accepted for publication in the Journal of Renewable and Sustainable Energy.
Authors: Bin Liu (1) and Eray S. Aydil (1)
- University of Minnesota
- Motorcycle helmets hard on hearing
The distinctive roar of a Harley's engine is loud, but studies have revealed the biggest source of noise for motorcyclists is actually generated by air whooshing over the riders' helmets. Even at legal speeds, the sound can exceed safe levels. Now, scientists have identified a key source of the rushing din. Researchers from the University of Bath and Bath Spa University placed motorcycles helmets atop mannequin heads, mounted them in a wind tunnel, and turned on the fans. By placing microphones at different locations around the helmet and at the mannequin's ear, the researchers found that an area underneath the helmet and near the chin bar is a significant source of the noise that reaches riders' sensitive eardrums. The team also investigated how helmet angle and wind speed affected the loudness. Future tests will move beyond the wind tunnel to real-life riders on the open road. The findings, described in the Journal of the Acoustical Society of America, may one day be used to design quieter helmets, saving riders' ears for the enjoyment of hard biker rock, the researchers say.
Article: "Aeroacoustic sources of motorcycle helmet noise," is accepted for publication in the Journal of the Acoustical Society of America.
Authors: J. Kennedy (1), O. Adetifa (1), M. Carley (1), N. Holt (2) and I. Walker (3)
- Department of Mechanical Engineering, University of Bath, Bath, U.K.
- School of Science, Society and Management, Bath Spa University, Bath, U.K.
- Department of Psychology, University of Bath, Bath, U.K.
- Warmed-up organic memory transistor has larger memory capacity
Plastics are cheap, flexible, and relatively easy to manufacture, but they can also be more heat sensitive than other materials such as metals. The same goes for plastic (or organic) electronics, which offer the promise of foldable displays or thin, inexpensive devices, but react to temperature swings differently than traditional silicon-based electronics. So, researchers at the Hong Kong Polytechnic University decided to explore this temperature-dependent behavior more closely. They took a non-volatile organic memory transistor, made from the plastic pentacene and a layer of silver nanoparticles, and heated the device to 90 degrees Celsius. After initial heating, the distribution of nanoparticles changed, with particles clumping together in larger groups. Also, the memory window of the device — the voltage range over which it retained an original on or off state — at first decreased. However, when researchers cycled the heat following the one-time structural change, they found that higher operating temperatures meant a larger memory window. The results appear in the AIP's Applied Physics Letters. The heat and memory window relationship could be put to use in temperature-sensing applications, such as measuring and storing the temperature profile of an object, the researchers write.
Article: "Thermal annealing and temperature dependences of memory effect in
organic memory transistor," is accepted for publication in Applied Physics Letters.
Authors: X.C. Ren (1), S.M. Wang (1), C.W. Leung (2), F. Yan (2) and P.K.L. Chan (1)
- Department of Mechanical Engineering, Hong Kong Polytechnic University, Hong Kong
- Department of Applied Physics, Hong Kong Polytechnic University, Hong Kong
Upcoming Conferences of Interest
- ASA Meeting: The 162nd meeting of the Acoustical Society of America will be held Oct. 31 – November 4, 2011, in San Diego, Calif.
Physics Today: August Articles
- Particle physics, from Rutherford to the LHC: Our understanding of fundamental particles has developed in ways that were unimaginable 100 years ago, when the atomic nucleus was first glimpsed.
- Looking for mantle plumes: Seismic images of Earth's interior offer evidence that hot columns of buoyant rock from deep in the mantle are the source of the volcanism at Yellowstone and similar hot spots. Yet mysteries remain.
- NASA art: 50 years of exploration: For half a century, selected artists have been invited to express their visions of NASA's undertakings. A new exhibit shares those visions with the public.
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