Eight/KAET outreach program receives national recognition


March 22, 2010

Eight/KAET’s Educational Outreach-ASSET received a My Source Education Innovation Award from the Corporation for Public Broadcasting (CPB) this weekend in Washington, D.C.

The My Source Education Innovation Awards recognize and showcase how public broadcasting stations use pioneering approaches and emerging digital technologies to serve the educational needs of their communities on-air, online and in the classroom. Download Full Image

“Stations across the country are using technology in creative and innovative ways to deliver educational tools and resources that are making a real difference to teachers, parents and children,” said Pat Harrison, president and CEO of CPB. “Public media is the definitive education partner for a new generation of learners and CPB congratulates Eight for its outstanding contribution to the community.”

Eight experimented with ways to bring virtual reality into professional development for K-12 teachers. Eight Educational Outreach-ASSET collaborates with the International Society of Technology in Education (ISTE) and Virtual Pioneers to provide virtual field trips, “real-time” workshops and other online resources, dramatically expanding how Arizona’s educators incorporate technology into the classroom.

The award was presented to Eight’s Associate General Manager of Education, Kim Flack, by 
Pat Harrison at the Council of Chief State School Officers/Public Media Executive Summit.

“While schools, districts or individual educators may not have all the resources necessary to implement a specific service,” said Flack, “ASSET always has believed strongly in setting a high standard to provide innovative learning options for all educators, no matter if they are in a rural or urban setting. Our cutting edge professional development for educators helps to provide equal access to high-quality learning.”

 

About Eight’s Educational Outreach
Arizona Pre K-12 students benefit from outreach programs and educator professional development distributed statewide by Eight Educational Outreach-ASSET. For more information visit, http://azpbs.org/asset.">http://azpbs.org/asset">http://azpbs.org/asset.

About CPB
CPB is a private, nonprofit corporation created by Congress in 1967 and is steward of the federal government's investment in public broadcasting. It helps support the operations of more than 1,100 locally-owned and -operated public television and radio stations nationwide, and is the largest single source of funding for research, technology, and program development for public radio, television and related online services.

About Eight/KAET-TV
Eight, Arizona PBS specializes in the education of children, in-depth news and public affairs, lifelong learning, and the celebration of arts and culture — utilizing the power of noncommercial television, the Internet, educational outreach services, and community-based initiatives. The PBS station began broadcasting from the campus of Arizona State University on January 30, 1961.  Now more than 80 percent of Arizonans receive the signal through a network of translators, cable and satellite systems.  With more than 1.3 million viewers each week, Eight consistently ranks among the most-viewed public television stations per capita in the country.  Arizonans provide more than 60 percent of the station’s annual budget. For more information, visit www.azpbs.org.">http://www.azpbs.org">www.azpbs.org.

Lisa Robbins

editor/publisher, Media Relations and Strategic Communications

480-965-9370

New alloys key to efficient energy and lighting


March 22, 2010

Nanowire advances promise improved light-emitting diodes and solar-energy generation

A recent advance by ASU researchers in developing nanowires could lead to more efficient photovoltaic cells for generating energy from sunlight, and to better light-emitting diodes (LEDs) that could replace less energy-efficient incandescent light bulbs. Download Full Image

Electrical engineers Cun-Zheng Ning and Alian Pan are working to improve quaternary alloy semiconductor nanowire materials.

Nanowires are tens of nanometers in diameter and tens of microns in length. Quaternary alloys are made of semiconductors with four elements, often made by alloying two or more compound semiconductors.

Semiconductors are the material basis for technologies such as solar cells, high-efficiency LEDs for lighting, and for visible and infrared detectors.

One of the most critical parameters of semiconductors that determine the feasibility for these technologies is the band gap. The band gap of a semiconductor determines, for example, if a given wavelength of sun light is absorbed or left unchanged by the semiconductor in a solar cell.

Band gap also determines what color of light an LED emits. To make solar cells more efficient, it’s necessary to increase the range of band gaps.

Ideally, the highest solar cell efficiency is achieved by having a wide range of band gaps that matches the entire solar spectrum, said Ning, a professor in the School of Electrical, Computer and Energy Engineering, a part of ASU’s Ira A. Fulton Schools of Engineering.

He said that in LED lighting applications, more available band gaps means more colors can be emitted, providing more flexibility in color engineering or color rendering of light.

For example, different proportions of red, green and blue colors would mix with different white colors. More flexibility would allow white color to be adjusted to suit various situations, or individual preferences.

Similarly, Ning said, detection of different colors requires semiconductors of different band gaps. The more band gaps that are available, the more information can be acquired about an object to be detected. Thus, all of these lighting applications can be improved by having semiconductors with a wide range of band gaps.

The researchers said the hurdle is that every manmade or naturally occurring semiconductor has only a specific band gap.

One standard way to broaden the range of band gaps is to alloy two or more semiconductors. By adjusting the relative proportion of two semiconductors in an alloy, it’s possible to develop new band gaps between those of the two semiconductors.

But accomplishing this requires a condition called lattice constant matching, which requires similar inter-atomic spaces between two semiconductors to be grown together.

“This is why we cannot grow alloys of arbitrary compositions to achieve arbitrary band gaps,” Ning said. “This lack of available band gaps is one of the reasons current solar cell efficiency is low, and why we do not have LED lighting colors that can be adjusted for various situations.”

In recent attempts to grow semiconductor nanowires with “almost” arbitrary band gaps, the research team led by Ning and Pan, an assistant research professor, have used a new approach to produce an extremely wide range of band gaps.

They alloyed two semiconductors, zinc sulfide (ZnS) and cadmium selenide (CdSe) to produce the quaternary semiconductor alloy ZnCdSSe, which produced continuously varying compositions of elements on a single substrate (a material on which a circuit is formed or fabricated).

Ning said this is the first time a quaternary semiconductor has been produced in the form of a nanowire or nanoparticle.

By controlling the spatial variation of various elements and the temperature of a substrate (called the dual-gradient method), the team produced light emissions that ranged from 350 to 720 nanometers on a single substrate only a few centimeters in size.

The color spread across the substrate can be controlled to a large degree, and Ning said he believes this dual-gradient method can be more generally applied to produce other alloy semiconductors or expand the band gap range of these alloys.

To explore the use of quaternary alloy materials for making photovoltaic cells more efficient, his team has developed a lateral multi-cell design combined with a dispersive concentrator.

The concept of dispersive concentration, or spectral split concentration, has been explored for decades. But the typical application uses a separate solar cell for each wavelength band.

With the new materials, Ning said he hopes to build a monolithic lateral super-cell that contains multiple subcells in parallel, each optimized for a given wavelength band. The multiple subcells can absorb the entire solar spectrum. Such solar cells will be able to achieve extremely high efficiency with low fabrication cost. The team is working on both the design and fabrication of such solar cells.

Similarly, the new quaternary alloy nanowires with large wavelength span can be explored for color-engineered light applications.

The researchers have demonstrated that color control through alloy composition control can be extended to two spatial dimensions, a step closer to color design for direct white light generation or for color displays.

The team’s research was initially supported by Science Foundation Arizona and by the U.S. Army Research Office.

For more information, see the research group’s Web site at http://nanophotonics.asu.edu.

Related">http://nanophotonics.asu.edu">http://nanophotonics.asu.edu.

Re... research by Ning and his colleagues has been reported in these articles:

• Pan, R. Liu, M. Sun and C.Z. Ning, Spatial Composition Grading of Quaternary ZnCdSSe Alloy Nanowires with Tunable Light Emission between 350 and 710 nm on a Single Substrate, ACS Nano, http://pubs.acs.org/doi/abs/10.1021/nn901699h

">http://pubs.acs.org/doi/abs/10.1021/nn901699h">http://pubs.acs.org/doi/a...• Pan, R. Liu, M. Sun and C.Z. Ning, Quaternary Alloy Semiconductor Nanobelts with Bandgap Spanning the Entire Visible Spectrum, J. Am. Chem. Soc, 131, 9502 (2009), DOI: 10.1021/ja904137m, http://pubs.acs.org/doi/abs/10.1021/ja904137m

">http://pubs.acs.org/doi/abs/10.1021/ja904137m">http://pubs.acs.org/doi/a...• C.Z. Ning, A. Pan, and R. Liu, Spatially composition-graded alloy semiconductor nanowires and wavelength specific lateral multi-junctions full-spectrum solar cells, Proceedings of 34th PVSC, IEEE, 001492(2009).

Joe Kullman

Science writer, Ira A. Fulton Schools of Engineering

480-965-8122