New nano-material combinations produce leap in infrared technology

February 13, 2012

Arizona State University researchers are finding ways to improve infrared photodetector technology that is critical to national defense and security systems, as well as used increasingly in medical diagnostics, commercial applications and consumer products.

A significant advance is reported in a recent article in the journal Applied Physics Letters. It details discovery of how infrared photodetection can be done more effectively by using certain materials arranged in specific patterns in atomic-scale structures. night-vision infrared photodetection system Download Full Image

It’s being accomplished by using multiple ultrathin layers of the materials that are only several nanometers thick. Crystals are formed in each layer. These layered structures are then combined to form what are termed “superlattices.”

Photodetectors made of different crystals absorb different wavelengths of light and convert them into an electrical signal. The conversion efficiency achieved by these crystals determines a photodectector’s sensitivity and the quality of detection it provides, explains electrical engineer Yong-Hang Zhang.

The unique property of the superlattices is that their detection wavelengths can be broadly tuned by changing the design and composition of the layered structures. The precise arrangements of the nanoscale materials in superlattice structures helps to enhance the sensitivity of infrared detectors, Zhang says.

Zhang is a professor in the School of Electrical, Computer and Energy Engineering, one of ASU’s Ira A. Fulton Schools of Engineering. He is leading the work on infrared technology research in ASU’s Center for Photonics Innovation. More information can be found at the center’s Optoelectronics Group website.

Additional research in this area is being supported by a grant from the Air Force Office of Scientific Research and a new Multidisciplinary University Research Initiative (MURI) program established by the U.S. Army Research Office.  ASU is a partner in the program led by the University of Illinois at Urbana-Champaign.

The MURI program is enabling Zhang’s group to accelerate its work by teaming with David Smith, a professor in the Department of Physics in ASU’s College of Liberal Arts and Sciences, and Shane Johnson, a senior research scientist in the ASU’s engineering schools.

The team is using a combination of indium arsenide and indium arsenide antimonide to build the superlattice structures. The combination allows devices to generate photo electrons necessary to provide infrared signal detection and imaging, says Elizabeth Steenbergen, an electrical engineering doctoral student who performed experiments on the supperlattice materials with collaborators at the Army Research Lab.

“In a photodetector, light creates electrons. Electrons emerge from the photodetector as electrical current. We read the magnitude of this current to measure infrared light intensity,” she says.

“In this chain, we want all of the electrons to be collected from the detector as efficiently as possible. But sometimes these electrons get lost inside the device and are never collected,” says team member Orkun Cellek, an electrical engineering postdoctoral research associate.

Zhang says the team’s use of the new materials is reducing this loss of optically excited electrons, which increases the electrons’ carrier lifetime by more than 10 times what has been achieved by other combinations of materials traditionally used in the technology. Carrier lifetime is a key parameter that has limited detector efficiency in the past.  

Another advantage is that infrared photodetectors made from these superlattice materials don’t need as much cooling. Such devices are cooled as a way of reducing the amount of unwanted current inside the devices that can “bury” electrical signals, Zhang says.

The need for less cooling reduces the amount of power needed to operate the photodetectors, which will make the devices more reliable and the systems more cost effective.

Researchers say improvements can still be made in the layering designs of the intricate superlattice structures and in developing device designs that will allow the new combinations of materials to work most effectively.

The advances promise to improve everything from guided weaponry and sophisticated surveillance systems to industrial and home security systems, the use of infrared detection for medical imaging and as a road-safety tool for driving at night or during sand storms or heavy fog.

“You would be able to see things ahead of you on the road much better than with any headlights,” Cellek says.

The research team’s paper is reported on in the article “One giant leap for IR technology” on the LAB & FAB TALK website of Compound Semiconductor magazine.

Joe Kullman

Science writer, Ira A. Fulton Schools of Engineering


Scientific advances promise better ways to engineer water-safety systems

February 13, 2012

Some of most recent advances in technology, chemistry, physics and materials science will be applied to new methods for ensuring water safety being developed by Arizona State University engineers.

In a project supported by a $500,000 grant from the Environmental Protection Agency (EPA), Paul Westerhoff will lead exploration of ways to improve the effectiveness of water treatment systems in the nation’s small communities. He will also head a project supported by the National Science Foundation (NSF) to optimize the use of new technology for reducing a prevalent contaminant in groundwater. Clean water Download Full Image

Westerhoff is the associate dean for research in ASU’s Ira A. Fulton Schools of Engineering, and a professor in the university’s School of Sustainable Engineering and the Built Environment.

His research partner for both projects is Kiril Hristovski, an assistant professor in ASU’s College of Technology and Innovation. For the EPA project, they will be joined by Aaron Dotson, an assistant engineering professor at the University of Alaska Anchorage, who earned his doctoral degree in engineering at ASU.

For the NSF project – supported by a grant of more than $295,000 – the research team will seek advances in the use of photocatalysts to reduce the amount of nitrates in water supplies. High concentrations of nitrates in water can pose significant risks – including causing life-threatening diseases – and lead to excessive growth of algae or plankton in aquatic ecosystems.
Westerhoff and Hristovski will experiment with different types of photocatalysts to reduce nitrates. Photocatalysis involves the acceleration of chemical reactions using the power of light. In this case, the researchers are seeking to produce reactions at the nanometer scale that will convert nitrate to a nonthreatening form.

“This will bring some of the most recent and significant advances in light-based technology and materials nanotechnology into engineering better water treatment systems,” Westerhoff says.

The researchers plan to eventually develop an open-access website to provide the public the latest information on nitrate occurrence, health risks and proven strategies for water treatment. Knowledge gained from the research will be used in graduate-level education in environmental engineering and to provide research themes for senior-year capstone projects by engineering undergraduates.

The EPA project will focus on ways to improve monitoring, testing and treatment of water systems in communities with populations of roughly 50 to 500 residents.

Such communities rarely have the resources to maintain timely, effective and thorough methods of ensuring their water meets basic safety standards, Westerhoff says.

Aiding those communities in water treatment efforts isn’t simply a matter of scaling down larger systems used in urban areas, he says, since rural and remote areas often face different environmental and contaminant issues.

Water systems in small communities typically must deal with multiple pollutants in groundwater, making treatment and compliance with health regulations complicated, Westerhoff explains.

The team plans to develop types of hybrid sorbents (materials designed to absorb liquids and gases) capable of simultaneously removing multiple contaminants. In addition, the researchers will develop monitoring and sensing networks to enable simplified automated operation and testing of water systems designed to optimize the groundwater sorbent treatment systems.

Local officials in the Tohono O’odham Native American Indian community in Arizona and in a remote area of Alaska are being asked to participate in the research by conducting on-site demonstration projects.

Systems that can work in those locations could be applied with success in the vast majority of small communities throughout the country, Westerhoff says.

Joe Kullman

Science writer, Ira A. Fulton Schools of Engineering