Perspective article examines conductivity at the LaAlO3 and SrTiO3 (001) interface

Complex oxides have the potential to inject new functionalities into technologies that require semiconductors.  The correlated behavior of itinerant electrons in these materials sets complex oxides apart from traditional semiconductors such as Si and GaAs. Potential applications abound, but the fundamental properties of these materials, particularly when combined to make interfaces, must be understood.  In an invited Perspective article in Surface Science, Dr. Scott Chambers of PNNL examines conductivity at the interface of polar and nonpolar complex oxides from outside the reigning paradigm and considers how unintentional dopants and defects, resulting from interfacial mixing, might affect the electronic properties.

The common paradigm used to explain the observation of conductivity at interfaces of materials such as lanthanum aluminate and strontium titanate is that electrons move across the interface to alleviate the so-called polar catastrophe created by polar/nonpolar interface creation.  Based on a number of different experimental results, Chambers argues that this simple paradigm is inadequate to explain observed conductivity.

"Intermixing occurs, and the resulting cation rearrangement cannot be ignored," said Chambers, a Fellow of the AVS and the American Association for the Advancement of Science. "Moreover, defects and dopants appear to play a role in facilitating, if not enabling conductivity."

Providing insights into the fundamental relationships between composition/structure, and the resulting electronic, magnetic, and surface chemical properties of complex oxides could enable these materials to have an impact on next-generation electronics, chemical sensors, and photocatalysts. These advances could include more energy-efficient field effect transistors and photocatalysts that use visible light from the sun.

Chambers and his colleagues around the world are continuing to make strides in understanding the complex relationships between atom distributions near the interface and conductivity. One upshot is that significantly more insight into the growth process is necessary to characterize and ultimately control defect creation during heterojunction formation.

"Then and only then can interface structures suspected of facilitating conductivity be changed to see if doing so actually reduces or eliminates conductivity," said Chambers.

More information: Chambers SA. 2011. "Understanding the Mechanism of Conductivity at the LaAlO3 and SrTiO3 (001) Interface." Surface Science 605:1133-1140.

Provided by Pacific Northwest National Laboratory (news : web)

New paper examines future of seawater desalinization

A paper co-authored by William Phillip of the University of Notre Dame's Department of Chemical and Biomolecular Engineering and Menachem Elimelech, Robert Goizueta Professor of Environmental and Chemical Engineering at Yale University, appearing in this week's edition of the journal Science offers a critical review of the state of seawater desalination technology.

Elimelech and Phillip and examine how seawater desalination technology has advanced over the past 30 years, in what ways the state-of-the-art technology can be improved, and if seawater desalination is a sustainable technological solution to global water shortages.

"At present, one-third of the world's population lives in water stressed countries, Phillip said. "Increasing population, contamination of fresh water sources and climate change will cause this percentage to increase over the coming decade. Additionally, the social and ecological benefits of adequate fresh water resources are well-documented. Therefore, it is important to find a way to alleviate this stress with a sustainable solution."

The authors point out that in recent years, large-scale seawater desalination plants have been built in water-stressed countries to augment available water resources and construction of new desalination plants is expected to increase in the near future. Despite major advancements in desalination technologies, seawater desalination is still more energy intensive compared to conventional technologies for the treatment of fresh water. There are also concerns about the potential environmental impacts of large-scale seawater desalination plants.

In their Science paper, Elimelech and Phillip review the possible reductions in energy demand by state-of-the-art desalination technologies, the potential role of advanced materials and innovative technologies in improving the performance, and the sustainability of desalination as a technological solution to global water shortages.

The authors believe that there are important policy implications in their Science paper.

"Seawater desalination is an energy-intensive process; desalinating seawater consumes significantly more energy than treating traditional fresh water sources," Phillip said. "However, these traditional sources aren't going to be able to meet the growing demand for water worldwide. Several options already exist to augment fresh water sources -- including the treatment of low-quality local water sources, water recycling and reuse and water conservation, -- understanding where seawater desalination fits into this portfolio of water supply options is critical. Hopefully, our paper helps provide some of the information needed to inform the decisions of policy makers, water resource planers, scientists, and engineers on the suitability of desalination as a means to meet the increasing demands for water."

Phillip, who joined the Notre Dame faculty this year, is interested in examining how membrane structure and chemistry affect the transport of chemicals across a variety of membranes. Understanding the connection between functionality and property enables the design and fabrication of next generation membranes that provide more precise control over the transport of chemical species. These material advantages can be leveraged to design more effective and energy-efficient systems. Chemical separations at the water- energy nexus (e.g. desalination) is one area where this knowledge can be applied.

Story Source:

The above story is reprinted (with editorial adaptations ) from materials provided by University of Notre Dame, via EurekAlert!, a service of AAAS.

Journal Reference:

Menachem Elimelech, William A. Phillip. The Future of Seawater Desalination: Energy, Technology, and the Environment. Science, 5 August 2011: Vol. 333 no. 6043 pp. 712-717 DOI: 10.1126/science.1200488