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)

Molecular-level analysis of organic particles put in perspective

 

When it comes to air pollution, further development and integration of complementary analytical methods are needed to understand the effect of atmospheric particles, according to scientists at Pacific Northwest National Laboratory and University of California, Irvine. Dr. Julia Laskin and Dr. Alexander Laskin at PNNL and Prof. Sergey Nizkorodov at UCI share this other insights into the state of organic aerosol chemistry in Physical Chemistry Chemical Physics, March 2011. Artwork from the article graces the cover.

Air pollution by emissions related to energy production and the transportation fleet presents economic and environmental consequences. Understanding and mitigating these consequences requires answering challenging questions about the chemically complex particles emitted by these sources. By reporting on the state of the science and discussing future needs, the Laskins and Nizkorodov are providing other scientists with a solid, foundational reference.

High-resolution mass spectrometry provides researchers with the ability to characterize organic matter in aerosols and water samples. In the review article, the scientists discuss all studies published to date using high-resolution mass spectrometry to characterize aerosols and cloud water samples.

The authors also discuss new ionization techniques necessary to advance analysis of aerosol samples using high-resolution mass spectrometers, overcoming previous sample preparation limitations. One example is nanoDESI or Nanospray Desorption Electrospray Ionization. This approach provides a highly sensitive analysis of complex analytes, enabling a molecular-level understanding of the particles.

The authors also cover data analysis and visualization tools to aid in sorting through the hundreds of features on each mass spectrum. Using various tools and careful analysis, scientists are attaining solid information about the molecular composition and fundamental chemistry of particles. For example, researchers in 2010 found that N-heteroatom organic compounds produced through atmospheric aging of aerosols can contribute to the absorption of the visible light by pollutants.

More information: Nizkorodov SA, et al. 2011. "Molecular Chemistry of Organic Aerosols Through the Application of High Resolution Mass Spectrometry." Physical Chemistry Chemical Physics 13(9):3612-3629. DOI: 10.1039/c0cp02032j

Provided by Pacific Northwest National Laboratory (news : web)