Funky Ferroelectric Properties Probed with X-Rays

WASHINGTON, June 10, 2014 /PRNewswire-USNewswire/ -- Ferroelectric materials like barium titanate, a ceramic used in capacitors, are essential to many electronic devices. Typical ferroelectric materials develop features called domain walls with unusual properties – such as lines of electrical conduction completely different from the surrounding material. These properties are technologically useful but poorly understood.

Now an international team of scientists has demonstrated the ability of a powerful imaging tool to provide new insight into the mystery of why domain walls behave in their peculiar ways. They report their results in the journal Applied Physics Letters, from AIP Publishing – work that promises to analyze so far unexplored domain wall properties that may lead to improved solar panels, electronic sensors, computer memory, and other applications.

Ferroelectric domain walls separate regions of material with different electric polarization orientations, and their physical properties can be completely different from the surrounding bulk material. Over the years, scientists have tried many different approaches to understand domain walls' funky properties.

A technique called scanning probe microscopy has provided valuable insight into domain wall nanophysics by measuring a material's electrical or mechanical response to a tiny, sharp-tipped probe. The scanning approach, however, is rather slow when high-resolution images are required, and may also produce unwanted measurement side effects due, for example, to contact resistance or inhomogeneous probe fields.

An alternative imaging method called X-ray photoemission electron microscopy (X-PEEM) allows researchers to bypass many of these limitations, but until now no one knew if it could capture the details of skinny domain walls, which can be only a few atoms thick. An international team of researchers from four different countries decided to join forces to test X-PEEM on domain walls in a model ferroelectric material called erbium manganese oxide (ErMnO₃).

"X-PEEM is a particularly interesting tool because it allows for studying properties such as the chemistry, electronic structure, and symmetry of a material," said Dennis Meier, a junior research team leader at the Swiss Federal Institute of Technology in Zurich and corresponding author on the new paper. Together with Ingo Krug, an instrument and beamline scientist at Technische Universität Berlin, he devised the X-PEEM experiments on domain walls using a state-of-the-art microscope (SPECS FE-LEEM P90 AC) at the synchrotron BESSY II in Berlin, Germany. X-PEEM works by bombarding a sample with X-rays that excite electrons in the material, and then uses variations in the electron emission to create image contrast.

Meier and his colleagues found that X-PEEM could image electrically conducting domain walls extremely well. In ErMnO₃ these walls are so-called tail-to-tail domain walls separating regions with polarizations that point away from each other.

The article, "Imaging and characterization of conducting ferroelectric domain walls by photoemission electron microscopy," is authored by Jakob Schaab, Ingo P. Krug, Florian Nickel, Daniel M. Gottlob, Hattice Doganay, Andres Cano, Mario Hentschel, Zewu Yan, E. Bourret-Courchesne, Claus M. Schneider, Ramamoorthy Ramesh, and Dennis Meier. It will be published in Applied Physics Letters on June 10, 2014 (DOI: 10.1063/1.4879260). After that date, it may be accessed at: http://scitation.aip.org/content/aip/journal/apl/104/23/10.1063/1.4879260

ABOUT THE JOURNAL
Applied Physics Letters features concise, rapid reports on significant new findings in applied physics. The journal covers new experimental and theoretical research on applications of physics phenomena related to all branches of science, engineering, and modern technology. See: http://apl.aip.org 

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SOURCE Applied Physics Letters