Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Promising Ferroelectric Materials Suffer From Unexpected Electric Polarizations

20.08.2014

Head-to-head charge configuration explains major performance issues in ferroelectrics

Electronic devices with unprecedented efficiency and data storage may someday run on ferroelectrics—remarkable materials that use built-in electric polarizations to read and write digital information, outperforming the magnets inside most popular data-driven technology. But ferroelectrics must first overcome a few key stumbling blocks, including a curious habit of "forgetting" stored data.


Brookhaven National Laboratory

Electrostatic potential landscapes reconstructed from electron holography data with 15 volts of positive or negative current applied to the substrate (Nb-STO). The much steeper potential drop from the +15 V signifies a higher electric field, whereas the -15 V yielded a much flatter curve—indicating the charge asymmetry within the material.

Now, scientists at the U.S. Department of Energy's Brookhaven National Laboratory have discovered nanoscale asymmetries and charge preferences hidden within ferroelectrics that may explain their operational limits.

"The positive or negative polarizations in these ferroelectric materials should be incredibly easy to switch, but the reality is much stranger," said Brookhaven Lab physicist Myung-Geun Han, lead author on the new study. "To our surprise, opposing electronic configurations only allowed for polarization in one direction—a non-starter for reading and writing data."

The researchers used a suite of state-of-the-art techniques—including real-time electrical biasing, electron holography, and electron-beam-induced current measurements—to reveal never-before-seen electric field distributions in ferroelectric thin films, which were custom-grown at Yale University. The results, published in Nature Communications, open new pathways for ferroelectric technology.

Physics of Flipping

Most electronic devices rely on ferromagnetism to read and write data. Each so-called ferromagnetic domain contains a north or south magnetic polarity, which translates into the flipping 1 or 0 of the binary code underlying all digital information. But ferromagnetic operations not only require large electric current, but the magnets can flip each other like dominoes when packed together too tightly—effectively erasing any data.

Ferroelectrics, however, use positive or negative electric charge to render digital code. Crucially, they can be packed together with domains spanning just a few atoms and require only a tiny voltage kick to flip the charge, storing much more information with much greater efficiency.

"But ferroelectric commercialization is held up by material fatigue, sudden polarization reversal, and intrinsic charge preferences," said Brookhaven Lab physicist and study coauthor Yimei Zhu. "We suspected that the origin of these issues was in the atomic interactions along the material's interface—where the ferroelectric thin film sits on a substrate."

Interface Exploration

The scientists examined ferroelectric films of lead, zirconium, and titanium oxide grown on conductive substrates of strontium, and titanium oxide with a small amount of niobium—chosen because it exhibits large polarization values with well-defined directions, either up or down. The challenge was mapping the internal electric fields in materials thousands of times thinner than a human hair under actual operating conditions.

Brookhaven scientists hunted down the suspected interface quirks using electron holography. In this technique, a transmission electron microscope (TEM) fired 200,000-volt electron wave packets through the sample with billionth-of-a-meter precision. Negative and positive electric fields inside the ferroelectric film then attracted or repelled the electron wave and slightly changed its direction. Tracking the way the beam bent throughout the ferroelectric film revealed its hidden charges.

"Rather than an evenly distributed electric field, the bending electron waves revealed non-uniform and unidirectional electric fields that induced unstable, head-to-head domain configurations," Han said. "For the first time, we could see these unusual and jagged polarizations mapped out in real space and real time."

These opposing polarizations—like rival football teams squaring off aggressively at the line of scrimmage—surprised scientists and challenged assumptions about the ferroelectric phenomenon.

"These results were totally unexpected based on the present understanding of ferroelectrics," Han said.

The asymmetries were further confirmed by measurements of electron-beam-induced current. When a focused electron beam struck the ferroelectric sample, electric fields within the film-substrate interface revealed themselves by generating additional current. Other techniques, including piezoresponse force microscopy—in which a sub-nanometer tip induces a reaction by pressing against the ferroelectric—also confirmed the strange domains.

"Each technique demonstrated this intrinsic polarization preference, likely the origin of the back-switching and poor coding performance in these ferroelectrics," Han said. "But these domain structures should require a lot of energy and thus be very unstable. The interface effect alone cannot explain their existence."

Missing Oxygen

The scientists used another ultra-precise technique to probe the material's interface: electron energy loss spectroscopy (EELS). By measuring the energy deposited by an electron beam in specific locations—a kind of electronic fingerprint—the scientists determined the material's chemical composition.

"We suspect that more oxygen could be missing near the surface of the thin films, creating electron pockets that may neutralize positive charges at the domain walls," Han said. "This oxygen deficiency naturally forms in the material, and it could explain the stabilization of head-to-head domains."

This electron-swapping oxygen deficiency—and its negative effects on reliably storing data—might be corrected by additional engineering, Han said. For example, incorporating a "sacrificial layer" between the ferroelectric and the substrate could help block the interface interactions. In fact, the study may inspire new ferroelectrics that either exploit or overcome this unexpected charge phenomenon.

Other authors include Lijun Wu and Marvin A. Schofield of Brookhaven Lab; Matthew S. J. Marshall, Jason Hoffman, Frederick J. Walker, and Charles H. Ahn of the Yale University Department of Applied Physics and Center for Research on Interfaces Structures and Phenomena; Toshihiro Aoki of JEOL USA Inc.; and Ray Twesten of Gatan Inc.

The samples used for transmission electron microscopy (TEM) were prepared by Kim Kisslinger at Brookhaven Lab's Center for Functional Nanomaterials, a U.S. Department of Energy user facility.

The research was supported by the U.S. Department of Energy's Office of Science.

Brookhaven National Laboratory is supported by the Office of Science of the U.S. Department of Energy. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.

One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. Brookhaven is operated and managed for DOE's Office of Science by Brookhaven Science Associates, a limited-liability company founded by the Research Foundation for the State University of New York on behalf of Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit applied science and technology organization.

Contact Information

Justin Eure
Public Affairs Representative
jeure@bnl.gov

Justin Eure | newswise
Further information:
http://www.bnl.gov/bnlweb/newsindex.html

Further reports about: Electric Energy Ferroelectric Physics Science materials polarization polarizations

More articles from Materials Sciences:

nachricht New method developed for timely detection of impending material failure
28.08.2015 | Universität Siegen

nachricht Soaking up carbon dioxide and turning it into valuable products
28.08.2015 | DOE/Lawrence Berkeley National Laboratory

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: OU astrophysicist and collaborators find supermassive black holes in quasar nearest Earth

A University of Oklahoma astrophysicist and his Chinese collaborator have found two supermassive black holes in Markarian 231, the nearest quasar to Earth, using observations from NASA's Hubble Space Telescope.

The discovery of two supermassive black holes--one larger one and a second, smaller one--are evidence of a binary black hole and suggests that supermassive...

Im Focus: What would a tsunami in the Mediterranean look like?

A team of European researchers have developed a model to simulate the impact of tsunamis generated by earthquakes and applied it to the Eastern Mediterranean. The results show how tsunami waves could hit and inundate coastal areas in southern Italy and Greece. The study is published today (27 August) in Ocean Science, an open access journal of the European Geosciences Union (EGU).

Though not as frequent as in the Pacific and Indian oceans, tsunamis also occur in the Mediterranean, mainly due to earthquakes generated when the African...

Im Focus: Self-healing landscape: landslides after earthquake

In mountainous regions earthquakes often cause strong landslides, which can be exacerbated by heavy rain. However, after an initial increase, the frequency of these mass wasting events, often enormous and dangerous, declines, in fact independently of meteorological events and aftershocks.

These new findings are presented by a German-Franco-Japanese team of geoscientists in the current issue of the journal Geology, under the lead of the GFZ...

Im Focus: FIC Proteins Send Bacteria Into Hibernation

Bacteria do not cease to amaze us with their survival strategies. A research team from the University of Basel's Biozentrum has now discovered how bacteria enter a sleep mode using a so-called FIC toxin. In the current issue of “Cell Reports”, the scientists describe the mechanism of action and also explain why their discovery provides new insights into the evolution of pathogens.

For many poisons there are antidotes which neutralize their toxic effect. Toxin-antitoxin systems in bacteria work in a similar manner: As long as a cell...

Im Focus: Fraunhofer IPA develops prototype of intelligent care cart

It comes when called, bringing care utensils with it and recording how they are used: Fraunhofer IPA is developing an intelligent care cart that provides care staff with physical and informational support in their day-to-day work. The scientists at Fraunhofer IPA have now completed a first prototype. In doing so, they are continuing in their efforts to improve working conditions in the care sector and are developing solutions designed to address the challenges of demographic change.

Technical assistance systems can improve the difficult working conditions in residential nursing homes and hospitals by helping the staff in their work and...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Networking conference in Heidelberg for outstanding mathematicians and computer scientists

20.08.2015 | Event News

Scientists meet in Münster for the world’s largest Chitin und Chitosan Conference

20.08.2015 | Event News

Large agribusiness management strategies

19.08.2015 | Event News

 
Latest News

Interstellar seeds could create oases of life

28.08.2015 | Physics and Astronomy

An ounce of prevention: Research advances on 'scourge' of transplant wards

28.08.2015 | Health and Medicine

Fish Oil-Diet Benefits May be Mediated by Gut Microbes

28.08.2015 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>