Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Deep Insight Into Interfaces

16.09.2016

Interfaces between different materials and their properties are of key importance for modern technology. Together with an international team, physicists of Würzburg University have developed a new method, which allows them to have an extremely precise glance at these interfaces and to model their properties.

In his Nobel Lecture on December 8, 2000, Herbert Kroemer coined the saying “the interface is the device”. Kroemer referred to the mature field of semiconductor heterostructures, which form the basis of all modern electronics.


Film of lanthanum cobalt oxide shows a sequence of positively and negatively charged atomic layers. Without electronic reconstruction an enormous electrostatic field would form between the layers

Graphic: J.E. Hamann-Borrero & Vladimir Hinkov

However, now, in the advent of novel, powerful devices based on the more complex and versatile topological and correlated materials, the statement is timelier than ever. Such materials are at the focus of research in the Department of Physics and Astronomy at Würzburg University: Currently, 16 groups are working in this field, and a Collaborative Research Center (CRC 1170) was established in 2015, which is funded by the German Science Foundation (DFG) with nearly 10 Million euro.

Publication in Nature Quantum Materials

In the recent years physicists from Würzburg University and coworkers from Germany, Canada, the U.S.A. and Korea developed a new method to uncover important charge properties of correlated oxide interfaces with unprecedented atomic scale resolution. The team of Professor Vladimir Hinkov and his coworkers report about this experimental method in the current issue of the Nature Journal “NPJ Quantum Materials”.

“Conventional electronic chips are based on networks of so-called p-n junctions, interfaces between semiconductors carrying positive and negative charges, respectively,” says Vladimir Hinkov, describing the background of this research. There are several drawbacks to such a setup: First, the junctions are thick, often of the order of hundreds of interatomic spacings. Second, operating the network requires the movement of many electrons, which costs a lot of energy due to electrical resistance. Third, semiconductors do not intrinsically have magnetic properties and their electron configuration is very basic. “This dramatically limits the ways to build functional junctions and to realize magnetic applications,” Hinkov reports.

Versatile properties require sophisticated methods

Transition-metal oxides, on the other hand, exhibit many different properties: Some of them are ferromagnetic, others are antiferromagnetic, and others in turn are high-temperature superconductors with very unconventional properties. Forming interfaces between such materials yields a plethora of phenomena, which hold promise for novel applications such as different sensors, lossless computer memory and ultrafast processors. The price one has to pay is that more sophisticated tools are necessary to study them: This is due to the variety of phenomena and due to the much shorter length scale, over which the properties of oxides change at such heterointerfaces, which is often just a few atomic spacings.

Of crucial importance is the behavior of electrons at the interface: Do they tend to accumulate? Which orbitals do they occupy, i.e. how do the electron clouds arrange around the atoms? Is there magnetic order, i.e. do the tiny magnetic moments of the electrons called spins align relative to each other, establishing magnetic order? Physicists around the world are seeking for answers to these questions.

Measurements on an atomic scale

Hinkov and coworkers developed a new method and analysis software, and it provides answers. It is based on “resonant x-ray reflectometry”, a technique exploiting x-ray light created at a synchrotron, with the atomic-scale resolution of less than one nanometer. The physicists apply the technique on thin films of lanthanum cobalt oxide, a material that has interesting magnetic properties.

In their present work, however, the scientists have concentrated on another aspect: "Before we can delve in the rich magnetic phenomena of this material, we first have to solve a fundamental, very wide spread problem," says Professor Hinkov. "Like many other materials, such as simple table salt and many semiconductors, lanthanum cobalt oxide consists of charged particles. These so-called ions form a sequence of positively and negatively charged atomic layers, stacked to a 15 nanometer thin film. “One can show that enormous electrostatic fields form between the layers, which is a problem, since they cost a lot of energy,” as Vladimir Hinkov explains.

“Nature is economical and avoids these field energy costs: It brings positive and negative charges to the opposite faces of the film, respectively, just like between the plates of a capacitor. A new field is formed, which is opposite to the original one and which cancels it."

Corrugated interfaces constitute a problem

This accumulation of pure electronic charge at the film faces is called “electronic reconstruction”. According to the physicists, this is a very elegant solution, since it preserves the film face smoothness. For materials, in which electronic reconstruction is not possible, the compensating charge is provided by comparatively large ions, which results in corrugated film faces. As Hinkov explains, such corrugations are detrimental for devices based on film interfaces, especially when, like in transition-metal oxides, the material properties change on an atomic scale at the interface.

Exploiting the new method, the present work shows microscopic evidence that electronic reconstruction is indeed realized at transition-metal oxide interfaces. The method also provides a possibility to study the microscopic properties of such interfaces, which are not limited to electronic reconstruction, but encompass the arrangement of chemical elements, the electronic occupation of atomic orbitals and the spin orientation.

Successful by close, international collaboration

The special “Würzburg environment” and the close international collaboration enabled this successful work. "Such a scientific endeavor is only possible when experts from many different fields work closely together," says Professor Hinkov. One needs excellent samples, high-precision x-ray scattering instruments, which are operated at modern synchrotron light sources, a dedicated software, and last but not least “colleagues who are willing to spend day and night at the synchrotron to perform the measurements."

Valence-state reflectometry of complex oxide heterointerfaces. Jorge E Hamann-Borrero, Sebastian Macke, Woo Seok Choi, Ronny Sutarto, Feizhou He, Abdullah Radi, Ilya Elfimov, Robert J Green, Maurits W Haverkort, Volodymyr B Zabolotnyy, Ho Nyung Lee, George A Sawatzky & Vladimir Hinkov. doi:10.1038/npjquantmats.2016.13

Contact

Prof. Dr. Vladimir Hinkov, Lehrstuhl für Experimentelle Physik IV , T: (0931) 31-84481, hinkov@physik.uni-wuerzburg.de

Gunnar Bartsch | Julius-Maximilians-Universität Würzburg
Further information:
http://www.uni-wuerzburg.de

More articles from Physics and Astronomy:

nachricht Space radiation won't stop NASA's human exploration
18.10.2017 | NASA/Johnson Space Center

nachricht Study shows how water could have flowed on 'cold and icy' ancient Mars
18.10.2017 | Brown University

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

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

Im Focus: Neutron star merger directly observed for the first time

University of Maryland researchers contribute to historic detection of gravitational waves and light created by event

On August 17, 2017, at 12:41:04 UTC, scientists made the first direct observation of a merger between two neutron stars--the dense, collapsed cores that remain...

Im Focus: Breaking: the first light from two neutron stars merging

Seven new papers describe the first-ever detection of light from a gravitational wave source. The event, caused by two neutron stars colliding and merging together, was dubbed GW170817 because it sent ripples through space-time that reached Earth on 2017 August 17. Around the world, hundreds of excited astronomers mobilized quickly and were able to observe the event using numerous telescopes, providing a wealth of new data.

Previous detections of gravitational waves have all involved the merger of two black holes, a feat that won the 2017 Nobel Prize in Physics earlier this month....

Im Focus: Smart sensors for efficient processes

Material defects in end products can quickly result in failures in many areas of industry, and have a massive impact on the safe use of their products. This is why, in the field of quality assurance, intelligent, nondestructive sensor systems play a key role. They allow testing components and parts in a rapid and cost-efficient manner without destroying the actual product or changing its surface. Experts from the Fraunhofer IZFP in Saarbrücken will be presenting two exhibits at the Blechexpo in Stuttgart from 7–10 November 2017 that allow fast, reliable, and automated characterization of materials and detection of defects (Hall 5, Booth 5306).

When quality testing uses time-consuming destructive test methods, it can result in enormous costs due to damaging or destroying the products. And given that...

Im Focus: Cold molecules on collision course

Using a new cooling technique MPQ scientists succeed at observing collisions in a dense beam of cold and slow dipolar molecules.

How do chemical reactions proceed at extremely low temperatures? The answer requires the investigation of molecular samples that are cold, dense, and slow at...

Im Focus: Shrinking the proton again!

Scientists from the Max Planck Institute of Quantum Optics, using high precision laser spectroscopy of atomic hydrogen, confirm the surprisingly small value of the proton radius determined from muonic hydrogen.

It was one of the breakthroughs of the year 2010: Laser spectroscopy of muonic hydrogen resulted in a value for the proton charge radius that was significantly...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ASEAN Member States discuss the future role of renewable energy

17.10.2017 | Event News

World Health Summit 2017: International experts set the course for the future of Global Health

10.10.2017 | Event News

Climate Engineering Conference 2017 Opens in Berlin

10.10.2017 | Event News

 
Latest News

Osaka university researchers make the slipperiest surfaces adhesive

18.10.2017 | Materials Sciences

Space radiation won't stop NASA's human exploration

18.10.2017 | Physics and Astronomy

Los Alamos researchers and supercomputers help interpret the latest LIGO findings

18.10.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>