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 Engineering team images tiny quasicrystals as they form
18.08.2017 | Cornell University

nachricht Astrophysicists explain the mysterious behavior of cosmic rays
18.08.2017 | Moscow Institute of Physics and Technology

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: Fizzy soda water could be key to clean manufacture of flat wonder material: Graphene

Whether you call it effervescent, fizzy, or sparkling, carbonated water is making a comeback as a beverage. Aside from quenching thirst, researchers at the University of Illinois at Urbana-Champaign have discovered a new use for these "bubbly" concoctions that will have major impact on the manufacturer of the world's thinnest, flattest, and one most useful materials -- graphene.

As graphene's popularity grows as an advanced "wonder" material, the speed and quality at which it can be manufactured will be paramount. With that in mind,...

Im Focus: Exotic quantum states made from light: Physicists create optical “wells” for a super-photon

Physicists at the University of Bonn have managed to create optical hollows and more complex patterns into which the light of a Bose-Einstein condensate flows. The creation of such highly low-loss structures for light is a prerequisite for complex light circuits, such as for quantum information processing for a new generation of computers. The researchers are now presenting their results in the journal Nature Photonics.

Light particles (photons) occur as tiny, indivisible portions. Many thousands of these light portions can be merged to form a single super-photon if they are...

Im Focus: Circular RNA linked to brain function

For the first time, scientists have shown that circular RNA is linked to brain function. When a RNA molecule called Cdr1as was deleted from the genome of mice, the animals had problems filtering out unnecessary information – like patients suffering from neuropsychiatric disorders.

While hundreds of circular RNAs (circRNAs) are abundant in mammalian brains, one big question has remained unanswered: What are they actually good for? In the...

Im Focus: RAVAN CubeSat measures Earth's outgoing energy

An experimental small satellite has successfully collected and delivered data on a key measurement for predicting changes in Earth's climate.

The Radiometer Assessment using Vertically Aligned Nanotubes (RAVAN) CubeSat was launched into low-Earth orbit on Nov. 11, 2016, in order to test new...

Im Focus: Scientists shine new light on the “other high temperature superconductor”

A study led by scientists of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg presents evidence of the coexistence of superconductivity and “charge-density-waves” in compounds of the poorly-studied family of bismuthates. This observation opens up new perspectives for a deeper understanding of the phenomenon of high-temperature superconductivity, a topic which is at the core of condensed matter research since more than 30 years. The paper by Nicoletti et al has been published in the PNAS.

Since the beginning of the 20th century, superconductivity had been observed in some metals at temperatures only a few degrees above the absolute zero (minus...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Call for Papers – ICNFT 2018, 5th International Conference on New Forming Technology

16.08.2017 | Event News

Sustainability is the business model of tomorrow

04.08.2017 | Event News

Clash of Realities 2017: Registration now open. International Conference at TH Köln

26.07.2017 | Event News

 
Latest News

A Map of the Cell’s Power Station

18.08.2017 | Life Sciences

Engineering team images tiny quasicrystals as they form

18.08.2017 | Physics and Astronomy

Researchers printed graphene-like materials with inkjet

18.08.2017 | Materials Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>