The interface between two tin-oxide semiconductors can exhibit unexpected metallic properties

June 4, 2018, King Abdullah University of Science and Technology

Metal oxidation is harnessed in many industrial applications. KAUST researchers have modeled the boundary between two metal oxides to reveal their metallic properties, which could lead to positive applications in electronics.

Our familiarity with rust, which occurs through the oxidation of iron to make it flaky and weak, means we usually consider oxidation of metals to be detrimental. But some are useful. For example, they have great potential in electronics because they can be both transparent and flexible. They can exhibit magnetic properties, which opens the door to high-performance, ultrafast computer memories. They can be sensitive to their environment, making them useful for gas sensors.

Recently, the potential of semiconducting tin monoxide (SnO) for electronic applications was revealed when KAUST scientists determined a record high mobility, which refers to how easily a charge-carrying particle can travel through the material. In this case, the were not electrons, but holes. Holes behave very similar to electrons, but they carry a positive rather than a negative electrical charge.

Obtaining pure tin monoxide is challenging because the fabrication process often also creates tin dioxide (SnO2). In general, the interface between two oxides can play host to a wide variety of exotic physics, from superconductivity to ferroelectricity, whereas the properties of the interface between tin monoxide and tin dioxide are largely unknown.

Arwa Albar, now an assistant professor at King Abdulaziz University, did this work as part of her Ph.D. studies at KAUST, together with Hassan Ali Tahini and her supervisor, Udo Schwingenschlögl. The scientists theoretically modeled the boundary between the two oxides using so-called . With this technique they were able to determine the density of electrical charge at the interface for different atomic arrangements. They showed that the boundary can support freely moving holes in what is known as a quantum gas, which gives the interface a metallic character.

"The new model accurately predicts the amount of charge at the interface," confirms Albar.

Quantum gases have already been identified at interfaces in other material systems. They can arise due to a discontinuity in charge between two materials.

"The quantum gas formation is explained by a mechanism known as polar catastrophe in which the electrons arrange themselves to avoid a divergence in electrostatic potential," says Schwingenschlögl. What is unusual about the tin monoxide–dioxide interface is that it lacks such a discontinuity in charge. "Instead, the amount of charge per interface area is different on the two sides of the ," explains Schwingenschlögl. "We call this 'charge density discontinuity' rather than the conventional 'charge discontinuity'."

The team predicts that this same phenomenon could also occur in other combinations of materials. "It will be necessary to investigate how the properties of the can be controlled," says Schwingenschlögl.

Explore further: Ultrathin semiconducting sheet showing gas-responsive electronic properties for highly sensitive gas sensors

More information: Arwa Albar et al. Metallicity at interphase boundaries due to polar catastrophe induced by charge density discontinuity, NPG Asia Materials (2018). DOI: 10.1038/am.2017.236

Related Stories

Energy level alignment for molecular electronics

March 14, 2018

NUS physicists have found that complex electron-electron interactions change the energy levels at molecule-metal interfaces, affecting the performance of molecular electronic devices.

New step towards future complex oxide electronics

November 22, 2017

Researchers from TU Delft, Cornell University and the University of Cagliari report an interesting method for turning a highly insulating material into a highly conducting system. The process involves combining three different ...

'Impossible' conductivity explained

May 19, 2010

(PhysOrg.com) -- Bring two materials that are not themselves conductive into contact and, exactly at their interface, something remarkable happens: at that precise point, conduction is possible.

Recommended for you

Gravitational wave detectors to search for dark matter

August 16, 2018

Gravitational wave detectors might be able to detect much more than gravitational waves. According to a new study, they could also potentially detect dark matter, if dark matter is composed of a particular kind of particle ...

Neutron stars may hold an answer to neutron puzzle on Earth

August 15, 2018

According to University of Illinois physicist Douglas H. Beck, "Neutrons play some unusual roles in our world. Free neutrons decay in about 900 s but, bound in nuclei, they are stable and make up somewhat more than half the ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.