Electron transport and visible light absorption in a plasmonic photocatalyst based on strontium niobate

11 Aug 2017

Researchers led by T. Venky Venkatesan (first row, center), director of NUSNNI, have uncovered extraordinary properties of the semiconductor material strontium niobate.
New family of plasmons uncovered in unconventional metal
 
New family of plasmons uncovered in unconventional metal 
In the first study, the researchers, who were led by Assistant Professor Andrivo Rusydi, and Director of NUSNNI Professor T Venky Venkatesan, had found that while strontium niobate is highly metallic in nature due to a very large population of electrons in the material, which is typical of most metals, it is still transparent at most photon energies, which is an exceptional property that is unlike most metals. Utilising spectroscopic techniques, the research team discovered that this unique property arose from an intrinsic plasmonic absorption. 

Dr Teguh Citra Asmara, the first author of the paper and also a postdoctoral researcher at NUSNNI, said, “From our studies, we found that this material is a semiconductor with a large bandgap of four electron volts. Based on our understanding of semiconductors and this material’s strong metallic behaviour, we did not expect this material to absorb any visible photons, so the results we found are indeed surprising.”

“Plasmons are resonant oscillations of a collection of electrons and typically occur in a metallic solid. Under the right conditions, photons can cause these plasmons to be excited in a solid and in this process the solid absorbs the photon energy. Before our team figured this out, this material was thought to consist of a smaller bandgap, of the order of two electron volts, and a secondary band above of comparable energy,” explained Prof Venkatesan.

In addition, the research team discovered a new family of plasmons which occurs at multiple frequencies. This new family of plasmons is observed even when strontium niobate is not a conventional metal. 

Asst Prof Rusydi said, “This novel discovery opens new research directions and paths for plasmonics research, and enables us to look into previously untapped insulating and strongly-correlated materials. We are also currently studying the possible applications of this new type of plasmons.”

This project was originally initiated by Dr Zhao Yongliang as a part of his PhD thesis, and Dr Wan Dongyang followed up on it as part of his doctoral thesis. Both of them carried out the project under the supervision of Prof Venkatesan. The novel findings were reported in prestigious scientific journal Nature Communications on 12 May 2017.

‘Water splitters’ to reduce carbon footprint 

In the second study, NUS researchers examined how strontium niobate catalyses water. The team, supervised by Prof Venkatesan, found that when strontium niobate is in contact with water under solar irradiation, the semiconductor material could spilt water into its constituents of oxygen and hydrogen. This study, which was also conducted in collaboration with researchers from the Nanyang Technological University, was first published online in the prestigious scientific journal Nature Communications on 19 April 2017.

Prof Venkatesan explained, “While this material converts water into hydrogen under solar irradiation, the mechanism behind this process was previously misinterpreted as being due to the high speed or mobility of the electrons in the material. Our group clearly showed that it was not the case. The measured electron mobility was significantly low, but the effect was enhanced by the resonant absorption of the solar photons by the intrinsic plasmons present in this material.”

The results strongly suggest a novel approach to designing catalysts for various applications, and the work could lead to new techniques of harvesting hydrogen – a sustainable fuel - from water, hence contribute towards reducing carbon footprint.

“At NUSNNI, we have a group that has found a family of materials, aside from strontium niobate, that work equally well as plasmonic water splitters. Moving forward, we are working towards finding the right combination of photo-catalytic process for producing useful chemicals,” added Prof Venkatesan.

NUS website:

https://news.nus.edu.sg/press-releases/strontium-niobate-demystified-nus-led-research-teams-uncover-extraordinary

 

Below are the media coverage as of this morning.

 

Phys Org, 15 May 2017

Research teams uncover extraordinary properties of strontium niobate

 

Nanowerk, 15 May 2017

The extraordinary properties of strontium niobate demystified

 

Science Daily, 15 May 2017

Strontium niobate demystified: Research teams uncover extraordinary properties of the semiconductor material

 

Science Newsline, 15 May 2017

NUS-led Research Teams Uncover Extraordinary Properties of Strontium Niobate

 

World News, May 15 2017

https://article.wn.com/.../Strontium_niobate_demystified_NUSled_research_teams_un...

 

Nature, May 19, 2017

www.nature.com/articles/ncomms15070

 

Materials Today

http://www.materialstoday.com/metals-alloys/news/novel-semiconductor-material-extraordinary/

High Tech days

http://www.hitechdays.com/news/216984/nus-led-research-teams-uncover-extraordinary-properties-of-strontium-niobate/

Converter News

http://www.converternews.com/scientists-discover-unique-properties-of-strontium-niobate/

Physics News

http://www.physnews.com/nano-materials-news/cluster1689769578/

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