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Metal nanoclusters can be used as semiconductors: Key properties observed for first time

27.03.2019

Tiny nanoclusters of metal atoms - such as gold and silver - have properties which mean they can be used as semiconductors, a joint Swansea-Hamburg research team has discovered.

The finding opens the door to a wide range of potential new applications, from phone displays and flatter screens to wearable technology.


Scheme of the phenomenon: light, which strikes the films of nanoclusters, promotes the charge flow between the two electrodes.

Credit: Galchenko/Klinke: University of Hamburg/Swansea University


Model of the atomically precise gold clusters with 25 gold atoms and stabilizing ligand molecules.

Credit: Galchenko/Klinke: University of Hamburg/Swansea University

Semiconductors are at the heart of modern electronics. Amongst their many uses are in display devices for mobile phones and televisions, light detectors, and solar cells for providing energy.

The two main types of particle-based semiconductors already in use are colloidal quantum dots and organic semiconductors. These materials are at the nanoscale. Their tiny size means they are subject to a phenomenon known as quantum confinement, which causes changes to their optical and electronic properties. These changes make them suitable for their intended applications.

Metal nanoclusters combine aspects of both these other materials. Like colloidal quantum dots, they are very stable. Like organic semiconductors, they are atomically precise, or molecular, containing a specific number of atoms in their metallic core.

However, despite containing all the right ingredients, metal nanoclusters had never before been shown to display semiconducting properties.

This is where the Swansea-Hamburg team made the breakthrough.

The team devised a way of making films of nanoclusters consisting of 25 gold atoms (Au25). They then observed that the nanoclusters displayed semiconducting properties. Specifically, they observed field effect and photoconductivity in phototransistors made of these films. These unique properties are hallmarks of all semiconducting materials.

The team is made up of researchers from Swansea University's chemistry department and the University of Hamburg in Germany.

Professor Christian Klinke of Swansea University chemistry department explained the potential applications of this finding:

"The discovery of semiconducting properties in metal nanoclusters could pave the way for a variety of new applications, from field effect transistors and photodetectors to light emitting diodes and solar cells.

These devices could be manufactured on flexible bases. Many metal nanoclusters, including the ones we investigated in this report, have almost infinite stability, which could make them suitable for ink-jet printing applications.

We need to build on this finding and refine the technique further. But this discovery points the way ahead. It shows that we can use metal nanoclusters to produce high quality semiconducting films that are easy to assemble."

Other researchers from the team explained other potential applications:

Dr. Andrés Black of the University of Hamburg said:

"The affinity of the metal core to different molecular functionalities could make them highly sensitive gas sensors"

Michael Galchenko, also of the University of Hamburg said:

"The integration with other low dimensional materials could yield heterostructures with new and interesting functionalities."

Professor Owen Guy, head of Swansea University chemistry department, said:

"Semiconductors are a big focus for our work here at Swansea, both in our chemistry department and our Centre for NanoHealth. Christian's work is very exciting for next generation semiconductor materials - an area in which Swansea University is leading activity, with our industry partners.

These findings, made possible by our close links with Hamburg, are a significant step forward in the field. It shows that for research, as for teaching, our chemistry department is at the forefront".

###

The findings were published in the journal, Advanced Materials.

Notes to editors:

Chemistry research at Swansea University is pioneering multidisciplinary technology development in key themes of energy and environment; health; new and advanced molecules and polymers; nanotechnologies and advanced materials. Find out more: https://www.swansea.ac.uk/chemistry/

University of Hamburg: Universität Hamburg is the largest institution for research and education in northern Germany. As one of the country's largest universities, it offers a diverse range of degree programs and excellent research opportunities. The University boasts numerous interdisciplinary projects in a broad range of fields and an extensive partner network of leading regional, national, and international higher education and research institutions. https://www.uni-hamburg.de/en.html

Swansea University is a world-class, research-led, dual campus university offering a first class student experience and has one of the best employability rates of graduates in the UK. The University has the highest possible rating for teaching - the Gold rating in the Teaching Excellence Framework (TEF) in 2018 and was commended for its high proportions of students achieving consistently outstanding outcomes.

Swansea climbed 14 places to 31st in the Guardian University Guide 2019, making us Wales' top ranked university, with one of the best success rates of graduates gaining employment in the UK and the same overall satisfaction level as the Number 1 ranked university. The 2014 Research Excellence Framework (REF) 2014 results saw Swansea make the 'biggest leap among research-intensive institutions' in the UK (Times Higher Education, December 2014) and achieved its ambition to be a top 30 research University, soaring up the league table to 26th in the UK.

The University is in the top 300 best universities in the world, ranked in the 251-300 group in The Times Higher Education World University rankings 2018. Swansea University now has 23 main partners, awarding joint degrees and post-graduate qualifications.

The University was established in 1920 and was the first campus university in the UK. It currently offers around 350 undergraduate courses and 350 postgraduate courses to circa 20,000 undergraduate and postgraduate students.

The University has ambitious expansion plans as it moves towards its centenary in 2020 and aims to continue to extend its global reach and realise its domestic and international potential.

Swansea University is a registered charity. No.1138342. Visit http://www.swansea.ac.uk

When reporting this story, please use Swansea University hyperlinks.

For more information:

Kevin Sullivan,Swansea University Public Relations Office

Tel: 01792 513245, k.g.sullivan@swansea.ac.uk

http://www.twitter.com/SwanseaUni http://www.facebook.com/swanseauniversity

Kevin Sullivan | EurekAlert!

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