Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Study Reveals Principles of Gold Nanocluster Stability

14.07.2008
A report published in the July 8 issue of the journal Proceedings of the National Academy of Sciences (PNAS) is the first to describe the principles behind the stability and electronic properties of tiny nanoclusters of metallic gold. The study, which confirms the “divide and protect” bonding structure, resulted from the work of researchers at four universities on two continents.

“While gold nanoparticles are being used by so many researchers – chemists, materials scientists and biomedical engineers – no one understood their molecular and electronic structures until now,” said Robert Whetten, a professor in the Georgia Institute of Technology’s School of Physics and School of Chemistry and Biochemistry. “This research opens a new window for nanoparticle chemistry.”

Gold and sulfur atoms tend to aggregate in specific numbers and highly symmetrical geometries. Sometimes these clusters are called “superatoms” because they can mimic the chemistry of single atoms of a completely different element.

Researchers commonly use gold nanoparticles because they are stable and exhibit distinct optical, electronic, electrochemical and bio-labeling properties. However, understanding the physicochemical properties of such clusters is a challenge, according to Whetten, because that requires knowledge of their atomic structures.

A significant advance came in late 2007 though, when Stanford University researchers reported the first-ever total structure determination of a 102-atom gold cluster. The X-ray structure study revealed that pairs of organic sulfur (“thiolate”) groups extracted gold atoms from the gold layer to form a linear thiolate-gold-thiolate bridge while interacting weakly with the metal surface below. These gold–thiolate complexes formed a sort of protective crust around the nanoparticles.

“This discovery contradicted what most chemists believed was going on – which was that the sulfur atom merely sat atop the uppermost gold layer, bound to three adjacent metal atoms,” said Whetten.

With the experimentally determined structural coordinates, an international team of researchers from Georgia Tech, Stanford University, the University of Jyväskylä in Finland and Chalmers University of Technology in Sweden set out to determine the electronic principles underlying the 102-atom gold compound and others like it. The team conducted large-scale electronic structure calculations in supercomputing centers in Espoo, Finland; Stockholm, Sweden; and Juelich, Germany.

The researchers found that the 102-atom gold cluster was a “superatom” with a core of 79 gold atoms arranged into a truncated decahedron: two pyramids with pentagonal bases joined together into a faceted shape, but with the pyramids’ tips chopped off. Around the core, 23 gold atoms formed an unusual pattern, joining the thiolates in shapes that resemble handles.

The results confirmed the “divide and protect” structure first predicted by team member Hannu Häkkinen, a professor at the University of Jyväskylä and former senior research scientist at Georgia Tech in the laboratory of Uzi Landman. Häkkinen and Henrik Grönbeck of the Chalmers University of Technology previously proposed that a cluster of 38-atom gold contained a central metallic core of 14 gold atoms and a protective layer of 24 gold atoms bound to sulfur.

“In 2006, we predicted that gold atoms in this bonding motif were divided in two groups – those that made the metal core and those that helped to protected it,” explained Häkkinen. “Now there was evidence that this was true.”

In the study reported in PNAS, the researchers found that the clusters were stable because the surface gold atoms in the core each had at least one surface-chemical bond and the gold core exhibited a strong electron shell closing.

With the 102-atom gold cluster, each gold atom in the cluster donated one valence electron. Forty-four of those electrons were immobilized in bonds between gold atoms and thiolates, leaving 58 electrons to fill a shell around the “superatom.” In this configuration, the cluster wouldn’t benefit from adding or shedding electrons, which would destabilize its structure. This process is similar to what happens in noble gases, which are chemically inert because they have just the right number of electrons to fill a shell around each atom’s nucleus.

Associated with the filled electron shell, the gold-thiolate compound also had a major energy gap to unoccupied states. The calculated energy gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital states for the 102-atom compound was significant – 0.5 electron volts. Metals typically have a gap of zero, so this gap indicates an atypical electronic stability of the compound, explained Whetten.

Besides the 102-atom compound, the researchers also determined the electronic structures for 11-, 13- and 39-atom gold cluster compounds. They found that the 11- and 13-gold atom clusters form closed electronic shells with 8 electrons and the 39-atom gold clusters with 34.

“The theoretical concepts published in this paper provide a solid background for further understanding of the distinct electrical, optical and chemical properties of the stable mono-layer-protected gold nanoclusters,” said Whetten, whose funding for this research came from the National Science Foundation and the U.S. Department of Energy. Former Georgia Tech graduate student Ryan Price and current graduate student James Bradshaw also contributed to this work.

The study also shows that experimentally well-characterized, structure-resolved, thermodynamically stable species of thiolate-, phosphine-halide-, and phosphine-thiolate-protected gold nanoparticles share common factors underlying their stability.

Once this initial work was completed, the researchers started predicting the structures of other stable gold cluster compositions that are still awaiting a precise structure determination.

In the March 26 issue of the Journal of the American Chemical Society, the research team predicted the structure for a cluster containing 25 gold atoms. They determined that the structure was comprised of an icosahedron-like 13-atom gold core protected by six “V-shaped” long units, creating a “divide and protect” composition. The structural prediction was recently confirmed by another group’s experimental work.

“We now have a unified model that provides a solid background for nanoengineering ligand-protected gold clusters for applications in catalysis, sensing, photonics, bio-labeling and molecular electronics,” said Häkkinen.

Additional authors on the PNAS paper included Michael Walter, Jaakko Akola and Olga Lopez-Acevedo of the University of Jyväskylä; and Pablo Jadzinsky, Guillermo Calero and Christopher Ackerson of Stanford University.

Abby Vogel | Newswise Science News
Further information:
http://www.gatech.edu

More articles from Studies and Analyses:

nachricht The Great Unknown: Risk-Taking Behavior in Adolescents
19.01.2017 | Max-Planck-Institut für Bildungsforschung

nachricht A sudden drop in outdoor temperature increases the risk of respiratory infections
11.01.2017 | University of Gothenburg

All articles from Studies and Analyses >>>

The most recent press releases about innovation >>>

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

Im Focus: Traffic jam in empty space

New success for Konstanz physicists in studying the quantum vacuum

An important step towards a completely new experimental access to quantum physics has been made at University of Konstanz. The team of scientists headed by...

Im Focus: How gut bacteria can make us ill

HZI researchers decipher infection mechanisms of Yersinia and immune responses of the host

Yersiniae cause severe intestinal infections. Studies using Yersinia pseudotuberculosis as a model organism aim to elucidate the infection mechanisms of these...

Im Focus: Interfacial Superconductivity: Magnetic and superconducting order revealed simultaneously

Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.

While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...

Im Focus: Studying fundamental particles in materials

Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales

Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...

Im Focus: Designing Architecture with Solar Building Envelopes

Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.

As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Sustainable Water use in Agriculture in Eastern Europe and Central Asia

19.01.2017 | Event News

12V, 48V, high-voltage – trends in E/E automotive architecture

10.01.2017 | Event News

2nd Conference on Non-Textual Information on 10 and 11 May 2017 in Hannover

09.01.2017 | Event News

 
Latest News

Helmholtz International Fellow Award for Sarah Amalia Teichmann

20.01.2017 | Awards Funding

An innovative high-performance material: biofibers made from green lacewing silk

20.01.2017 | Materials Sciences

Ion treatments for cardiac arrhythmia — Non-invasive alternative to catheter-based surgery

20.01.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>