Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Intriguing structures of gold nanoparticles

05.08.2008
Scientists from Germany, Canada and the Netherlands have studied tiny gold nanoparticles, so-called clusters, and found them to have fascinating arrangements of their constituent atoms.

For example, twenty gold atoms form a tetrahedron, a sort of pyramid. The nineteen-atom cluster is a truncated pyramid, which can be formed by cutting off one corner atom from the twenty-atom gold pyramid. The structures have been identified using the Free Electron Laser for Infrared eXperiments FELIX at the FOM-Institute for Plasma Physics Rijnhuizen in Nieuwegein.

Detailed knowledge about the geometries of such nanoparticles can lead to a better understanding of the unexpected catalytic activity of very small gold particles. The researchers published their results in Science on 1 august 2008.

Gold is known to be a noble metal which means that it is inert and shows little reactivity. The resistance of gold to corrosion has been known to the human for millennia and is reflected in the use of gold in jewelry and currency. For the chemist, however, the reluctance of gold to undergo reactions was a reason to show little interest in this metal once the days of alchemy were past. This changed a few years ago when it was found that very small gold particles can catalyze, i.e. accelerate, important chemical reactions, for example the oxidation of hydrogen and carbon monoxide.

... more about:
»FELIX »Physic »Pyramid »nanoparticles »neutral »vibrational

Reasons for the high reactivity of these nanoscopic particles, so-called clusters, are assumed to be hidden in their atomic structure. As the active nanoparticles are smaller than the wavelength of visible light their structure cannot be inspected using an optical microscope. In the recent past, the structure of charged gold clusters had been determined, but that of the neutral clusters, thought to be more relevant for the catalytic activity, remained elusive.

Now, an international collaboration of scientists from the FOM-Institute for Plasma Physics Rijnhuizen in Nieuwegein, the Fritz-Haber-Institut der Max-Planck-Gesellschaft in Berlijn and the Steacie Institute for Molecular Sciences in Ottawa, Canada, has succeeded in identifying the structures of neutral gold clusters. They observed how the gold clusters interact with infrared laser light from the free-electron laser FELIX at the FOM-Institute for Plasma Physics in Nieuwegein.

The scientists produced the gold clusters by evaporating them from solid gold metal and subsequently using a helium gas beam to pick them up and to cool the particles. The cold beam of gold clusters contains cluster sizes from three to twenty atoms. The clusters are exposed to the intense infrared light. The scientists investigate the response to different frequencies of the infrared light. The atoms in molecules and clusters are held together by chemical bonds, which can be thought of as springs. If the frequency of the infrared light is matched to the frequency of the spring the light will amplify this vibration. In the very intense light of FELIX the spring can start to vibrate so strongly that the particle falls apart. Using a mass spectrometer the scientists can measure this process and reconstruct the vibrational spectrum.

The structure of the gold clusters can be determined by comparing the vibrational spectrum with those predicted using quantum chemistry theory. The complexity of the vibrational spectrum relates strongly to the symmetry of the cluster. Highly symmetric clusters, i.e. clusters which appear to be the same when observed from different sides, exhibit simple spectra with few but often intense signals. For example, only a single intense feature was observed in a cluster that contained precisely twenty gold atoms.

This is the finger print of a highly symmetric structure that is shown to be a triangular pyramid, a tetrahedron that has four equivalent corners and faces. The spectrum of the cluster with nineteen gold atoms is more complex, reflecting a drop in symmetry. Analysis of the vibrational spectrum shows that the structure is that of the twenty atom cluster with a gold atom missing from one of the corners.

The neutral clusters with nineteen and twenty atoms show the same structures that are familiar from their negative counterparts. A neutral cluster with seven gold atoms shows an even more complicated spectrum that matches a two-dimensional, asymmetric structure where six atoms form a triangle with one additional gold atom attached. In contrast to the larger clusters, for gold-seven the positively charged cluster arranges differently. In this cluster six atoms form a hexagon with one atom in its centre.

A new way is opened to study a whole range of gold clusters and clusters of other catalytically important metals at the molecular level. Once their structures are revealed the same techniques can be applied to follow intermediate steps of catalytic reactions on nanoparticles.

Annemarie Zegers | alfa
Further information:
http://www.fom.nl
http://www.fom.nl/live/home.pag

Further reports about: FELIX Physic Pyramid nanoparticles neutral vibrational

More articles from Life Sciences:

nachricht Nanoparticle Exposure Can Awaken Dormant Viruses in the Lungs
16.01.2017 | Helmholtz Zentrum München - Deutsches Forschungszentrum für Gesundheit und Umwelt

nachricht Cholera bacteria infect more effectively with a simple twist of shape
13.01.2017 | Princeton University

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

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

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...

Im Focus: How to inflate a hardened concrete shell with a weight of 80 t

At TU Wien, an alternative for resource intensive formwork for the construction of concrete domes was developed. It is now used in a test dome for the Austrian Federal Railways Infrastructure (ÖBB Infrastruktur).

Concrete shells are efficient structures, but not very resource efficient. The formwork for the construction of concrete domes alone requires a high amount of...

Im Focus: Bacterial Pac Man molecule snaps at sugar

Many pathogens use certain sugar compounds from their host to help conceal themselves against the immune system. Scientists at the University of Bonn have now, in cooperation with researchers at the University of York in the United Kingdom, analyzed the dynamics of a bacterial molecule that is involved in this process. They demonstrate that the protein grabs onto the sugar molecule with a Pac Man-like chewing motion and holds it until it can be used. Their results could help design therapeutics that could make the protein poorer at grabbing and holding and hence compromise the pathogen in the host. The study has now been published in “Biophysical Journal”.

The cells of the mouth, nose and intestinal mucosa produce large quantities of a chemical called sialic acid. Many bacteria possess a special transport system...

Im Focus: Newly proposed reference datasets improve weather satellite data quality

UMD, NOAA collaboration demonstrates suitability of in-orbit datasets for weather satellite calibration

"Traffic and weather, together on the hour!" blasts your local radio station, while your smartphone knows the weather halfway across the world. A network of...

Im Focus: Repairing defects in fiber-reinforced plastics more efficiently

Fiber-reinforced plastics (FRP) are frequently used in the aeronautic and automobile industry. However, the repair of workpieces made of these composite materials is often less profitable than exchanging the part. In order to increase the lifetime of FRP parts and to make them more eco-efficient, the Laser Zentrum Hannover e.V. (LZH) and the Apodius GmbH want to combine a new measuring device for fiber layer orientation with an innovative laser-based repair process.

Defects in FRP pieces may be production or operation-related. Whether or not repair is cost-effective depends on the geometry of the defective area, the tools...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

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

Nothing will happen without batteries making it happen!

05.01.2017 | Event News

 
Latest News

Multiregional brain on a chip

16.01.2017 | Power and Electrical Engineering

New technology enables 5-D imaging in live animals, humans

16.01.2017 | Information Technology

Researchers develop environmentally friendly soy air filter

16.01.2017 | Power and Electrical Engineering

VideoLinks
B2B-VideoLinks
More VideoLinks >>>