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 Single-stranded DNA and RNA origami go live
15.12.2017 | Wyss Institute for Biologically Inspired Engineering at Harvard

nachricht New antbird species discovered in Peru by LSU ornithologists
15.12.2017 | Louisiana State 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: First-of-its-kind chemical oscillator offers new level of molecular control

DNA molecules that follow specific instructions could offer more precise molecular control of synthetic chemical systems, a discovery that opens the door for engineers to create molecular machines with new and complex behaviors.

Researchers have created chemical amplifiers and a chemical oscillator using a systematic method that has the potential to embed sophisticated circuit...

Im Focus: Long-lived storage of a photonic qubit for worldwide teleportation

MPQ scientists achieve long storage times for photonic quantum bits which break the lower bound for direct teleportation in a global quantum network.

Concerning the development of quantum memories for the realization of global quantum networks, scientists of the Quantum Dynamics Division led by Professor...

Im Focus: Electromagnetic water cloak eliminates drag and wake

Detailed calculations show water cloaks are feasible with today's technology

Researchers have developed a water cloaking concept based on electromagnetic forces that could eliminate an object's wake, greatly reducing its drag while...

Im Focus: Scientists channel graphene to understand filtration and ion transport into cells

Tiny pores at a cell's entryway act as miniature bouncers, letting in some electrically charged atoms--ions--but blocking others. Operating as exquisitely sensitive filters, these "ion channels" play a critical role in biological functions such as muscle contraction and the firing of brain cells.

To rapidly transport the right ions through the cell membrane, the tiny channels rely on a complex interplay between the ions and surrounding molecules,...

Im Focus: Towards data storage at the single molecule level

The miniaturization of the current technology of storage media is hindered by fundamental limits of quantum mechanics. A new approach consists in using so-called spin-crossover molecules as the smallest possible storage unit. Similar to normal hard drives, these special molecules can save information via their magnetic state. A research team from Kiel University has now managed to successfully place a new class of spin-crossover molecules onto a surface and to improve the molecule’s storage capacity. The storage density of conventional hard drives could therefore theoretically be increased by more than one hundred fold. The study has been published in the scientific journal Nano Letters.

Over the past few years, the building blocks of storage media have gotten ever smaller. But further miniaturization of the current technology is hindered by...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

See, understand and experience the work of the future

11.12.2017 | Event News

Innovative strategies to tackle parasitic worms

08.12.2017 | Event News

AKL’18: The opportunities and challenges of digitalization in the laser industry

07.12.2017 | Event News

 
Latest News

Engineers program tiny robots to move, think like insects

15.12.2017 | Power and Electrical Engineering

One in 5 materials chemistry papers may be wrong, study suggests

15.12.2017 | Materials Sciences

New antbird species discovered in Peru by LSU ornithologists

15.12.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>