Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


Physicists Discover Structures of Gold Nanoclusters

Using different experimental techniques, two separate and independent research groups in collaboration with a team from the Center for Computational Materials Science (CCMS) at the Georgia Institute of Technology, have unveiled the size-dependent evolution of structural and electronic structural motifs of gold nanoclusters ranging in size from 11 to 24 atoms. The experiments, in conjunction with the theoretical analysis performed by the Georgia Tech team, show near perfect agreement pertaining to the cluster structures occurring in the experiments.
Understanding the electronic and geometric structures of gold nanoclusters is a key step towards understanding their behavior under different conditions, such as their use as nanocatalysts or in certain medical applications. The results appear in separate papers in The Physical Review B and in the journal ChemPhysChem.

In its bulk form, gold is treasured for its property as a non-reactive metal. Its use in electronics, dentistry, jewelry and art, depends on this inertness. But at the nano scale, when gold clusters contain only a small number of atoms, gold shows very different properties, which exhibit chemical reactivity that make them potent catalysts. Because their chemical and physical properties depend greatly on their physical structures, significant efforts have been invested by scientists to determine what the most stable configurations of gold clusters are in this size range. Understanding this is of great importance for elucidating the chemical properties of these clusters and in research aiming to discover the physical patterns that govern how the clusters are put together.

Between 2000 and 2002, a Georgia Tech team, led by Uzi Landman, director of CCMS, Regents’ and Institute professor, and Callaway chair of physics at Georgia Tech, predicted that negatively charged gold nanoclusters, up to 13 atoms in size, would exhibit two-dimensional, flat structures. The appearance of two-dimensional structures for such relatively large metal clusters is unique to gold, and the researchers showed that it is related to the strong relativistic effects for this metal. When these predictions were verified experimentally, research in Landman’s group and in other places focused on what happens when the nanoclusters are even larger.

"We wanted to know, what happens after 13 atoms,” said Landman. “What happens when these clusters become three-dimensional and what is their structural motif?” For the past few years, scientists at the CCMS have made theoretical predictions about the structures of gold nanoclusters in the larger size range. Now, working with two independent experimental groups, Landman and his collaborators have found firm evidence pertaining to the size-dependent structural development of these nanoclusters.

One of these collaborations involved researchers from the University of Freiburg and the Fraunhofer Institute for Mechanics of Materials, both in Germany, and a scientist from the University of Jväskylä in Finland. The Freiburg team performed photoemission experiments, in which a laser is shot at the gas-phase cluster causing it to eject an electron. Measuring the energy profiles of the emitted electrons using lasers of different wavelengths allowed the researchers to gain knowledge about the occupied electronic energy levels in the clusters. The distribution of these levels depends on the specific geometric arrangement of atoms in the clusters. Indeed, the theoretical analysis of the correlation between the distributions of the electronic energy levels and the atomic spatial arrangements allowed the researchers to determine the clusters’ electronic properties, as well as geometric structures.

In the other collaboration, the Georgia Tech researchers worked with a team from the Rowland Institute at Harvard University. They used electron diffraction, a technique in which a beam of electrons is fired at the clusters, causing the electrons to scatter. By measuring the intensity of the scattered electrons and comparing it to the change in momenta of the electrons caused by their collisions with the atoms of the clusters, they obtaines information about the spatial arrangements of the atoms in the clusters. Theoretical analysis of the interference patterns in these measured intensities allowed them to determine the clusters’ structures.

"It turns out that close to all the stable structures that were found through our theoretical analysis of the photoemission measurements were the same as those that emerged from analysis of the electron scattering experiments,” said Landman. “In our analysis we have used first-principles electronic structure calculations based on density-functional theory, in conjunction with structural optimization techniques. This is likely the first time that two separate and independent experimental tools, in conjunction with a common theoretical analysis, have shown such a high degree of agreement in the challenging area of structural determination of nano clusters.”

To avoid any bias, and ensure that the groups’ analyses weren’t being unintentionally influenced by knowledge of each other, neither experimental group saw the results of the other until the publication of their respective papers.

The results of the Georgia Tech collaborative investigations with the European group are published in the journal ChemPhysChem Volume 8, (2007), and those obtained from the collaboration with the Rowland Institute are published in The Physical Review B volume 74, (2006).

Through this comparison between experiment and theory, the teams found that the clusters start out as two-dimensional structures till 13 or 14 atoms in size, changing to three-dimensional hollow cages from about 16 atoms, and developing a face-centered-cubic tetrahedral structure at 20 atoms, resembling the bulk gold crystalline structure. However, at 24 atoms the gold clusters take an unexpected capped tubular cigar shape.

"These results assist us not only in determining the structures of the clusters, but also provide insight into the factors that underlie their self-assembly,” said Landman. “In some ways, we are determining the ‘structural grammar’ of these gold nanoclusters and by understanding that, we may better understand what motifs appear as we continue to search for the structures of clusters larger than 24 atoms.

The Georgia Tech team consisted of Uzi Landman and research scientist Bokwon Yoon. The collaborations consisted of Pekka Kosiken, Bernd Huber and Michael Moseler from the Fraunhofer Institute for Mechanics of Materials and the University of Freiburg, Oleg Kostko and Bernd von Issendorff from the University of Freiburg and Hannu Hakkinen from the University of Jyvaskla. The Rowland Institute team was made up of Xiaopeng Xing and Joel H. Parks.

David Terraso | EurekAlert!
Further information:

More articles from Physics and Astronomy:

nachricht Move over, lasers: Scientists can now create holograms from neutrons, too
21.10.2016 | National Institute of Standards and Technology (NIST)

nachricht Finding the lightest superdeformed triaxial atomic nucleus
20.10.2016 | The Henryk Niewodniczanski Institute of Nuclear Physics Polish Academy of Sciences

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

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

Im Focus: New 3-D wiring technique brings scalable quantum computers closer to reality

Researchers from the Institute for Quantum Computing (IQC) at the University of Waterloo led the development of a new extensible wiring technique capable of controlling superconducting quantum bits, representing a significant step towards to the realization of a scalable quantum computer.

"The quantum socket is a wiring method that uses three-dimensional wires based on spring-loaded pins to address individual qubits," said Jeremy Béjanin, a PhD...

Im Focus: Scientists develop a semiconductor nanocomposite material that moves in response to light

In a paper in Scientific Reports, a research team at Worcester Polytechnic Institute describes a novel light-activated phenomenon that could become the basis for applications as diverse as microscopic robotic grippers and more efficient solar cells.

A research team at Worcester Polytechnic Institute (WPI) has developed a revolutionary, light-activated semiconductor nanocomposite material that can be used...

Im Focus: Diamonds aren't forever: Sandia, Harvard team create first quantum computer bridge

By forcefully embedding two silicon atoms in a diamond matrix, Sandia researchers have demonstrated for the first time on a single chip all the components needed to create a quantum bridge to link quantum computers together.

"People have already built small quantum computers," says Sandia researcher Ryan Camacho. "Maybe the first useful one won't be a single giant quantum computer...

Im Focus: New Products - Highlights of COMPAMED 2016

COMPAMED has become the leading international marketplace for suppliers of medical manufacturing. The trade fair, which takes place every November and is co-located to MEDICA in Dusseldorf, has been steadily growing over the past years and shows that medical technology remains a rapidly growing market.

In 2016, the joint pavilion by the IVAM Microtechnology Network, the Product Market “High-tech for Medical Devices”, will be located in Hall 8a again and will...

Im Focus: Ultra-thin ferroelectric material for next-generation electronics

'Ferroelectric' materials can switch between different states of electrical polarization in response to an external electric field. This flexibility means they show promise for many applications, for example in electronic devices and computer memory. Current ferroelectric materials are highly valued for their thermal and chemical stability and rapid electro-mechanical responses, but creating a material that is scalable down to the tiny sizes needed for technologies like silicon-based semiconductors (Si-based CMOS) has proven challenging.

Now, Hiroshi Funakubo and co-workers at the Tokyo Institute of Technology, in collaboration with researchers across Japan, have conducted experiments to...

All Focus news of the innovation-report >>>



Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

Agricultural Trade Developments and Potentials in Central Asia and the South Caucasus

14.10.2016 | Event News

World Health Summit – Day Three: A Call to Action

12.10.2016 | Event News

Latest News

Resolving the mystery of preeclampsia

21.10.2016 | Health and Medicine

Stanford researchers create new special-purpose computer that may someday save us billions

21.10.2016 | Information Technology

From ancient fossils to future cars

21.10.2016 | Materials Sciences

More VideoLinks >>>