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Scientists Study And Learn To Prevent Nanoparticle 'Merging'

Date:
October 8, 2005
Source:
DOE/Brookhaven National Laboratory
Summary:
Researchers at the US Department of Energy's Brookhaven National Laboratory have identified how billionth-of-a-meter sized metal particles -- gold-atom clusters within carbon-atom shells -- can mesh together to form larger particles and have also found a way to control this process. The results, published in the September 27, 2005, online edition of Nano Letters, may help scientists determine how these "nanoparticles," which have unique physical, chemical, and electronic properties, could be incorporated into new technologies.
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UPTON, NY - Researchers at the U.S. Department of Energy’sBrookhaven National Laboratory have identified how billionth-of-a-metersized metal particles — gold-atom clusters within carbon-atom shells —can mesh together to form larger particles and have also found a way tocontrol this process. The results, published in the September 27, 2005,online edition of Nano Letters, may help scientists determine how these“nanoparticles,” which have unique physical, chemical, and electronicproperties, could be incorporated into new technologies.

“Nanostructuresthat consist of a metal nanoparticle trapped within a carbon cage havegreat technological promise, such as in electronics and biomedicalimaging systems, but scientists have more to learn about them,” saidEli Sutter, a scientist at Brookhaven’s Center for FunctionalNanomaterials and the study’s lead author. “For example, knowing how tocontrol the size of the particles is very important because size isstrongly linked to properties like electronic structure and meltingtemperature.”

The researchers studied small groups of goldnanoparticles supported by a layer of carbon atoms. They watched theparticles interact using a transmission electron microscope, whichcreates an image of a sample by bombarding it with a beam of electrons.They imaged the particles at “low” temperatures, from room temperatureto 400 degrees Celsius (ºC), and again at high temperatures from 400ºCto 800ºC.

At low temperatures, the group found that goldparticles can mesh together by forming a bridge between them that isonly one atom wide. Once this bridge is built, gold atoms can shuttleback and forth between the particles, much as automobile traffic flowsover a bridge. This exchange of gold atoms eventually leads to themerging of the nanoparticles connected by the bridge, and the formationof a larger particle.

At high temperatures, however, theinteraction between the nanoparticles changed significantly, andinvolved the carbon atoms underneath. The carbon atoms near eachparticle, immobile at low temperatures, began to cluster together,forming a jumble of fragments and layers. When the researchersincreased the intensity of the microscope’s electron beam, the carbonfragments began to creep up and around the particles, eventuallyforming shells that completely enclosed them, much like nut shellsenclosing small kernels.

“Almost immediately we noticed that thecarbon shells seem to prevent the gold nanoparticles from coalescing,even over long periods of time,” said Sutter. “We wondered if therewere conditions that would allow them to merge.”

They discoveredthat repeatedly switching the electron-beam intensity from high to lowcaused a carbon shell to form around the entire particle assembly. Andthen something surprising happened: Instead of further preventing theparticles from interacting, the large carbon shell seemed to physicallysqueeze them together, much like a nutcracker cracking a nutshell.

“Thelarge shell exerted pressure on the particles within it, broke theirindividual shells, and triggered a merging process that is similar towhat occurred at low temperatures,” said Sutter. “This was not at allwhat we expected to happen.”

Sutter and her collaboratorsconcluded that encapsulating individual metal nanoparticles withinshells made of carbon or similar materials, which they showed ispossible under the right conditions, might be a good way to preventuncontrolled size changes in nanoparticle arrays.

The Brookhavenresearch was funded by the Office of Basic Energy Sciences within theDepartment of Energy’s Office of Science, which also sponsored andmanaged construction of the Center for Functional Nanomaterials (CFN),one of the suite of five DOE Nanoscale Sciences Research Centers. Moreinformation about the CFN can be found at http://www.cfn.bnl.gov.


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Cite This Page:

DOE/Brookhaven National Laboratory. "Scientists Study And Learn To Prevent Nanoparticle 'Merging'." ScienceDaily. ScienceDaily, 8 October 2005. <www.sciencedaily.com/releases/2005/10/051006083014.htm>.
DOE/Brookhaven National Laboratory. (2005, October 8). Scientists Study And Learn To Prevent Nanoparticle 'Merging'. ScienceDaily. Retrieved March 29, 2024 from www.sciencedaily.com/releases/2005/10/051006083014.htm
DOE/Brookhaven National Laboratory. "Scientists Study And Learn To Prevent Nanoparticle 'Merging'." ScienceDaily. www.sciencedaily.com/releases/2005/10/051006083014.htm (accessed March 29, 2024).

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