Atomic structure of nanoparticles measured

New insights could help to better understand the properties of nanoparticles

The yellow spheres are the schematically represented atoms, which form the approximately two nanometer sized silver particles. © ETH Zurich
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Scientists have for the first time succeeded in measuring the atomic structure of individual nanoparticles. In the future, the experimental data could make it possible to better understand the properties of nanoparticles, the researchers report in "Nature".

Nanoparticles have chemically different properties than their "big sisters and brothers": they have a very large surface area and a small number of atoms in relation to their tiny mass. This can lead to quantum effects that lead to changed material properties. For example, ceramics made from nanomaterials may suddenly bend, or a gold nugget may be golden while a nanosplitter of it is reddish.

So far, little is known about the effects of these altered properties on living organisms. Only recently, a study caused a stir, according to the nanoparticles such as titanium oxide in toothpaste or sun creams in the human lung to act similar to asbestos.

New method developed

The exact 3D structure, the atomic arrangement and especially the surface properties of nanoparticles determine their chemical and physical properties.

In a new study, initiated by ETH Zurich scientist Marta D. Rossell from the group of Markus Niederberger, a professor at the Institute for Multifunctional Materials and Empa researcher Rolf Erni, the three-dimensional structure of individual nanoparticles has now been achieved on a more atomic scale Base to determine. The new process could in the future help to better understand the nature of nanoparticles, including their reactivity and toxicity. display

Protective procedure for imaging

For their electron microscopic study, Rossell and Erni prepared silver nanoparticles in an aluminum matrix. The matrix makes it easier to tilt the nanoparticles under the electron beam into different crystallographic orientations while protecting the particles from damage by the electron beams. The basic requirement for the study was a special electron microscope that achieved a maximum resolution of less than 50 picometers. By comparison, the diameter of an atom is about one angstrom, that is 100 picometers.

To further protect the sample, the electron microscope was set to produce images at atomic resolution even at low acceleration voltage, at 80 kilovolts. Typically, such electron microscopes - of which there are only a few worldwide - operate at 200 or 300 kilovolts. The two scientists used a microscope in California at their Lawrence Berkeley National Laboratory for their experiments. The experimental data were finally completed by additional electron microscopic measurements made at Empa.

Happy pictures

Sandra Van Aert from the University of Antwerp used the micrographs to create models that allowed them to be 'scanned' and quantified: the images refined by the model enabled the individual silver atoms forming the The crystal lattices of the Natoteilchens spanned to count along different crystallographic orientations.

For the three-dimensional reconstruction of the atomic arrangement in the nanoparticle, Rossell and Erni finally added the tomography specialist Joost Batenburg from Amsterdam. He used the acquired data to tomographically reconstruct the arrangement of the atoms in the nanoparticle using special mathematical algorithms. Only two shots were enough to replicate the nanoparticle, which consists of around 784 atoms. Two more experimental projections of Rossell and Erni finally verified the reconstruction.

Characterization of doped nanoparticles

"Until now, only the rough outlines of nanoparticles could be portrayed from many perspectives, " says Rossell. Atomic structures, on the other hand, could only be simulated on the computer without any experimental basis. "Applications of the method, for example for the characterization of doped nanoparticles, are now planned", explains Erni.

For example, the method could be used in the future to determine which atomic configurations become active on the surface of the nanoparticles, for example if they have a toxic or catalytic effect. Rossell emphasizes that the study is in principle applicable to all nanoparticles. Prerequisite, however, is experimental data, as obtained in the study. (Nature 2011; doi: 10.1038 / nature09741)

(ETH Life Online, ETH Zurich, 18.02.2011 - DLO)