A dynamic game of hide and seek at the nanoscale

(Nanowerk News) A novel statistical model analyses an electron microscopy movie to reveal atomic rearrangements in nanoparticles over time. A team of researchers from the University of Antwerp, the University of Oxford and the University of Dublin have introduced this model in a paper published in Physical Review Letters ("Measuring Dynamic Structural Changes of Nanoparticles at the Atomic Scale Using Scanning Transmission Electron Microscopy").
The size, shape and chemical content of nanomaterials determine their properties. When the size or shape changes, properties such as catalytic activity can change as well. Therefore, to understand the properties of nanomaterials, it is important to correctly quantify their atomic structure.
“The atoms in a nanoparticle are hiding behind each other in atomic columns. We only see a ‘top view’ projection of this stack of atoms in the electron microscopy image. Our goal is to find precisely how many atoms hide in each of the atomic columns of the nanoparticle, thus unravelling the atomic structure.” says Annick De Backer of the University of Antwerp. Prior research efforts have enabled scientists to count how many atoms are hiding behind each other in the atomic columns with single-atom precision. From one snapshot, it is however impossible to gain insight in the dynamics of the nanoparticle.
The newly proposed model is therefore specifically designed to analyse a series of images, the ‘movie’ of the nanoparticle. During the recording of this movie, the atoms could move around in the structure. The model estimates how likely it is for an atomic column to lose or gain one or more atoms from one frame of the movie to the next. Using these probabilities, the model reveals the most likely number of atoms in each column at each time.
“We can beat the atoms at an advanced game of hide and seek, even though they may cheat and change hiding place by moving to another column in the nanoparticle, or even leave the nanoparticle completely.” says Annelies De wael, Ph.D. student in the team of professor Sandra Van Aert of the University of Antwerp.
Thanks to the specific dynamic design of the new statistical model, the researchers could reliably analyse a movie of a platinum nanoparticle, shot at the University of Oxford. The results reveal how the nanoparticle loses its facetted morphology and provides a measure for the probability and cross section for surface diffusion. This information can lead to understanding surface related phenomena such as catalysis.
Source: University of Antwerp
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