Dutch and US microscopy experts are imaging the transport of individual atoms in thin films, and hope within a few years to move their technique from lab to real world environments.
Potential applications are diverse, and include the monitoring of biological processes, and close observation of chemical catalysis.
Henny Zandbergen, from Delft University of Technology, together with colleagues and Princeton and Yeshiva Universities, prepared a 20-nm thick film of gold atoms on a gold surface. With a high resolution electron microscope, the researchers then observed in real time how atoms in the film collectively sink into the underlying layer and form a surface dislocation.
The surface dislocation glides along the underlying layer, but is trapped by the layer edges. It eventually disappears by squeezing out in the dislocation line direction, but the process is too fast to be resolved with the 0.05-s frame interval in the imaging.
The results, published in Physical Review Letters, could have profound implications for nanofilm growth. What they show is how atoms can be transported across layers of atoms without being obstructed by the Ehrlich-Schwoebel energy barrier. Industrial researchers modelling the production of thin layers will need to take this behaviour into account.
But this is much more than an interesting study in solid state physics. It is wonderfully illustrative of the rapid progress being made in practical nano-imaging. With the work of Zandbergen and his co-workers, we can see clearly how atoms move in real time, and pinpoint their position with 0.01-nm precision.
‘The PRL paper shows real time changes,’ says Zandbergen. ‘The progress in Delft is towards doing such experiments also at atmospheric pressure. High pressures and elevated temperatures are very interesting for industrial research, and this is within short range reach (one to a few years).’
Delft University of Technology, Leiden University and the microscope manufacturer FEI are conducting joint research into nano-microscopy.
Figure: Time series of 12 electron microscope images taken from a movie showing the transport of gold atoms through a nanofilm. In the middle 10 images, a moving surface dislocation can be seen in the top layer of atoms. Taken from: Zandbergen et al., Phys. Rev. Lett. 98, 036103 (2007) (subscription required). © 2007 American Physical Society.
For the movie, visit the EPAPs site and enter the document reference: E-PRLTAO-98-052703.
Article first published in Nanomaterials News.