U. SHEFFIELD (UK) — A new electron microscope that works without a lens may create the highest resolution images ever seen.
Transmission electron microscopy (TEM), which looks through an object to see atomic features within it, has been constrained for over 70 years by the relatively poor lenses that are used to form the image.
The new method—called electron ptychography—dispenses with the lens and instead forms the image by reconstructing the scattered electron-waves after they have passed through the sample using computers.
Scientists at the University of Sheffield who consider their findings to be a first step in a “completely new epoch of electron imaging,” say the process has no fundamental experimental boundaries and could transform sub-atomic scale transmission imaging.
“To understand how material behaves, we need to know exactly where the atoms are. This approach will enable us to look at how atoms sit next to one another in a solid object as if we’re holding them in our hands,” says project leader John Rodenburg, professor in the department of electronic and electrical engineering.
“We’ve shown we can improve upon the resolution limit of an electron lens by a factor of five. An extension of the same method should reach the highest resolution transmission image ever obtained; about one tenth of an atomic diameter. No longer does TEM have to be bound by the paradigm of the lens, its Achilles’ heel since its invention in 1933.”
The technique, described in the journal Nature Communications, is applicable to microscopes using any type of wave and has other key advantages over conventional methods. For example, when used with visible light, the new technology forms a type of image that means scientists can see living cells very clearly without the need to stain them, a process which usually kills the cells.
The new method also disposes of the need to put a lens very close to a living sample, meaning that cells can be seen through thick containers like petri dishes or flasks. This means that as they develop and grow over days or weeks, they don’t have to be disturbed.
Plans are being put into place with the European Space Agency to take the new, more robust, microscope technology to the moon in 2018 to examine the structure of moon soil.
“We measure diffraction patterns rather than images. What we record is equivalent to the strength of the electron, X-ray or light waves which have been scattered by the object—this is called their intensity. However, to make an image, we need to know when the peaks and troughs of the waves arrive at the detector—this is called their phase.
“The key breakthrough has been to develop a way to calculate the phase of the waves from their intensity alone. Once we have this, we can work out backwards what the waves were scattered from: that is, we can form an aberration-free image of the object, which is much better than can be achieved with a normal lens.
“A typical electron or X-ray microscope image is about one hundred times more blurred than the theoretical limit defined by the wavelength. In this project, the eventual aim is to get the best-ever pictures of individual atoms in any structure seen within a three-dimensional object.”
The ground-breaking results were part of a three-year study costing £4.3 million which was funded by the Engineering and Physical Sciences Research Council (EPSRC).
The investigation was carried out with the help of Phase Focus Ltd, a University of Sheffield spin-out company, and Gatan Inc.
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