Novel STEM for 3D Imaging Improves 3D Visualization of Curvilinear Nanostructures

Scientists have developed a scanning transmission electron microscopy (STEM) method that generates fast and reliable 3D images of curvilinear structures from a single sample orientation.

This STEM method can acquire images in a single shot, making it possible to study samples dynamically as they change over time. Further, it can rapidly provide a “sense” of three dimensions, similar to a movie viewed in 3D.

Like traditional TEM, the STEM 3D microscopy method can provide high-resolution views of samples that are just a few nanometers across. However, it has the additional ability to identify the 3D morphology of the sample.

In the STEM method developed by researchers at Ecole Polytechnique Fédérale De Lausanne (EPFL), the sample stands still while the microscope sends two beams of electrons tilted against each other. Two detectors are used simultaneously to record the signal, making the process much faster than previous TEM 3D imaging techniques, with almost no possibility of artefacts.

This is a superposed, tilt-less electron microscopy stereo image (color-filtered) of carbon nanospheres decorated with nanoparticles. The same structures appear in red and blue and the nanoparticles are slightly shifted according to their 3D distribution in the carbon sphere. This image shows the applicability of the new tilt-less 3D imaging techniques to other structures. Courtesy of Cécile Hébert/Emad Oveisi/EPFL.

The researchers used an image-processing algorithm to reduce the number of images needed for 3D reconstruction to only two images taken at different electron beam angles. The algorithm increases the efficiency of data acquisition and 3D reconstruction by one to two orders of magnitude, compared to conventional TEM 3D techniques. It also prevents structural changes from occurring to the sample due to high doses of electrons.

Traditionally, use of TEM to reconstruct 3D images has required tilting the sample through an arc to image hundreds of views, then using sophisticated image processing techniques to reconstruct the sample’s 3D shape. This approach requires extreme precision and can be prone to artefacts. Taking multiple images with TEM requires shooting a beam of electrons through the sample each time an image is taken, and the total dose of radiation can affect the sample’s structure.

3-D configuration of dislocations is reconstructed by only two stereo images acquired with the tilt-less 3D electron imaging technique. Courtesy of Cécile Hébert/Emad Oveisi/EPFL.

Because of its speed and advantages over standard TEM methods, this “tilt-less 3D electron imaging” method could be useful for studying radiation-sensitive, polycrystalline, or magnetic materials. Because the total electron dose is reduced to a single scan, the method is expected to open up new avenues for real-time 3D electron imaging of dynamic material and biological processes.

The research was published in Scientific Reports (doi:10.1038/s41598-017-07537-6).

This is a movie made by combining four stereo images of a carbon nanosphere acquired in a single shot with the tilt-less 3-D imaging technique. Courtesy of Cécile Hébert/Emad Oveisi/EPFL.