Tomography

In order to reveal the true nature of many specimens we have to study the third dimension of our sample. Most of the TEM techniques provides two-dimensional (2D) projections of a 3D structure. However, the complexity of the new material and the biological structures highlights the need to develop tools and techniques to explore the morphologies and compositions of materials in three dimensions. An object viewed from many different angles will generate slightly different projections. These images can be recorded and analyzed to create a tomographic rendering of the specimen. The resolution obtained depends of the diameter of the object and the number of projections.

There is a maximum angle that can be reached tilting the sample, which is known as the missing wedge limitation. This gap produces artefacts in the reconstructed object: the elongation factor.

Examples of Vitrification and observation by cryo-TEM of polymeric vesicles (left), polymeric Nanoribbon (right). Both samples belong to the INMA group of Liquid Crystals and Polymers.

In biology field, bright-field TEM (BF-TEM) is the most appropriated imaging method for tomography tilt series acquisition because, for amorphous sample, the projected image intensities vary monotonically with material thickness. On the other hand, for material science this condition, the variation monotonically of the intensities is difficult to guarantee in BF/HRTEM, where image intensities in crystalline samples are dominated by phase-contrast, which change when change the relative angle between the sample and the electronic beam. However, the technique of annular dark-field scanning transmission electron microscopy (ADF-STEM) and high angular ADF detector (HAADF) are more effectively suppressing phase and diffraction contrast, providing image intensities that vary with the projected mass-thickness of samples up to micrometres thick for materials with low atomic number. ADF-STEM also acts as a low-pass filter, eliminating the edge-enhancing artifacts common in BF/HRTEM.

Tomography can yield a reliable reconstruction of the underlying specimen which is extremely important for its application in nanoscience and nanotechnology.

Laboratorio de Microscopías Avanzadas

We are a unique initiative at national and international levels. We provide the scientific and industrial community with the most advanced infrastructures in Nanofabrication, Local Probe and Electron Microscopies for the observation, characterization, nanopatterning and handling of materials at atomic and molecular scale.

Contact information

Campus Río Ebro, Edificio Edificio I+D+i

C/ Mariano Esquillor, s/n
50018 Zaragoza (España)

Tel.:(+34) 976 762 980
lma@unizar.es
Monday-Friday:
08:00h-15:00h

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