IT-1-P-2685 Low Voltage Mini TEM

On the basis of experience with the low voltage transmission electron microscopy at 5 kV, which is intended for the study of samples with low contrast (organic matters), we tried to design a TEM optimized in many aspects:
1) Maintaining relatively low voltage to keep up high contrast.
2) The use of such energy, which would open the possibility to increase the resolution of the system to the area of atomic (molecular) resolution using the monochromatization of the primary beam and Cs correction in future.
3) Practical standpoints – reasonable dimensions, resistance to external influences.
4) Energy sufficient for the transmissivity of electrons through samples of "standard" thickness.
It turned out to be suitable to base such electron-optical system on the use of magnetostatic (the objective lens) and electrostatic (projection system) elements. For the above reasons, we have chosen a range of energy of 10-25 keV. This choice enables to maintain the concept of combination of electron-optical and light-optical magnification, which leads to a significant reduction of the dimensions of the unit and solving simultaneously the problem of TEM image digitalization. It emerged that the working energy of 25 keV is the highest possible energy, at which there is no degradation of the applicable high light-optical magnification due to scattering in the single crystal fluorescent screen.
Using light lenses with large numerical aperture (up to 0.95), we achieve a high collection efficiency of the light from the screen. Also, the level of the light signal is high enough at 25keV energy. We have verified that the electron-optical system can be operated in several modes:
1) TEM at 25 keV
2) STEM at 15, 10 keV
3) DIFF at 25keV
The first experimental results confirm the assumptions obtained by electron-optical simulations, in particular the expected resolution in various modes.
It is further confirmed that the contrast inevitably decreases at the energy of 25 keV compared to the lower energies, however, it is still significantly higher than in the energy area of above 50 keV. Even thin sections for which there is no significant increase of chromatic aberration provide sufficient contrast in the image at this working energy. This brings the opportunity to study both stained and unstained samples at low radiation damage.
This version has been optimized for identification of viruses – samples prepared with negative staining and fixation. It allows mobility of the device, and is equipped with user friendly control system with a simple concept that provides remote control resources to allow to be controlled by upper level image analysis software for automatic virus recognition (Kylberg and Sintorn EURASIP J. on Image and Video Processing 2013, 2013:17).