The basic principle of the electron microscopy is the interaction between an electron beams shooting through the sample by an electron gun. The results of the collision between an electron and an atom can be categorize in elastic and inelastic scattering (figure 1).
Elastic scattering: the result of this interaction is that the sum of the kinetic energy of the atoms and the kinetic energy of the electron is unchanged. The scattering angle is direct related with the distance to which the electron pass, and shorter it is and greater the angle. When the electron hits the nucleus or it passes very close to the nucleus, the electron is backscattered and it go back.
Inelastic scattering: this phenomenon takes place when an…show more content… The main process used is a chemical fixation combined with critical point drying; after these processes the sample, after been positioned on a ‘stub’ of aluminium, is covered by a thin layer of silver, gold or platinum (in the lab we used a mixture of gold and platinum). This cover is necessary to remove the electrons that accumulate on the surface of the sample, which can contribute to the noise. To perform this covering is used the machinery in figure 4: the purple fluorescence derived from the argon, the gas used instead of the air during this process of anodic-cathode deposition. The resulting coting layer is more or less 40 nm…show more content… The preparation of the sample for TEM is trickier than the preparation for SEM because the sample has to be very thin and perfectly dry because it is subject to a very low pressure (high vacuum).
The first step in this process of preparation is the fixation of the sample to preserve the structure as close to the living state as possible. Then the sample is dehydrated with ethanol and acetone, a transition solvent (i.e. propylene oxide) is used before embedded it in a liquid resin (i.e. epoxy).
After this fixation, the sample is sectioned: first, with a glass knife to obtain a semi-thin section to observe it at the microscope and see if there are what are you looking for, after that with a diamond knife is obtained a ultra-thin section. To evaluate the thickness of the section, which is variable with the hard of resin at room temperature, it is used a colour interference as showed in figure 7. Figure 7) Colour