SEM samples must meet two conditions: they must be dry and conductive. The drying process must preserve the original sample structure as much as possible. There are two alternatives to achieve this: using the classic method of fixing and chemical dehydration by the user in their lab, ending with critical point drying at our facilities, or using the modern, physical cryofixation method; one of our microscopes is already equipped for this method.
In both cases the sample must then be coated with a material to make it conductive and to be able to observe it in the microscope.
Low vacuum sample coating
This method uses two types of coating: gold sputter coating for the best image conditions, and carbon thread coating if X-ray microanalysis is required.
High vacuum sample coating
It is applied to more than the need for a conductive SEM sample, obtaining coatings with a much finer grain, and can sputter with different metals. It also uses the evaporation method, increasing the range of possible coating elements. It uses carbon electrodes for evaporation and obtains films that coat the target TEM grids.
Observing cryofixed samples
The scanning electron microscope (SEM) can be fitted with a system to observe samples at a very low temperature for maximum structural preservation without affecting the microscope operation capacity as it is not a hydrated sample, rather a frozen sample.
The process begins outside the microscope, by cooling the sample at the maximum possible speed using slush nitrogen. Next it is passed to the cryo-observation system where it can be fractured, surface ice sublimated and coated with gold or carbon for observation and/or analysis. The advantage of this system is that any biological or hydrated sample can be observed with minimum, rapid preparation and good structural preservation