Sample preparation at Plymouth Electron Microscopy Centre (PEMC)

Plymouth Electron Microscopy Centre (PEMC) offers a wide variety of sample preparation techniques for both scanning and transmission electron microscopy investigations. Many different types of material can be imaged and analysed using an electron microscope, with the exception of any liquid that cannot be frozen or living specimens. Samples typically need to be conductive for analysis, but PEMC's low vacuum systems allow for imaging and analysis of uncoated specimens.

PEMC has specimen preparation equipment such as saws, precision cutters, ultramicrotomes, polishers and lappers, critical point and freeze dryers, and several coating systems for a variety of specimen types and analytical specifications.

The team at PEMC can advise the best sample preparation method for imaging and analysis, depending on the anticipated outcome of a study. Some samples require minimal preparation, such as mounting on carbon-infiltrated tabs. This technique is most commonly used for samples that require imaging or indicative Energy Dispersive Spectroscopy (EDS) . Other methods are more complex and require cutting, embedding, and polishing. This technique is used to ensure a flat surface, which allows for quantitative and standardised analyses to take place. PEMC has the capabilities to polish to imaging, Energy Dispersive Spectroscopy (EDS) , and Electron Backscatter Diffraction (EBSD) quality, and also has a JEOL IB-19520CCP Cooling Cross Section Polisher for precise ion beam milling in an argon atmosphere. PEMC also anticipates the addition of thin section preparation for rock samples in the new year.

Biological samples can be prepared in a number of ways. The team at PEMC has expertise in resin embedding and sectioning for Transmission Electron Microscopy (TEM) . Some samples will not require sectioning, and can prepared in other ways. Large samples (e.g., insects, hair, and pollen) can simply be air dried to remove water. Other samples may require more preparation: most biological samples especially microbes and fungus will need to be fixed before drying can occur. Once fixed, the samples are dehydrated with alcohol and dried by replacing the alcohol with liquid CO2. Samples are then heated and put at pressure so that the liquid CO2 becomes a gas and is removed. Another drying process available is freeze drying. Samples are cryo-fixed using liquid nitrogen and then placed in a vacuum to remove the water from within the sample via sublimation.