Final answer:
An ultramicrotome is used to prepare ultra-thin sections of specimens, less than 100 nm thick, for observation under a transmission electron microscope (TEM).
Step-by-step explanation:
The device used to prepare sections thinner than 100 nm for transmission electron microscopy (TEM) is called an ultramicrotome. Cells first need to be embedded in plastic resin and dehydrated through a series of ethanol soaks before ultra-thin sections are cut with this device. The resin solidifies inside the cells, providing the needed support for the ultramicrotome to cut the extremely thin sections required for TEM observation, which involves electrons transmitted through the sample to create a highly magnified image with incredibly fine detail resolution.