Final answer:
A specimen for an electron microscope is supported on a metal specimen grid. This is particularly crucial for TEM, where the specimen must be thin enough for electrons to transmit through it, revealing detailed internal structures.
Step-by-step explanation:
When placing a specimen into the electron beam of an electron microscope, the specimen is supported on a metal specimen grid. This is essential because the specimen needs to be very thin, especially in the case of a Transmission Electron Microscope (TEM), to allow electrons to pass through it. Preparing a specimen for a TEM involves ensuring the specimen is thin (20-100 nm thick), dehydrated, and sometimes stained with electron-dense materials to enhance opacity and thus contrast.
In contrast to Scanning Electron Microscopes (SEM), which render surface characteristics by reflecting a beam of electrons across a specimen that has usually been coated with a metal like gold, TEMs transmit electrons through the specimen, allowing us to view internal cellular structures with magnifications up to 100 million times the size of the original object.