Suite B - Electron Microscopy (Parmly Hall 202B)
Room 202B of the IQ Center is home to a Zeiss EVO 15 Scanning Electron Microscope. This is a flexible variable pressure SEM with wide range of detectors and analysis software. Sample prep is supported with a Cressington gold sputter coater and a Leica carbon coater.
Scanning Electron Microscopes use electrons instead of light to illuminate samples. Because electrons have much shorter wavelengths than light, much higher magnification is possible. The process of forming and image in the electron microscope starts by creating electrons using an electron gun. The electrons are then focused into a narrow beam using a series of magnetic lenses. To form an image, the beam is scanned across a sample in a grid pattern and detectors record what comes from the sample.
When the electron beam from the SEM strikes the sample, it generates many electrons and electromagnetic radiation including x-rays. The type of detector used determines what the image looks like and what it is telling you. The SEM in the IQ Center is outfitted with several detectors.
Secondary electrons are electrons that are ejected from the outer shells of the sample through inelastic collisions with the electron beam. Because these electrons are the most numerous and they are generated close to the surface of the sample, they give the best image of the surface features of a sample. This is the most common type of detector and unless it is otherwise stated on an image it has probably been produced with secondary electrons.
The Zeiss SEM in the IQ Center is also outfitted with a backscatter detector. Backscattered electrons are electrons from the SEM beam that have interacted with the sample atoms and have escaped. This process occurs deeper in the sample, so surface details are not as clear with this detector. However, it can provide other useful information - the number of backscatter electrons is proportional to the atomic number of the sample. The higher the atomic number the more backscattered electrons, which corresponds to a brighter image.