The main components of an electron microscope are:
Electron source: a cathode that releases free electrons and a ring-shaped anode that accelerates the electrons. The voltage difference between the cathode and anode must be very high, typically between a few thousand and 3 million volts.
Electron: used to focus the electrons. Usually a magnetic lens is used, sometimes an electrostatic lens is used. An electron lens acts in the same way as an optical lens in an optical microscope. The focus of the optical lens is fixed, while the focus of the electron lens can be adjusted, so the electron microscope does not have a movable lens system like the optical microscope.
Vacuum unit: The vacuum unit is used to ensure a vacuum inside the microscope so that electrons are not absorbed or deflected in their path.
Sample Holder: The sample can be stabilised in the sample holder. In addition there are often devices that can be used to alter the sample (e.g. move, rotate, heat, cool, stretch, etc.).
Detector: Used to collect signals or secondary signals from electrons. Types utilise transmission electron microscopy
Microscope (TransmissionElectronMicroscopyTEM) it is possible to obtain a direct projection of a sample. In this type of microscope electrons pass through the sample, so the sample must be very thin. The atomic weight of the atoms that make up the sample, the voltage at which the electrons are accelerated, and the desired resolution determine the thickness of the sample. The thickness of the sample can vary from a few nanometres to a few microns. The higher the atomic weight and the lower the voltage, the thinner the sample must be.
By changing the lens system of the objective lens one can directly magnify the image at the focal point of the objective lens. This allows one to obtain an electron diffraction image.
diffraction image. Using this image, the crystal structure of the sample can be analysed.
In Energy Filtered Transmission Electron Microscopy (EFTEM) one measures the change in speed of the electrons as they pass through the sample. From this it is possible to deduce the chemical composition of the sample, such as the distribution of chemical elements within the sample.
