A set of the electron microscope's parts
Electron source: It is a cathode that releases free electrons, and a ring-shaped anode accelerates electrons. The voltage difference between the cathode and anode must be very high, typically between several thousand volts and three million volts.
Electrons: Used to focus electrons. Generally, magnetic lenses are used, and sometimes electrostatic lenses are also used. The function of the electron lens is the same as that of the optical lens in the optical microscope. The focus of the optical lens is fixed, but the focus of the electronic lens can be adjusted, so the electron microscope does not have a movable lens system like an optical microscope.
Vacuum device: The vacuum device is used to ensure the vacuum state inside the microscope, so that electrons will not be absorbed or deflected on their path.
Sample holder: Samples can be placed on the sample holder stably. In addition, there are often devices that can be used to change the sample (such as moving, rotating, heating, cooling, elongating, etc.).
Detector: A signal or secondary signal used to collect electrons. The projection of a sample can be obtained directly by using a transmission electron microscope (Transmission Electron Microscopy TEM). Electrons pass through the sample in this microscope, so the sample must be very thin. The atomic weight of the atoms making 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 nanometers to a few micrometers. The higher the atomic mass and the lower the voltage, the thinner the sample must be.
By changing the lens system of the objective, one can directly magnify the image at the focal point of the objective. From this one can obtain electron diffraction images. Using this image, the crystal structure of the sample can be analyzed.
In Energy Filtered Transmission Electron Microscopy (EFTEM), people measure changes in the speed of electrons as they pass through a sample. From this, the chemical composition of the sample can be deduced, such as the distribution of chemical elements in the sample.
