Getting Started with Transmission Electron Microscopy
Transmission Electron Microscope (TEM for short), can see in the optical microscope can not see clearly in less than 0.2 um microstructure, these structures are called sub-microscopic structure or ultramicrostructure. To see these structures clearly, it is necessary to select a shorter wavelength light source to improve the resolution of the microscope.
Introduction
The imaging principle of electron microscope and optical microscope is basically the same, the difference is that the former uses an electron beam as a light source and an electromagnetic field as a lens. In addition, due to the weak penetration of the electron beam, so the specimen used for electron microscopy must be made into an ultra-thin section with a thickness of about 50nm. Such slices need to be made with an ultramicrotome. Electron microscope magnification up to nearly a million times, by the illumination system, imaging system, vacuum system, recording system, power supply system consists of five parts, if subdivided: the main part of the electron lens and imaging recording system, placed in a vacuum by the electron gun, condensing mirror, the object chamber, objective, diffracting mirror, intermediate mirror, projection mirror, fluorescent screen and camera.
An electron microscope is a microscope that uses electrons to visualise the interior or surface of an object. The wavelength of high-speed electrons is shorter than that of visible light (wave-particle duality), and the resolution of a microscope is limited by the wavelength it uses, so the theoretical resolution of an electron microscope (about 0.1 nanometres) is much higher than that of an optical microscope (about 200 nanometres).
A transmission electron microscope (Transmissionelectronmicroscope, abbreviated TEM), or transmission electron microscope for short [1], projects an accelerated and aggregated beam of electrons onto a very thin sample, where the electrons change direction by colliding with atoms in the sample, resulting in steric angle scattering. The magnitude of the scattering angle is related to the density and thickness of the sample, so that different light and dark images can be formed, and the images will be displayed on imaging devices (e.g., phosphor screens, films, and photocoupled assemblies) after magnification and focusing.
Due to the very short De Broglie wavelength of electrons, the resolution of transmission electron microscopy is much higher than that of optical microscopy, reaching 0.1 to 0.2 nm, with a magnification of tens of thousands to millions of times. As a result, the use of a transmission electron microscope can be used to observe the fine structure of a sample, or even the structure of just a single row of atoms, tens of thousands of times smaller than the smallest structure that can be observed with an optical microscope.The TEM is an important analytical method in many fields of science related to neutral physics and biology, such as cancer research, virology, materials science, as well as nanotechnology, semiconductor research, and so on.
At lower magnifications, the contrast of TEM imaging is mainly due to the different thicknesses and compositions of materials resulting in different absorption of electrons. When the magnification is high, complex fluctuation effects cause differences in the brightness of the image, and therefore expertise is needed to analyse the resulting image. By using the different modes of the TEM, it is possible to analyse the sample by its chemical properties, crystal orientation, electronic structure, the electronic phase shift caused by the sample, and the usual electronic absorption on the sample.
as well as the usual absorption of electrons into the sample.
The first TEM was developed by Max Knorr and Ernst Ruska in 1931, this research group developed the first TEM with a resolution exceeding that of the visible light in 1933, while the first commercial TEM was developed in 1939.
