In modern scientific research and industrial production, Scanning Electron Microscopes (SEM) and Transmission Electron Microscopes (TEM) act as powerful tools for exploring the microscopic world, playing a pivotal role. They allow us to peek into the mysteries of matter at the microscopic scale, and these two robust analytical tools are indispensable in numerous fields, including materials science, biology, and the semiconductor industry. However, do you really understand the differences between SEM and TEM? This article will conduct an in-depth analysis of the differences between the two, guiding you to gain a comprehensive understanding of these two types of electron microscopes. 01 Great Differences in Working Principles (1) Working Principle of SEM SEM obtains information by using an electron beam to scan the surface of a sample. When a high-energy electron beam is focused on the sample surface, the electrons interact with the atoms in the sample, generating a variety of signals. Among these, secondary electrons and backscattered electrons are mainly used for imaging. Secondary electrons are low-energy electrons excited from the sample surface by incident electrons, and their yield is closely related to the morphology of the sample surface. Backscattered electrons, on the other hand, are incident electrons bounced back by the atomic nuclei in the sample, and their intensity is related to the atomic number of the sample. By collecting these signals and converting them into images, we can obtain information about the sample surface. The electron beam does not penetrate the sample; it only scans the sample surface, which determines that SEM mainly reflects the conditions of the sample surface. (2) Working Principle of TEM The working principle of TEM is completely different. It projects an accelerated and focused electron beam onto an extremely thin sample. Due to the thinness of the sample, electrons can pass through it. During the process of electrons passing through the sample, they collide with the atoms in the sample, changing their direction of motion and producing scattering. Based on the relationship between the size of the scattering angle and the density and thickness of the sample, we can image the scattered electrons. The imaging principle of TEM enables it to penetrate into the interior of the sample, obtain structural information about the sample interior, and allow us to see the mysteries of the microscopic world inside the sample. 02 Unique Characteristics in Imaging (1) SEM: Presenting 3D Surface Images The most prominent imaging characteristic of SEM is its ability to provide 3D stereoscopic images of the sample surface. This allows us to observe the morphology of the sample surface very intuitively, such as the surface roughness, the presence of pore structures, and the distribution of particles on the surface. Through SEM images, it is as if we can touch the surface of the sample with our hands and feel its microscopic undulations and features. This intuitive surface imaging is of great significance for studying the surface properties of materials, the surface morphology of biological samples, and defects on the surface of semiconductor chips. (2) TEM: Showing Fine Internal Structures TEM presents 2D projection images of the sample, but its advantage lies in enabling us to observe extremely fine internal structures of the sample. Details such as the lattice arrangement in crystal structures, the presence of defects in the lattice, and the specific morphology inside nanoparticles are all crucial for materials science research on crystal properties and nanotechnology research on the characteristics of nanomaterials. TEM is like a "scalpel" that can penetrate into the interior of the sample, clearly displaying the microscopic structure inside the sample before our eyes. 03 A Comparison of Resolution and Magnification (1) Resolution and Magnification of SEM The resolution of SEM is generally around 0.5 nm, which means it can distinguish two features on the sample surface that are 0.5 nm apart. Its magnification usually ranges from 1 million to 2 million times. Such resolution and magnification are sufficient for observing the microscopic morphology of the sample surface, meeting the needs of many fields such as material fracture morphology analysis and research on the surface characteristics of rocks and minerals. When observing fine textures on the material surface or tiny structures on the surface of biological samples, SEM can provide clear images. (2) Resolution and Magnification of TEM The resolution of TEM is even more remarkable, reaching 0.5 nm or even smaller, which enables it to achieve atomic-level observation. Its magnification is usually more than 50 million times. With such high resolution and magnification, TEM can penetrate to the atomic level to study the atomic arrangement of materials and the atomic-level growth mechanism of nanomaterials. When researching the crystal structure of materials, TEM can clearly show the lattice positions of atoms, providing strong support for in-depth research in materials science. 04 Differences in Sample Requirements (1) Sample Requirements for SEM SEM has no strict requirements on the thickness of the sample, which makes sample preparation relatively simple. It only requires the sample surface to be clean and dry. For samples with poor conductivity, to avoid charge accumulation under electron beam irradiation (which affects imaging), a layer of conductive film may need to be coated on the sample surface. These relatively loose sample requirements allow SEM to be applied to various types of samples, including bulk materials, powder samples, and biological samples, all of which can be observed under SEM. (2) Sample Requirements for TEM The sample requirements for TEM are extremely strict. The sample must be very thin, usually less than 100 nm, and for high-resolution imaging, the sample thickness must even be less than 30 nm. To meet such thickness requirements, the sample preparation process is very complex, involving a series of delicate operations such as sectioning, grinding, and thinning. When preparing biological samples, special embedding technology needs to be used, followed by cutting the sample into ultra-thin sections with an ultramicrotome. These strict sample requirements limit the range of samples applicable to TEM, but it is precisely because of such requirements that TEM can obtain the finest structural information about the sample interior. 05 A Comparison of Operation and Cost (1) Operation and Cost of SEM SEM usually uses an accelerating voltage of more than 15 kV. Its operation is relatively simple, and the requirements for the operator's professional skills and experience are relatively low. At the same time, SEM has a large field of view and high depth of field, which allows it to obtain information about a large range of the sample surface in a single observation. In terms of equipment cost, SEM is relatively low-priced, which enables many scientific research institutions and enterprises to be equipped with SEM for daily research and testing work. (2) Operation and Cost of TEM The accelerating voltage of TEM generally ranges from 60 kV to 300 kV. Its operation process is complex, requiring operators to have profound professional knowledge and rich experience. When operating TEM, it is necessary to accurately control multiple factors such as the parameters of the electron beam and the position of the sample to obtain high-quality images. Due to the technical complexity and high-precision requirements of TEM, its equipment price is expensive, and the maintenance cost is also relatively high. This limits the use of TEM, and only some large-scale scientific research institutions and high-end industrial R&D departments are equipped with it. 06 Emphases in Application Fields (1) Wide Application Fields of SEM In the field of materials science, SEM is often used to observe the fracture morphology of materials. By analyzing the microscopic characteristics of the fracture, we can understand the fracture mechanism of the material. At the same time, it is also used to observe the surface coating of materials to evaluate the quality and uniformity of the coating. In geology, SEM can be used to study the surface characteristics of rocks and minerals, helping geologists understand the formation process of rocks and the composition of minerals. In biology, SEM can observe the surface morphology of biological samples, such as the surface structure of cells and tissues, providing important microscopic morphological information for biological research. In the semiconductor industry, SEM is an indispensable testing tool, used to detect defects on the chip surface, circuit patterns, etc., to ensure the quality and performance of the chip. (2) Key Application Fields of TEM In the field of materials science, TEM is mainly used to study the relationship between the microscopic structure (such as crystal structure, dislocations, and phase transitions) and properties of materials. By observing the distribution of dislocations in the crystal structure, we can understand the mechanical properties of the material. In nanotechnology, TEM is an important tool for observing the internal structure and growth mechanism of nanomaterials, helping scientists develop new types of nanomaterials. In biology, TEM can be used to study the structure of organelles inside cells and the morphology of biological macromolecules, in-depth exploring the mysteries of life. In the field of chemistry, TEM is used to study the microscopic structure of catalysts and chemical reaction intermediates, providing microscopic support for chemical research. In summary, although both SEM and TEM are electron microscopes, they have significant differences in terms of working principle, imaging characteristics, resolution and magnification, sample requirements, operation and cost, and application fields. Understanding these differences is of great significance for us to select and use these two types of microscopes correctly and give full play to their roles in scientific research and industrial production. Whether it is exploring the microscopic world of materials or studying the mysteries of life, SEM and TEM will continue to open the door to the microscopic world for us and promote the continuous progress of science and technology.