Scanning electron microscopy (SEM) uses a focused beam of high-energy electrons to produce high-definition, magnified, two-dimensional images of a sample. For this purpose, the electron beam is directed onto selected parts of the solid sample surface. The interaction between the beam's electrons and the sample results in the generation of various signals. These signals are recorded and further processed to produce images in digital format. It can be used to reveal information such as the internal structure of a sample, the external texture of the sample, the chemical composition of the substance, and the orientation and arrangement of the elements that make up the sample. The scanning electron microscope was first built in 1937 by German researcher, applied physicist and inventor Manfred von Arden. Magnifications for scanning electron microscopes typically range from 20X to approximately 30,000X. The spatial resolution of scanning electron microscopy ranges from 50 to 100 nm.
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Scanning electron microscope working
Applications of scanning electron microscopy
Advantages of Scanning Electron Microscopy
Disadvantages of Scanning Electron Microscopy
Scanning electron microscope working
The work of a scanning electron microscope often depends on the detection of reflected electrons after they strike the surface of a sample. The main component of a scanning electron microscope is the electron source. Typically, in most scanning electron microscopes, a heated tungsten wire is used as the electron source. Here, the heat tends to provide more energy to the electrons, guiding them in a specific direction and creating a single focused beam of electrons. The anode, or positively charged electrode plate, exists between the electron source and the capacitor. The main purpose of the anode is to deflect the electrons and align them into a thin, single straight line. This is because the electrons have a negative charge and the anode plate has a positive charge. The scan coil and objective lens are located below the condenser. The electron beam generated by the source passes through the condenser, scanning coil and objective lens. When the electrons contained in the electron beam hit the sample, they are randomly reflected and scattered in all directions. This is called electron escape, and it helps the user establish a relationship between the number of scattered and retained electrons. Signals resulting from electron-sample interactions and electron escape are detected by the detector. The detector is also connected to the sensor. Samples usually consist of bumps and valleys. When electrons hit bumpy areas of a sample, more electrons tend to escape, while when electrons hit valleys, relatively few manage to reflect and escape.
Scanning electron microscope working
Applications of scanning electron microscopy
Scanning electron microscopy is used as an analytical tool in many fields, including biology, the pharmaceutical industry, manufacturing, physics laboratories, and more. Some of the main uses of scanning electron microscopy are:
1. Scanning electron microscopy is widely used with energy dispersive X-ray spectrometers for point chemical analysis.
2. Mainly used in biological laboratories to study the internal structure of microorganisms at the cellular level.
3. Scanning electron microscopy has many applications in industry. For example, it can be used to study the surface of solid objects and analyze the distribution of atoms in various elements.
4. Beauticians use scanning electron microscopes to analyze minute details of cosmetic ingredients.
5. Manufacturing uses scanning electron microscopy to look for contaminants and impurities in finished products.
6. Quality control departments in various industries use scanning electron microscopy to determine the purity of specific substances. For example, the pharmaceutical industry uses them to test whether drugs, medicines, and other products are good or bad.
7. Scanning electron microscopy is also used for qualitative chemical analysis of elements by providing clearly magnified images of crystal structures.
8. Scanning electron microscopy has considerable advantages in related fields such as nanotechnology. It provides precise measurements and detailed images of objects with dimensions exceeding 50nm.
9. Can be used to distinguish different phases of multi-phase samples.
10. Some scanning electron microscopes are equipped with diffractive backscattered electron detectors, which help to examine and determine the microstructure and crystal orientation of substances.
11. Scanning electron microscopy is often used to produce high-definition images of objects that can show spatial changes in compounds.
12. Scanning electron microscopy is usually preferred when analysis of selected spot locations on a sample is required.
13. Generally used in the medical field to observe the interaction of bacteria with skin and body organs. This helps doctors determine the nature of the bacterial disease and find a treatment.
Advantages of Scanning Electron Microscopy
Scanning electron microscopy has great advantages compared to other microscopes. Some of these advantages are listed below:
1. Scanning electron microscopes are user-friendly and easy to use.
2. They can produce and produce results in digital format.
3. Scanning electron microscopy can produce results quickly, i.e. data can be obtained within a few minutes.
4. Scanning electron microscopy requires minimal sample preparation.
5. The resolution of scanning electron microscope is significantly improved.
Disadvantages of Scanning Electron Microscopy
Scanning electron microscopy has certain limitations and disadvantages. Some of them are as follows:
1. Scanning electron microscopes are relatively expensive.
2. Some microscopes must meet certain special conditions before use. For example, the room must be free of vibration and electromagnetic radiation.
3. The scanning electron microscope has a large structure.
4. Consistent voltage levels must be maintained for normal operation of the scanning electron microscope. This may require additional electronic circuitry or a voltage regulator to fix the voltage amplitude to a constant value.
5. This type of microscope should be equipped with a cooling system.
6. The sample should be small enough to fit in the microscope chamber. The horizontal dimensions of the sample should not exceed 10 cm, while the vertical dimensions are more restricted and must be less than 40 mm.
7. Samples to be examined using scanning electron microscopy must be solid. Wet samples are not suitable and need to be blasted first.
8. Scanning electron microscopes cannot be used for lightweight materials such as hydrogen, helium, and lithium.
9. In order to study an insulator sample with the aid of a scanning electron microscope, a conductive coating is applied to its surface. However, this can be ignored if the device is capable of operating in low vacuum mode.
10. Living samples cannot be scanned with the help of a scanning electron microscope.
