What is an electron beam?

An electron beam is a one-dimensional beam of electrons moving through a vacuum. Electron beams may be generated by mechanical, thermal, or other means. The electrical potential limits the kinetic energy of the electrons in the beam to 2.0 eV or 4.0 eV concerning ground; however, an electron beam with high current density has high power density and may be destructive when focused on certain materials. 

How Do You Make an Electron Beam?

You can make an electron beam through the following two sources:

1. Thermionic

2. Field emission 


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1. Thermionic emission: The electrons are generated by a high voltage created by a spark gap. This electron gun is used in vacuum tube television sets and other electronic devices, producing the electron beam using a spark gap between two electrodes. 

The thermionic gun consists of a metal grid, an insulating tube with selenium rectifying elements at both ends to convert alternating current into direct current, and a high-voltage power supply to provide the potential difference across the selenium rectifiers.

Tungsten filament:

When a mixture of gases is passed through a high-temperature spark gap, electrons and holes in the gas collide and produce hot electrons and heated atoms. The hot atoms may be removed from the filament by cooling it off with liquid helium or slowing down the emission rate by inserting a device such as a double resistor. 

The filament consists of tungsten wires coated with fluorine and hydrofluoric acid that emits energetic electrons when heated. Tungsten filaments are used to drive cathode ray tubes, fluorescent lamps, television picture tubes, lasers, solid-state light sources, etc. 

The tungsten filament is operated in a controlled vacuum. When the tungsten filament is heated to about 2000°C, electrons are emitted. The energy required to remove an electron from the tungsten filament is about 2 eV, corresponding to a temperature of 2000°C. 

A simple tube with two metal contacts at either end, similar in construction to a cold-cathode device, but operating at much higher voltages and temperatures. [Artificial light] 

2. Field emission:

The electrostatic field is used, and the beam of electrons is generated by applying a high voltage between a sharp point or wire and a metal plate. The electrons are emitted from the abrupt end in the form of an electron beam. The field emission theory is closely related to thermionic emission since the two phenomena are the same, except for the difference in geometry. 

Field emission takes place when a significant potential difference between a surface and an electrode is created. When this happens, electrons can tunnel through the repulsive energy barrier they encounter on being accelerated by an electric field toward a surface. An external source provides the high voltage through terminals on the back of the device under test. The high voltage controls how many electrons there are in your beam.

Schottky FEG vs. cold FEG (CFEG):

The Schottky FEG is a field emission gun that has become the standard for transmitting lines, medical equipment, and many other applications. The term ‘cold’ FEG is used by some manufacturers to describe field emission guns that are relatively slow-operating, typically requiring on the order of 1 ms per millimeter of gain. To achieve this voltage-resolving precision requires a meticulous mechanical design to produce a homogeneous electric field across an electrode of sufficient height.

A cold FEG gun consists of a sharp point or wire (a cathode) and an anode located about 5 mm away. 

An evacuated chamber is filled with gas at high pressure. A voltage is applied between the cathode and the anode. The sharp point of the cathode removes electrons from this gas and emits them into space, further increasing the voltage. 

The electrons collide and produce secondary electrons and energetic ions, which are removed by a dissociation chamber. They can be collected and stored for later use in some application, such as a laser or ion beam generator.

How do you prepare a sample for an electron microscope?

To prepare your sample for an electron microscope, you should make sure that it is not magnetic. Any magnetic material must be removed. Otherwise, you won’t see the sample in the electron microscope because the beam will be deflected. If you want to analyze how materials react in certain conditions (e.g., temperature), you should heat the substance in question in a vacuum before placing it on a surface and freezing it. If you want to determine any impurities, you should grind up the material finely and spread out a thin layer of powder on a surface. The sample needs to be kept in a vacuum to ensure that it doesn’t contaminate your beam. If you want to prepare a powder for a lab to analyze its composition, you should crush the material finely and grind up the powder. 

Laser or Electron Beam?

1. Laser is a more coherent source of light as compared to an electron beam. 

2. Laser light can be focused on a tiny spot as compared to an electron beam. 

3. A laser emits more light as compared to an electron beam.

3. An electron beam can give information about the surface topography of a sample and the composition of the material being studied by producing a topographical map and chemical analysis, respectively. 

4. An electron beam can be used to establish the magnetic field, while a laser can only determine the magnetic field. 

5. An electron beam is less likely to cause damage to materials than a laser beam.

6. As an electron beam must be incident on the material for them to interact, it has applications in the analysis of viruses where there is no possibility of direct contact with samples, which makes it useful in medical research, etc. 

7. An electron beam can examine small structures within materials, which are inaccessible to lasers because the sample needs to be opaque. 

8. An electron beam is more economical than a laser because it uses less power and does not require cooling for most applications.

Can I make an electron gun at home?

Yes, you can make an electron gun in your home. If you cannot find the right parts, you can take a small circuit board with a transistor in it and connect the negative side of the circuit board to the positive side of the battery. 

Then put this together with a sharp point or wire and an external power source, and it will ignite your beam. 

You will need to find out how much voltage is required for your particular electron gun because there are values for different firearms, such as Schottky FEGguns require very high voltages for them to work correctly. It also depends on what material you want to analyze and how fine or coarse you want your beam to be. 

The higher the voltage, the higher the voltage your beam will be. If you want to make a laser, you will also need to consider how many electrons there are in your beam. 

For instance, if you wanted to study proteins, you would need an excellent beam, or if you wanted to study cells, it might be better to have a large beam. 

Electrons are not very good at penetrating through water, so don’t expect your electron gun to work in water because nothing can get through it, so don’t try.

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Conclusion

In a nutshell, an electron microscope is a valuable piece of equipment for those who study various materials. It provides a visual image from varying distances using a cathode ray tube and a camera. The electron gun uses this beam to magnify the sample by a factor of thousands to millions. Suppose you would like to see the structure of any substance. In that case, you should use an electron microscope because it gives prominent optical images that can be used to gain valuable information.

FAQ’s

Q1. What is an electron microscope?
A: An electron microscope is a device that uses electrons or light beams to create an image of a specimen that can then be viewed through an optical system and viewed on a monitor, and displayed as a picture.

Q2. How does the electron gun work?
A: The electron gun works by accelerating the electrons emitted from the cathode until they hit the target. When this happens, excitation occurs, and the negatively charged electrons move towards the positively charged cathode. More the electrons, the faster they move; and therefore, the higher the voltage needs to be.

Q3. How does a cathode ray tube work?
A: A cathode-ray tube works on the principle that a current passes from a positive to a negative terminal of a vacuum tube or semiconductor until it reaches another element or surface. It heats up and emits electrons across an electron field.

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