Electron Microscope

An Electron microscope uses electron beams and their wave-like characteristics for magnifying an object’s image. In fact, images more than one million times smaller can be observed using an electron microscope.

They work like other optical microscopes, except that they use electron beams instead of photons for imaging the specimen. They are used to know an object’s composition and structure. It can magnify images up to 10,000,000 times and has a resolution of fifty picometers or 0.05 nanometers.

Uses of electron microscope vary from investigating biological to inorganic specimens. 

Who Invented the Electron Microscope?

In the 1930s, scientists seemed to show interest in exploring the interior structure of organic cells’ fine details. But, the available instrument, the light microscope, could not give 10,000 times plus magnification required to watch interior parts of the cell such as the nucleus, mitochondria etc. The light microscope can magnify only 1000 times with a resolution of 0.2 micrometres. Thus, a need to develop high magnification and resolution microscopes came to surface. 

In 1931, Ernst Ruska and Max Knoll developed the first electron microscope in Germany. It used the same principle as other microscopes, but used an electron beam instead of light to watch through the specimen. The electron microscope developed was named as the Transmission Electron Microscope (TEM).

In 1942, the first scanning electron microscope debuted, and its first commercial instrument was developed around 1965. 

Thus, the answer to “who invented electron microscope” is Ernst Ruska and Max Knoll.

Working of Electron Microscope

Electron microscopes are capable of magnifying an object up to one million times. Let us understand how they do so.

• An Electron source such as a field emission filament or heated tungsten produces a high voltage electrons stream ranging from 5-100KeV. It is then accelerated towards the specimen in a vacuum by a positive electrical potential.

• Metal apertures and magnetic lenses confine and focus this electron stream into a monochromatic, focused, thin beam.

• Magnetic lenses are used to focus the electron beam on the sample.

• The interactions occurring in the irradiated sample affect the beam of electrons.

• The detected effects and interactions transform into an image.

Types of Electron Microscope

The electron microscope is of three types. Their classification is based on the following factors.

• Formation of Image

• Sample Preparation

• Image Resolution

Based on these factors, electron microscopes are classified as:

• Transmission Electron Microscope (TEM)

• Scanning Electron Microscope (SEM)

• Tunnelling Microscope (STM)

• Transmission Electron Microscope

TEM was the earliest invented electron microscope. In this microscope, the partial transmission of a high voltage electron beam takes place through a thin object, forming an image on a sensor, photographic plate or fluorescent screen. The developed image is black and white like an X-ray and two-dimensional. 

The main advantage of TEM is its high magnification and resolution. The most significant disadvantage of TEM is that it works well with thin samples only.

• Scanning Electron Microscope (SEM)

In SEM, the electron beams scan across the sample surface in a raster pattern. The image develops from the surface’s secondary electrons emitted on the excitement by the focussed electron beam. The detector maps the electron signals and forms a photo showing the field’s depth and surface structure. 

SEM has a lower resolution than TEM. However, the two main advantages of SEM over TEM are: 

• Forms specimen’s three-dimensional image.

• It can magnify thick specimens because it scans only the surface.

It is essential to note in both TEM and SEM that the image does not accurately represent the sample. The specimen may change while preparing for the electron microscope because of exposure to vacuum or the incident electron beam.

• Scanning Tunnelling Microscope (STM)

The STM or Scanning Tunnelling Microscope scans image surfaces at the atomic level. It is the only electron microscope type that can form images of a single atom. The resolution of STM is around 0.1 nanometer with a depth of approximately 0.01 nanometers. Therefore, STM can be used in vacuum, air, water and other gases and liquids. Furthermore, one can use it in varied temperature conditions where the temperature ranges from absolute zero to 1000 degrees Celsius. 

The STM works on the principle of Quantum Tunnelling. An electrically conducting tip is driven near the sample surface in this electron microscope. Electrons tunnel between the sample and the tip when we apply a voltage difference. The changing current at the tip is measured while scanning it across the piece for image formation.

STM are easily made and affordable, unlike TEM and SEM. However, the samples require being extremely clean, and making it work is tricky.

Gerd Binnig and Heinrich Rohrer were awarded the Nobel Prize in Physics in 1986 for developing scanning tunnelling microscopes.

Uses Of Electron Microscope

Electron microscopes use highly energetic electron beams for examining the object at a fine scale. Uses of Electron Microscope are many. Its ability to view a specimen’s microscopic structure at high resolution has rendered it a unique role in industry and scientific research.

Some of the prominent uses of Electron Microscopes are as follows

• Electron Microscopes are widely used in universities, research laboratories, and nanotechnology centres to study the specimen structure for its functioning. In addition, these findings help develop specimens for industrial use.

• In industries, electron microscopes play a significant role in manufacturing. In addition, they assist in making new products. 

• Mining Companies use an electron microscope to characterise and analyse organic materials. They provide objective, quantitative and automated information about the environment.

• One of the practical uses of electron microscopes is forensic science. It is a branch of science that provides a detailed analysis of evidence for law and crime purposes. For instance, one can gather acute details of specimens such as gunshot residue, blood samples, cloth fibres or other biological substances from an electron microscope.

Conclusion

The development of the electron microscope took place because of the limitations shown by light microscopes. The light microscopes depend on light, whereas the electron microscope uses the electron beam for magnification. In addition, electron wavelengths are shorter than the wavelength of light, and hence, they give more magnification with high resolution. As a result, the EM images are invariably accurate, and they help obtain images of many small specimens and understand their functioning. Thus, electron microscopes contribute hugely to studying small particles that can be useful commercially.