Electron Microscopes

An electron microscope (EM) is a type of microscope that uses an electron beam as a light source. It uses electron optics, which are similar to light microscope lenses, to guide the electron beam.

Electron microscopes can be used to examine the ultra-structural structure of a broad variety of biological and non-biological samples, including microorganisms and cells, large molecules and biopsy samples, as well as metals and crystals. Electron microscopes are also commonly used in industrial settings for quality assurance and failure analysis.

Working Principle of Electron Microscopes

Working principle of electron microscopes is:

• The Electron Source emits a stream of high-voltage electrons (typically 5-100 keV) and accelerates them in a vacuum towards the sample using electrical potentials.
• The stream is condensed into a thin, single-colored, focused electron beam by using electromagnetic lenses and directed onto the sample by means of magnetic lenses.
• Interactions between the irradiated sample and the primary electron beam influence each other and produce products like secondary electrons or X-rays.
• The products of these interactions are identified and converted into an image.

Types of Electron Microscope

Electron Microscopes come in various forms, such as:

• Transmission Electron Microscope (TEM)
• Scanning Electron Microscope (SEM)
• Scanning Transmission Electron Microscope (STEM)
• Environmental Scanning Electron Microscope (ESEM)

Following this, we’ll take a closer look at each type, examining their characteristics in detail.

Transmission Electron Microscope (TEM)

It is the original type of electron microscope and uses a narrow but high voltage electron beam to illuminate the object and create an image. The beam of electron is created using an electron gun.

The beam is focused on electromagnetic lenses and transmitted through the object. The beam, once it emerges out of the object, carries information about its structure which is converted into an image. TEM typically magnifies an object upto 50 million times.

Scanning Electron Microscope (SEM)

Scanning Electron Microscope or SEM uses a focused electron beam to scan across the specimen called as raster scanning. When the beam collides with the object, it loses some of its energy which is converted into other forms such as X-ray or secondary electrons. These alternative signals carry information about the structure of the object. The varying intensities of these signals is converted into high-resolution object image.

The image resolution of a SEM is lower than that of a TEM. In SEM thick samples of the object can be used contrary to TEM which is able to scan only thin specimens.

Scanning Transmission Electron Microscope (STEM)

It is a type of Transmission Electron Microscope. In STEM, a very fine electron beam is scanned over the specimen,keeping it parallel to optical axis, so that the entire object is illuminated. The resultant image is a raster image of the object. STEM is useful for high-resolution imaging and elemental mapping.

Environmental Scanning Electron Microscope (ESEM)

Environmental Scanning Electron Microscope (ESEM) is a type of Scanning Electron Microscope that has the advantage that an object can be scanned in its natural environmental state ie even when it is wet and uncoated. There is little to no specimen preparation required before scanning.

Microscopes are essential tools in various scientific fields for observing objects and specimens at the microscopic level. There are several types of microscopes, each designed for specific applications and offering unique capabilities such as Optical Microscope, Compound Microscope, Electron Microscope, and Scanning Probe Microscope etc.

In this article, we will learn about various Types of Microscopes including their working principles as well as application in the real world.