Electron microscopy is a valuable tool used to obtain high-resolution images in a variety of applications, including biomedical research, forensics, and technology. Electron microscopes can capture much higher resolution images than light microscopes, contributing information that is otherwise unattainable.
Every electron microscope works by accelerating a focused stream of electrons in a vacuum towards a sample. Interactions between the electron beam and the sample create an image, similar to how optical microscopes use light to capture images. The image created reveals details of a sample’s surface or internal composition, depending on the type of electron microscope that is used.
Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) are the two most common types of electron microscopy. TEM and SEM differ in how they work and what types of images they are able to capture. This article will overview SEM and TEM, including what they are, how they work, and how they compare to one another.
What is SEM?
SEM can stand for either Scanning Electron Microscopy or Scanning Electron Microscope. An SEM is a kind of electron microscope that uses a fine beam of focused electrons to scan a sample’s surface. The microscope records information about the interaction between the electrons and the sample, creating a magnified image. SEM has the potential to magnify an image up to 2 million times.
A closer look at an SEM microscope.
SEM images give insight into a sample’s topography and elemental composition. SEM is able to capture 3-D black-and-white images of thin or thick samples. The sample’s size is limited only by the size of the electron microscope chamber.
How does SEM work?
To obtain a high-resolution image, an electron source (also known as an electron gun) emits a stream of high-energy electrons towards a sample. The electron beam is focused using electromagnetic lenses. Once the focused stream reaches the sample, it scans its surface in a rectangular raster.
The interaction between the electron beam and the sample creates secondary electrons, backscattered electrons, and X-rays. These interactions are captured to create a magnified image.
What is TEM?
TEM can stand for Transmission Electron Microscopy or Transmission Electron Microscope (TEM). A TEM is a type of electron microscope that uses a broad beam of electrons to create an image of a sample’s internal structure. A beam of electrons is transmitted through a sample, creating an image that details a sample’s morphology, composition, and crystal structure.
A closer look at a TEM microscope.
Samples must be incredibly thin, often less than 150 nm
thick, to allow electrons to pass through them. After the transmission of the electrons through the sample, they arrive at a detector below and a 2-D image is created.
TEMs have an incredible magnification potential
of 10-50 million times. The details provided are at the atomic level, the highest resolution of any electron microscope. TEMs are often used to examine molecular and cellular structures.
How does a TEM work?
An electron source sends a beam of electrons through an ultrathin sample. When the electrons penetrate the sample, they pass through lenses below. This data is used to create images directly on a fluorescent screen or onto a computer screen using a charge-coupled device (CCD) camera.
SEM vs TEM
SEM and TEM are both valuable tools in the biological, physical, and chemical sciences. By understanding the differences between these two electron microscopes, scientists can choose the correct type of microscope for their needs.
SEM vs TEM advantages
Scanning Electron Microscopes and Transmission Electron Microscopes each contain unique advantages when compared to the other.
In comparison to TEMs, SEMs:
- Cost less
- Take less time to create an image
- Require less sample preparation
- Accept thicker samples
- Can examine larger samples
In comparison to SEMs, TEMs:
- Create higher resolution images
- Provide crystallographic and atomic data
- Create 2-D images that are often easier to interpret than SEM 3-D images
- Allow users to examine more characteristics of a sample
SEM vs TEM similarities and differences
There are many similarities between SEMs and TEMs. The components of these two high-resolution microscopes are very similar. Each has an electron source/gun that emits an electron stream towards a sample in a vacuum, and each contains lenses and electron apertures to control the electron beam and capture images.
But the differences in function between the two are vast. They differ in how they work, the types of samples that they require, the resolution of images that they create, and more.
The below table summarizes the differences between Scanning Electron Microscopes and Transmission Electron Microscopes.
|Scanning Electron Microscopes (SEM)||Transmission Electron Microscopes (TEM)|
|Electron stream||Fine, focused beam||Broad beam|
|Image taken||Topographical/surface||Internal structure|
|Resolution||Lower resolution||Higher resolution|
|Magnification||Up to 2,000,000 times ||Up to 50,000,000 times|
|Sample thickness||Thin and thick samples okay||Ultrathin samples only|
|Sample restriction||Less restrictive||More restrictive|
|Sample preparation||Less preparation required||More preparation required|
|Cost||Less expensive||More expensive|
|Operation||Easy to use||More complicated; requires training|