How do Electron Microscopes Work? 🔬🛠🔬 Taking Pictures of Atoms
Summary
TLDRThis script explores the world of electron microscopy, crucial for designing nanoscale transistors and revealing intricate structures like butterfly wing scales. It explains the two main types: SEM for surface imaging and TEM for internal structures, highlighting TEM's ability to resolve individual atoms. The script delves into the physics of electron manipulation, the engineering of magnetic lenses, and the technological advancements that have made such high-resolution imaging possible, with a special thanks to sponsor Thermo Fisher Scientific.
Takeaways
- 🔬 Electron microscopes revolutionize the way we observe the micro and nanoscopic world, enabling the imaging of structures as small as individual atoms.
- 🦋 The European Peacock Butterfly's wing showcases the difference between light and electron microscopy, with the latter revealing intricate details invisible to the naked eye or light microscopes.
- 🔍 There are two main types of electron microscopes: Scanning Electron Microscopes (SEM) for surface imaging and Transmission Electron Microscopes (TEM) for internal structure imaging.
- 📏 SEMs have a maximum resolution of about 1 nanometer, while TEMs can achieve up to 50 picometers, roughly the size of a hydrogen atom.
- 🚀 The basic operation of a TEM involves accelerating electrons to nearly 70% the speed of light to create a beam that passes through a specimen, capturing its internal structure.
- 🧲 Magnetic lenses in TEMs focus and magnify the electron beam, with the objective lens being crucial for defining the final resolution due to its optical aberrations.
- 🌌 The resolution of electron microscopes is limited not by the electron beam itself but by the aberrations introduced by the magnetic lenses used for focusing.
- 🔋 A vacuum environment is essential for electron microscopy to prevent scattering of the electron beam by air molecules, which would degrade image quality.
- 🔬 Thermo Fisher Scientific, the sponsor of the video, provides a 3D model and insight into the complex technology of electron microscopes, emphasizing their role in scientific research and development.
- 🌐 The STEM (Scanning Transmission Electron Microscope) is a variation of TEM that combines features of both SEM and TEM for enhanced imaging and elemental analysis capabilities.
- 💡 Electron microscopes are vital tools in advancing scientific knowledge and technology, with applications ranging from material science to nanotechnology.
Q & A
What role does the electron microscope play in modern science and technology?
-The electron microscope allows scientists and engineers to see and analyze structures at the nanoscale, far beyond the capabilities of light microscopes. It has been instrumental in advancing fields like semiconductor technology, materials science, and biology by providing detailed images of materials at the atomic level.
How does the Scanning Electron Microscope (SEM) differ from the Transmission Electron Microscope (TEM)?
-The SEM creates images by scanning a focused electron beam across the surface of a specimen, producing detailed surface images. In contrast, the TEM transmits electrons through a thin specimen to capture internal structural details. SEM is better for surface topology, while TEM is used for internal analysis.
Why is light microscopy limited in its ability to resolve nanoscopic features?
-Light microscopy is limited by the wavelength of visible light, which is around 540 nanometers. This wavelength is too large to resolve features smaller than about 300 nanometers, leading to blurred images when attempting to observe nanoscopic structures.
How does accelerating electrons to 70% of the speed of light enhance the capabilities of an electron microscope?
-Accelerating electrons to such high speeds reduces their wavelength to around 2.5 picometers, allowing the microscope to achieve much higher resolution than light microscopes. This enables the visualization of features at the atomic level, which is essential for detailed nanoscopic analysis.
What are the main components of a Transmission Electron Microscope (TEM)?
-A TEM consists of a field emission source to generate electrons, a series of magnetic lenses (condenser, objective, and projector lenses) to focus and magnify the electron beam, and a detector or camera system to capture the final image. The entire system operates in a vacuum to prevent electron scattering.
What is the significance of the objective lens in a TEM?
-The objective lens is considered the heart of the TEM, as it is responsible for the initial magnification and resolution of the image. It determines the final resolution by minimizing optical aberrations, which are critical for achieving clear and detailed images at the atomic scale.
Why is a vacuum necessary in the operation of an electron microscope?
-A vacuum is essential to remove atmospheric molecules that could scatter the high-speed electrons, causing them to deviate from their path and blur the image. The vacuum ensures that the electron beam remains focused and accurate, which is crucial for producing high-resolution images.
What are optical aberrations, and how do they affect the resolution of a TEM?
-Optical aberrations are distortions introduced by the lenses in the TEM, which can blur and reduce the resolution of the image. Despite the potential for incredibly high resolution, aberrations limit the microscope's ability to clearly resolve the smallest features, making it a critical area of focus in microscope design.
How does the Scanning Transmission Electron Microscope (STEM) combine features of both TEM and SEM?
-The STEM operates similarly to a TEM but scans a focused electron beam across the specimen like an SEM. This approach allows it to create images with different contrast mechanisms and perform elemental analysis, making it versatile for detailed structural and compositional studies.
What advancements in electron microscopy have been made possible by companies like Thermo Fisher Scientific?
-Companies like Thermo Fisher Scientific have developed advanced electron microscopes with higher resolution, better imaging capabilities, and more precise control over electron beams. These advancements have enabled breakthroughs in nanotechnology, materials science, and biological research by allowing scientists to observe and analyze structures at the atomic level.
Outlines
🔬 The Fascinating World of Electron Microscopy
This paragraph introduces the concept of electron microscopy and its significance in understanding the microscopic world. It uses the example of a European Peacock Butterfly’s wing to illustrate how electron microscopes can reveal details invisible to light microscopes, like the intricate texture of scales. The paragraph highlights the importance of electron microscopes in advancing technology, especially in the development of smaller transistors by imaging at the atomic level. It also introduces the two main types of electron microscopes: Scanning Electron Microscopes (SEM) for surface imaging and Transmission Electron Microscopes (TEM) for viewing internal structures.
🧬 The Limits of Visible Light and the Power of Electrons
This section delves into the limitations of visible light in microscopy, explaining why light microscopes cannot resolve features smaller than 300 nanometers due to the diffraction of light waves. It contrasts this with electron microscopes, which use electrons with much shorter wavelengths, allowing them to achieve resolutions down to 50 picometers, enough to see individual atoms. The paragraph emphasizes the superior resolving power of electron microscopes, crucial for studying nanoscale structures that light microscopes cannot reveal.
⚛️ How Transmission Electron Microscopes (TEM) Work
This paragraph details the working principle of a Transmission Electron Microscope (TEM). It explains how TEMs generate a beam of electrons accelerated to 70% of the speed of light, which then passes through a specimen, scattering based on its density and composition. The scattered electrons create an imprinted image, which is magnified by a series of magnetic lenses. The process of magnification involves both objective and projector lenses, with the final image captured by a high-resolution camera. The paragraph also touches on the necessity of using electrons instead of light to achieve the high magnifications required for atomic-level imaging.
🔍 The Complex Engineering Behind TEMs
This section explores the intricate engineering involved in TEMs, starting with the field emission source that generates free electrons. It describes the process of accelerating these electrons and the use of magnetic lenses to focus them onto the specimen. The paragraph also discusses the challenges of controlling electron beams, including the introduction of optical aberrations that limit resolution. The physics behind magnetic lenses and the Lorentz force is explained, demonstrating how magnetic fields focus the electrons to create magnified images. The paragraph concludes by highlighting the additional systems in a TEM, such as phosphorescent screens, CMOS cameras, and various detectors, all contributing to the microscope's functionality.
Mindmap
Keywords
💡Electron Microscope
💡Scanning Electron Microscope (SEM)
💡Transmission Electron Microscope (TEM)
💡Resolution
💡Nanometer
💡Magnification
💡Electrons
💡Field Emission Source
💡Magnetic Lenses
💡Aberrations
Highlights
Scientists and engineers use electron microscopes to develop transistors as small as the width of a DNA strand.
Electron microscopes allow us to capture images of individual atoms, revolutionizing our understanding of the micro and nanoscopic world.
There are two main types of electron microscopes: Scanning Electron Microscope (SEM) for surface images and Transmission Electron Microscope (TEM) for internal structures.
SEM can reveal incredible details like the texture of butterfly wings or bacteria on human cells, with a maximum resolution of around 1 nanometer.
TEM can capture images of structures inside materials with a resolution of up to 50 picometers, roughly the size of a hydrogen atom.
The TEM operates by accelerating electrons to 70% of the speed of light and transmitting them through a specimen, imprinting an image on the electron beam.
The magnification process in TEM involves magnetic lenses that focus and magnify the image up to 2 million times.
TEM is crucial for developing cutting-edge technology, allowing scientists to see inside materials at an atomic level.
Visible light has limitations in magnification, which electron microscopes overcome by using electrons with wavelengths 200,000 times smaller than visible light.
Magnetic lenses in electron microscopes focus the electron beam, acting like convex lenses but using magnetic fields to control electron trajectories.
Optical aberrations in magnetic lenses limit the resolution of electron microscopes, making reducing these aberrations a key area of research.
The Scanning Transmission Electron Microscope (STEM) combines elements of both TEM and SEM, allowing for elemental analysis and contrast imaging.
Thermo Fisher Scientific, a leader in laboratory equipment, played a significant role in the development and understanding of these microscopes.
The electron microscope's technology is supported by extensive engineering, including vacuum systems, magnetic lenses, and sophisticated imaging detectors.
Electron microscopes are essential tools in scientific research, enabling discoveries in fields like nanotechnology, biology, and material science.
Transcripts
Have you ever wondered how scientists and engineers design transistors that are around
the width of a strand of DNA?
How do we even take pictures of such nanoscopic transistors?
Well, that’s the role of the electron microscope which has literally changed the way humanity
sees the micro and nanoscopic world.
Don’t believe us?
Take this European Peacock Butterfly for example.
When we zoom in on its wing using a light microscope, we see that it’s composed of
tiny overlapping scales.
But, when we zoom in using an electron microscope, we can clearly see the shape of each scale,
and zooming in further, we see how the scales have a truly incredible texture entirely foreign
to anything that humans manufacture.
Although this wing may not be directly related to the technology you’re familiar with,
scientists and engineers have been using electron microscopes for the past 60 years to develop
smaller and smaller transistors, and with today’s technology this microscope can zoom
in millions of times to where it’s able to capture images of individual atoms.
There are two main types of electron microscopes.
The Scanning Electron Microscope or SEM is used to see surface images like this butterfly
wing, or the bristles of a used toothbrush.
See, here are cells from your body, and all around here in yellow is bacteria.
It’s gross, but let’s move on.
Scanning Electron Microscopes have a maximum resolution of around 1 nanometer.
Meaning the spacing between two adjacent features or dots of resolvable data in an image is
1 nanometer.
The other type is the Transmission Electron Microscope or TEM which is used to take images
of structures that are inside materials, much like an x-ray machine takes pictures of the
bones inside our bodies.
For example, TEMs are used to take the pictures of these sections of a transistor.
However, in other domains of science TEMs can be used to take images of proteins inside
mitochondria, the powerhouse of the cell, or of nanoparticles of pure gold.
Transmission Electron Microscopes are typically more complex than SEMs and have a resolution
up to 50 picometers, which is roughly the size of a hydrogen atom.
One quick note is that this video’s sponsor, Thermo Fisher Scientific, provided us with
a basic 3D model of one of their transmission electron microscopes and assisted in our understanding
of the complex technology involved.
Let’s first focus on the TEMs as they are more commonly used in developing cutting-edge
technology, and later we’ll provide an overview of the scanning electron microscope.
And note that there’s considerable overlap between the engineering inside them both.
The basic idea behind a TEM is that it generates electrons and accelerates them to around 70%
the speed of light, thus creating a beam of electrons.
Next a series of magnetic lenses focuses the electrons down to a small area and shoots
or transmits these electrons through the specimen that we’re looking at.
Depending on the different densities and materials inside the specimen, the electrons are scattered
as they pass through it, thereby imprinting an image of what’s inside the specimen onto
the beam of electrons.
The imprinted beam of electrons is then magnified 40 times using an objective lens and further
magnified 50,000 times using a set of projector lenses.
At this point, the imprinted image is 5 or so centimeters wide and large enough to be
captured by a high-resolution camera sensor at the bottom of the microscope.
We’ll explore the detailed engineering in a little bit, but for now, you might be wondering
why do we have to go through the hassle of manipulating electrons, and why can’t we
just use light?
Well, visible light is physically limited to magnifications up to around 2000 times,
and, if you try to zoom in further the image remains blurred without revealing any more
details.
On the other hand, electrons can reach meaningful magnifications up to 2 million times.
Why then is light physically limited?
Well, let’s return to this image of the European peacock butterfly and the scales
on its wings.
This image was captured with a camera, this image was taken with a light microscope, and
these images were captured with an electron microscope.
Let’s consider two features from the specimen that are only 100 nanometers apart.
Visible light has an average wavelength of 540 nanometers, which is larger than the distance
between these two points.
Due to the physics of waves, as light hits these two features it’s bent around, thus
creating a pair of propagating waves with a diffraction pattern resulting from the interference
of the two waves.
If the features are substantially closer than the wavelength of visible light, then the
diffraction pattern will make the two features appear like a single blurred feature.
In short, visible light can’t really resolve features that are less than 300 nanometers
apart.
However, in this electron microscope, electrons are accelerated to 70% of the speed of light
and have a wavelength of 2.5 picometers which is around 200,000 times smaller than visible
light’s wavelength.
In principle, such an electron microscope could resolve features spaced just 1 picometer
apart, but, due to the magnetic lenses’ physical limitations the real resolution is
around 50 picometers, which is enough to see individual atoms in a material.
Also, if you’re wondering about the scale of micrometers, nanometers, and picometers,
here’s a comparison of the size of each unit.
Note that there are many more details and facts that were cut from this video’s script
and thrown into the creator’s comments which you can find in the English Canadian Subtitles.
That said, let’s now dive into the complex science and engineering behind each part of
this Transmission Electron Microscope.
We’ll begin at the top with a device called a field emission source which generates free
electrons.
The basic principle is that negatively charged electrons are attracted to positive electric
fields.
Here we have a tungsten crystal needle, and below is a ring called the extractor.
This extraction ring is connected to positive 5 thousand volts, and as a result the negatively
charged electrons in the tungsten are pulled towards the extractor.
The electric field’s effect on the electrons is amplified by the sharply pointed tungsten
crystal, which is only a few nanometers wide, and as a result the electrons are freed from
the tungsten.
The next step is to accelerate them to 70% the speed of light.
To do this we use a series of metal rings which are graduated to be tens of thousands
of volts apart from one another.
And, just like before, these positively charged rings use electrostatics to attract the negatively
charged electrons which are accelerated through the center of the rings.
There are two key reasons for the incredible speed of the electron.
First is so they can travel through the specimen, whether it be a transistor, protein or a crystal
lattice or something else that has been sliced to typically only 100 nanometers in thickness;
and second, as mentioned earlier, electrons exhibit wavelike properties, and the faster
they are, the shorter the wavelength and the higher the resolution achievable.
One important detail is that when the microscope is running and electrons are being accelerated
to relativistic speeds, vacuum pumps are used to remove all the atmospheric molecules, thus
creating a vacuum, similar to the vacuum of outer space.
This is because incredibly fast-moving electrons will scatter in random directions as they
collide with air molecules and thus ruin the images of the specimen.
Now that we have a beam of electrons, we’ll explore the magnetic lenses of which there
are essentially three sets: the condenser, the objective, and the projector.
The role of the condenser magnetic lenses is to focus the electrons from the source
and project them onto the sample so that they illuminate an area the size of a micrometer
to several nanometers depending on the desired magnification.
Additionally, the microscope uses apertures, or holes placed in the path of the beam to
filter out any electrons that are fanning too far from the center of the column, or
optical axis, resulting in electrons more parallel to one another before they hit the
specimen.
The specimen is placed on a holder which is inserted through an airlock into the vacuum
chamber.
To see different aspects of the specimen such as the crystal lattices, the holder can move,
or translate the specimen in all three directions, X,Y, and Z, and rotate the specimen along
the X-axis, and with some holders, also the Y-axis.
With this we can get images exactly perpendicular to the features such as these transistors
inside.
The incredibly small beam then hits the specimen composed of different elements and densities
of materials, thus scattering the electrons in different ways thereby imprinting an image
on the transmitted electron beam.
The next lenses, the objective and a series of four projector lenses, are used to resolve
and magnify the miniscule image imprinted into the electron beam up to a width of a
few centimeters.
This process is separated into two parts.
First the objective lens – often considered the heart of the microscope – magnifies
the image by 40 times and its optical aberrations define the final resolution.
Then the projector lenses magnify the image the rest of the way by 50,000 times.
What are optical aberrations and why is 2 million times the typical maximum magnification?
Well, let’s look at this image of 962 blurry atoms of gold.
With today’s technology, the TEM’s ability to resolve the smallest features is not limited
by the electrons in the beam, but rather by the lenses and the aberrations and distortions
that they add to the image-imprinted electron beam after it has been magnified.
There are a few main types of aberrations such as spherical and chromatic, which we
won’t explore further, but the main idea is that perfectly controlling a beam of electrons
is far from trivial and the aberrations add blurriness and impede resolution after the
magnification.
The projector lenses magnify what has already been magnified by the objective lens, including
the added aberrations, and this second magnification adds its own aberrations afterwards.
Therefore, a considerable amount of science and engineering is dedicated to reducing the
aberrations introduced by the objective lens, as that is what ultimately limits the sub-nanometer
scale resolution of the microscope.
One thing you’re probably wondering is why these magnetic lenses look nothing like microscope
or camera lenses and how do magnetic lenses operate on fast moving electrons?
Well, inside the lens is a coil of copper wire surrounded by an iron housing.
When a current is run through these coils, a magnetic field is produced.
This magnetic field is then routed through the iron to the pole pieces where it’s channeled
into an optical column.
These magnetic fields are then used to change the trajectory of the electron by bending
the electrons towards the center, or optical axis, in a shrinking helical direction.
The physics at play is the Lorentz Law.
To summarize, the force on the electron is equal to its charge, Q, times V or the electron’s
velocity vector crossed with B, the magnetic field vector.
In short, if the electron were to have a velocity away from the optical axis, it would be forced
by the magnetic field down towards the center.
However, if the electron were traveling perfectly down the center along the optical axis, it
wouldn’t experience any Lorentz force from the magnetic fields and would just continue
down the center.
As a result, the magnetic lenses act as convex or converging lenses, focusing all the electrons
down to a focal point.
As the electrons continue their trajectory past the focal point and expand, they produce
a magnified image.
This magnification depends on the strength of the magnetic fields, the position of the
lenses, and the position of the detectors and cameras.
Let’s move further down the microscope and explore how we turn electrons into images.
There are two separate systems.
First, we have a phosphorescent screen which has a special coating that glows when electrons
hit it and a camera is used to view the screen.
This system is used to align the microscope and provide an overview of the specimen.
When you’re ready to capture a high-resolution image, the phosphorescent screen moves out
of the way, and the image is captured using the second system with a more sensitive CMOS
camera that has a higher resolution and dynamic range.
The purpose of having two systems is that the phosphorescent screen and camera is used
to ensure that the electron beam and magnetic lenses are set up properly, as an incorrectly
focused beam could damage the sensitive CMOS camera.
We’ve covered many key parts of the microscope, but there are other pieces of equipment and
modules that provide additional features.
For example, there are X-Ray detectors, energy filters, phase plates, monochromators, multipole
correctors, mechanisms to hold and adjust apertures, water cooling for the magnetic
lenses, tons of circuitry to control the magnetic lenses and the field emission source, vacuum
pumps, power supplies, and much more.
Additionally, the entire microscope sits on air cushions to remove external vibrations.
Undoubtedly, this microscope represents an incredible amount of science and engineering,
and we’re thankful to this video’s sponsor, Thermo Fisher Scientific, for allowing us
to look inside.
In addition to electron microscopes, Thermo Fisher also makes a wide range of laboratory
equipment such as centrifuges, incubators, x—ray and mass spectrometers, and in fact
they make PCR systems that can be used to test for Covid 19.
Undeniably, Thermo Fisher products are some of the backbones of scientific research in
labs across the world.
Thermo Fisher isn’t sponsoring this video because they want you to buy a multi-million-dollar
electron microscope, but rather, just like us at Branch Education, they believe that
the future of humanity lies in the hands of scientists’ and engineers’ abilities to
discover, innovate, and engineer solutions to the problems that face humanity.
If you’re pursuing a career in science or engineering, take a look at Thermo Fisher
Scientific.
You too could work on creating the tools that propel science and engineering forward.
Now that we understand the transmission electron microscope, let’s look at the Scanning Electron
Microscope or SEM which Thermo Fisher Scientific also manufactures.
The main idea is that, instead of illuminating an area of a specimen and imprinting the image
all at once, with a SEM we create a focused spot, and scan this spot across the object
we’re trying to magnify.
These electrons then bounce off, and, in the process, create secondary electrons, back-scattered
electrons and X-Rays, which we measure to get details as to the surface topology and
chemical composition.
For example, this process was used to create these images of the butterfly wing, or of
this salt crystal.
The issue with SEM is that it only takes images of the surfaces of materials and the resolution
is limited by how small we can create the focused spot and by how deep the electrons
penetrate into the sample, or the so-called interaction volume.
The practical resolution is typically around 1 nanometer.
Additionally, a useful variation of the Transmission Electron Microscope that’s worth mentioning
is called an STEM, where the S is for scanning.
This microscope is similar to the TEM, but like the SEM, we focus the beam into a spot
and then use deflection coils to scan the spot through the specimen.
The benefit of STEM is that it has a different mechanism for creating image contrast and,
when paired with an x-ray detector, is capable of elemental analysis of the sample.
More expensive TEMs typically have the optical elements and circuitry to perform both TEM
and STEM, and the user can toggle between the two modes.
We’re sure you have many questions; feel free to put them in the comments below, and
we’ll try to answer them in the top pinned comment.
Also, one of the scientists from Thermo Fisher who works on these microscopes and helped
us to research and write this script, has written the creator’s comments with loads
of additional information, so take a look at them in the English Canadian Subtitles.
We believe the future will require a strong emphasis on engineering education and we’re
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If you want to support us on YouTube Memberships, or Patreon, you can find the links in the
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