How do Electron Microscopes Work? 🔬🛠🔬 Taking Pictures of Atoms

0:00 Have you ever wondered how scientists and engineers design transistors

0:04 that are around the width of a strand of DNA?

0:08 How do we even take pictures of such nanoscopic transistors?

0:12 Well, that’s the role of the electron microscope which has

0:16 literally changed the way humanity sees the micro and nanoscopic world.

0:21 Don’t believe us?

0:22 Take this European Peacock Butterfly for example.

0:26 When we zoom in on its wing using a light microscope,

0:29 we see that it’s composed of tiny overlapping scales.

0:33 But, when we zoom in using an electron microscope,

0:37 we can clearly see the shape of each scale, and zooming in further,

0:42 we see how the scales have a truly

0:45 incredible texture entirely foreign to anything that humans manufacture.

0:49 Although this wing may not be directly related

0:52 to the technology you’re familiar with, scientists and engineers

0:56 have been using electron microscopes for the past

0:59 60 years to develop smaller and smaller transistors,

1:02 and with today’s technology this microscope can zoom in millions

1:07 of times to where it’s able to capture images of individual atoms.

1:13 There are two main types of electron microscopes.

1:16 The Scanning Electron Microscope or SEM is used

1:20 to see surface images like this butterfly wing,

1:24 or the bristles of a used toothbrush.

1:27 See, here are cells from your body, and all around here in yellow is bacteria.

1:33 It’s gross, but let’s move on.

1:37 Scanning Electron Microscopes have a maximum resolution of around 1 nanometer.

1:42 Meaning the spacing between two adjacent features or dots

1:46 of resolvable data in an image is 1 nanometer.

1:50 The other type is the Transmission Electron Microscope or TEM which

1:54 is used to take images of structures that are inside materials,

1:59 much like an x-ray machine takes pictures of the bones inside our bodies.

2:04 For example, TEMs are used to take

2:07 the pictures of these sections of a transistor.

2:10 However, in other domains of science TEMs can

2:13 be used to take images of proteins inside mitochondria,

2:17 the powerhouse of the cell, or of nanoparticles of pure gold.

2:24 Transmission Electron Microscopes are typically more complex than

2:27 SEMs and have a resolution up to 50 picometers,

2:31 which is roughly the size of a hydrogen atom.

2:35 One quick note is that this video’s sponsor, Thermo Fisher Scientific,

2:39 provided us with a basic 3D model of one of their transmission

2:44 electron microscopes and assisted in our understanding

2:47 of the complex technology involved.

2:50 Let’s first focus on the TEMs as they

2:53 are more commonly used in developing cutting-edge technology,

2:57 and later we’ll provide an overview of the scanning electron microscope.

3:02 And note that there’s considerable overlap

3:04 between the engineering inside them both.

3:07 The basic idea behind a TEM is that it generates

3:11 electrons and accelerates them to around 70% the speed of light,

3:16 thus creating a beam of electrons.

3:19 Next a series of magnetic lenses focuses the electrons down to a small

3:24 area and shoots or transmits these electrons

3:27 through the specimen that we’re looking at.

3:30 Depending on the different densities and materials inside the specimen,

3:34 the electrons are scattered as they pass through it,

3:38 thereby imprinting an image of what’s inside

3:40 the specimen onto the beam of electrons.

3:43 The imprinted beam of electrons is then magnified 40 times using an objective

3:49 lens and further magnified 50,000 times using a set of projector lenses.

3:57 At this point, the imprinted image is 5 or so centimeters wide and large

4:01 enough to be captured by a high-resolution

4:04 camera sensor at the bottom of the microscope.

4:07 We’ll explore the detailed engineering in a little bit, but for now,

4:11 you might be wondering why do we have

4:14 to go through the hassle of manipulating electrons,

4:16 and why can’t we just use light?

4:19 Well, visible light is physically limited

4:22 to magnifications up to around 2000 times, and, if you try to zoom in further

4:28 the image remains blurred without revealing any more details.

4:33 On the other hand, electrons can reach

4:36 meaningful magnifications up to 2 million times.

4:40 Why then is light physically limited?

4:42 Well, let’s return to this image of the European

4:45 peacock butterfly and the scales on its wings.

4:48 This image was captured with a camera,

4:51 this image was taken with a light microscope,

4:55 and these images were captured with an electron microscope.

4:59 Let’s consider two features from the specimen

5:02 that are only 100 nanometers apart.

5:05 Visible light has an average wavelength of 540 nanometers,

5:08 which is larger than the distance between these two points.

5:12 Due to the physics of waves, as light hits these two features it’s bent around,

5:18 thus creating a pair of propagating waves with a diffraction

5:22 pattern resulting from the interference of the two waves.

5:26 If the features are substantially closer than the wavelength of visible light,

5:30 then the diffraction pattern will make the two

5:33 features appear like a single blurred feature.

5:36 In short, visible light can’t really resolve

5:39 features that are less than 300 nanometers apart.

5:43 However, in this electron microscope,

5:45 electrons are accelerated to 70% of the speed of light and have a wavelength

5:52 of 2.5 picometers which is around

5:55 200,000 times smaller than visible light’s wavelength.

5:59 In principle, such an electron microscope could

6:02 resolve features spaced just 1 picometer apart,

6:06 but, due to the magnetic lenses’ physical

6:09 limitations the real resolution is around 50 picometers,

6:12 which is enough to see individual atoms in a material.

6:17 Also, if you’re wondering about the scale of micrometers, nanometers,

6:22 and picometers, here’s a comparison of the size of each unit.

6:27 Note that there are many more details and facts that were cut from this video’s

6:31 script and thrown into the creator’s comments which

6:34 you can find in the English Canadian Subtitles.

6:38 That said, let’s now dive into the complex science

6:45 and engineering behind each part of this Transmission Electron Microscope.

6:53 We’ll begin at the top with a device

6:56 called a field emission source which generates free electrons.

7:00 The basic principle is that negatively charged

7:03 electrons are attracted to positive electric fields.

7:07 Here we have a tungsten crystal needle,

7:10 and below is a ring called the extractor.

7:13 This extraction ring is connected to positive 5 thousand volts,

7:17 and as a result the negatively charged electrons

7:20 in the tungsten are pulled towards the extractor.

7:24 The electric field’s effect on the electrons

7:27 is amplified by the sharply pointed tungsten crystal,

7:30 which is only a few nanometers wide,

7:32 and as a result the electrons are freed from the tungsten.

7:37 The next step is to accelerate them to 70% the speed of light.

7:41 To do this we use a series of metal rings which are

7:45 graduated to be tens of thousands of volts apart from one another.

7:49 And, just like before,

7:51 these positively charged rings use electrostatics to attract the negatively

7:56 charged electrons which are accelerated through the center of the rings.

8:01 There are two key reasons for the incredible speed of the electron.

8:06 First is so they can travel through the specimen, whether it be a transistor,

8:11 protein or a crystal lattice or something else that has

8:14 been sliced to typically only 100 nanometers in thickness;

8:18 and second, as mentioned earlier,

8:21 electrons exhibit wavelike properties, and the faster they are,

8:25 the shorter the wavelength and the higher the resolution achievable.

8:29 One important detail is that when the microscope is

8:32 running and electrons are being accelerated to relativistic speeds,

8:36 vacuum pumps are used to remove all the atmospheric molecules,

8:41 thus creating a vacuum, similar to the vacuum of outer space.

8:45 This is because incredibly fast-moving electrons

8:48 will scatter in random directions as they

8:51 collide with air molecules and thus ruin the images of the specimen.

8:56 Now that we have a beam of electrons,

8:59 we’ll explore the magnetic lenses of which there are essentially three sets:

9:04 the condenser, the objective, and the projector.

9:08 The role of the condenser magnetic lenses is to focus

9:12 the electrons from the source and project them onto

9:15 the sample so that they illuminate an area the size

9:18 of a micrometer to several nanometers depending on the desired magnification.

9:24 Additionally, the microscope uses apertures,

9:26 or holes placed in the path of the beam to filter out

9:31 any electrons that are fanning too far from the center of the column,

9:36 or optical axis, resulting in electrons more parallel

9:39 to one another before they hit the specimen.

9:43 The specimen is placed on a holder which

9:45 is inserted through an airlock into the vacuum chamber.

9:49 To see different aspects of the specimen such as the crystal lattices,

9:53 the holder can move, or translate the specimen in all three directions,

9:58 X,Y, and Z, and rotate the specimen along the X-axis,

10:03 and with some holders, also the Y-axis.

10:07 With this we can get images exactly perpendicular

10:11 to the features such as these transistors inside.

10:15 The incredibly small beam then hits the specimen

10:19 composed of different elements and densities of materials,

10:22 thus scattering the electrons in different ways thereby

10:26 imprinting an image on the transmitted electron beam.

10:30 The next lenses, the objective and a series of four projector lenses,

10:35 are used to resolve and magnify the miniscule image imprinted

10:39 into the electron beam up to a width of a few centimeters.

10:45 This process is separated into two parts.

10:48 First the objective lens– often considered

10:51 the heart of the microscope– magnifies

10:54 the image by 40 times and its optical aberrations define the final resolution.

11:01 Then the projector lenses magnify the image the rest of the way by 50,000 times.

11:07 What are optical aberrations and why is

11:11 2 million times the typical maximum magnification?

11:14 Well, let’s look at this image of 962 blurry atoms of gold.

11:20 With today’s technology, the TEM’s ability to resolve the smallest features

11:25 is not limited by the electrons in the beam,

11:29 but rather by the lenses and the aberrations and distortions that they

11:33 add to the image-imprinted electron beam after it has been magnified.

11:38 There are a few main types of aberrations such as spherical and chromatic,

11:43 which we won’t explore further,

11:45 but the main idea is that perfectly controlling a beam of electrons is

11:50 far from trivial and the aberrations add

11:54 blurriness and impede resolution after the magnification.

11:58 The projector lenses magnify what has

12:01 already been magnified by the objective lens, including the added aberrations,

12:05 and this second magnification adds its own aberrations afterwards.

12:10 Therefore, a considerable amount of science and engineering is

12:14 dedicated to reducing the aberrations introduced by the objective lens,

12:19 as that is what ultimately limits

12:22 the sub-nanometer scale resolution of the microscope.

12:26 One thing you’re probably wondering is

12:29 why these magnetic lenses look nothing like

12:31 microscope or camera lenses and how do

12:34 magnetic lenses operate on fast moving electrons?

12:37 Well, inside the lens is a coil of copper wire surrounded by an iron housing.

12:44 When a current is run through these coils, a magnetic field is produced.

12:49 This magnetic field is then routed through the iron

12:52 to the pole pieces where it’s channeled into an optical column.

12:57 These magnetic fields are then used to change the trajectory

13:01 of the electron by bending the electrons towards the center,

13:05 or optical axis, in a shrinking helical direction.

13:09 The physics at play is the Lorentz Law.

13:12 To summarize, the force on the electron is equal to its charge, Q,

13:18 times V or the electron’s velocity vector crossed with B,

13:23 the magnetic field vector.

13:25 In short, if the electron were to have a velocity away from the optical axis,

13:30 it would be forced by the magnetic field down towards the center.

13:36 However, if the electron were traveling perfectly

13:38 down the center along the optical axis,

13:41 it wouldn’t experience any Lorentz force from the magnetic

13:45 fields and would just continue down the center.

13:49 As a result, the magnetic lenses act as convex or converging lenses,

13:54 focusing all the electrons down to a focal point.

13:58 As the electrons continue their trajectory past the focal point and expand,

14:03 they produce a magnified image.

14:06 This magnification depends on the strength of the magnetic fields,

14:10 the position of the lenses, and the position of the detectors and cameras.

14:15 Let’s move further down the microscope

14:17 and explore how we turn electrons into images.

14:21 There are two separate systems.

14:23 First, we have a phosphorescent screen which has a special coating that glows

14:28 when electrons hit it and a camera is used to view the screen.

14:33 This system is used to align the microscope

14:36 and provide an overview of the specimen.

14:38 When you’re ready to capture a high-resolution image,

14:41 the phosphorescent screen moves out of the way,

14:45 and the image is captured using the second system with a more

14:49 sensitive CMOS camera that has a higher resolution and dynamic range.

14:53 The purpose of having two systems is

14:56 that the phosphorescent screen and camera is

14:58 used to ensure that the electron beam and magnetic lenses are set up properly,

15:03 as an incorrectly focused beam could damage the sensitive CMOS camera.

15:08 We’ve covered many key parts of the microscope,

15:11 but there are other pieces of equipment

15:13 and modules that provide additional features.

15:17 For example, there are X-Ray detectors,

15:20 energy filters, phase plates, monochromators, multipole correctors,

15:24 mechanisms to hold and adjust apertures, water cooling for the magnetic lenses,

15:30 tons of circuitry to control the magnetic lenses and the field emission source,

15:36 vacuum pumps, power supplies, and much more.

15:40 Additionally, the entire microscope sits

15:43 on air cushions to remove external vibrations.

15:46 Undoubtedly, this microscope represents an incredible

15:49 amount of science and engineering, and we’re thankful to this video’s sponsor,

15:55 Thermo Fisher Scientific, for allowing us to look inside.

15:59 In addition to electron microscopes, Thermo Fisher also makes a wide range

16:04 of laboratory equipment such as centrifuges, incubators,

16:08 x—ray and mass spectrometers,

16:10 and in fact they make PCR systems that can be used to test for Covid 19.

16:17 Undeniably, Thermo Fisher products are some of the backbones

16:20 of scientific research in labs across the world.

16:24 Thermo Fisher isn’t sponsoring this video because they

16:27 want you to buy a multi-million-dollar electron microscope,

16:30 but rather, just like us at Branch Education,

16:34 they believe that the future of humanity lies

16:37 in the hands of scientists’ and engineers’ abilities to discover,

16:41 innovate, and engineer solutions to the problems that face humanity.

16:46 If you’re pursuing a career in science or engineering,

16:49 take a look at Thermo Fisher Scientific.

16:52 You too could work on creating

16:55 the tools that propel science and engineering forward.

16:58 Now that we understand the transmission electron microscope,

17:02 let’s look at the Scanning Electron Microscope

17:05 or SEM which Thermo Fisher Scientific also manufactures.

17:10 The main idea is that, instead of illuminating an area

17:13 of a specimen and imprinting the image all at once,

17:17 with a SEM we create a focused spot,

17:20 and scan this spot across the object we’re trying to magnify.

17:24 These electrons then bounce off, and, in the process,

17:29 create secondary electrons, back-scattered electrons and X-Rays,

17:32 which we measure to get details

17:35 as to the surface topology and chemical composition.

17:39 For example, this process was used to create these images of the butterfly wing,

17:44 or of this salt crystal.

17:47 The issue with SEM is that it only takes

17:50 images of the surfaces of materials and the resolution is

17:54 limited by how small we can create the focused spot

17:57 and by how deep the electrons penetrate into the sample,

18:01 or the so-called interaction volume.

18:03 The practical resolution is typically around 1 nanometer.

18:08 Additionally, a useful variation of the Transmission Electron

18:12 Microscope that’s worth mentioning is called an STEM,

18:16 where the S is for scanning.

18:18 This microscope is similar to the TEM, but like the SEM,

18:22 we focus the beam into a spot and then

18:25 use deflection coils to scan the spot through the specimen.

18:28 The benefit of STEM is that it has a different mechanism

18:33 for creating image contrast and, when paired with an x-ray detector,

18:38 is capable of elemental analysis of the sample.

18:42 More expensive TEMs typically have the optical elements

18:45 and circuitry to perform both TEM and STEM,

18:49 and the user can toggle between the two modes.

18:53 We’re sure you have many questions; feel free to put them in the comments below,

18:59 and we’ll try to answer them in the top pinned comment.

19:02 Also, one of the scientists from Thermo Fisher who works

19:06 on these microscopes and helped us to research and write this script,

19:10 has written the creator’s comments with loads of additional information,

19:13 so take a look at them in the English Canadian Subtitles.

19:18 We believe the future will require

19:20 a strong emphasis on engineering education and we’re

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19:29 If you want to support us on YouTube Memberships,

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19:36 This is Branch Education, and we create 3D animations that dive deeply

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19:51 Thanks for watching to the end!