2 The Principle of the Electron Microscope

Summary

This script explores the functioning of microscopes, highlighting the advancements from optical to electron microscopes. It explains how optical microscopes magnify up to 10,000 times, while electron microscopes achieve resolutions down to 50 picometers. The script introduces Dr. Ernst Ruska, inventor of the electron microscope, and describes the necessity of a vacuum and electron guns for their operation. It differentiates between scanning and transmission electron microscopy, emphasizing their applications in various scientific fields, from biology to geology. The script also mentions modern capabilities of electron microscopes, such as analysis and modification of samples in 2D, 3D, and 4D.

Takeaways

• 🔬 Optical microscopes have been around since the 17th century and can magnify up to about 10,000 times, allowing us to see objects as close as two ten-thousandths of a millimeter.
• 👀 The resolving power of a microscope is a critical parameter, which is the ability to distinguish between two very close objects in an image.
• 🌌 The human eye has a resolution of 0.2 millimeters, while an optical microscope can resolve down to two ten-thousandths of a millimeter, and an electron microscope can reach up to fifty picometers.
• 🚀 The electron microscope was invented by Dr. Ernst Ruska in 1931, and he was awarded the Nobel Prize for Physics more than 50 years later for this invention.
• ⚛️ Electrons, which are negatively charged particles of an atom, can be used like light in electron microscopes, with their wavelength being about 100,000 times smaller than that of light.
• 💡 The electron microscope requires a vacuum to function, as electrons can only move freely in a vacuum and are easily deflected by air molecules.
• 🧲 The column of an electron microscope has similar parts to an optical microscope, but with electron guns as the light source and electromagnetic lenses instead of glass lenses.
• 🔋 An electron gun produces a beam of electrons by heating a filament, such as tungsten, to high temperatures and applying high voltage.
• 📉 To achieve high resolution, the accelerating voltage and series of lenses in an electron microscope must be extremely stable, with power sources that fluctuate by no more than one millionth of their output value.
• 🌐 There are two main types of electron microscopes: scanning electron microscopes (SEM) and transmission electron microscopes (TEM), each used for different types of sample analysis.
• 🧐 Modern electron microscopes are capable of not only displaying images but also analyzing, measuring, and modifying samples in 2D, 3D, and even 4D.

Q & A

What is the resolving power of a modern optical microscope?

The resolving power of a modern optical microscope is about two ten thousandth of a millimeter, which allows the human eye to distinguish objects that are that distance apart.

How does the resolving power of an optical microscope compare to that of an electron microscope?

The resolving power of an optical microscope is significantly lower than that of an electron microscope, which can reach up to fifty picometers.

What is the main limitation of optical microscopes in terms of resolution?

The main limitation of optical microscopes in terms of resolution is the wavelength of light used, which prevents the distinction of points closer than several hundred nanometers.

Who is credited with the invention of the electron microscope?

Dr. Ernst Ruska is credited with assembling the first electron microscope in 1931 and was awarded the Nobel Prize for Physics for his invention.

What is an electron and how does it relate to the electron microscope?

An electron is the negatively charged particle of an atom orbiting around the nucleus. In an electron microscope, electrons are accelerated and used to create an image of a sample, similar to how light is used in an optical microscope.

Why is a vacuum necessary in an electron microscope?

A vacuum is necessary in an electron microscope because electrons move freely only in a vacuum. Any interaction with air molecules could deflect the electron beam and degrade the image quality.

How does the electron beam interact with the sample in a transmission electron microscope?

In a transmission electron microscope, the electron beam goes through a very thin sample, showing its inner structure. The sample must be thin enough for the electrons to pass through.

What are the two basic types of electron microscopes?

The two basic types of electron microscopes are scanning electron microscopes and transmission electron microscopes, which differ in how the electron beam interacts with the sample.

How does the image quality in a scanning electron microscope depend on the sample?

The image quality in a scanning electron microscope depends on the orientation and distance of the sample from detectors and the final lens, as well as the stability of the accelerating voltage and lenses.

What are some applications of electron microscopes in scientific research?

Electron microscopes are used in various fields such as biology to examine the structure of cells, bacteria, and viruses; in materials science to observe entities and faults in metals, crystals, and ceramics; and in geology to study rocks, minerals, and fossils.

What is special about the cryos electron microscope mentioned in the script?

The cryos electron microscope is special because it can work with biological samples that would otherwise be dehydrated by the vacuum. Each sample is permanently frozen to at least the temperature of liquid nitrogen from its production to its examination.

Outlines

00:00

🔬 Optical and Electron Microscopes

The script discusses the functioning of optical microscopes, which have been known since the 17th century and can magnify up to 10,000 times, allowing the human eye to distinguish objects as close as two ten-thousandths of a millimeter apart. The resolving power of a microscope is highlighted as a key parameter, alongside magnification. The script then contrasts the optical microscope's resolution with that of the electron microscope, which can achieve up to fifty picometers. The discovery of electron behavior under electric and magnetic fields led to the invention of the electron microscope by Dr. Ernst Ruska in 1931, for which he was awarded the Nobel Prize in Physics. Electrons, being 2,000 times lighter than the smallest atom, are used in electron microscopes, which require a vacuum to function. The script explains the components of an electron microscope, including the electron gun and electromagnetic lenses, and the importance of stability in the accelerating voltage and lenses for high-resolution imaging. The vacuum pumps used to create the necessary vacuum are also mentioned, emphasizing the extreme difference in pressure between the outside air and the vacuum inside the microscope.

05:01

🔎 Types and Uses of Electron Microscopes

The script differentiates between two types of electron microscopes: scanning and transmission. In scanning electron microscopy, the electron beam scans the surface of the sample, while in transmission electron microscopy, a very thin sample is placed on a grid and the beam passes through it to reveal its inner structure. The script explains that the sample for a transmission electron microscope must be thin enough to allow electrons to pass through, whereas the sample for a scanning electron microscope can be much larger. It also discusses the various sample holders available for different applications and the importance of the vacuum and electron irradiation in the scanning process. The script further explains how the sample can be manipulated within the microscope, including movement along the x, y, and z axes, as well as rotation. The influence of sample orientation, distance from detectors, and the final lens on image quality in scanning electron microscopes is highlighted. The script concludes by mentioning the diverse applications of electron microscopes in fields such as biology, material science, and geology, and notes that modern electron microscopes can analyze, measure, and modify samples in 2D, 3D, and even 4D.

10:02

🎶 Miscellaneous and Unrelated Content

The content of this paragraph does not seem to be related to the main discussion about microscopes. It includes miscellaneous phrases and references that do not form a coherent narrative or provide additional information about the topic at hand.

Keywords

💡Optical Microscope

An optical microscope is a device that uses visible light and a system of lenses to magnify images, details, or objects. It has been known since the 17th century and is fundamental in various scientific fields. In the video, it is mentioned that modern optical microscopes can magnify up to about 10,000 times, allowing the human eye to distinguish objects that are two ten thousandth of a millimeter apart. This magnification is crucial for studying microscopic details that are beyond the resolution of the human eye.

💡Resolution

Resolution in microscopy refers to the ability to distinguish two very close objects in an image. It is one of the most important parameters of a microscope. The video script explains that while magnification enlarges the image, resolution determines the clarity and detail that can be seen within that image. The human eye has a resolution of 0.2 millimeters, whereas an optical microscope can achieve a resolution of two ten thousandth of a millimeter.

💡Electron Microscope

An electron microscope uses a beam of electrons instead of light to create an image. The video script highlights that electron microscopes have a much higher resolution than optical microscopes, up to fifty picometers, which allows for the observation of much smaller structures. This high resolution is due to the shorter wavelength of electrons compared to light, which enables the microscope to resolve finer details.

💡Wavelength

Wavelength is the distance between two consecutive peaks of a wave. In microscopy, the wavelength of light or electrons used to illuminate the sample is crucial because it determines the resolving power of the microscope. The video explains that scientists encountered the limits of the wavelength of light when trying to improve the resolution of optical microscopes. Electrons, with a much shorter wavelength, can be used to overcome these limits.

💡Ernst Ruska

Dr. Ernst Ruska is credited with assembling the first electron microscope in 1931. The video script mentions his significant contribution to the field, for which he was awarded the Nobel Prize for Physics over fifty years later. Ruska's work revolutionized microscopy by enabling the visualization of much smaller structures within materials.

💡Electron

An electron is a negatively charged subatomic particle that orbits the nucleus of an atom. The video script describes electrons as being 2,000 times lighter than the smallest atom, which allows them to be easily manipulated by electric and magnetic fields. This property is essential for the operation of electron microscopes, where electrons are accelerated and used to probe the structure of samples.

💡Vacuum

A vacuum is a space devoid of matter, including gaseous matter. The video script explains that electron microscopes require a vacuum to operate because electrons can only move freely in the absence of air molecules. The vacuum prevents electrons from colliding with air molecules, which would otherwise disrupt the electron beam and degrade image quality.

💡Electron Gun

An electron gun is a source of electrons in an electron microscope. The video script describes how it operates by heating a filament, such as tungsten, to 2,700 degrees Celsius and applying a high voltage to release electrons. These electrons are then accelerated to form an electron beam, which is used to scan or penetrate the sample.

💡Electromagnetic Lenses

Electromagnetic lenses are used in electron microscopes to focus the electron beam. They function similarly to glass lenses in optical microscopes but use magnetic and electric fields to manipulate electron beams instead of light. The video script mentions that these lenses are crucial for maintaining the stability and focus of the electron beam as it interacts with the sample.

💡Scanning Electron Microscope (SEM)

A scanning electron microscope (SEM) is a type of electron microscope that scans the surface of a sample with a focused beam of electrons. The video script explains that SEMs can be used to examine larger samples, even up to dozens of centimeters, and provide information about the surface topography of the sample. SEMs are essential for studying the morphology and composition of materials at high resolution.

💡Transmission Electron Microscope (TEM)

A transmission electron microscope (TEM) allows electrons to pass through an ultra-thin specimen. The video script describes how TEMs require very thin samples, on the order of hundreds of nanometers, to allow electrons to penetrate and create an image of the internal structure. TEMs are used to study the internal structure of cells, viruses, and other nanoscale materials.

Highlights

Optical microscopes have been known since the 17th century.

Modern optical microscopes have a magnification of about 10,000 times.

The resolving power of a microscope is a key parameter, allowing the distinction of objects that are two ten thousandth of a millimeter apart.

The human eye has a resolution of 0.2 millimeters, compared to the optical microscope's two ten thousandth of a millimeter.

Electron microscopes have a resolution up to fifty picometers.

The wavelength of accelerated electrons is about 100,000 times smaller than light, allowing higher resolution.

Dr. Ernst Ruska assembled the first electron microscope in 1931 and was awarded the Nobel Prize for Physics.

Electrons are negatively charged particles of an atom, 2,000 times lighter than the smallest atom.

Electron microscopes require a vacuum to prevent electrons from hitting air molecules.

The electron beam is produced by heating a filament up to 2,700 degrees Celsius and applying high voltage.

High voltage stability is crucial for high-resolution electron microscopy.

The electron beam can either scan the surface of a sample or go through it to show its inner structure.

There are two basic types of electron microscopes: scanning and transmission.

Transmission electron microscopes require very thin samples placed on a grid.

Scanning electron microscopes can examine larger samples and provide information about the surface.

The sample holder in a scanning electron microscope allows for movement and rotation of the sample.

Image quality in scanning electron microscopes depends on the sample's orientation and distance from detectors.

Electron microscopes are used in biology to examine cells, bacteria, viruses, and in material science to observe entities and faults in metals and crystals.

Modern electron microscopes can display, analyze, measure, and modify samples in 2D, 3D, and even 4D.

Cryogenic electron microscopy allows the examination of biological samples without dehydration.

Transcripts

[Music]

how does such a microscope work the

optical microscope has been known since

the 17th century the modern optical

microscope has magnification of about

10,000 times and makes it possible for

the human eye to distinguish objects

that are two ten thousandth of a

millimeter away from each other

it is this resolving power of the

microscope ie

the ability to distinguish two very

close objects in an image which is one

of the most important parameters the

level of magnification just makes it

possible to picture how the image was

enlarged however it does not say whether

we can see anything in the picture a

human eye at its best has only a

resolution of 0.2 millimeters while the

optical microscope has two ten

thousandth of a millimeter and the

electron microscope has up to fifty Pico

meters wait a minute that's too many

numbers well it's as if you were

watching a tennis match from the moon

and we're still able to follow the small

tennis ball hmm interesting

let's go back to the optical microscope

when attempting to reach a better

resolution scientists encountered the

limits of the wavelength of the light

used for the elimination of the sample

it was not possible to distinguish

points closer than several hundreds of

nanometers in 1920 it was discovered

that accelerated electrons in a vacuum

can act as light while the wavelength of

these electrons is about 100,000 times

smaller than light it was also

discovered that electric and magnetic

fields influence electrons similarly to

how lenses and mirrors influence the

light Hey who is this handsome fellow

that's dr. Ernst Ruska who assembled the

first electron microscope in 1931 and

after more than 50 years he was awarded

the Nobel Prize for Physics for his

invention well the main thing is that he

lived to receive it I am still waiting I

would still like to know what an

electron actually is an electron is the

negatively charged particle of an atom

orbiting around the nucleus it can be

released by

or an electric field electrons are 2,000

times lighter than the smallest atom

thus they can easily be stopped or

diverted when hitting materials now I

see that's why there must be a vacuum in

the microscope great the column of the

electron microscope consists of

basically the same parts as the optical

one

however the source of light is replaced

by the so called electron guns and the

glass lenses by electromagnetic ones the

electron beam is produced by an electron

gun in which for example a tungsten

filament can be placed as the electron

source the beam is produced by heating

the filament up to 2,700 degrees Celsius

and connecting it to high-voltage to

higher the voltage the higher the energy

of the electrons the electrons

accelerated by three hundred kilovolts

almost reached the speed of light

however to reach a high resolution the

accelerating voltage and series of

lenses must be immensely stable the

power cabinet contains a number of

sources whose output voltage or current

fluctuate not more than one millionth of

the output value I probably understand

but don't you have another example the

one with tennis was excellent

I do try to imagine that the allowed

voltage fluctuation in a common socket

has the height of Mount Everest

then the allowed voltage fluctuation of

a 200 kilovolt high voltage source as

the height of only seven centimeters

such stability needs very efficient and

sophisticated electronic circuits you

see how good you are with examples let's

go on since electrons move freely only

in a vacuum there must be a vacuum in

the entire column to achieve this the

vacuum pumps are used various levels of

vacuum are needed the highest is around

the electron gun the difference between

common air pressure and residual

pressure in the microscope is about 10

orders of magnitude so it means that the

probability that an electron will hit an

air molecule on

this pressure when passing through the

column is zero yes almost zero

however dozens of millions to billions

of electrons hit the samples per second

poor lizard electromagnetic lenses

focused the electron beam on the

examined sample in an optimal way during

its entire journey the electron beam

goes through a number of apertures with

various diameters the smallest ones can

be just a few thousandths of a

millimeter these apertures stop

electrons undesirable for creating the

image the electron beam hits the

observed object and it either scans its

surface step by step as if we were

reading an inscription on the wall with

a torch at night or it goes through the

sample and shows its inner structure I

see and according to the way the

electron beam hits the sample we

distinguish two basic types of electron

microscope scanning and transmission

exactly the sample for the transmission

electron microscope is very thin several

hundred nanometers and it is placed on a

grid if it wasn't then electrons would

be stopped and no image would be created

in the transmission microscope there are

various holders available for the

examination of samples in the

transmission markets but depending on

the application a customer would like to

use here we can see a holder where more

samples can be placed at the same time

on the other hand the sample examined in

the scanning microscope can be bigger

even dozens of centimeters

[Music]

therefore the scanning microscope is

always used where information about this

surface of the sample is required yes

the only requirement is that the sample

must withstand a vacuum and the

irradiation with electrons a holder is

not necessary samples are placed in a

small table which is placed under the

electron column as soon as the electron

beam hits the sample or scans through it

the various detectors placed in the

microscope create the final image and

can I manipulate the sample place this

way in the microscope you are right that

it is not enough to move most of the

examined objects along a horizontal axis

information can be gained from various

depths of the sample and we can observe

them if we slightly turn the sample the

sample holder in no transmission

microscope is inserted through a vacuum

interlock in the goniometer this enables

that not only movement along the x and y

axes but also its inclination around one

or both axes also the rotation or

movement along the z-axis in parallel to

the electron beam whew that sentence is

a little complicated and would be enough

to say yes it's possible we'd better

move on what influences the quality of

the picture the image quality in the

scanning microscope depends on the

orientation and distance of the sample

from detectors and the final lens the

stage on which the sample is placed

makes it possible to move it vertically

along the x and y axes up and down in

the direction of the z-axis and with a

possible inclination and rotation these

movements are performed with step motors

and are controlled by the computer great

but show me some pictures already

biologists use electron microscopes to

examine the structure of cells bacteria

viruses and colloidal particles

scientists who are concerned with

material characteristics wants to

observe in Hommage entities and faults

in metals crystals and ceramic material

in geological fields the electron

microscope allowed the detailed studies

of rocks minerals and fossils and to

understand the origin of our planet and

its valuable mineral resources modern

electron microscopes not only display

but also analyze measure and modify in

2d 3d and even 4d weights I know it here

this is say tech in Brno Central

European Institute of Technology yes

there is a kryos electron microscope

here with a special function it can work

with biological samples they would soon

be dehydrated by the vacuum in the

common electron microscope and thus

would be destroyed for the research

however Fei has developed a system where

each sample is permanently frozen to at

least the temperature of liquid nitrogen

from its production to its examination

in the cryos microscope I understand

thus the damage is permanent Jiki

transmission electron microscopy

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[Music]