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.