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Electron Microscopy Solutions

An Introduction to Electron Microscopy

Types of Microscopes

There are three basic types of microscopes: optical, charged particle (electron and ion), and scanning probe. Optical microscopes are the ones most familiar to everyone from the high school science lab or the doctor's office. They use visible light and transparent lenses to see objects as small as about one micrometer (one millionth of a meter), such as a red blood cell (7 μm) or a human hair (100 μm). Electron and ion microscopes use a beam of charged particles instead of light, and use electromagnetic or electrostatic lenses to focus the particles. They can see features as small as one-tenth of a nanometer (one ten billionth of a meter), including individual atoms.

 

Scanning probe microscopes allow researchers to image, characterize and even manipulate material structures at exceedingly small scales including features of atomic proportions.  Scanning probe microscopes use no lenses, but rather a very sharp probe(a very small, very sharp needle) that interacts with the sample surface. It maps various forces and interactions that occur between the probe and the sample to create an image.  These instruments also are capable of the resolution required to create atomic scale images (ten billionth of a meter). A modern light microscope, by comparison, has a magnification of about 1000x and enables the eye to resolve objects separated by 200 nm.

As scientists and inventors toiled to achieve better resolution, they soon realized that the resolving power of the microscope was not only limited by the number and quality of the lenses, but also by the wavelength of the light

used for illumination. With visible light it was impossible to resolve points in the object that were closer together than a few hundred nanometers. Using light with a shorter wavelength (blue or ultraviolet) gave a small improvement. Immersing the specimen and the front of the objective lens in a medium with a high refractive index (such as oil) gave another small improvement, but these measures together only brought the resolving power of the microscope to just under 100 nm.

 

The first electron microscope, built in 1931 by Ruska and Knoll, used two magnetic lenses, and three years later a third lens was added, demonstrating a resolution of 100 nm, twice as good as that of the light microscope. Today, electron microscopes have reached resolutions of better than 0.05 nm, more than 4000 times better than a typical light microscope and 4,000,000 times better than the unaided eye.


In the next section, we'll examine the major types of electron- and ion-beam microscopes.


Next: The Transmission Electron Microscope (TEM)

Electron Microscopy Solutions

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