Electron+Microscope

=Electron Microscope (SEM and TEM)=

The image capability of the microscope is a trade-off between operating voltage and resolution. The resolution can be described by the following equation:

Where D = resolution in angstroms, Cs is the spherical aberration coefficient of the objective lens, lambda is the electron wavelength, and A is a constant. D typically ranges from 1.2 to 5 angstroms.



There are two basic types of electron microscopes in operation: The scanning electron microscope (SEM) and the transmission electron microscope (TEM).

Scanning Electron Microscope
The scanning electron microscope (SEM) employs a rastering electron beam Electrons in the sample are scattered by the high energy electron beam and are collected by a detector and amplified to yield an image of the sample.

Transmission Electron Microscope
The TEM utilizes a broad spectrum of electrons that //pass through// a very thin sample. The image is very highly magnified and can reveal much more information about a sample than a SEM.

Scanning Transmission Electron Microscope
The STEM combines both the SEM and TEM and detects electrons that have passed through the sample along with a rastoring beam. The amount of scattering of the electrons depends apon the elemental composition of the sample.

In all electron microscopes, if the probe is stopped over and area of the sample the irridiated area generates x-rays and characterististic spectrum for elemental analysis.