The Scanning Electron Microscope  -  its properties and applications

The main application of the scanning electron microscope (SEM) is the inspection of the surface morphology of more or less structured objects. Today it is an important tool in many fields of technology and science.

  Advantages of scanning electron microscopy : silicium,etched silicium, etched
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* Magnifications in the range of 5x up to and exceeding 50000x can be obtained, the depth of focus may be 300x greater than with the light optical microscope. Take a look at some examples in our SEM image archive.
* The pretreatment of the samples is in most cases extraordinarily simple, size and weight of the samples can vary more than with the light optical microscope. You´ll find this in more detail at samples and sample preparation.
* It is possible to gather additional chemical analytical information on the samples - without destruction, quick, and, if necassery down to the range of microscopical small volumina. At material analysis you´ll find more information on this matter.
 
Because of these properties it is in many cases possible to gather far more information on your samples than by light optical methods.
These advantages lead to numerous applications, e.g. in the investigation of materials (alloys, ceramics, high tech materials), in the evaluation of surfaces, in the analysis of failure (investigation of fractures), in forensic investigations (comparison of very small objects), in biology and medicine (investigation of morphology and pathology), semiconductor technologies (quality control of technical parts), and many more applications.

The Scanning Electron Microscope  -  Construction and principal function

  A Scanning Electron Microscope consists of :
 
SEM sketch
* an electron source together with a high voltage powersupply (typically between 1000 and 30000 Volt), which generates an electron beam,
* an electron optic, that forms a very fine electron beam (a probe) and scans the beam across the specimen,
* a sample chamber with a sample stage, that can be moved and rotated in many ways with the sample fixed on it,
* a detector, which collects the so called secondary electrons, freed by the primary electrons of the beam hitting the sample and makes them available as image information,
* a vacuum system, that holds the above systems under vacuum, because an effective electron beam can´t be generated under atmospheric pressure,
* an electronic unit, which supplies the necessary currents and voltages and amplifies the image information,
* a CRT with an electron beam synchronized to the electron beam in the microscope and a beam intensity controlled by the amplified video signal provided by the secondary electron detector.
The image contrast is produced, because different areas of the object supply different numbers of secondary electrons and therefore appear at different levels of brightness on the monitor. The number of secondary electrons is dependent on the position of the specimen surface with regard to the electron beam and the elemental composition at the surface.
* In order to take micrographs most SEM´s use a separate special high resolution CRT.

The scanning electron microscope as described above can be equipped with numerous optional accessories like other detectors, special beam controls, special stage accessories and different types of analytical accessories. The EDX system is the analytical accessory which is by far mostly utilized at SEM´s. The EDX makes use of the characteristic X-ray radiation generated by the electrons hitting the sample. Information on this matter you´ll find on our page material analysis.


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