FE-SEM and Environmental SEM

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pic21A SEM is a type of electron microscope that images a sample by scanning it with a beam of electrons in a raster scan pattern. The electrons interact with the atoms that make up the sample producing signals that contain information about the sample’s surface typography, composition, and other properties such as electrical conductivity.

SEM is a powerful technique commonly use is particle analysis, contamination, delamination, element composition and many other applications. The global use of different SEM machines is in Quality control, problem solving, material development, and failure analysis.

Here, some of the specific use of the technique are listed too:

Specific Uses

Instrument Specifications:

Our SEM have three different detectors:

pic25Secondary Electrons:

Caused by an incident electron passing "near" an atom in the specimen, which ionizes an electron in the specimen atom. This “secondary” ionized electron then leaves the atom with a very small kinetic energy (5eV).Production of secondary electrons is very topography related. Due to their low energy, only secondary electrons that are very near the surface (<10 nm) can exit the sample and be examined.

Backscattered Electrons:

Caused by an incident electron interacting with the nucleus of an atom in the specimen. Like a billiard ball, the incident electron is then scattered "backwards". The number of backscattered electrons is proportional to the specimen's atomic number. Denser, more massive materials appear brighter than lighter materials. Sometimes, backscatter contrast can be seen that depends of the sample crystal orientation with respect to the electron beam.

pic26X-rays:

Since an electron was emitted from the atom during the secondary electron process, an inner (lower energy) shell now has a electron vacancy. When a valence electron fills this lower energy shell, it lowers its energy. The electron emits this excess energy, usually in the form of x-rays. X-rays emitted from an atom will have an energy which is characteristic of the element from which it originated. EDAX (Energy dispersive x-ray spectroscopy) measures the number of x-rays versus energy, and then applies a ZAF fit to determine the sample composition.

Ultra and Leo 1530 FE-SEMs have resolutions of approximately 1-3 nm (using the Rayleigh criterion on gold nanoparticles).

Some examples of SEM images, from left to right: Polymer balls, Iron oxide nanoparticles,

Bottom: zinc oxide nanotube, and gold nanoparticles of silicon

Light Microscope Image of a medicine tablet with contamination

SEM Image and EDS shows metal particles in the dark spot

 

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