Sem microscope how does it work

The electron beam follows a vertical path through the microscope, which is held within a vacuum. The beam travels through electromagnetic fields and lenses, which focus the beam down toward the sample. Once the beam hits the sample, electrons and X-rays are ejected from the sample.

Detectors collect these X-rays, backscattered electrons, and secondary electrons and convert them into a signal that is sent to a screen similar to a television screen. This produces the final image. Because the SEM utilizes vacuum conditions and uses electrons to form an image, special preparations must be done to the sample. All water must be removed from the samples because the water would vaporize in the vacuum. All metals are conductive and require no preparation before being used.

All non-metals need to be made conductive by covering the sample with a thin layer of conductive material. This is done by using a device called a "sputter coater. The sputter coater uses an electric field and argon gas. The sample is placed in a small chamber that is at a vacuum. Argon gas and an electric field cause an electron to be removed from the argon, making the atoms positively charged.

Scientists are making new materials based on nanotechnology, like these "flowers" of silicon carbide and gallium. Image courtesy Ghim Wei Ho and Prof. Cite This! Print Citation. Try Our Crossword Puzzle! What Is the Missing Number? Try Our Sudoku Puzzles! More Awesome Stuff. Field emission sources take advantage of quantum tunneling to create an electron beam.

Field emission sources are capable of producing sub-nanometer resolution images, however, this source type is much more expensive and usually cost prohibitive.

In order to achieve a sufficient electron mean free path, the SEM chamber must be pumped to low vacuum conditions. The electron beam passes through a number of electromagnetic lenses to demagnify and focus the beam, allowing a higher resolution for more detailed imaging.

An objective aperture controls the electron beam by means of limiting electrons far from the beam center. A smaller aperture will shrink the electron probe radius, but will also reduce the current as it essentially removes the electrons not near the beam center.

A stigmator is used to ensure the electron beam is not elliptical in nature, but perfectly round; this allows us for consistent imaging in all axises. Lastly, an objective lens is used to focus the electron beam onto the sample. When the electron beam reaches the sample, a number of interactions occur. As dimensions are shrinking for materials and devices, many structures can no longer be characterized by light microscopy.

For example, to determine the integrity of a nanofiber layer for filtration, as shown here, electron microscopy is required to characterize the sample. The main SEM components include:. Electrons are produced at the top of the column, accelerated down and passed through a combination of lenses and apertures to produce a focused beam of electrons which hits the surface of the sample.

The sample is mounted on a stage in the chamber area and, unless the microscope is designed to operate at low vacuums, both the column and the chamber are evacuated by a combination of pumps. The level of the vacuum will depend on the design of the microscope. The position of the electron beam on the sample is controlled by scan coils situated above the objective lens.

These coils allow the beam to be scanned over the surface of the sample.