Scanning Electron Microscopy (SEM)

Instead of visible light, a scanning electron microscope uses a finely focused electron beam. Because electrons have a much shorter wavelength than light, SEM reaches resolutions in the nanometer range — far beyond what a light microscope can achieve.

How the image is formed

The electron beam scans the sample surface line by line. On impact it generates secondary electrons, backscattered electrons, and characteristic X-rays. These signals are assembled point by point into an image of the surface.

What it reveals

• Secondary electrons: provide detailed topographic information.
• Backscattered electrons: reveal contrast that depends on material composition.
• Characteristic X-rays: enable chemical elemental analysis of the sample.

Applications

SEM is used in materials research, the semiconductor industry, biology and medicine, and geology and archaeology — anywhere the finest surface structures need to be made visible.