SEM

Scanning Electron Microscope
Scanning Electron Microscopy (SEM) is an imaging technique that uses a focused beam of electrons to scan the surface of a sample. Unlike light microscopy, which relies on photons, SEM employs electrons, which have much shorter wavelengths, allowing for significantly higher resolution imaging.

When the electron beam interacts with the atoms in the material, it generates various signals, including secondary electrons, backscattered electrons, and characteristic X-rays. Secondary electrons, which originate from the outer shells of atoms near the sample’s surface, are primarily responsible for forming high-resolution images of the sample's topography. Backscattered electrons, which come from deeper within the sample, provide contrast based on atomic number differences, revealing compositional variations. Energy-dispersive X-ray spectroscopy (EDS or EDX) can also be used alongside SEM to analyze the elemental composition of the sample.

This technique is widely used in materials science, biology, forensics, geology, nanotechnology, and semiconductor research due to its ability to magnify specimens up to several hundred thousand times while maintaining a depth of field that allows for sharp imaging of complex surface structures. Samples must typically be conductive, and non-conductive materials (such as biological specimens) are often coated with a thin layer of gold, platinum, or carbon to prevent charging effects during imaging.