1. Elastic Scattering:
* What happens: The electrons are deflected by the electrostatic field of the atoms in the specimen without losing energy. This type of interaction is primarily responsible for image formation in Transmission Electron Microscopy (TEM), as the scattered electrons are projected onto a screen or detector, creating a magnified image.
* Fate: Some electrons are scattered through large angles and are blocked by the objective aperture, contributing to contrast in the image. Others are scattered through small angles and contribute to the overall signal.
2. Inelastic Scattering:
* What happens: The electrons lose some of their energy due to interactions with the specimen's electrons, resulting in excitation of atoms or ionization. This occurs in both TEM and Scanning Electron Microscopy (SEM).
* Fate:
* In TEM: Inelastically scattered electrons contribute to diffraction patterns and energy loss spectroscopy (EELS), providing information about the chemical composition and bonding of the specimen.
* In SEM: Inelastically scattered electrons can be used for backscattered electron (BSE) imaging, which provides information about the atomic number of the specimen. The remaining energy can be lost as secondary electrons (SE), which are emitted from the surface and are used for secondary electron imaging, providing topographic information.
3. Absorption:
* What happens: Some electrons lose all of their energy in the interaction with the specimen and are absorbed. This occurs more readily in thick specimens.
* Fate: The absorbed electrons contribute to heat generation within the specimen, potentially causing damage.
4. Bremsstrahlung:
* What happens: High-energy electrons interact with the nucleus of the atom, producing bremsstrahlung radiation (X-rays). This phenomenon is more prominent in SEM.
* Fate: X-rays can be detected and used for energy-dispersive X-ray spectroscopy (EDS), which provides information about the elemental composition of the specimen.
In Summary:
The fate of electrons interacting with a specimen in an electron microscope is multifaceted. They can be scattered elastically or inelastically, absorbed, or generate X-rays. Each interaction provides valuable information about the specimen's structure, composition, and properties.
The relative proportions of these interactions vary depending on the specific microscope, the specimen, and the electron beam energy. Understanding these interactions is crucial for interpreting the data obtained from electron microscopy and extracting meaningful insights.
