What signals are SEM generated ?​

Signals Generated in Electron Microscopy
When a high-energy electron beam interacts with a specimen, several types of signals are produced.
These signals provide critical information about the surface morphology, composition, and structure of the material.

1. Secondary Electrons (SE)
   Generated when incident electrons eject low-energy electrons from atoms near the specimen’s surface.
   They carry surface-sensitive information (depth < 10 nm).
   ➡ Used for: High-resolution surface imaging and morphology observation.
2. Backscattered Electrons (BSE)
   Primary electrons that are reflected back from the specimen with minimal energy loss.
   The signal intensity depends on the atomic number — heavier elements appear brighter.
   ➡ Used for: Compositional contrast and material phase differentiation.
3. Characteristic X-rays
   Produced when inner-shell electrons are knocked out and replaced by outer-shell electrons, releasing X-rays of element-specific energy.
   ➡ Used for: Elemental analysis via EDS or WDS detectors.
4. Auger Electrons
   Emitted when excess energy from an electron transition is transferred to another electron instead of emitting an X-ray. Highly surface-sensitive (1–5 nm depth).
   ➡ Used for: Surface chemical analysis through Auger Electron Spectroscopy (AES).
5. Cathodoluminescence (CL)
   Occurs when electron bombardment excites a material, causing it to emit light (visible or near-UV).
   ➡ Used for: Studying semiconductors, minerals, and defect-related luminescence.