What is inside the Scanning Electron Microscope? Explained in detail with Animated Videos


A Scanning Electron Microscope (SEM) is a highly advanced instrument, and its internal structure is very different from an X-ray tube. Inside an SEM, multiple subsystems work together to generate and control an electron beam and produce high-resolution images.

Main Components Inside an SEM

1. Electron Gun (Source)

  • Produces electrons
  • Types:
    • Tungsten filament (thermionic emission)
    • Field emission gun (FEG – high resolution)

Function: Generates the primary electron beam

2. Anode

  • Positively charged plate
  • Accelerates electrons to high energy (1–30 keV)

Function: Controls beam energy

3. Condenser Lenses

  • Electromagnetic lenses
  • Control beam size and intensity

Function: Focuses the beam before it reaches the sample

4. Objective Lens

  • Final focusing lens near the sample

Function: Produces a very fine electron probe (nm scale)

5. Scanning Coils or Scanner

  • Deflect the beam in X–Y directions

Function: Scan the beam over the sample surface (raster scan)

6. Sample Chamber

  • Where the specimen is placed
  • Includes stage movement (X, Y, Z, tilt, rotation)

Function: Holds and positions the sample

7. Detectors

Different signals are collected:

  • Secondary Electron Detector (SE)
    • Surface morphology (topography)
  • Backscattered Electron Detector (BSE)
    • Atomic number contrast
  • EDS Detector
    • Elemental composition (X-ray analysis)

8. Vacuum System

  • Pumps (rotary + turbomolecular)
  • Maintains high vacuum (~10⁻⁵ to 10⁻⁷ torr)

Function: Prevents electron scattering by air

9. Electronics & Display System

  • Amplifiers
  • Signal processors
  • Computer & monitor

Function: Converts signals into images

Working Flow (Simple)

  1. Electron gun emits electrons
  2. Accelerated by anode
  3. Focused by lenses
  4. Scanned by coils
  5. Hits sample → signals generated
  6. Detectors collect signals
  7. Image formed on screen

Quick Comparison

Feature

SEM

X-ray Tube

Beam

Electrons

X-rays

Purpose

Imaging

Radiation generation

Key Output

Surface image

X-ray photons







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