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Electron Microscopes Overview 2/5

Aug 16, 2025

Overview

This lecture covers the principles, differences, and uses of electron microscopes, focusing on transmission electron microscopes (TEM) and scanning electron microscopes (SEM).

Light vs. Electron Microscopes

  • Light microscopes use glass lenses to focus visible light, reaching up to 1,000-2,500x magnification and micrometer-level resolution.
  • Electron microscopes use electron beams and electromagnets, allowing much higher magnification and resolution.

Transmission Electron Microscope (TEM)

  • TEM uses a beam of electrons that passes through very thin specimens.
  • Provides extremely high resolution (~10 picometers) and high magnification (up to 100,000x or more).
  • Ideal for viewing internal cell structures.
  • Main limitation: specimens must be ultra-thin (30–150 nanometers), requiring special cutting tools like an ultramicrotome.

Scanning Electron Microscope (SEM)

  • SEM bombards the specimen with electrons and detects secondary electrons bouncing off its surface.
  • Resolution is lower than TEM (~10 nanometers), with magnification typically up to 10,000–20,000x.
  • Ideal for viewing the external, three-dimensional surfaces of specimens.
  • Can use thicker specimens since only the surface is imaged.

Comparison of TEM and SEM

  • Both use electron beams and magnetic fields instead of lenses and visible light.
  • TEM has higher resolution and magnification but requires ultra-thin samples and shows internal structures.
  • SEM provides 3D surface images, allows for thicker samples, but has lower resolution and magnification.

Key Terms & Definitions

  • Micrometer (Ξm) — one millionth of a meter.
  • Nanometer (nm) — one billionth of a meter.
  • Picometer (pm) — one trillionth of a meter.
  • Transmission Electron Microscope (TEM) — uses electrons transmitted through ultra-thin specimens for high-res internal images.
  • Scanning Electron Microscope (SEM) — scans surfaces with electrons and detects secondary electrons for 3D surface images.
  • Resolution — the smallest distance between two points that can still be distinguished as separate.
  • Ultramicrotome — a tool for cutting extremely thin specimen slices for TEM.

Action Items / Next Steps

  • Review textbook images labeled TEM (internal detail) and SEM (surface structure).
  • Be able to compare and contrast TEM and SEM in terms of resolution, magnification, and sample requirements.

Full transcript