Low-Energy Electron Diffraction
Definition and meaning of Low-Energy Electron Diffraction in chemistry.
Low-energy electron diffraction (LEED) is a surface-sensitive analytical technique that uses electrons with kinetic energies of 20-200 electron volts to probe the crystal structure of solid surfaces. The diffraction pattern produced reveals the atomic arrangement and symmetry of the top few atomic layers.
In more detail
Electrons used in LEED have wavelengths comparable to atomic spacing, allowing them to undergo diffraction similar to X-rays but with much shorter penetration depths. The low kinetic energy restricts electrons to penetrating only the top few atomic layers (1-5 atomic planes), making LEED highly sensitive to surface structure rather than bulk properties. A fluorescent screen displays the diffraction pattern, which appears as bright spots arranged in a pattern that reflects the surface symmetry. LEED is widely used in surface chemistry, catalysis research, and materials science.
Key facts
| Field | Analytical Chemistry |
|---|---|
| Typical Electron Energy | 20-200 eV |
| Penetration Depth | 1-5 atomic layers |
| Common Abbreviation | LEED |
When LEED is used to study a gold (111) surface, the characteristic hexagonal diffraction pattern confirms the close-packed surface structure, while any ordered adsorbates (such as sulfur atoms or organic molecules) produce additional diffraction spots that reveal their arrangement relative to the gold lattice.
Frequently asked questions
Why does LEED not penetrate deep into materials like X-ray diffraction?
Low-energy electrons interact strongly with matter and lose energy through inelastic scattering. This limits their mean free path to only a few atomic layers, making LEED surface-specific.
What does the arrangement of spots in a LEED pattern reveal?
Each bright spot corresponds to a diffraction condition; the spatial arrangement of spots reveals the symmetry and lattice parameters of the surface crystal structure.