How do electron microscopes reveal the structure of quasicrystals?

Electron microscopes are essential tools for investigating the structure of quasicrystals, revealing features that distinguish them from both ordinary crystals and amorphous solids. These instruments function at different scales to provide structural insights:

• Scanning Electron Microscopy: Low-resolution imaging allows researchers to observe the shapes of individual grains. For example, imaging of aluminum-copper-iron quasicrystals has revealed pentagonal dodecahedral grain shapes, which exhibit fivefold rotational symmetry—a symmetry forbidden in periodic crystal lattices.1
• High-Resolution Electron Microscopy: This technique magnifies materials sufficiently to resolve patterns of atomic positions. In quasicrystals, these images reveal parallel rows of atoms arranged in five sets rotated by 72°, confirming that the fivefold symmetry observed at the grain level is reflected in the actual atomic structure.1
• Electron Diffraction: By utilizing the wave-like properties of electrons, this method produces sharp diffraction patterns (Bragg peaks) that confirm the presence of long-range order. Unlike amorphous metals, which produce only diffuse rings, quasicrystals produce discrete, symmetrical spots that indicate a highly ordered, non-periodic arrangement of atoms.2