Creating 3D Quasicrystals

New York University physicists have applied a nanotechnology method to create 3D quasicrystals, highly ordered structures that, unlike conventional crystals, never repeat themselves.

Metallic quasicrystals created from exotic alloys have shown promise for storing hydrogen more efficiently than crystalline hosts. Their non-repeating structure has the potential to dramatically strengthen industrial and commercial products. The NYU quasicrystals, by contrast, are made of glass and plastic and have potentially revolutionary optical properties.

Quasicrystals are different from crystals, whose periodic structures resemble the patterns of tiles on a bathroom floor. By contrast, quasicrystals do not have this property, called translational symmetry, but, like crystals, can be rotated into registry with themselves, a property called rotational symmetry.

Quasicrystals' rotational symmetry gives them many of the properties of conventional crystals. These same symmetries are responsible for conventional semiconducting crystals' ability to act as switches for electrons. However, because quasicrystals do not possess the translational symmetry of conventional crystals, they have the freedom to take a broader range of forms, opening up the potential to serve a range of functions.

The NYU team's quasicrystals are created from tiny glass spheres, each comparable in size to the wavelength of light, stacked precisely in mathematically defined configurations. Like the crystalline structures responsible for the iridescence of gem opals and the colors of butterfly wings, these quasicrystalline sphere packings diffract different wavelengths of light into different directions, creating a rainbow-like display. For particular structures, and particular wavelengths, however, the quasicrystals offer no path at all for light. The resulting gaps in the rainbow, known as photonic bandgaps, can be manipulated to create switches for light. For instance, when translated into structures with features comparable to the wavelength of light, these properties of quasicrystals should enable them to manipulate light in much the same way that semiconductors manipulate electrons.

This has already been achieved for two-dimensional structures by previous researchers. However, prior to this work, scientists had not been able to branch out into three-dimensional quasicrystals - thereby reaping the full benefits of their unique properties-because of the inability to create this class of quasicrystals with the proper materials at the right size scale.

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