- Scientists discover a strange type of crystal whose existence was considered impossible before the 1980s.
- It’s a new kind of quasicrystal that self-assembles from a single component.
Quasicrystals are special objects. They consist of ordered patterns, but unlike crystals, their patterns do not repeat. Any given quasicrystalline pattern can continuously fill all free space, but it lacks translational symmetry.
These unusual types of crystal were first discovered in the 1980s by an Israeli scientist Dan Shechtman. He won 2011 Nobel Prize in chemistry for his discovery.
A crystal usually has 3-fold symmetry (form by repeating triangles) or 4-fold symmetry (from by repeating cubes). It can also consist of 2- or 6-fold symmetries but that’s the rare case. A Quasicrystal, on the other hand, can have exotic 5-, 10- or 12-fold symmetry.
Now, researchers at Brown have discovered a new kind of quasicrystal that self-assembles from a single component. This is the first time someone has observed a quasicrystalline superlattice emerged from a single type of nanoparticle building blocks. It will help scientists better understand how these strange structures actually form.
Although single-component quasicrystal superlattices have been designed in computer simulations, they had not been demonstrated until now. The research team did not set out to investigate quasicrystals. They were just trying to bridge the gap between macroscale and nanoscale by developing superstructures made of nanoparticles.
Two years ago, researchers came up with a pyramid-like (tetrahedral) quantum dot, a new class of nanoparticle building block. They can form more robust and complex structures and their properties depend on their orientation relative to each other, which means they are anisotropic.
Using this quantum dot, researchers demonstrated one of the most complex superstructures, in which nanoparticles interacted with a solid substrate. They then decided to test the nanoparticles with a liquid substrate, and surprisingly, they found that these particles were assembling themselves in a quasicrystal lattice.
The researchers used transmission electron microscopy to show that these nanoparticles organized into discrete 10-side shapes (decagons), which attached with each other to form a superlattice with 10-fold rotational symmetry. This type of symmetry is not possible in conventional crystals.
To fit together in a confined space, the nanoparticle decagons can flex their edges. They can morph themselves into polygons with 5, 6, 7, 8, and 9 sides. Researchers believe that numerous quasicrystals can be developed with this flexible polygon tiling system.
How Is It Useful?
From different observations, researchers made new rules for making quasicrystals, and they are calling it the flexible polygon tiling rule. It will be helpful in the continued examination of quasicrystalline structures.
Flexible polygon tiling | Orange spheres show centers of each polygon | Courtesy of researchers
The first quasicrystals discovered were alloys of metals, such as aluminum alloys. They are mostly used in anti-corrosive coatings for surgical tools and non-stick coatings for frying pans.
The newly discovered quasicrystals have a wide range of applications. The discovery can inform research in mathematics, chemistry, material science, and even design and art.