Team images tiny quasicrystals as they form

August 17, 2017 by Tom Fleischman
A transmission electron microscope image of a mesoporous silica nanoparticle, showing the tiling with triangles and squares, and the Fourier analysis (inset) showing 12-fold symmetry. Credit: Lab of Uli Wiesner, Cornell University

When Israeli scientist Daniel Shechtman first saw a quasicrystal through his microscope in 1982, he reportedly thought to himself, "Eyn chaya kazo"—Hebrew for, "There can be no such creature."

But there is, and the quasicrystal has become a subject of much research in the 35 years since Shechtman's Nobel Prize-winning discovery. What makes quasicrystals so interesting? Their unusual structure: Atoms in quasicrystals are arranged in an orderly but nonperiodic way, unlike most crystals, which are made up of a three-dimensional, orderly and periodic (repeating) arrangement of atoms.

The lab of Uli Wiesner, the Spencer T. Olin Professor of Engineering in the Department of Materials Science and Engineering (MSE) at Cornell University, has joined scientists pursuing this relatively new area of study. And much like Shechtman, who discovered quasicrystals while studying diffraction patterns of aluminum-manganese crystals, Wiesner came upon quasicrystals a bit by accident.

While working with silica nanoparticles—from which the Wiesner lab's patented Cornell dots (or C dots) are made—one of his students stumbled upon an unusual non-periodic but ordered silica structure, directed by chemically induced self-assembly of groups of molecules, or micelles.

"For the first time, we see this [quasicrystal] structure in nanoparticles, which had never been seen before to the best of our knowledge," said Wiesner, whose research team proceeded to conduct hundreds of experiments to capture the formation of these structures at early stages of their development.

Their work resulted in a paper, "Formation Pathways of Mesoporous Silica Nanoparticles With Dodecagonal Tiling," published Aug. 15 in Nature Communications. Lead authors are former MSE doctoral student Yao Sun, current postdoc Kai Ma and doctoral student Teresa Kao. Other contributors included Lena Kourkoutis, assistant professor of applied and engineering physics; Veit Elser, professor of physics; and graduate students Katherine Spoth, Hiroaki Sai and Duhan Zhang.

To study the evolution of silica nanoparticle quasicrystals, the best solution would be to take video of the growth process, but that was not possible, Wiesner said.

"The structures are so small, you can only see them through an electron microscope," he said. "Silica degrades under the electron beam, so to look at one particle over a longer period of time is not possible."

The solution? Conduct many experiments, stopping the growth process of the quasicrystals at varying points, imaging with transmission electron microscopy (TEM), and comparing results with computer simulations, conducted by Kao. This imaging, done by Sun and Ma, gave the team a sort of time-lapse look at the quasicrystal , which they could control in a couple of different ways.

One way was to vary the concentration of the chemical compound mesitylene, also known as TMB, a pore expander. The imaging, including cryo-TEM performed by Spoth, showed that as TMB concentration increased, micelles became bigger and more heterogeneous. Adding TMB induced four mesoporous nanoparticle structure changes, starting as a hexagonal and winding up as a dodecagonal (12-sided) quasicrystal.

"The more TMB we add, the broader the pore size distribution," Wiesner said, "and that perturbs the crystal formation and leads to the quasicrystals."

The other way to make these structures evolve is mechanical. Starting with a hexagonal crystal , the team found that by simply stirring the solution more and more vigorously, they introduced a disturbance that also changed the micelle size distribution and triggered the same structural changes "all the way to the ," Wiesner said.

A lot of the discovery in this work was "serendipity," Wiesner said, the result of "hundreds and hundreds" of growth experiments conducted by the students.

The more insight gained into the early formation of these unique particles, the better his understanding of silica nanoparticles, which are at the heart of his group's work with Cornell dots.

"As the techniques become better, the ability to see small structures and better understand their assembly mechanisms is improving," he said. "And whatever helps us understand these early formation steps will help us to design better materials in the end."

Explore further: Khatyrka meteorite found to have third quasicrystal

Related Stories

Khatyrka meteorite found to have third quasicrystal

December 9, 2016

(Phys.org)—A small team of researchers from the U.S. and Italy has found evidence of a naturally formed quasicrystal in a sample obtained from the Khatyrka meteorite. In their paper published in the journal Scientific Reports, ...

Researchers discover new group of quasicrystals

March 6, 2014

(Phys.org) —A team of researchers working at the university of Notre Dame has discovered a whole new group of quasicrystals. In their paper published in the journal Nature, the team describes how they accidently created ...

Researchers discover new rules for quasicrystals

October 25, 2016

Crystals are defined by their repeating, symmetrical patterns and long-range order. Unlike amorphous materials, in which atoms are randomly packed together, the atoms in a crystal are arranged in a predictable way. Quasicrystals ...

Quasicrystal "movie" shows error-correction process at work

August 18, 2015

(Phys.org)—A team of researchers with affiliations to the University of Tokyo and Tohoku University, both in Japan, have succeeded in filming the growth of a sample quasicrystal for the first time. In their paper published ...

Researchers discover new form of 12-sided quasicrystal

October 10, 2013

(Phys.org) —A team of researchers working at Germany's Martin-Luther-Universität has discovered a new form of a 12-sidded quasicrystal. In their paper published in the journal Nature, the team describes how they accidently ...

Recommended for you

Two teams independently test Tomonaga–Luttinger theory

October 20, 2017

(Phys.org)—Two teams of researchers working independently of one another have found ways to test aspects of the Tomonaga–Luttinger theory that describes interacting quantum particles in 1-D ensembles in a Tomonaga–Luttinger ...

Using optical chaos to control the momentum of light

October 19, 2017

Integrated photonic circuits, which rely on light rather than electrons to move information, promise to revolutionize communications, sensing and data processing. But controlling and moving light poses serious challenges. ...

Black butterfly wings offer a model for better solar cells

October 19, 2017

(Phys.org)—A team of researchers with California Institute of Technology and the Karlsruh Institute of Technology has improved the efficiency of thin film solar cells by mimicking the architecture of rose butterfly wings. ...

Terahertz spectroscopy goes nano

October 19, 2017

Brown University researchers have demonstrated a way to bring a powerful form of spectroscopy—a technique used to study a wide variety of materials—into the nano-world.

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.