Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Technique simplifies the creation of high-tech crystals

23.07.2014

Highly purified crystals that split light with uncanny precision are key parts of high-powered lenses, specialized optics and, potentially, computers that manipulate light instead of electricity. But producing these crystals by current techniques, such as etching them with a precise beam of electrons, is often extremely difficult and expensive.

Now, researchers at Princeton and Columbia universities have proposed a new method that could allow scientists to customize and grow these specialized materials, known as photonic crystals, with relative ease.

Sorting Crystal Shapes

In this graphic representation of the analysis, colloids form the initial two layers of a crystal, at left. With the addition of the third layer, the crystal forms one of two possible shapes, which are shown at right. The vertical blue line to the right of each crystal shows a representative shape of the polymer when confined in the voids between colloids in each crystal.

Credit: Nathan Mahynski et al

"Our results point to a previously unexplored path for making defect-free crystals using inexpensive ingredients," said Athanassios Panagiotopoulos, the Susan Dod Brown Professor of Chemical and Biological Engineering and one of the paper's authors. "Current methods for making such systems rely on using difficult-to-synthesize particles with narrowly tailored directional interactions."

In an article published online July 21 in the journal Nature Communications, the researchers proposed that photonic crystals could be created from a mixture in which particles of one type are dispersed throughout another material. Called colloidal suspensions, these mixtures include things like milk or fog. Under certain conditions, these dispersed particles can combine into crystals.

Creating solids from colloidal suspensions is not a new idea. In fact, humans have been doing it since the invention of cheese and the butter churn. But there is a big difference between making a wheel of cheddar and a crystal pure enough to split light for an optical circuit.

One of the main challenges for creating these optical crystals is finding a way to create uniform shapes from a given colloidal mixture. By definition, crystals' internal structures are arranged in an ordered pattern. The geometry of these patterns determines how a crystal will affect light. Unfortunately for optical engineers, a typical colloidal mixture will produce crystals with different internal structures.

In their paper, the researchers demonstrate a method for using a colloidal suspension to create crystals with the uniform structures needed for high-end technologies.

Essentially, the researchers showed that adding precisely sized chains of molecules – called polymers – to the colloid mixture allows them to impose order on the crystal as it forms.

"The polymers control what structures are allowed to form," said Nathan Mahynski, a graduate student in chemical and biological engineering at Princeton and the paper's lead author. "If you understand how the polymer interacts with the colloids in the mixture, you can use that to create a desired crystal."

The researchers created a computer model that simulated the formation of crystals based on principles of thermodynamics, which state that any system will settle into whatever structure requires the least energy. Panagiotopoulos's group analyzed the equilibrium state of different possible crystal shapes to understand how they were affected by the presence of different polymers.

They found that when the crystals formed, tiny amounts of polymer were trapped between the colloids as they came together. It looks like mortar in a stone wall, although the researchers say the polymer has no adhesive property. These polymer-filled spaces, called interstices, play a key role in determining the energy state of a crystal.

"Changing the polymer affects which crystal form is most stable," Mahynski said. "As the crystal forms, the polymer helps set the crystal's shape."

The polymer and the forming crystal work like a lock and key – they fit together in the crystal structure with the lowest energy state. Because of this, scientists can use their knowledge of polymer physics to tailor crystal structures.

Because the researchers conducted their analysis using computer modeling, they cautioned that experimentally reproducing the results in a lab presents some difficult challenges. One early concern involved the uniformity of colloids in the suspension; models often assume colloids are all the same shape and size but this rarely occurs in natural systems. Anticipating this, the researchers tested their theory using a non-uniform solution.

"One of the things we did in our study was to look at realistic systems, that were realizable in the lab, and it appears that the phenomenon that we describe is robust," said Sanat Kumar, a professor and chair of chemical engineering at Columbia and a researcher on the project. "That tells us that there is no conceptual problem to realizing this in the lab."

Gravity could also pose a problem for experimenters, although Kumar pointed out that similar experiments have overcome this difficulty. Gravity causes crystals to filter to the bottom of a container and pack in mismatched layers. This can make it very difficult, and perhaps impractical, to try to produce the crystals by using a colloid mix in a tank.

But Mahynski said there are several techniques that could avoid problems. For example, to deal with gravity, researchers could create the crystals in a very thin film. That approach should avoid the disruption of gravity pulling the crystals to the bottom.

It also could be important to select the right size of colloid and type of polymer for a successful experimental result. Panagiotopoulos said that one possible path for these ideas to be experimentally verified will be to use polymer chains that are stiff, such as double-stranded DNA, together with micrometer-sized colloids.

###

Besides Panagiotopoulos, Kumar and Mahynski, the paper's authors also included Dong Meng, a postdoctoral researcher at Columbia. Support for the project was provided in part by the National Science Foundation.

John Sullivan | Eurek Alert!
Further information:
http://www.princeton.edu/main/

More articles from Materials Sciences:

nachricht New design improves performance of flexible wearable electronics
23.06.2017 | North Carolina State University

nachricht Plant inspiration could lead to flexible electronics
22.06.2017 | American Chemical Society

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Can we see monkeys from space? Emerging technologies to map biodiversity

An international team of scientists has proposed a new multi-disciplinary approach in which an array of new technologies will allow us to map biodiversity and the risks that wildlife is facing at the scale of whole landscapes. The findings are published in Nature Ecology and Evolution. This international research is led by the Kunming Institute of Zoology from China, University of East Anglia, University of Leicester and the Leibniz Institute for Zoo and Wildlife Research.

Using a combination of satellite and ground data, the team proposes that it is now possible to map biodiversity with an accuracy that has not been previously...

Im Focus: Climate satellite: Tracking methane with robust laser technology

Heatwaves in the Arctic, longer periods of vegetation in Europe, severe floods in West Africa – starting in 2021, scientists want to explore the emissions of the greenhouse gas methane with the German-French satellite MERLIN. This is made possible by a new robust laser system of the Fraunhofer Institute for Laser Technology ILT in Aachen, which achieves unprecedented measurement accuracy.

Methane is primarily the result of the decomposition of organic matter. The gas has a 25 times greater warming potential than carbon dioxide, but is not as...

Im Focus: How protons move through a fuel cell

Hydrogen is regarded as the energy source of the future: It is produced with solar power and can be used to generate heat and electricity in fuel cells. Empa researchers have now succeeded in decoding the movement of hydrogen ions in crystals – a key step towards more efficient energy conversion in the hydrogen industry of tomorrow.

As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton...

Im Focus: A unique data centre for cosmological simulations

Scientists from the Excellence Cluster Universe at the Ludwig-Maximilians-Universität Munich have establised "Cosmowebportal", a unique data centre for cosmological simulations located at the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences. The complete results of a series of large hydrodynamical cosmological simulations are available, with data volumes typically exceeding several hundred terabytes. Scientists worldwide can interactively explore these complex simulations via a web interface and directly access the results.

With current telescopes, scientists can observe our Universe’s galaxies and galaxy clusters and their distribution along an invisible cosmic web. From the...

Im Focus: Scientists develop molecular thermometer for contactless measurement using infrared light

Temperature measurements possible even on the smallest scale / Molecular ruby for use in material sciences, biology, and medicine

Chemists at Johannes Gutenberg University Mainz (JGU) in cooperation with researchers of the German Federal Institute for Materials Research and Testing (BAM)...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Plants are networkers

19.06.2017 | Event News

Digital Survival Training for Executives

13.06.2017 | Event News

Global Learning Council Summit 2017

13.06.2017 | Event News

 
Latest News

Quantum thermometer or optical refrigerator?

23.06.2017 | Physics and Astronomy

A 100-year-old physics problem has been solved at EPFL

23.06.2017 | Physics and Astronomy

Equipping form with function

23.06.2017 | Information Technology

VideoLinks
B2B-VideoLinks
More VideoLinks >>>