Scientists have developed a groundbreaking technique called “Crystal Clear” that allows them to see inside crystals. This new method uses transparent particles, microscopes, and lasers to create 3D models of the crystals. This is a powerful platform for studying crystals,” said Stefano Sacanna, the study’s principal investigator and a professor at New York University.
Crystals are solid materials made up of atoms arranged in a repeating pattern. Sometimes, an atom is missing or out of place, causing a defect. The arrangement of atoms and defects determines the properties of different crystals, from table salt to diamonds.
Many scientists, including Sacanna, study crystals made of tiny spheres called colloidal particles instead of atoms. These particles are around a micrometer in size, which is much larger than atoms. This makes them easier to see under a microscope.
The researchers created transparent colloidal particles and labeled them with dye molecules. This allowed each particle to be seen under a microscope based on its fluorescence. The team also used confocal microscopy to look inside a crystal.
This imaging method uses a laser beam to scan through the material, making the dye molecules fluoresce. This shows each 2D plane of a crystal, which can be stacked to create a 3D digital model. The model shows the position of each particle.
The models can be rotated, cut, and taken apart to study the crystals and find defects. The researchers used this technology to study crystals formed when two of the same type of crystal grow together, a process called twinning.
Visualizing crystal interiors in 3D
When they looked inside models of crystals with structures like table salt or a copper-gold alloy, they found the common plane where the crystals joined. This defect showed how twinning happens at the molecular level. The new technology also lets scientists see crystals as they change.
For example, they can watch what happens when crystals melt. Do the particles rearrange? Do defects move?
In one experiment, the researchers melted a crystal with the structure of cesium chloride. They were surprised to see that the defects stayed in place and did not move as expected. The researchers also used computer simulations to build crystals with the same properties.
This confirmed their “Crystal Clear” approach accurately captured what is inside crystals. “In a sense, we are trying to put our own simulations out of business with this experiment,” said Glen Hocky, a study co-author and a faculty member at NYU. “If you can see inside the crystal, you may not need simulations anymore.”
Now that scientists can see crystals inside, they can better study their formation and chemical history.
This could lead to better crystals and materials that interact with light in new ways. “Being able to see inside crystals gives us greater insight into how the crystallization process works and can perhaps help us to optimize the process of growing crystals by design,” Sacanna said. The study was published in the journal Nature Materials.
The authors include Shihao Zang, Adam Hauser, and Sanjib Paul of NYU. The US Army Research Office funded the research with additional support from the National Institutes of Health. It used NYU’s high-performance computing resources, including those supported by the Simons Center for Computational Physical Chemistry at NYU.
