NYC Gazette

A team of New York University researchers has developed a new technique to visualize the internal structure of crystals, akin to having X-ray vision. This method, named “Crystal Clear,” employs transparent particles and microscopes with lasers, enabling scientists to see each unit within the crystal and create dynamic three-dimensional models.

“This is a powerful platform for studying crystals,” stated Stefano Sacanna, professor of chemistry at NYU and principal investigator for the study published in Nature Materials. “Previously, if you looked at a colloidal crystal through a microscope, you could only get a sense of its shape and structure on the surface. But we can now see inside and know the position of every unit in the structure.”

Atomic crystals are solid materials whose building blocks are arranged in an orderly fashion. Occasionally, an atom may be missing or out of place, resulting in defects that influence the properties of crystalline materials—from table salt to diamonds.

To study these structures, many scientists use colloidal particles instead of atoms due to their larger size, making them easier to observe under a microscope. In their quest to understand how colloidal crystals form, Sacanna’s team recognized the need for visualizing internal structures. Led by PhD student Shihao Zang, they developed transparent colloidal particles labeled with dye molecules distinguishable under fluorescence microscopy.

The researchers utilized confocal microscopy—a technique employing laser beams that scan through material—to produce targeted fluorescence from dye molecules within each particle. This process reveals two-dimensional planes of a crystal that can be stacked into three-dimensional digital models. These models allow scientists to rotate, slice apart, and examine defects within crystals.

In experiments on twinning—a phenomenon where two identical types of crystals grow together—the researchers used this imaging method on structures equivalent to table salt or copper-gold alloys. They observed shared planes between adjoined crystals revealing molecular origins of twinning.

Additionally, this technique enables visualization of dynamic changes in crystals. For instance, when melting cesium chloride crystals during an experiment, they found that defects remained stable rather than moving as anticipated.

To validate their findings on static and dynamic crystals, computer simulations were conducted confirming that the “Crystal Clear” method accurately captured internal structures.

“In a sense we’re trying to put our own simulations out of business with this experiment—if you can see inside the crystal you may not need simulations anymore,” joked Glen Hocky assistant professor at NYU’s Simons Center for Computational Physical Chemistry and co-corresponding author.

This visualization method allows scientists greater insight into crystallization processes potentially optimizing crystal growth design paving way for developing better photonic materials interacting with light.

“Being able to see inside crystals gives us greater insight into how crystallization works which could help optimize growing processes by design,” added Sacanna.

Additional authors include Adam Hauser Sanjib Paul from NYU supported by US Army Research Office (award number W911NF-21-1-0011) National Institute Health (R35GM138312) utilizing NYU IT High Performance Computing resources including those supported by Simons Center Computational Physical Chemistry (grant number 839534).