The researchers at New York University have pioneered an innovative technique named “Crystal Clear” that enables the visualization of crystal structures using transparent particles, microscopes, and lasers. This cutting-edge method allows scientists to gain X-ray vision-like insight into crystals, enabling them to observe individual units within the crystal and generate dynamic three-dimensional models.
“This is a powerful platform for studying crystals,” says Stefano Sacanna, professor of chemistry at NYU and the principal investigator for the study. “Previously, if you looked at a colloidal crystal through a microscope, you could only get a sense of its shape and structure of the surface. But we can now see inside and know the position of every unit in the structure.”
Atomic crystals are remarkable materials with a precise and repetitive arrangement of building blocks. Occasionally, defects such as missing or misplaced atoms can occur, influencing the properties of the crystalline materials, from table salt to diamonds.
In the study of crystals, researchers like Sacanna are exploring structures made of colloidal particles, which are tiny spheres much larger than atoms. These particles, typically around a micrometer in diameter, offer researchers a visible and accessible way to investigate crystal formations.
In their continuous efforts to comprehend the formation of colloidal crystals, the researchers, led by Shihao Zang, a PhD student in Sacanna’s lab and the study’s primary author, realized the necessity of gaining insight into these structures. The team, which included researchers from various disciplines, embarked on developing a method to visualize the constituents inside a crystal, a task that required expertise in chemistry, materials science, and crystallography.
They initially devised transparent colloidal particles and introduced dye molecules for labeling, enabling each particle to be distinguishable under a microscope using their fluorescence.
A microscope alone would not suffice for observing the interior of a crystal, so the researchers turned to confocal microscopy, an imaging technique that employs a laser beam to scan through the material and produce targeted fluorescence from the dye molecules.
This technique reveals each two-dimensional plane of a crystal, which can then be stacked to create a three-dimensional digital model for identifying the location of each particle. These models can be manipulated to gain different perspectives and dissected to examine the interior of the crystals and identify any defects.
One of the experiments involved the use of an advanced imaging method to study crystals that form when two identical crystals grow together, a phenomenon known as “twinning.” By examining models of crystals with structures akin to table salt or a copper and gold alloy, researchers were able to observe the shared plane of the joined crystals, a defect that contributes to the formation of these distinct shapes. This shared plane provided insight into the molecular basis of twinning.
Using this new technique, scientists can now observe crystals undergoing changes, such as melting, to understand how particles rearrange and whether defects move. In an experiment involving the melting of a crystal with the structure of cesium chloride, researchers discovered that defects remained stable instead of moving as expected. This finding, made possible by the ‘Crystal Clear’ technique, challenges previous assumptions about crystal behavior and opens up new avenues for research in crystal dynamics and phase transitions.
To verify their findings, the team conducted computer simulations, which confirmed that their “Crystal Clear” method accurately represents the internal behaviors of crystals.
“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,” jokes Glen Hocky, assistant professor of chemistry at NYU, and the study’s co-corresponding author.
With the development of a method for visualizing the internal structure of crystals, scientists are on the brink of unlocking valuable insights into their chemical history and formation process. This breakthrough not only holds the potential for enhancing crystal quality but also for innovating photonic materials capable of advanced light interactions, paving the way for exciting advancements in crystallography.
“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,” adds Sacanna.
Journal reference:
- Shihao Zang, Adam W. Hauser, Sanjib Paul, Glen M. Hocky & Stefano Sacanna. Enabling three-dimensional real-space analysis of ionic colloidal crystallization. Nature Materials, 2024; DOI: 10.1038/s41563-024-01917-w