Imagine a material so thin it’s just one atom thick, yet it exists in a state that’s neither solid nor liquid—something scientists have only dreamed of observing. This mind-bending phenomenon has just been captured for the first time, and it’s rewriting the rules of physics as we know it. But here’s where it gets even more fascinating: the key to this discovery lies in a clever technique dubbed the 'graphene sandwich.'
Researchers from the University of Vienna and the Vienna University of Technology (TU) achieved this breakthrough by sandwiching a single layer of silver iodide crystal between two sheets of graphene. This protective setup prevented the fragile crystal from collapsing during the melting process, allowing scientists to observe it like never before. Using a cutting-edge scanning transmission electron microscope (STEM), they heated the sample to a scorching 1,100 °C and recorded the melting process in real time at the atomic level.
And this is the part most people miss: without the help of artificial intelligence, this discovery would have been impossible. Kimmo Mustonen, the study’s senior author, explains that AI tools like neural networks were essential for tracking the movement of individual atoms. The team trained the AI on massive datasets of simulated atomic behavior before analyzing the thousands of high-resolution images generated by the experiment.
Their findings? Within a narrow temperature range—about 25 °C below silver iodide’s melting point—a mysterious 'hexatic' phase emerged. This intermediate state, confirmed by electron diffraction measurements, suggests that atomically thin materials can exist in a unique, partially ordered form between solid and liquid. But here’s the controversial part: this challenges decades-old theories about how materials melt.
Traditionally, scientists believed the transition from solid to hexatic and then to liquid should be smooth. However, the researchers observed that while the solid-to-hexatic shift was gradual, the hexatic-to-liquid transition was shockingly abrupt—more like ice melting into water. 'This reveals that melting in two-dimensional covalent crystals is far more complex than we ever imagined,' says David Lamprecht, one of the study’s lead authors.
This discovery not only upends long-held theoretical predictions but also opens exciting new avenues for studying materials at the atomic level. 'Kimmo and his team have demonstrated the incredible potential of atomic-resolution microscopy combined with AI,' notes Jani Kotakoski, head of the research group. The study, published in Science (Volume 390), deepens our understanding of two-dimensional melting and highlights the transformative role of advanced microscopy and AI in materials science.
But what does this mean for the future? Could this hexatic phase lead to new types of materials with unprecedented properties? And how might AI continue to reshape our ability to explore the atomic world? Let us know your thoughts in the comments—this is a conversation that’s just getting started.
