Credit: CC0 Public DomainA new liquid that is thinly deposited in thin films has been described in the Proceedings of the National Academy of Sciences. This creates a high density glass. Researchers at Penn's Department of Chemistry demonstrated that these glasses, and similar materials, can be made denser and more durable, which provides a framework for the development of new applications and devices.The process of creating glass is usually solidification or the loss of equilibrium of liquids when they are cooled to temperatures that stop their motion. Although the structure of glass is very similar to that of liquid, its properties are more like solids.OLED displays and optical fibres are common applications for glasses made from ultrathin films at nanometer scale. These glasses can behave more like liquids at low temperatures, so they are susceptible to crystallization or droplet formation. This limits the possible size of the most tiny features.Researchers have found a way to make glass that is more durable than cooling liquids. Vapor deposition is a method by which a material can be transformed directly from a gas to a solid. Although this technique has enabled researchers to create denser bulk glasses, initially it was thought that thin glass films created using this method would still exhibit liquid-like properties which could lead to instability and degradation.Yi Jin, a Ph.D. student who worked in Zahra Fakharaai's lab, conducted experiments that proved otherwise. Fakhraai says that Yi kept finding different properties. None of the data made sense so we continued digging until we had enough data.Jin spent many years performing detailed experiments. These included changing the properties of glass, deposition rates, and substrates, as well as cleaning all equipment to eliminate contamination.After conducting all the necessary control experiments, the researchers were shocked to discover that vapor deposition could be used to access a different type liquid. This liquid would undergo a phase change to the bulk liquid after heating. Phase transition refers to the process by which a material moves from one state (gases, liquids, or solids) to another. The two liquids are similar to graphene or diamond, which are solids made from carbon, but have very distinct structures.Fakhraai says, "There are many interesting properties that have come out of nowhere. Nobody had expected that thin films would allow you to see these phases." It's a novel type of material.Researchers can make very dense thin-film glass by using vapor deposition. This is due to the packing of the new liquid phase with a density much greater than expected without having to apply enormous pressure. These thin films can be thicker than crystal.The researchers obtained detailed structural information from Brookhaven National Laboratory to confirm their findings. The researchers were able to confirm that they had seen a new phase in the glass through this analysis.Based on their data, they believe that access to this phase could be due to the geometry of the glass. This means that this work could also have implications for other materials. Jin says that he is currently working in the materials science field to develop materials that can be scaled down. "What we see in glasses shows that there may be interesting phenomena that arise from other materials like the metallic materials used in semiconductors.Fakhraai's laboratory is already conducting follow-up experiments to find out more about the critical parameters that cause this unique phase transition. To learn more about the newly discovered phenomenon, Fakhraai's lab is studying films during deposition and "zooming-in" on the region of the phase transition. Fakhraai says that this work is crucial in order to gain a better understanding about glasses as a whole. There remains a disconnect between theories which could be used as a predictive platform for the development of new materials for applications.She says, "To package Moderna or Pfizer vaccinations, you need a glass which can go really low in temperature without shattering, and that technology is a shoutout for how well we engineer bulk glass mechanics." We hope that this fundamental understanding will motivate more applications and allow us to develop thin film glasses with similar properties. We can design better thin film glasses if we understand the structure-property relationship in thin films.Continue exploring New insights and discoveries into the glass transition
