For a long time, one of the key defining factors of glasses has been their molecular randomness; but when a team at the University of Chicago, led by Professor Juan de Pablo, were analyzing a glass that they had grown in their lab they saw unusual peaks in “what should have been featureless optical data.” Initially they thought the peaks the result of an error in their calculations, but instead the team found that the particular technique they had used to make the glass had enabled them to control the organization of the molecules. It might sound like a small thing, but the capacity to tune the orientation of molecules in glass, which improves the density and thermal stability of the material, could be a breakthrough to improving organic electronic devices, such as LEDs and solar cells.
As the University of Chicago described in a statement, the scientists “grew the glass by vaporizing large organic molecules in a high vacuum and depositing them slowly, thin layer by thin layer, onto a substrate at a precisely controlled temperature [a process known as vapor deposition].” They then examined the resulting material using spectroscopic ellipsometry, and found that a significant portion of the molecules in the glass were “aligning themselves in concert.”
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They discovered that the reason for this alignment lay in the precise way they were creating the glass. As the glass was created through a process of vapor deposition, placing one layer over another, the molecules of each thin layer were getting trapped in the orientation that they had in relation to molecules in air. As this process was repeated, so too was the alignment of the molecules in the glass. Once the deposition process was complete, the material—and the molecules in it—is stable, and forms a molecularly ordered glass. Something that has never been seen before.
De Pablo explained “Glasses are one of the least understood classes of materials… They have the structure of a liquid—disorder—but they’re solids. And that’s a concept that has mystified people for many decades. So the fact that we can now control the orientation of these disordered materials is something that could have profound theoretical and technological implications. We don’t know what they are yet—this is a new field of research and a class of materials that didn’t exist before. So we’re just at the beginning.”
But, what the team are confident of is that this discovery could yield significant advances in organic electronic devices. With the capacity to tune and orient molecules within organic glass, then it will be possible to make more durable, efficient electronics that utilize this glass. OLEDs and solar cells are two of the most notable examples of commercial electronics that could benefit. As U-W Madison Professor Mark Ediger, who collaborated in the research said: “We’re thinking about the next generation of photovoltaics… That technology is commercially immature and improved control over material properties could have a big impact.”
+ Tunable molecular orientation and elevated thermal stability of vapor-deposited organic semiconductors
Via Physorg
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