Using physical vapor deposition, researchers produced glassy films that are smooth and uniform, but which also have the molecules aligned with one another and organized in layers. This added structure could make the glass more efficient for conductors and expand the range of materials that can be used in future organic electronics. The colorful images in the figure show measurements using synchrotron x-rays that contrast the disordered starting material and the ordered glass.
IRG 1 showed how the atoms around the defects can restrict their ability to jump between configurations and how defects can talk to each other via sound waves. Both phenomena keep the defects from interfering with sound waves allowing the waves to travel long distances.
Camille Bishop, a 5th-year graduate student working in Mark Ediger’s group as part of the MRSEC IRG 1, presented her work on liquid crystal-like order in vapor-deposited glasses at the Gordon Conference on Liquid Crystals in New London, NH that took place from July 7th-12th, 2019. The conference brings together researchers in a diverse range of disciplines involving liquid crystal science and technology.
Many kinds of materials, including thin films, are created by adding atoms or molecules to a surface. As a result, understanding how molecules move along a surface is an important part of making new materials. In general, diffusion and crystal growth are much faster on the surface of glasses than in the interior. How much faster depends on how big the molecules are, and how many hydrogen bonds the surface molecule has to the bulk, as MRSEC researchers have recently discovered. This model works for many different molecules, giving a quick and easy way to predict surface motion and guide the synthesis of new materials.
Creating glassy thin films of organic molecules at different temperatures changes both their stability in the glassy state – their density, and how hard they are to melt – and it changes how the molecules in the films are arranged – whether they tend to lie down flat on the surface or stand straight up. Wisconsin MRSEC researchers have shown that these changes in stability and average molecular orientation also change the mechanical properties of the film, including how stiff it is and how hard it is.
Graduate students from IRG1 of the Wisconsin MRSEC used MRSEC-developed educational materials in two Wisconsin outreach programs: Pre-college Enrichment Opportunity Program for Learning Excellence (PEOPLE) and Science Expeditions. These programs provide experiences that help students become
scientifically literate citizens and explore careers in science and engineering. The PEOPLE program has a proven record of increasing the rate at which minority and low-income high school students matriculate to colleges and universities.
Glasses are usually isotropic, with the molecules oriented in all directions, but anisotropic glasses with a preferred molecular orientation are better for
applications such as organic electronics. Liquid crystals (LCs) can have strong preferred orientation, but it has not been possible previously to take full advantage of that order in solid, glassy materials.
One of the main drawbacks of metallic glasses is their low thermodynamic stability, which limits their formability and service life. Recently, experiments by
members of the Wisconsin MRSEC showed that organic glasses with high thermodynamic stability can be synthesized via physical vapor deposition (PVD)
onto a substrate at a controlled temperature. Now, this team of researchers has used molecular dynamics simulations to predict that the same PVD methods can enhance the stability of metallic glasses.