The Wisconsin MRSEC is developing an ultrafast direct electron camera for use on a scanning transmission electron microscope (STEM) in its Shared Instrument Facilities. One application of the camera will be experiments to map strains – tiny variations in the distance between atoms – inside materials caused by defects in the crystal lattice or interfaces between two different materials. The MRSEC acquired an existing, slower camera to support technique development before the new camera arrives. An example strain map is shown to the right. The gray-scale image is a small Nb particle formed inside a larger Zr crystal. The color image shows the rotation of the Zr lattice caused by the interface between the two materials. Higher sensitivity maps covering larger areas with more points will be possible with the new camera.
Bacteria communicate via molecular signals that they produce in high concentrations. Bacterial communication promotes the formation of biofilms that can be harmful to humans and costly to industry. We have shown that collections of individual bacterial signaling molecules interact in water to form soft materials (“self-assemble”) with spherical, layered, or cylindrical structures. Simulation images showing the formation of a spherical structure (“micelle”) are shown with corresponding experimental images.
Heusler compounds are promising materials for next generation devices for direct conversion of heat to electricity (thermoelectricity) and for magnetic computer memory. Performance in these applications depends sensitively on the arrangement of the atoms and the behavior of electrons, both of which are hard to predict and harder to control for Heuslers. We have grown thin films of FeVSb, a new Heusler compound, using molecular beam epitaxy, a kind of spray painting with “cans” of different atoms. The top picture is an electron microscope image showing the arrangement of the Fe, V, and Sb as different size dots. On the right, the image shows the material we want, FeVSb. On the left, there is a completely new, unexpected material, Fe2VSb, which is a new kind of magnet.
Not all members of our community have the time or resources to attend science outreach events. To reach some of those people, the Wisconsin MRSEC conducts its engaging, hands-on science activities to a local food pantry. Customers can wait up to 90 minutes at the food pantry, providing ample time for educational activities for kids, their parents, and other curious adult visitors. By bringing science and engineering activities to the food pantry, the Wisconsin MRSEC forms connections with and helps inspire a new, diverse audience composed entirely of economically disadvantaged members of the community.
During the Wisconsin Science Festival, a statewide event that reaches over 30,000 people, the Wisconsin MRSEC developed an improvised science program held on a trolley that shuttled passengers between 27 science activities around Madison’s Capitol Square. On the trolley, an all-female team interviewed eight early career researchers about their research and lives to enable the ever-changing trolley audience to learn about the scientists and their science as well as ask their own questions of the researchers. More than 150 people rode the trolley and learned about scientific research during their journey. The event was an excellent professional development opportunity in science communication for the researchers and was covered by the Wisconsin State Journal.
Oxide compounds with multiple metal atoms are called complex oxides because they can have many chemical states, crystal structures, and a wide range of useful properties. Wisconsin MRSEC researchers have developed a new way to create crystals of an important series of oxides for quantum electronics, involving the lanthanide row of elements on the periodic table. The MRSEC team deposited lanthanide oxide films using a method called atomic layer deposition, using chemical precursors they developed. The resulting films are amorphous, with a disordered atomic structure, but heating them in contact with the surface of a substrate widely employed in oxide research transforms them into crystals templated by the substrate. This work required interdisciplinary collaboration among chemists, chemical engineers, and materials scientists, brought together by the MRSEC.
Small (nanometer-sized) crystals of multi-component, complex metal oxides have useful properties for applications in electronics, optics, sensors, and mechanical actuators. In order to realize this potential, engineers need to be able to put tiny crystals exactly where they are needed and to control the orientation of the crystal’s lattice. Researchers at the Wisconsin MRSEC and Argonne National Lab have studied a new way to place tiny oxide crystals through controlled, seeded crystallization of disordered, amorphous thin films. They have demonstrated controlled crystal growth at desired locations either from seeds of the same material (homoepitaxy) or seeds of a different material (heteroepitaxy). This work is an important step toward general control of oxide crystals and new applications.
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.