Europe Materials Collaboration Atomic Structure of Nanosize crystalline grains in diamond-SiC compsites Award Num: Intellectual Merit The primary origin of unique properties of nanomaterials is that atoms forming grain surface have different environment and structure than the atoms constituting the grain interior. It has a pronounced effect on the overall properties of the materials. Since those properties are strongly dependent on the material structure, a meaningful investigation of nanocrystals requires knowledge of their specific atomic configuration. Due to a small size of the crystals and their complex structure, application of standard procedures of analysis of x-ray diffraction data is not adequate. We have developed a unique method of elaboration of diffraction data of nanocrystals. One of the important nanomaterials is nano-diamond, particularly in view of its applications in nanocomposites. Properties of nanoceramics depend strongly on fabrication conditions, and the key to an effective control of the process is a good understanding of the underlying physical processes occurring both at the surface of the grain, as well as in the grain interior. These processes, in turn, depend critically on the specific structure of the surface of diamond nanograins. Determination of this structure and its change under different processing conditions enables understanding and effective modification of the process. Our studies on the structure of 5 nm in diameter diamond led to a model shown in the attached figure: The grain core has a structure similar to a perfect diamond lattice. However, the structure contains about 8% of hexagonal layers, which means that the lattice, although it still maintains closed-packed structure has trigonal, not cubic symmetry. The lattice is under tensile strain, and its magnitude depends on the history of the preparation technique. After annealing the powder at 1200°C the core is compressed with the apparent stress of GPa. The grain core is surrounded by a surface shell, about 0.3 nm thick, which is compressed by about 3% relative to the relaxed diamond lattice.

Europe Materials Collaboration Atomic Structure of Nanosize crystalline grains in diamond-SiC compsites Award Num:

Broader Impact : To date this project has involved five PhD and three undergraduate students, plus one REU student. The students took part in the Students Research Symposium organized by our college, an initiative now extended to all university colleges and departments. Next month, students participating in this project will make presentations at local high schools. International exchange of students was an important aspect of the program and allowed one of our graduate students, Stephen Nauyoks, to conduct extensive research on structure of nanosize diamond and silicon carbide in Budapest and Warsaw. Levente Balogh, a PhD student from Budapest, is now learning high pressure techniques at TCU. Efforts to attract minority students were successful and now three female and one Hispanic students study structure and properties of diamond-silicon carbide composites. Including nanosize diamond in the manufacturing protocol has lead to improvement in mechanical properties of low cost diamond-silicon carbide composites.