Direct visualization of nanoscale structural domains in complex sulfide glasses Sabyasachi Sen (University of California at Davis), DMR The existence and nature of structural order at the intermediate length scale (~1 nm) has remained controversial and poorly understood in complex chalcogenide glasses. Using a combination of diffraction and simulation techniques, Prof. Sabyasachi Sen and graduate student Sezen Soyer-Uzun have recently observed the existence of arsenic-rich nanoscale structural domains, with correlation lengths of ~2 nm, in complex, moderately sulfur-deficient Ge-As sulfide glasses. These domains result from violation of chemical order, give rise to strong density and compositional fluctuations, and disappear on increasing or decreasing the sulfur content of these glasses. Such clustering of arsenic atoms have important implications in understanding and predicting the compositional dependence of a wide variety of physical and thermodynamic properties of these glasses. Fig. 1. Clockwise from left: Atomic structure of Ge x As x S 1-2x glasses with x = 18.2, 25 and 33.3, as obtained from RMC simulation of Neutron and x-ray diffraction data. Ge, As and S atoms are denoted by Green, purple and yellow, respectively. Simulation box size ~3.6 nm, ~1800 atoms. Note the nanoclusters of As atoms In the glass with x=25 (top right). Ge and As atoms are homogeneously distributed in glasses with x = 18.2 and 33.3.

Direct visualization of nanoscale structural domains in complex sulfide glasses Sabyasachi Sen (University of California at Davis), DMR Strong impacts have been made in several areas this year. Some of the notable ones are listed below: Education: The PI has developed a graduate course (EMS 282) titled “Glass: Science and Technology” that has been offered in Spring, 2008 for the first time. Students from Materials Science, Chemistry, Applied Science and Chemical Engineering have taken the course and it was very well received. International Collaboration: Graduate student Erica Gjersing has spent this summer at Tohuku University in Sendai, Japan to work with Prof. Hideki Maekawa on ultra high-field NMR of chalcogenide glasses (see photo). We hope this visit will initiate a very fruitful collaboration between our research groups. Industrial Collaboration: We have maintained our strong tie with the glass research division of Corning Inc., one of the nation’s leading glass companies. Erica has visited their research lab at Corning, NY, in February, 2008 and have worked with Drs. B.G. Aitken and R.E. Youngman on chalcogenide glasses. Symposium organization: The PI has co-organized (with Dr. Lothar Wondraczek, University of Erlangen, Germany) an international symposium titled “Glass and Entropy” at the European Glass Congress that was held in June, 2008 at Trencin, Slovakia. The symposium was a success and was attended by more than 50 participants from all over the world. Prof. Hideki Maekawa and graduate student Erica Gjersing (first and second from left, respectively) standing in front of one of the world’s most powerful NMR magnets in Tsukuba, Japan.