MICROSTRUCTURAL AND MICROANALYTICAL CHARACTERIZATION OF PD CLUSTERS IN ORMOCER MATRIX

Noble-metal clusters dispersed in glass matrix are of great interest f or their technological applications such as heterogeneous catalysis, i n the realization of non-linear optical devices, in sensor technology, for absorption control in solar reflecting glasses (IROX(R) coatings) etc. The physical properties of these materials strongly depend on cl uster concentration, size distribution and on their structural and che mical nature. High spatial resolution structural and analytical charac terization techniques are needed to understand the cluster formation m echanism and the physical properties of these materials. In this work, palladium clusters dispersed in ORMOCER matrix via a modified sol-gel process are structurally and chemically characterized by conventional transmission electron microscopy, high-resolution electron microscopy , electron nanodiffraction and X-ray diffractometry, in order to obtai n information on the clusters shape, structure, spatial distribution i n the matrix and chemical nature. Samples heat treated both in inert N -2 atmosphere and in air at 400 degrees C for different times are anal yzed in order to obtain a deeper insight in the formation and structur al evolution of the clusters and in the oxidation process. In fact aft er heat treatment in air, clusters oxidation occurs and a PdO shell su rrounding a core with different structure similar to 1.5 nm in diamete r is formed. Heat treatment in inert N-2 atmosphere does not affect th e clusters shape, structure and distribution.