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The microstructure of SnO& prepared by the sol-gel method, was studied by scanning electron microscopy, transmission electron microscopy, high-resolution electron microscopy, and x-ray difFraction. A nanosponge structure was observed. There is much surface and interface structure. The interfaces vary in type from amorphous to crystalline. The high-density of defects greatly influences the physical and chemical properties of this material.

The three-dimensional computerized ionospheric tomography (3DCIT) technique is used to reconstruct the spatial distribution of storm-enhanced density (SED) based on the global positioning system total electron content measurements over the North American area during the 17 March 2013 storm. The reconstruction results are carefully validated with observations from three ionosonde stations, the constellation observing system for meteorology, ionosphere, and climate (COSMIC) radio occultations, and the Millstone Hill incoherent scatter radar. The electron density profiles from the 3DCIT reconstruction show a good agreement with the ionosonde and COSMIC electron density profiles. The 3DCIT-derived electron density difference between the storm day of 17 March and the quiet day of 16 March also captures the similar SED plume signature that was observed by the Millstone Hill incoherent scatter radar. The 3DCIT reconstruction allows us for the first time to unveil the 3-D configuration of the SED plume and its spatiotemporal evolution. It was found that the SED plume first appeared around 400 km and then expanded downward to~300 km as well as upward to~500 km over the course of a 3-hr period from 19 to 22 UT on 17 March. Our study also showed that the density enhancement within the SED plume occurred mostly above the storm time F layer peak height.

The atomic and electronic properties of dislocations in III-N semiconductor layers, especially GaN are presented. The atomic structure of the a r edge threading dislocation is now well established with three different cores (8 or full core, 5/7 or open core and 4 atom ring). The use of atomistic simulations has confirmed these atomic structures and has given a good understanding of the electronic structure of the screw dislocation. Partial dislocations which are mostly confined in the area close to the substrate are now also being investigated. It is becoming clear that the electrical activity of all these defects is dependent on the layer quality, which is governed by the growth conditions.