We present a magnetic force microscopy @IF&i) analysis of arrays of submicron-scale Co dots fabricated by interference lithography. The dots are thin (I%--300 A) and elliptical in shape. MFiM reveals that these structures relax into highly ordered remanent states whose symmetry and configuration are governed by their shape anisotropy. In particular, when the dots are saturated alon g their long-axis, a uniformly magnetized state persists at remanence. However, when the dots are saturated along their short-axis, they relax into a single-vortex state in which the circulation can have either sign. Both states are characterized by smoothly varying magnetization patterns and a high degree of uniformity across the array. We attribute the ordered behavior of these.structures to the film microstructure, which allows the shape anisotropy to dominate over magnetocrystalline anjsotropy. By imaging a series of minor-loop remanent states, we show that magnetization reversal in these structures occurs via the nucleation and annihilation of a single vortex. Magnetic hysteresis loop measurements are consistent with these observations and provide additional details. Furthexnore. we present the results ofmicromagneticsimulations.which are in excellent agreement with both the klFiL1 images and the hysteresis loop measurements. G
Neutron radiography has been in use as a nondestructive testing technique for the past fifty years. The neutrons' unique ability to image certain elements and isotopes that are either completely undetectable or poorly detected by other NDI methods makes neutron radiography an important tool for the NDI community. Neutron radiography like other imaging techniques takes a number of different forms (i.e., film, radioscopic, transfer methods, tomography, etc.) This paper will describe the neutron tomography system developed at the University of California, Davis McClellan Nuclear Radiation Center (UC Davis/MNRC), and the applications for both research and commercial uses.The neutron radiography system at the UC Davis/MNRC has been under development for four years. The initial system was developed to find very low concentrations of hydrogen (i.e., < 200 ppm). In order to achieve these low detection levels, it was necessary to perform both pre-and post-processing of the tomographs.The pre-processing steps include corrections for spatial resolution and random noise effects. Images are corrected for systematic noise errors and beam hardening. From these data the attenuation coefficient is calculated.The post-processing steps include alignment of the collected images, determining the center of mass, and, finally, using the filtered back-projection routine from the Donner Algorithms Library to obtain the final images.Since its initial development, the tomography system has been used very successfully to find low levels of hydrogen in a metal matrix. Further uses of the system have been to verify the exact placement, in three dimensions, of "O -rings" in large metal valve bodies, and to map the location and extent of veins in porous and high-density rocks of various different kinds.These examples show that neutron tomography is becoming a needed inspection technique for the 21 st century.
Advances in microelectronics technology strongly depend on the thermal optimization of metal/ dielectric interfaces, which requires precise modeling and thermal characterization of metal/ dielectric structures. This work experimentally investigated the influence of metallic layers on the thermal boundary resistance of silicon nitride dielectric material. The results reveal that the thermal boundary resistance of silicon nitride thin films depends on the metallic layers. The thermal boundary resistance at the interface between Au and SiN x is larger than that between Co 0.9 Fe 0.1 and SiN x . The reasons to cause this difference are discussed with phonon transmission probability and the ratio of the Debye temperature between metals and dielectrics. V C 2012 American Institute of Physics. [http://dx.
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