Contrast analysis of Shockley partial dislocations in 4H-SiC observed by synchrotron Berg–Barrett X-ray topography

Shockley partial dislocations in 4H-SiC were observed using monochromatic synchrotron X-ray topography with a grazing-incidence Bragg-case geometry, that is, Berg–Barrett topography. The contrast of partial dislocations at the edges of Shockley-type stacking faults is discussed in terms of whether they have C- or Si-core edge components, or screw components. The dissociated state of basal-plane dislocation is discussed on a basis of the stacking sequence for basal-planes in the 4H-SiC crystal structure. It is expected that the results obtained in this study will be useful for characterizing Shockley-type stacking faults in Berg–Barrett topography.     

Properties and Phenomena: Basic Plasma Physics and Fusion Research in Postwar America

I review the changing conceptions of basic physics that the U.S. plasma-physics community put forward in postwar America. I give special attention to the tense relationship between fusion research and the more general study of plasmas in astrophysics, space science, and industry.Although fusion research often led to results that were regarded as basic plasma physics, its dominating influence tended to weaken other plasma work, as becomes evident when I compare the public statements and professional fortunes of plasma scientists during the 1960s, when fusion research experienced a downturn, with those of the 1970s, when fusion research flourished. I also show that the plasmaphysics community’s conceptions of basic physics were not highly regarded or easily understood by science administrators and the general physics community. To make this point, I contrast two general ideas of basic physics: the Big Questions conception and the Properties and Phenomena conception. Gary J.Weisel; Gary J.Weisel is Associate Professor of Physics at Penn State Altoona in Altoona, Pennsylvania. His historical research focuses on the development of subdisciplines in twentieth-century physics. He also carries out research in nuclear physics and materials science.