Amorphous Fe-Zr Alms of the same average Fe and Zr concentration of 50 at. %made by cosputtering as well as by solid-state reaction of multilayershave been compared by x-ray anomalous scattering experiments, magnetization measurements at low temperature, and transmission electron microscopy. After preparation the samples are notably different. However, annealing at temperatures between 350 and 450'C results in the same phase separation of the amorphous state.
Nanowire (NW) structures are being extensively investigated as components for energy devices such as solar cells [1] and batteries [2]. The large aspect ratio of NWs makes them ideal candidates for maximizing surface reactions, minimizing carrier transport distances, fabricating semi-transparent contact layers, and other device optimization pathways. Although methods for growing NWs are well established, and much current research is focused on device fabrication and characterization, much remains unknown about fundamental aspects of the nucleation and growth mechanisms, and the effect of such parameters as different substrates and catalysts. The work presented here focuses on the growth and microstructure of Ge and PbSe NWs. Ge NWs, while not a prime candidate for single-component solar cells, offer interesting opportunities for lattice matching in multijunction devices and as templates for novel architectures. Epitaxial Ge NWs are readily grown at low temperatures on Si substrates [3], so are easily integrated into current fabrication processes. PbSe is of interest for multi-exciton generation (MEG) devices and solar cells with PbSe quantum dots have been demonstrated. However, NWs provide a better morphology for building connected structures.Epitaxial Ge NWs grow vertically on (111) Ge or Si substrates, with Au nanoparticles acting as a catalyst [3]. However the NW yield and size distribution is consistently better on Ge than on Si. We have found that using porous Si as the substrate also improves the yield and uniformity; SIMS and EDS data show Ge and Au diffusion into the porous substrate (Fig.1). Cross-section TEM indicates that formation of the ternary eutectic phase at the substrate competes with binary phase melting at the Au surface, leading to embedded rather than vertical NWs (Fig.2). Porous Si diminishes this effect by diverting the ternary phase into the pores. Concomitantly, the greatly enhanced surface area provided by the pores (estimated as 900X) prevents Au nanoparticle coarsening and breakup, also leading to improved NW yield and uniformity.We observe both VLS (vapor-liquid-solid) and dislocation-mediated growth in PbSe NWs synthesized during the same processing run [4]. PbSe has a rocksalt structure and the NWs grow in the [001] direction, exhibiting secondary branching in the [100/010] directions as catalysts redeposit on the NW. Some of the NWs propagate via a screw dislocation down the center of the wire, exhibiting chiral structures observed in SEM as a rotating branch structure (Fig. 3.) Two-beam imaging confirms that the dislocation has pure screw character. The chirality is caused by the elastic strain of the axial screw dislocation, which produces a corresponding Eshelby Twist.
Studies of the many authentically dated specimens of ancient glass in museums and private collections have enabled investigators interested in the origin and progress of glass manufacture to reach some tentative conclusions on the succession of glass-forming processes. There is, however, a dearth of information on the chemical compositions of ancient glassware or the raw materials used by early glass workers. R. Campbell Thompson in " The Chemistry of the Ancient Assyrians" (published in a limited edition in 1925) offered a careful translation of certain seventh century B.C. Assyrian cuneiform tablets dealing with glass compositions and melting technic. This work is reviewed and used as the basis of an estimate of the chemical knowledge of the Assyrian glass workers.
Laboratory testing was done to determine the dispersive characteristics of typical clay soils from two sites near Houston, Texas. The tests included (a) the crumb test, (b) the Soil Conservation Service Laboratory Dispersion Test, (c) chemical analysis of pore water, and (d) the pinhole test. The soils tested consisted of inorganic clay of low to medium plasticity (CL) and inorganic clay of high plasticity (CH) with plastic limits varying from 12 to 32, liquid limits varying from 26 to 99, and activity ratios of 0.7 to 1.3. With a few exceptions, each of the four types of tests showed good reproducibility. The pinhole test results were not affected by variations in compaction moisture content, from three points dry to three points wet of the plastic limit. The four types of tests were found to be in excellent agreement for nondispersive clays. Of the tests judged as dispersive on the basis of sodium content or percent dispersion from the SCS test or both, surprisingly few were dispersive in the pinhole test.
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