Electrical and Structural Characterization of Web Dendrite Crystals

Minority carrier lifetime distributions in silicon web dendrites are measured. Emphasis is placed on measuring areal homogeneity of lifetime, show its dependency on structural defects, and its unique change during hot processing. The internal gettering action of defect layers present in web crystals and their relation to minority carrier lifetime distributions is discussed. Minority carrier lifetime maps of web dendrites obtained before and after high temperature heat treatment are compared to similar maps obtained from 100 mm diameter Czochralski silicon wafers. Such maps indicate similar or superior areal homogeneity of minority carrier lifetime in webs

Electricity from photovoltaic solar cells: Flat-Plate Solar Array Project final Report. Volume III: Silicon sheet: wafers and ribbons

The Flat-Plate Solar Array (FSA) Project, funded by the U.S. Government and managed by the Jet Propulsion Laboratory, was formed in 1975 to develop the module/array technology needed to attain widespread terrestrial use of photovoltaics by 1985. To accomplish this, the FSA Project established and managed an Industry, University, and Federal Government Team to perform the needed research and development. The primary objective of the Silicon Sheet Task of the FSA Project was the development of one or more low-cost technologies for producing silicon sheet suitable for processing into cost-eompetitive solar cells. Silicon sheet refers to high-purity crystalline silicon of size and thickness for fabrication into solar cells. The Task effort began with state-of-the-art sheet technologies and then solicited and supported any new silicon sheet alternatives that had the potential to achieve the Project goals. A total of 48 contracts were awarded that covered work in the areas of ingot growth and casting, wafering, ribbon growth, other sheet technologies, and programs of supportive research. Periodic reviews of each sheet technology were held, assessing the technical progress and the long-range potential. Technologies that failed to achieve their promise, or seemed to have lower probabilities for success in comparison with others, were dropped. A series of workshops was initiated to assess the state of the art, to provide insights into problems remaining to be addressed, and to support technology transfer. The Task made and fostered significant improvements in silicon sheet including processing of both ingot and ribbon technologies. An additional important outcome was the vastly improved understanding of the characteristics associated with high-quality sheet, and the control of the parameters required for higher efficiency solar cells. Although significant sheet cost reductions were made, the technology advancements required to meet the Task cost goals were not achieved. This FSA Final Report (JPL Publication 86-31, 5101-289, DOE/JPL 1012-125, October 1986) is composed of eight volumes, consisting of an Executive Summary and seven technology reports: Volume I: Executive Summary. Volume II: Silicon Material. Volume III: Silicon Sheet: Wafers and Ribbons Volume IV: High-Efficiency Solar Celis. Volume V: Process Development. Volume VI: Engineering Sciences and Reliability. Volume VII: Module Encapsulation. Volume VIII: Project Analysis and Integration. Two supplemental reports included in the final report package are: FSA Project: 10 Years of Progress, JPL Document 400-279. 5101-279, October 1985. Summary of FSA Project Documentation: Abstracts of Published Documents, 1975 to 1986, JPL Publication 82-79 (Revision 1),5101-221, DOE/JPL-1 012-76, September 1986

Deconvoluting Reversal Modes in Exchange Biased Nanodots

Ensemble-averaged exchange bias in arrays of Fe/FeF2 nanodots has been deconvoluted into local, microscopic, bias separately experienced by nanodots going through different reversal modes. The relative fraction of dots in each mode can be modified by exchange bias. Single domain dots exhibit a simple loop shift, while vortex state dots have asymmetric shifts in the vortex nucleation and annihilation fields, manifesting local incomplete domain walls in these nanodots as magnetic vortices with tilted cores.Comment: 17 pages, 3 figures. Phys. Rev. B in pres

Controlling magnetization reversal in Co/Pt nanostructures with perpendicular anisotropy

We demonstrate a simple method to tailor the magnetization reversal mechanisms of Co/Pt multilayers by depositing them onto large area nanoporous anodized alumina (AAO) with various aspect ratios, A = pore depth/diameter. Magnetization reversal of composite (Co/Pt)/AAO films with large A is governed by strong domain-wall pinning which gradually transforms into a rotation-dominated reversal for samples with smaller A, as investigated by a first-order reversal curve method in conjunction with analysis of the angular dependent switching fields. The change of the magnetization reversal mode is attributed to topographical changes induced by the aspect ratio of the AAO templates.Comment: 12 pages, 3 figure

Quantitative Decoding of Interactions in Tunable Nanomagnet Arrays Using First Order Reversal Curves

To develop a full understanding of interactions in nanomagnet arrays is a persistent challenge, critically impacting their technological acceptance. This paper reports the experimental, numerical and analytical investigation of interactions in arrays of Co nanoellipses using the first-order reversal curve (FORC) technique. A mean-field analysis has revealed the physical mechanisms giving rise to all of the observed features: a shift of the non-interacting FORC-ridge at the low-H$_c$ end off the local coercivity H$_c$ axis; a stretch of the FORC-ridge at the high-H$_c$ end without shifting it off the H$_c$ axis; and a formation of a tilted edge connected to the ridge at the low-H$_c$ end. Changing from flat to Gaussian coercivity distribution produces a negative feature, bends the ridge, and broadens the edge. Finally, nearest neighbor interactions segment the FORC-ridge. These results demonstrate that the FORC approach provides a comprehensive framework to qualitatively and quantitatively decode interactions in nanomagnet arrays.Comment: 19 pages, 4 figures. 9 page supplemental material including 3 figure

The PdBI Arcsecond Whirlpool Survey (PAWS): Multi-phase cold gas kinematic of M51

The kinematic complexity and the favorable position of M51 on the sky make this galaxy an ideal target to test different theories of spiral arm dynamics. Taking advantage of the new high resolution PdBI Arcsecond Whirlpool Survey (PAWS) data, we undertake a detailed kinematic study of M51 to characterize and quantify the origin and nature of the non-circular motions. Using a tilted-ring analysis supported by several other archival datasets we update the estimation of M51's position angle (PA=(173 +/- 3) deg) and inclination (i=(22 +/- 5) deg). Harmonic decomposition of the high resolution (40 pc) CO velocity field shows the first kinematic evidence of an m=3 wave in the inner disk of M51 with a corotation at R(CR,m=3)=1.1 +/- 0.1 kpc and a pattern speed of Omega_p(m=3) = 140 km/(s kpc). This mode seems to be excited by the nuclear bar, while the beat frequencies generated by the coupling between the m=3 mode and the main spiral structure confirm its density-wave nature. We observe also a signature of an m=1 mode that is likely responsible for the lopsidedness of M51 at small and large radii. We provide a simple method to estimate the radial variation of the amplitude of the spiral perturbation (Vsp) attributed to the different modes. The main spiral arm structure has =50-70 km/s, while the streaming velocity associated with the m=1 and m=3 modes is, in general, 2 times lower. Our joint analysis of HI and CO velocity fields at low and high spatial resolution reveals that the atomic and molecular gas phases respond differently to the spiral perturbation due to their different vertical distribution and emission morphology.Comment: 42 pages, 12 figures, accepted for publication in Ap

A Comparative Study of Giant Molecular Clouds in M51, M33 and the Large Magellanic Cloud

We compare the properties of giant molecular clouds (GMCs) in M51 identified by the Plateau de Bure Interferometer Whirlpool Arcsecond Survey (PAWS) with GMCs identified in wide-field, high resolution surveys of CO emission in M33 and the Large Magellanic Cloud (LMC). We find that GMCs in M51 are larger, brighter and have higher velocity dispersions relative to their size than equivalent structures in M33 and the LMC. These differences imply that there are genuine variations in the average mass surface density of the different GMC populations. To explain this, we propose that the pressure in the interstellar medium surrounding the GMCs plays a role in regulating their density and velocity dispersion. We find no evidence for a correlation between size and linewidth in any of M51, M33 or the LMC when the CO emission is decomposed into GMCs, although moderately robust correlations are apparent when regions of contiguous CO emission (with no size limitation) are used. Our work demonstrates that observational bias remains an important obstacle to the identification and study of extragalactic GMC populations using CO emission, especially in molecule-rich galactic environments.Comment: 25 pages, 11 figures, accepted for publication in ApJ. Uses emulateapj LaTeX macros. For more information on PAWS, further papers and data, see http://www.mpia.de/PAWS