Low cost, single crystal-like substrates for practical, high efficiency solar cells

It is well established that high efficiency (20%) solar cells can be routinely fabricated using single crystal photovoltaic (PV) materials with low defect densities. Polycrystalline materials with small grain sizes and no crystallographic texture typically result in reduced efficiences. This has been ascribed primarily to the presence of grain boundaries and their effect on recombination processes. Furthermore, lack of crystallographic texture can result in a large variation in dopant concentrations which critically control the electronic properties of the material. Hence in order to reproducibly fabricate high efficiency solar cells a method which results in near single crystal material is desirable. Bulk single crystal growth of PV materials is cumbersome, expensive and difficult to scale up. We present here a possible route to achieve this if epitaxial growth of photovoltaic materials on rolling-assisted-biaxially textured-substrates (RABiTS) can be achieved. The RABiTS process uses well-established, industrially scaleable, thermomechanical processing to produce a biaxially textured or single-crystal-like metal substrate with large grains (50-100 {mu}m). This is followed by epitaxial growth of suitable buffer layers to yield chemically and structurally compatible surfaces for epitaxial growth of device materials. Using the RABiTS process it should be possible to economically fabricate single-crystal-like substrates of desired sizes. Epitaxial growth of photovoltaic devices on such substrates presents a possible route to obtaining low-cost, high performance solar cells

Formation of delta ferrite in 9 wt.% Cr steel investigated by in-situ X-ray diffraction using synchrotron radiation

In-situ X-ray diffraction (XRD) measurements using high energy synchrotron radiation were performed to monitor in real time the formation of delta ferrite in a martensitic 9 wt pct chromium steel under simulated weld thermal cycles. Volume fractions of martensite, austenite, and delta ferrite were measured as a function of temperature at a 10 K/s heating rate to 1573 K (1300 °C) and subsequent cooling. At the peak temperature, the delta ferrite concentration rose to 19 pct, of which 17 pct transformed back to austenite on subsequent cooling.Max Kade Foundation, Inc.Austrian Academy of SciencesUnited States. Dept. of Energy (Division of Materials Sciences and Engineering, Office of Science, and Office of Basic Energy Sciences

Lattice instabilities of PbZrO3/PbTiO3 [1:1] superlattices from first principles

Ab initio phonon calculations for the nonpolar reference structures of the (001), (110), and (111) PbZrO_3/PbTiO_3 [1:1] superlattices are presented. The unstable polar modes in the tetragonal (001) and (110) structures are confined in either the Ti- or the Zr-centered layers and display two-mode behavior, while in the cubic (111) case one-mode behavior is observed. Instabilities with pure oxygen character are observed in all three structures. The implications for the ferroelectric behavior and related properties are discussed.Comment: 12 pages, 2 figures, 7 tables, submitted to PR

Factors Associated with Revision Surgery after Internal Fixation of Hip Fractures

Background: Femoral neck fractures are associated with high rates of revision surgery after management with internal fixation. Using data from the Fixation using Alternative Implants for the Treatment of Hip fractures (FAITH) trial evaluating methods of internal fixation in patients with femoral neck fractures, we investigated associations between baseline and surgical factors and the need for revision surgery to promote healing, relieve pain, treat infection or improve function over 24 months postsurgery. Additionally, we investigated factors associated with (1) hardware removal and (2) implant exchange from cancellous screws (CS) or sliding hip screw (SHS) to total hip arthroplasty, hemiarthroplasty, or another internal fixation device. Methods: We identified 15 potential factors a priori that may be associated with revision surgery, 7 with hardware removal, and 14 with implant exchange. We used multivariable Cox proportional hazards analyses in our investigation. Results: Factors associated with increased risk of revision surgery included: female sex, [hazard ratio (HR) 1.79, 95% confidence interval (CI) 1.25-2.50; P = 0.001], higher body mass index (fo

Microdiffraction measurements of the effects of grain alignment on critical current in high temperature superconductors

While single crystals and epitaxial thin films of high temperature superconductors can carry large current densities, devices useful for applications such as power transmission and magnets cannot be produced because polycrystalline material cannot carry sufficient current densities. Efforts are underway to produce polycrystalline material in which grains are aligned to carry high current densities. We report x-ray and electron microdiffraction measurements of local grain alignment and models of how this grain alignment affects the critical current densities. TlCa{sub 2}Sr{sub 2}Cu{sub 3}O{sub x}(Tl-1223) samples can be grown on polycrystalline substrates with good c axis alignment but no overall {alpha} axis alignment. In TlCa{sub 2}Sr{sub 2}Cu{sub 3}O{sub x}, high critical current occurs in regions in which there is local {alpha} axis alignment. X-ray microdiffraction measurements of grain orientation were made with a monochromatic, 100 {mu}m diameter beam produced by inserting a pinhole at the focus of an NSLS bending magnet beamline. Local grain orientation was measured by observing Bragg reflection as the sample was rotated. While x-ray data was taken at this low resolution over large areas, the orientation of individual grains was measured over small regions by measuring the Kikuchi pattern produced by inelastic scattering from a 100 nm electron beam. In both cases, the sample position was scanned to map grain orientation. With advanced x-ray optics currently under development, high-resolution maps of grain orientation will be available without the elaborate surface preparation required for electron diffraction. This will facilitate study of samples prepared in a wider variety of forms

{open_quotes}Local texture, current flow, and superconductive transport properties of Tl1223 deposits on practical substrates{close_quotes}

Quantitative investigations of the crystal grain orientations and electrical transport properties of high temperature superconducting (HTS)TiBa{sub 2}Ca{sub 2}Cu{sub 3}O{sub 8+x} (Tl1223) deposits on polycrystalline substrates show that current flow comprises percolative networks of strongly-coupled material. Superconductive transport properties on different samples, on the same samples at different widths, and on samples with artificially-induced strong flux pinning defects confirm the nature of current flow, and suggest that these materials may be useful as a new class of HTS conductors

Atomic defects in the structural layers of hexagonal Er sub 2 Fe sub 17

X-ray and neutron powder diffraction has been carried out on the compound Er{sub 2}Fe{sub 17} which crystallizes in the Th{sub 2}Ni{sub 17} type (P6{sub 3}/mmc) hexagonal phase. H {minus} 2K = 3n L = 2n are the strongest reflection in both x-ray and neutron powder diffraction pattern (for example 302) showing the ordered transition metal substitutions on the planes perpendicular to c axis resulting in ABABAB{hor ellipsis}sequence of basic structural layers. However, H {minus} K {ne} 3n L = 2n type reflections have been observed with sizable intensities in the neutron diffraction spectrum. The very appearance of these reflections indicates that there is less than complete order on A and B chains, and some random substitutions take place on C chains, resulting in Fe-rich side of the 2:17 stoichiometry. These defects in the stacking sequences of hexagonal layers linked with the fine scale metallurgical microstructure have profound influence on the magnetic properties required in the design of new hard magnetic materials. 7 figs

Formation of Delta Ferrite in 9 Wt Pct Cr Steel Investigated by In-Situ X-Ray Diffraction Using Synchrotron Radiation

In-situ X-ray diffraction (XRD) measurements using high energy synchrotron radiation were performed to monitor in real time the formation of delta ferrite in a martensitic 9 wt pct chromium steel under simulated weld thermal cycles. Volume fractions of martensite, austenite, and delta ferrite were measured as a function of temperature at a 10 K/s heating rate to 1573 K (1300 °C) and subsequent cooling. At the peak temperature, the delta ferrite concentration rose to 19 pct, of which 17 pct transformed back to austenite on subsequent cooling