2014, Burghoorn, M., Kniknie, B., van Deelen, J., Xu, M., Vroon, Z., van Ee, R., van de Belt, R., Buskens, P.

Textured transparent conductors are widely used in thin-film silicon solar cells. They lower the reflectivity at interfaces between different layers in the cell and/or cause an increase in the path length of photons in the Si absorber layer, which both result in an increase in the number of absorbed photons and, consequently, an increase in short-circuit current density (Jsc) and cell efficiency. Through optical simulations, we recently obtained strong indications that texturing of the transparent conductor in copper indium gallium (di-)selenide (CIGS) solar cells is also optically advantageous. Here, we experimentally demonstrate that the Jsc and efficiency of CIGS solar cells with an absorber layer thickness (dCIGS) of 0.85 μm, 1.00 μm and 2.00 μm increase through application of a moth-eye textured resist with a refractive index that is sufficiently similar to AZO (nresist = 1.792 vs. nAZO = 1.913-at 633 nm) to avoid large optical losses at the resist-AZO interface. On average, Jsc increases by 7.2%, which matches the average reduction in reflection of 7.0%. The average relative increase in efficiency is slightly lower (6.0%). No trend towards a larger relative increase in Jsc with decreasing dCIGS was observed. Ergo, the increase in Jsc can be fully explained by the reduction in reflection, and we did not observe any increase in Jsc based on an increased photon path length. © 2014 Author(s).

2014, Oka, T., Yamada, Y., Horiuchi, T., Ogawa, J., Fukui, S., Sato, T., Yokoyama, K., Langer, M.

The magnetic flux penetration into the melt-textured Y-Ba-Cu-O high temperature superconducting bulk magnets were precisely evaluated during and after the pulsed field magnetization processes operated at 30 K. The bulk magnets were carefully fabricated by the cold seeding method with use of a single and a pair of seed crystals composed of the Nd-Ba-Cu-O thin films. These seed crystals were put on the top surfaces of the precursors to let the large grains grow during the heat treatments. We observed the flux penetrations which occurred in the lower applied-field regions at around 3.1 T for the samples bearing the twin seeds than those of the single-seeded crystals at around 3.8 T. This means that the magnetic fluxes are capable of invading into the twin-seeded samples more easily than the single-seeds. It suggests that the anisotropic grain growths of parallel and normal to the rows of seed crystals affects the variations of Jc values with different distributions of the pinning centers, results in the preferential paths for the invading magnetic fluxes.

2023, Bez, Elena, Himmerlich, Marcel, Lorenz, Pierre, Ehrhardt, Martin, Gunn, Aidan Graham, Pfeiffer, Stephan, Rimoldi, Martino, Taborelli, Mauro, Zimmer, Klaus, Chiggiato, Paolo, Anders, André

Ultrashort-pulse laser processing of copper is performed in air to reduce the secondary electron yield (SEY). By UV (355 nm), green (532 nm), and IR (1064 nm) laser-light induced surface modification, this study investigates the influence of the most relevant experimental parameters, such as laser power, scanning speed, and scanning line distance (represented as accumulated fluence) on the ablation depth, surface oxidation, topography, and ultimately on the SEY. Increasing the accumulated laser fluence results in a gradual change from a Cu 2 O to a CuO-dominated surface with deeper micrometer trenches, higher density of redeposited surface particles from the plasma phase, and a reduced SEY. While the surface modifications are less pronounced for IR radiation at low accumulated fluence (,1000 J/cm2 ), analogous results are obtained for all wavelengths when reaching the nonlinear absorption regime, for which the SEY maximum converges to 0.7. Furthermore, independent of the extent of the structural transformations, an electron-induced surface conditioning at 250 eV allows a reduction of the SEY maximum below unity at doses of 5×10 -4 C/mm2 . Consequently, optimization of processing parameters for application in particle accelerators can be obtained for a sufficiently low SEY at controlled ablation depth and surface particle density, which are factors that limit the surface impedance and the applicability of the material processing for ultrahigh vacuum systems. The relations between pro- cessing parameters and surface features will provide guidance in treating the surface of vacuum components, especially beam screens of selected magnets of the Large Hadron Collider or of future colliders.

2015, Gargarella, P., Pauly, S., Stoica, M., Vaughan, G., Afonso, C.R.M., Kühn, U., Eckert, J.

The structural evolution of Ti50Cu43Ni7 and Ti55Cu35Ni10 metallic glasses during heating was investigated by in-situ synchrotron X-ray diffraction. The width of the most intense diffraction maximum of the glassy phase decreases slightly during relaxation below the glass transition temperature. Significant structural changes only occur above the glass transition manifesting in a change in the respective peak positions. At even higher temperatures, nanocrystals of the shape memory B2-Ti(Cu,Ni) phase precipitate, and their small size hampers the occurrence of a martensitic transformation.

2011, Ren, J.L., Chen, C., Wang, G., Mattern, N., Eckert, J.

Under compression loading, bulk metallic glasses (BMGs) irreversibly deform through shear banding manifested as a serrated flow behavior. By using a statistical analysis together with a complementary dynamical analysis of the stress-time curves during serrated flow, we characterize the distinct spatiotemporal dynamical regimes and find that the plastic dynamic behavior of a Cu50Zr45Ti5 BMG changes from chaotic to self-organized critical behavior with increasing strain rate. This plastic dynamics transition with the strain rate is interpreted in the frame of the competence between the neighboring elastic strain field forming and relaxation processes.

2012, Kirchner, A., Erbe, M., Freudenberg, T., Hühne, R., Feys, J., Van Driessche, I., Schultz, L., Holzapfel, B.

Environmentally friendly water-based YBa2Cu3Ox (YBCO) and GdBa2Cu3Ox (GdBCO) precursor solutions were synthesized to realize thin films by chemical solution deposition. Pure YBCO and GdBCO precursor solutions were used for ink plotting on SrTiO3 substrates and subsequent thermal treatment at the corresponding crystallization temperature. Phase formation of Gd123 requires a higher crystallization temperature of 840 °C compared to the Y123 phase. The critical temperature of YBCO films is about 92 K with a sharp transition into the superconducting state. Micro liter sized ink volumes of YBCO and GdBCO were successfully mixed for two-dimensional ink plotting of a (YxGd1-x)Ba2Cu3Ox film library. A homogeneous surface and no indication of a-axis growth were found in all mixed films.

2020, Rowolt, Christian, Milkereit, Benjamin, Springer, Armin, Kreyenschulte, Carsten, Kessler, Olaf

Continuous heating transformation (CHT) diagrams and continuous cooling transformation (CCT) diagrams of precipitation-hardening steels have the drawback that important information on the dissolution and precipitation of Cu-rich phases during continuous heating and cooling are missing. This work uses a comparison of different techniques, namely dilatometry and differential scanning calorimetry for the in situ analysis of the so far neglected dissolution and precipitation of Cu-rich phases during continuous heating and cooling to overcome these drawbacks. Compared to dilatometry, DSC is much more sensitive to phase transformation affecting small volume fractions, like precipitation. Thus, the important solvus temperature for the dissolution of Cu-rich phases was revealed from DSC and integrated into the CHT diagram. Moreover, DSC reveals that during continuous cooling from solution treatment, premature Cu-rich phases may form depending on cooling rate. Those quench-induced precipitates were analysed for a broad range of cooling rates and imaged for microstructural analysis using optical microscopy, scanning electron microscopy and transmission electron microscopy. This information substantially improves the CCT diagram.

2014, Sieger, M., Hänisch, J., Iida, K., Gaitzsch, U., Rodig, C., Schultz, L., Holzapfel, B., Hühne, R.

YBa2Cu3O7-δ (YBCO) films with a thickness of up to 3 μm containing nano-sized BaHfO3 (BHO) have been grown on Y2O3/Y-stabilized ZrO2/CeO 2 buffered Ni-9at% W tapes by pulsed laser deposition (PLD). Structural characterization by means of X-ray diffraction confirmed that the YBCO layer grew epitaxial. A superconducting transition temperature T c of about 89 K with a transition width of 1 K was determined, decreasing with increasing BHO content. Critical current density in self-field and at 0.3 T increased with increasing dopant level.

2012, Ehrhardt, M., Lorenz, P., Frost, F., Zimmer, K.

Micro- and submicrometer structures have been transferred from nickel foils into solid copper surfaces by laser microembossing. The developed arrangement for laser microembossing allows a large-area replication using multi- pulse laser scanning scheme, guaranties a low contamination of the embossed surface and enables the utilization of thick workpieces. In the micrometer range the replicated patterns feature a high accuracy regarding the shape. A significant difference between the master and the replication pattern could be observed for the laser embossing of submicrometer patterns. In conclusion, the results show that the proposed laser embossing process is a promising method with a number of applications in microengineering.

2014, Kauffmann-Weiss, S., Hamann, S., Reichel, L., Siegel, A., Alexandrakis, V., Heller, R., Schultz, L., Ludwig, A., Fähler, S.

Smallest variations of the lattice parameter result in significant changes in material properties. Whereas in bulk, lattice parameters can only be changed by composition or temperature, coherent epitaxial growth of thin films on single crystals allows adjusting the lattice parameters independently. Up to now only discrete values were accessible by using different buffer or substrate materials. We realize a lateral variation of in-plane lattice parameters using combinatorial film deposition of epitaxial Cu-Au on a 4-in. Si wafer. This template gives the possibility to adjust the in-plane lattice parameter over a wide range from 0.365 nm up to 0.382 nm.