Cu doped NiO (Cu:NiO) back contact layers are inserted between FTO substrates and CuBi2O4 thin films to improve the performance of CuBi2O4 photocathodes.

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Single quasicrystals of Al?oPd2iMn9 were plastically deformed by 25% under compression at 750°C. Both these samples as well as control samples of as-grown and heat-treated material were investigated by transmission electron microscopy. It was found that upon deformation the dislocation density increases by about 2 orders of magnitude. This provides the first direct evidence for quasicrystal deformation by a dislocation mechanism. The dislocations were found to have twofold and fivefold Burgers vector directions in physical space.PACS numbers: 61.44.+p, 6L66.Dk, 61.72.Bb, 62.20.Fe In a number of ternary aluminum-transition metal alloy systems thermodynamically stable quasicrystalline phases occur which can be produced with high structural perfection [l]. Of these alloys Al-Pd-Mn is particularly attractive. It contains an icosahedral phase of F-type lattice structure, of which single quasicrystals can be grown by the Czochralski technique [2,3]. After the first observation of lattice defects in the form of dislocations in decagonal AI65CU20C015 and icosahedral Al65Cu2oFei5, similar observations were reported for other stable quasicrystalline phases [4][5][6][7][8][9]. These observations raised the question of the origin of the dislocations, in particular, whether they can be induced by plastic deformation. Indeed hardness and compression tests demonstrated a relatively high ductility which increases with temperature [10][11][12][13][14][15]. With the exception of a hardness test at room temperature [10], these studies were all carried out in polyquasicrystalline material. We are reporting here on the first high-temperature single quasicrystal deformation experiments. Transmission electron microscopy of deformed and undeformed single quasicrystals of Al7 0 Pd2r Mn9 indicates an increase in dislocation density by about 2 orders of magnitude after plastic deformation, providing the first direct evidence for quasicrystal deformation by a dislocation mechanism.A master alloy of composition Al7 0 Pd2iMn9 was prepared in an induction furnace under an Ar atmosphere. Employing the Czochralski technique the resulting ingot was used to grow a single quasicrystal 7 cm in length and 1 cm in diameter of [0/0,0/0,0/2] orientation (notation of Cahn, Schechtman, and Gratias [16]). Small columns of 3x3x7 mm 3 were cut from this with their long axis parallel to [0/0,0/0,0/2]. Deformation under compression along this axis was performed at 750 °C in an INSTRON 1122 machine in air at a deformation velocity of 0.05 mm/min. A second sample was placed on the lower piston of the machine in order to serve as a reference. Because of a reduced length it was not deformed but went through the same temperature program as the deformation sample. In the following this sample is referred to as the heat-treated sample. After a deformation of 25% the load was released and the samples were quenched in water. Specimens for investigation in the transmission electron microscope (TEM) were prepared from the deformed and the heat-treated samples was well...

The development of earth‐abundant catalysts for selective electrochemical CO2 conversion is a central challenge. CuSn bimetallic catalysts can yield selective CO2 reduction toward either CO or formate. This study presents oxide‐derived CuSn catalysts tunable for either product and seeks to understand the synergetic effects between Cu and Sn causing these selectivity trends. The materials undergo significant transformations under CO2 reduction conditions, and their dynamic bulk and surface structures are revealed by correlating observations from multiple methods—X‐ray absorption spectroscopy for in situ study, and quasi in situ X‐ray photoelectron spectroscopy for surface sensitivity. For both types of catalysts, Cu transforms to metallic Cu0 under reaction conditions. However, the Sn speciation and content differ significantly between the catalyst types: the CO‐selective catalysts exhibit a surface Sn content of 13 at. % predominantly present as oxidized Sn, while the formate‐selective catalysts display an Sn content of ≈70 at. % consisting of both metallic Sn0 and Sn oxide species. Density functional theory simulations suggest that Snδ+ sites weaken CO adsorption, thereby enhancing CO selectivity, while Sn0 sites hinder H adsorption and promote formate production. This study reveals the complex dependence of catalyst structure, composition, and speciation with electrochemical bias in bimetallic Cu catalysts.

For the first time quasicrystal surfaces produced by in situ cleavage in ultrahigh vacuum have been investigated by scanning tunneling microscopy. Twofold and fivefold surfaces of icosahedral AlPdMn single quasicrystals have been studied. The surfaces were found to be rough. Their structure is determined by cluster aggregates formed on the basis of an elementary cluster whose contrast behavior and diameter of about 1 nm point to the Mackay-type cluster. Crack propagation occurs along zones of lower strength between clusters. This supports the cluster approach to quasicrystal structure. [S0031-9007(96)01557-8] PACS numbers: 61.44.Br, 61.16.Ch, 62.20.Mk, 68.35.Bs The structural basis of a quasicrystal is a lattice which exhibits orientational but not translational order [1,2]. Neutron and x-ray diffraction experiments [3][4][5] have led to structure models containing as a basic element large atom clusters, whose particular noncrystallographic symmetry is assumed to play a decisive part in the formation of the quasicrystal lattice. In icosahedral AlLiCu [4] the elementary cluster is related to a Bergman polyhedron of about 100 atoms, whereas in AlCuFe [3] and AlPdMn [5] icosahedral quasicrystals it is derived from the Mackay icosahedron with 55 atoms [6]. For the decagonal Al-NiCo quasicrystal, columnar clusters forming pentagonal antiprismatic channels were identified by x-ray scattering experiments [7]. The structure of quasicrystals has been studied in real space by high-resolution transmission electron microscopy and by scanning tunneling microscopy (STM). Since high-resolution electron microscopy is based on the imaging of atom columns, a study of nonperiodic structures encounters particular difficulties. Nevertheless, the wheel-shaped features of tenfold symmetry occurring in lattice images taken along the fivefold axes of icosahedral and the tenfold axis of decagonal quasicrystals were attributed to projections of the mentioned elementary clusters [8,9]. In an STM study on decagonal AlCuCo atomic resolution was obtained on tenfold surfaces [10]. The observed atom arrangements were used to construct a model based on pentagonal columnar clusters [11]. In a recent study on icosahedral AlPdMn quasicrystals by STM atomic resolution could not be obtained [12,13]. However, the two-dimensional autocorrelation function of the images exhibited typical quasicrystal symmetries.In the present work the STM approach is resumed avoiding a particular problem of the previous investigations. This problem arises from the fact that atomically clean surfaces are required. In the earlier work, the samples were prepared outside the microscope under ambient conditions. After transfer into the microscope vacuum, they had to be subjected to repeated cycles of ion bombardment and high-temperature annealing in order to remove the oxide coating. This is a well-tried technique for semiconductor surfaces. However, in its application to metallic alloys problems may arise from surface segregation, as indeed observed in Ref. [13], and from ...