Nematic order often breaks the tetragonal symmetry of iron-based superconductors. It arises from regular structural transition or electronic instability in the normal phase. Here, we report the observation of a nematic superconducting state, by measuring the angular dependence of the in-plane and out-of-plane magnetoresistivity of Ba0.5K0.5Fe2As2 single crystals. We find large twofold oscillations in the vicinity of the superconducting transition, when the direction of applied magnetic field is rotated within the basal plane. To avoid the influences from sample geometry or current flow direction, the sample was designed as Corbino-shape for in-plane and mesa-shape for out-of-plane measurements. Theoretical analysis shows that the nematic superconductivity arises from the weak mixture of the quasi-degenerate s-wave and d-wave components of the superconducting condensate, most probably induced by a weak anisotropy of stresses inherent to single crystals.

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The actual light absorption photovoltaic responses realized in three-dimensional (3D) radial junction (RJ) units can be rather different from their planar counterparts and remain largely unexplored. We here adopt a laser excitation photoelectric microscope (LEPM) technology to probe the local light harvesting and photoelectric signals of 3D hydrogenated amorphous silicon (a-Si:H) RJ thin film solar cells constructed over a Si nanowire (SiNW) matrix, with a high spatial resolution of 600 nm thanks to the use of a high numerical aperture objective. The LEPM scan can help to resolve clearly the impacts of local structural damages, which are invisible to optical and SEM observations. More importantly, the high-resolution photoelectric mapping establishes a straightforward link between the local 3D geometry of RJ units and their light conversion performance. Surprisingly, it is found that the maximal photoelectric signals are usually recorded in the void locations among the standing SiNW RJs, instead of the overhead positions above the RJs. This phenomenon can be well explained and reproduced by finite element simulation analysis, which highlights unambiguously the dominant contribution of inter-RJ-unit scattering against direct mode incoupling in the 3D solar cell architecture. This LEPM mapping technology and the results help to achieve a straightforward and high-resolution evaluation of the local photovoltaic responses among the 3D RJ units, providing a solid basis for further structural optimization and performance improvement.

In this work, the authors fabricated Cu2O porous nanostructured films (PNFs) on glass slide substrates by the newly developed positive bias deposition approach in a balanced magnetron sputtering (MS) system. It was found that the surface morphology, crystal structure and optical property of the as-deposited products were greatly dependent on the applied positive substrate bias. In particular, when the substrate was biased at +50 V and +150 V, both of the as-prepared Cu2O PNFs exhibited a unique triangular pyramids-like structure with obvious edges and corners and little gluing, a preferred orientation of (111) and a blue shift of energy band gap at 2.35 eV. Quantitative calculation results indicated that the traditional bombardment effects of electrons and sputtering argon ions were both negligible during the bias deposition in the balanced MS system. Instead, a new model of tip charging effect was further proposed to account for the controllable formation of PNFs by the balanced bias sputtering deposition.

tered Cu atoms. It thus can be imaged that the sufficient oxygen source would lead to a partial or even full oxidation of the growing Cu film. Obviously, such undesirable oxidation would influence the performance, stability and lifetime of Cu film used as interconnection in ULSIC. Moreover, the parameter-dependent oxidation of Cu during physical sputtering deposition has not been investigated systemically yet. Thus, study on the parameter-dependent oxidation of physically sputtered Cu is crucial not only to mechanism understanding but also to practical avoidance of the undesirable oxidation.On the other hand, one recent interest in material research is the fabrication of high mobility semiconductors such as graphene-like MoS 2 [5] for the application in optoelectronic devices. Among Cu-based family, Cu is a typical metal material with a low resistivity of 1.67×10 −6 Ω cm, while its oxide Cu 2 O is a representative p-type semiconductor material with a band gap of 2.17 eV and a high resistivity of 3×10 6 Ω cm. Switzer et al. [6] found that the resistivity of layered Cu/Cu 2 O film could be tuned from 3.0×10 6 to 8.1×10−5 Ω cm. In spite of this, the optical property of the layered Cu/Cu 2 O film with a metallic resistivity was not studied in Ref. [6]. Thus, it is imperative to fabricate a certain structure of Cu-based films which can exhibit both metal and semiconductor characteristics.With the above considerations, we particularly studied the parameter-dependent oxidation of physically sputtered Cu and fabricated Cu-based semiconductor films with metallic resistivity. It was found that various Cu-based (oxide) films such as pure Cu, Cu 2 O, CuO films and Cu/ Cu 2 O, Cu 2 O/CuO composite films could be obtained by simply adjusting the deposition parameters during physical sputtering deposition. The main oxygen source for the oxidation of Cu and the parameter-dependent oxidation mechanisms were explored. Further, the electrical and op-ABSTRACT In this paper, we report the parameter-dependent oxidation of physically sputtered Cu and the related fabrication of Cu-based semiconductor films with metallic resistivity. It was found that various Cu-based (oxide) films such as pure Cu, Cu2O, CuO films and Cu/Cu2O, Cu2O/CuO composite films could be obtained by simply adjusting the deposition parameters during physical sputtering deposition. The main oxygen source for the oxidation of Cu and the parameter-dependent oxidation mechanisms were explored. Further, the electrical and optical testing results show that the obtained pure Cu film and Cu/Cu2O composite film both present an intriguing combination of metal and semiconductor characteristics.

Abstract:In this paper, the oxidation-assisted dealloying (OAD) of Cu0.7Al0.3 films with different microstructures which were obtained by high vacuum annealing at different temperatures were studied using powder X-ray diffraction, field-emission scanning electron microscopy and energy dispersive X-ray analysis. It was observed that different microstructures such as eutectic mixture or solid solution, the grain size of Cu or Al component in eutectic-mixture Cu0.7Al0.3 films affected the corrosion morphology greatly. It thus provided a practical route to fabricate flexible CuO porous nanostructure-films (PNFs) with controllable pore size, porosity, block size and shape.Further, the underlying OAD mechanisms for the structure-resultant different corrosion morphologies of Cu0.7Al0.3 films were also explored. In these senses, the study is suggestive and crucial to both the mechanism understanding of OAD process and the technical controlling of PNF fabrication.

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