We report the fabrication procedure and the characterization of an Al0.3Ga0.7As solar cell containing high‐density GaAs strain‐free quantum dots grown by droplet epitaxy. The production of photocurrent when two sub‐bandgap energy photons are absorbed simultaneously is demonstrated. The high quality of the quantum dot/barrier pair, allowed by the high quality of nanostructured strain‐free materials, opens new opportunities for quantum dot based solar cells.
A polymer nanohybrid material with enhanced dielectric permittivity was prepared using the fluorine‐containing polyimide (PI) 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride/4,4′‐oxydianiline (6FDA/ODA) as matrix and graphene as conductive filler in our present work. Studies on the dielectric properties of the 6FDA/ODA–graphene nanohybrid films show that the dielectric permittivity (ε) can be significantly enhanced by the layer‐by‐layer structure of graphene and the presence of fluorine also has an important influence on the improvement of ε. The percolation theory and microcapacitor model are used to explain the change of dielectric properties and a percolation threshold fc = 0.0152 (2.45 wt%) was obtained by a linear‐fit calculation.
Bulk polycrystalline La0.8Li0.2MnO3 is found to switch between a low‐resistance state and a high‐resistance state on thermal cycling. The low‐temperature, high‐resistance state exhibits strong electroresistance whereas the high‐temperature, low‐resistance state does not. The change in resistance between the two distinct states is of two orders of magnitude. It is proposed that the observed metastability may serve as the basis for resistive thermal‐switching devices.
A high‐efficiency bulk heterojunction organic photovoltaic cell (OPV) was achieved by the electrospray deposition method. The surface roughness of the P3HT:PCBM thin film can be reduced using the mixed solvent consisting of o‐dichlorobenzene (o‐DCB) and acetone. The effect of acetone concentration is related to its dielectric constant. Under an optimized concentration of acetone in o‐DCB (20 vol%), the P3HT/PCBM active layer with a smooth surface can be formed, and the power conversion efficiency of the OPV was 1.9%.
This Letter reports on the assembly on the tip of an optical fibre of a metamaterial film fabricated by a self‐assembly bottom‐up method, composed of silver nanowires embedded in an alumina matrix. By illuminating the film through the fibre in a reflection configuration, we observe experimentally the optical response of the metamaterial in agreement with theoretical predictions and interpreted as the excitation of surface plasmon‐polaritons in the cylindrical surface of the nanowires. These results pave the way for low‐cost optical fibre devices that incorporate metamaterial films.
Lead carbonate chloride, Pb2CO3Cl2, known as mineral phosgenite, is introduced as a novel SRS‐active carbonate crystal with tetragonal symmetry. Under picosecond one‐micron laser pumping Raman‐induced χ(3)‐nonlinear generation in the near‐IR is observed. All recorded high‐order Stokes and anti‐Stokes sidebands are identified and attributed to two SRS‐promoting vibration modes with ωSRS1 ≈ 1062 cm–1 and ωSRS2 ≈ 86 cm–1.
In this Letter, a novel modified anodization was utilized to synthesize high‐aspect‐ratio, top‐open and ultraflat‐surface TiO2 nanotubes. The interruption of voltage during anodization leads to the formation of a double‐layered structure. Due to the weak mechanical connection between the upper and the underlying layer, the two parts can be easily detached. Compared with the conventional ultrasonication method to remove the clusters of nanotubes where rough surfaces resulted, this efficient and reliable strategy may facilitate further applications of TiO2 nanotubes in diverse conditions.
Spin crossover compounds are considered to be a viable alternative for creating display, memory and switching devices due to the bistability of their magnetic, optical, mechanical and electrical properties. This Letter presents the study of the dielectric and transport properties of the [Fe(Htrz)2(trz)](BF4) (Htrz = 1H‐1,2,4‐triazole) complex in a wide temperature and frequency range. Our results reveal a singular behavior of the dielectric modulus upon the spin transition in conjunction with the switching of the conductivity between the high spin and low spin states.
Electric control of magnetism is demonstrated in a multiferroic metal–organic framework with a perovskite structure. A moderate electric field of a few kV/cm applied during the cooling process is able to cause a large (more than 50%) change of the magnetization at low temperature. This significant magnetoelectric effect is ascribed to the electric field manipulation of orientation of hydrogen bonds that modify the superexchange interaction between metal ions.
We study graphene growth on hafnia (HfO2) nanoparticles by chemical vapour deposition using optical microscopy, high resolution transmission electron microscopy and Raman spectroscopy. We find that monoclinic HfO2 nanoparticles neither reduce to a metal nor form a carbide while nucleating nanometer domain‐sized few layer graphene. Hence we regard this as an interesting non‐metallic catalyst model system with the potential to explore graphene growth directly on a (high‐k) dielectric.
We report a very simple and novel approach to produce anodic TiO2 nanotube arrays with highly defined and ordered tube openings. It is based on carrying out anodization through a slowly soluble photoresist coating. This eliminates the formation of undesired initiation layers on the tube tops and protects them to a certain extent from etching by the electrolyte.
The metastability of the bixbyite‐ and corundum‐type In2O3 polymorphs up to 33 GPa (at room temperature) is shown. While compressed (in diamond anvil cells) and laser‐heated, both polymorphs undergo a phase transition to the Rh2O3‐II‐type structure (space group Pbcn, No. 60). The direct transition from bixbyite to Rh2O3‐II structure has not yet been observed for any other oxide.
We have shown that nitrophenyl groups may be added to the surface of few‐layer epitaxial graphene (EG) by the formation of covalent carbon–carbon bonds thereby changing the electronic structure and transport properties of EG from near‐metallic to semiconducting. In the present Letter we discuss the opportunities afforded by such chemical processes to engineer device functionality in graphene by modification of the electronic properties without physical patterning.
The crystallization process of mechanically alloyed Fe75Zr25 metallic glasses is investigated by means of both thermo‐magnetization and in situ neutron powder thermo‐diffraction experiments in the temperature range 300–1073 K. It was found that the crystallization takes place in a two‐step process, involving firstly the appearance of metastable Fe and Fe2Zr crystalline phases between 880 K and 980 K, and a subsequent polymorphic transformation into Fe3Zr above 980 K. These findings explain the anomalous magnetization vs. temperature behaviour on heating–cooling cycles.
Heteroepitaxial growth of kesterite Cu2ZnSnS4 (CZTS) thin film on cubic ZnS(100) single crystal substrate was achieved by radio frequency magnetron sputtering from a single CZTS target. An optimal substrate temperature in the range of 470–500 °C is found suitable for this epitaxial growth. The growth of CZTS was confirmed to be along a‐axis. The sputtered CZTS thin film is homogeneous throughout the whole film. The band gap of the film is found to be approximately 1.51 eV, i.e., promising for high efficiency thin film solar cells.
Polymer nanocomposites containing different concentrations of Au nanoparticles have been investigated by small angle X‐ray scattering and electronic absorption spectroscopy. The variation in the surface plasmon resonance (SPR) band of Au nanoparticles with concentration is described by a scaling law. The variation in the plasmon band of ReO3 nanoparticles embedded in polymers also follows a similar scaling law.
MgZnO‐based ultraviolet avalanche photodetectors (APDs) have been fabricated from Au/MgO/Mg0.44Zn0.56O/MgO/Au Schottky structures. The carrier avalanche multiplication is realized via an impact ionization process occurring in the MgO layer under relatively large electric field. The APDs exhibit an avalanche gain of 587 at 31 V bias, and the response speed of the APDs is in the order of microseconds.
The Fe3O4(111)/graphene/Ni(111) trilayer is proposed to be used as an ideal spin‐filtering sandwich where the half‐metallic properties of magnetite are used. Thin magnetite layers on graphene/Ni(111) were prepared via successive oxidation of a thin iron layer predeposited on graphene/Ni(111) and the formed system was investigated by means of low‐energy electron diffraction and photoelectron spectroscopy. The electronic structure and structural quality of the graphene film sandwiched between two ferromagnetic layers remain unchanged upon magnetite formation as confirmed by experimental data.
