High‐pressure high‐temperature synthesis of Rh2O3‐II‐type In2O3 polymorph

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.

     

Enhanced dielectric permittivity of fluorine polyimide matrix with embedded graphene

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 f_c = 0.0152 (2.45 wt%) was obtained by a linear‐fit calculation.

     

The impact of twinning on the local texture of chalcopyrite‐type thin films

Twinning in a CuInS₂ layer in a completed thin‐film solar cell was analyzed by means of electron backscatter diffraction. This technique revealed the microstructure of the CuInS₂ thin films and local orientation relationships between the grains. At various locations within the layer it was possible to retrace how twinning occurred comparing the local orientations with the theoretically possible changes in orientation by twinning. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

     

Epitaxial TiC/SiC multilayers

Epitaxial TiC/SiC multilayers were grown by magnetron sputtering at a substrate temperature of 550 °C, where SiC is normally amorphous. The epitaxial TiC template induced growth of cubic SiC up to a thickness of ～2 nm. Thicker SiC layers result in a direct transition to growth of the metastable amorphous SiC followed by renucleation of nanocrystalline TiC layers.

     

Monolithically integrated organic waveguide photodiode

We demonstrate the monolithic integration of a microstructured organic photodiode with a planar optical stripe waveguide. The manufacturing of this waveguide‐integrated organic photodiode is based on an UV photolithography process. The integration of photodiodes with optical waveguides represents an essential building block in the field of optoelectronic‐photonic integrated circuits.

     

Layer‐by‐layer fabrication of hierarchical structures in sol–gel templated thin titania films

The fabrication of titania nanostructures with hierarchical order of different structural levels is investigated. The nanostructures are prepared with a diblock‐copolymer assisted sol–gel process. By iterative spin‐coating of the solution onto silicon substrates a thin polymer‐nanocomposite film is deposited and transformed to purely anatase titania nanostructures via calcination. In total, this procedure is repeated three times on top of the substrate. The approach is monitored with grazing incidence small angle X‐ray scattering after each fabrication step. With scanning electron microscopy the final hierarchical structure is imaged. From the characterization different structural levels are clearly identified.

     

Chemical approach to the realization of electronic devices in epitaxial graphene

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.

     

Prediction of giant antiferromagnetic coupling in exotic fluorides of AgII

We show, using Density Functional Theory (DFT) calculations, that compressed AgF₂ should turn above 17 GPa into a layered narrow‐gap material with a huge intralayer antiferromagnetic (AFM) coupling constant, reminiscent of those seen for parent copper (II) oxides (e.g., La₂CuO₄). Compressed AgF₂ is thus the first candidate for the non‐oxocuprate two‐dimensional antiferromagnet. Calculations indicate that AgF₂ could subsequently be metallised above 38 GPa, likely giving rise to superconductivity (SC).

     

Spin–orbit coupling in low‐dimensional gold

We present experimental and theoretical evidence of the role played by the spin–orbit coupling in the electronic structure of a pseudomorphic Au monolayer on Nb(001) substrate. The bands found with the help of the angle‐resolved ultraviolet photoelectron spectroscopy (ARUPS) are compared with those obtained from ab initio self‐consistent calculations by the VASP and WIEN2k codes. The slab calculations are performed including geometric relaxation and using both the generalized‐gradient (GGA) and local‐density (LDA) approximations for the exchange–correlation energy. The dispersions and energy positions of the calculated bands agree with the experimentally determined band structure only if the LDA is used and the spin–orbit coupling is included. Therefore, both the structure relaxation and spin–orbit coupling are essential in understanding the electronic structure of the Au/Nb(001) system.

     

Evidence of two‐photon absorption in strain‐free quantum dot GaAs/AlGaAs solar cells

We report the fabrication procedure and the characterization of an Al_0.3Ga_0.7As 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.

     

Synthesis and catalytic activity of hybrid metal/silicon nanocomposites

In this Letter we demonstrate that hydrogen‐terminated porous silicon (PSi) layers and powders can serve as highly efficient reductive templates for noble metal salts. The reduction results in metal nanoparticle (NP) formation in the pores of PSi. Gold NP formation has been monitored in‐situ by measuring the plasmon resonance response. Pt NPs, formed in the PSi matrix, were investigated by transmission electron microscopy and energy‐dispersive X‐ray analysis. Furthermore, hybrid Pt/PSi nanocomposites exhibit a high catalytic activity for CO oxidation.

     

How the SiC substrate impacts graphene's atomic and electronic structure

Graphene, the two‐dimensional form of carbon presents outstanding electronic and transport properties. This gives hope for the development of applications in nanoelectronics. However, for industrial purpose, graphene has to be supported by a substrate. We focus here on the graphene‐on‐SiC system to discuss how the SiC substrate interacts with the graphene layer and to show the effect of the interface on graphene atomic and electronic structures.

     

Simple near‐infrared photodetector based on charge transfer complexes formed in molybdenum oxide doped N,N′‐di(naphthalene‐1‐yl)‐N,N′‐diphenyl‐benzidine

We have demonstrated a simple near‐infrared (NIR) photodetector (PD) based on charge transfer complex (CTC) formed in molybdenum trioxide (MoO₃) doped N,N′‐di(naphthalene‐1‐yl)‐N,N′‐diphenyl‐benzidine (NPB), which shows a photocurrent of about 0.35 A/cm² at –3 V under 980 nm illumination. The existence of CTC formation promotes photocurrent generation which is investigated by comparison with MoO₃ doped 2‐methyl‐9,10‐di(2‐naphthyl)anthracene (MADN) film which has no CTC absorption. It can be evolved that this kind of simple‐structure photodetector has potential application in the near‐infrared (NIR) detection area. It is shown in this Letter that although both MoO₃ and NPB have larger energy gaps of about 3 eV and weak absorption in the NIR region, the charge transfer complexes formed by mixing the two materials show an extra absorption band and good photoelectric response in the NIR region.

     

Electric control of magnetism in a multiferroic metal–organic framework

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.

     

Trigonal Na3Li(SeO4)2·6H2O crystal – a novel SRS‐active material with high Raman gain coefficient

We discovered and characterized the χ ⁽³⁾‐active Na₃Li(SeO₄)₂·6H₂O crystal with considerably high Raman gain coefficients for laser physics and nonlinear optics. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

     

In‐situ neutron reflectometry probing competitive swelling and de‐swelling of thin polystyrene films

The competitive penetration of toluene with respect to oxygen, nitrogen and carbon dioxide into a thin and initially dry film of deuterated polystyrene (dPS) is compared to the reverse process of de‐swelling. In‐situ neutron reflectometry is used to follow the swelling and de‐swelling kinetics, allowing the determination of the total dPS thickness, roughness and solvent penetration. Swelling cannot be described in terms of case II diffusion due to the small film thickness and undersaturation results in a small swelling rate of 0.03 nm s^–1. De‐swelling is slower by more than two orders in magnitude, thereby underlining the difficulty to remove once incorporated solvent molecules. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

     

Combinatorial investigation of nanostructures formed in a titanium dioxide based nanocomposite film on top of fluor‐doped tin oxide layers

Nanostructures formed in a titanium dioxide (TiO₂)–poly(styrene)‐block‐poly(ethyleneoxide) nanocomposite film on top of fluor‐doped tin oxide (FTO) layers are investigated. The combinatorial approach is based on probing a wedge‐shaped FTO‐gradient with grazing incidence small angle X‐ray scattering (GISAXS) in combination with a moderate micro‐focus X‐ray beam. The characteristic lateral length is given by adjacent nanowire‐shaped TiO₂ regions. It decreases from 200 nm on the thick FTO layer to 90 nm on the bare glass surface.

     

Polarization dependent,surface plasmon induced photoconductance in gold nanorod arrays

We report on the photoconductance in two‐dimensional arrays of gold nanorods. The arrays are formed by a combination of droplet deposition and stamping methods. We find that the plasmon induced photoconductance is sensitive to the linear polarization of the exciting photons consistent with the excitation of the longitudinal surface plasmon resonance of the nanorods.

     

Raman spectroscopy of pentyl‐functionalized carbon nanotubes

We present Raman scattering on carbon nanotubes functionalized with pentyl groups. Studies of the intermediate frequency region and the C–H bond stretching signal along with the D mode show evidence of the addition reaction by Raman spectroscopy. From the resonance profiles of the radial breathing mode (RBM) we assign the chiral indices of the tubes and study the influence of the functionalization on the transition energies, shift and intensity of the RBM signal. The largest effect we observe is on the Raman intensity of the radial breathing mode. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)