Dirk C. Meyer

Voltage-controlled epitaxial strain in La0.7Sr0.3MnO3∕Pb(Mg1∕3Nb2∕3)O3-PbTiO3(001) films

Epitaxially grown La0.7Sr0.3MnO3 thin films show resistance modulations induced by the inverse piezoeffect of the employed Pb(Mg1∕3Nb2∕3)O3-PbTiO3(001) (PMN-PT) substrates. The in-plane strain state of the films can continuously be tuned by application of a piezovoltage to PMN-PT. The lattice deformation of a PMN-PT(001) substrate was quantified by x-ray measurements under an electric field. Variation of in-plane lattice parameters by ∼0.06% reversibly changes the resistance of the manganite films by up to 9% at 300 K and shifts the magnetic Curie temperature. Films of different thicknesses from 50 to 290 nm, offering different as-grown strain states, have been studied.

1,2,4-Triazole-Based Tunable Aryl/Alkyl Ionic Liquids

Ionic liquids based on aryl-/alkyl-substituted imidazolium salts constitute a new generation of ionic liquids with a high degree of flexibility. The new concept could now also be extended to aryl-/alkyl-substituted 1,2,4-triazolium salts. The two different phenyl-substituted 1H- and 4H-1,2,4-triazoles have been synthesized by a coupling reaction or a one-pot synthesis with diformylhydrazine, respectively. Reaction with alkyl bromides provided the 1,2,4-triazolium bromides, and an anion-exchange reaction led to the corresponding bis(trifluoromethylsulfonyl)imide salts with melting points well below 100 °C.

Thermal stability of Mo/Si multilayers with boron carbide interlayers

Abstract Mo/Si multilayer systems with boron carbide (B 4 C) diffusion barrier layers were deposited on sapphire and silicon substrates by DC magnetron sputtering. Samples were subsequently annealed in vacuum at temperatures between 100 and 800 °C for duration of between 20 min and 30 h. Thermally stimulated solid state reactions have been characterized by X-ray analysis methods. Mo/Si multilayers without barrier layers are stable up to 100 °C. Interdiffusion was observed to start by 150 °C. It was found that B 4 C diffusion barrier layers with thicknesses between 0.3 and 1.0 nm, depending on the stack sequence, give rise to an increase of the thermal stability up to 400 °C. The impact of thermal treatments, at various temperatures and annealing times, on thickness and composition of the interdiffusion layers was investigated by X-ray reflectometry, wide angle X-ray scattering, cross-sectional high resolution transmission electron microscopy and fluorescence extended X-ray absorption fine structure measurements in combination with excitation of X-ray standing waves. The last method was used to investigate the short-range order of Mo/Si multilayers depth-resolved.

An extreme biomimetic approach: hydrothermal synthesis of β-chitin/ZnO nanostructured composites

β-Chitinous scaffolds isolated from the skeleton of marine cephalopod Sepia officinalis were used as a template for the in vitro formation of ZnO under conditions (70 °C) which are extreme for biological materials. Novel β-chitin/ZnO film-like composites were prepared for the first time by hydrothermal synthesis, and were thoroughly characterized using numerous analytical methods including Raman spectroscopy, HR-TEM and XRD. We demonstrate the growth of hexagonal ZnO nanocrystals on the β-chitin substrate. Our chitin/ZnO composites presented in this work show antibacterial properties against Gram positive bacteria and can be employed for development of inorganic-organic wound dressing materials.

Solvothermal preparation of metallized titania sols for photocatalytic and antimicrobial coatings

The one-pot preparation of metal doped titania sols for coatings with photocatalytic and antimicrobial properties can be realized by using solvothermal conditions in alcoholic solvents at temperatures of 140 °C and above. Under these conditions, hydrolysis of Ti(OR)4 results in photoactive anatase modification while simultaneously added silver or palladium salts will be reduced to colloidal metals. The formation of the nanosized anatase particles is confirmed by wide-angle X-ray scattering (WAXS) and Raman measurements, and the formation of nanosized metal particles of silver and palladium is demonstrated by WAXS and high-resolution transmission electron microscopy (HRTEM). Dynamic light scattering investigations into the particle size of solvothermal TiO2 and Ag sols (compared with their mixtures) suggest that common composite agglomerates are formed due to considerable interactions between the sol particles. After being coated onto viscose fabrics the Ag/TiO2 and Pd/TiO2 composite sols show strong photocatalytic properties. These were determined via decomposition of the organic dye Acid Orange 7, and by antimicrobial effects against gram negative bacteria E. coli even in the dark. Therefore, since no annealing is required to form the photoactive anatase modification, solvothermal sols are well suited to functionalizing less thermally-stable materials such as textiles, polymer foils or paper.

Extreme biomimetic approach for developing novel chitin-GeO2 nanocomposites with photoluminescent properties

This work presents an extreme biomimetics route for the creation of nanostructured biocomposites utilizing a chitinous template of poriferan origin. The specific thermal stability of the nanostructured chitinous template allowed for the formation under hydrothermal conditions of a novel germanium oxide-chitin composite with a defined nanoscale structure. Using a variety of analytical techniques (FTIR, Raman, energy dispersive X-ray (EDX), near-edge X-ray absorption fine structure (NEXAFS), and photoluminescence (PL) spectroscopy, EDS-mapping, selected area for the electron diffraction pattern (SAEDP), and transmission electron microscopy (TEM)), we showed that this bioorganic scaffold induces the growth of GeO2 nanocrystals with a narrow (150–300 nm) size distribution and predominantly hexagonal phase, demonstrating the chitin template’s control over the crystal morphology. The formed GeO2–chitin composite showed several specific physical properties, such as a striking enhancement in photoluminescence exceeding values previously reported in GeO2-based biomaterials. These data demonstrate the potential of extreme biomimetics for developing new-generation nanostructured materials.

Synthesis of nanostructured chitin–hematite composites under extreme biomimetic conditions

Chitin of poriferan origin is a unique and thermostable biological material. It also represents an example of a renewable materials source due to the high regeneration ability of Aplysina sponges under marine ranching conditions. Chitinous scaffolds isolated from the skeleton of the marine sponge Aplysina aerophoba were used as a template for the in vitro formation of Fe2O3 under conditions (pH ∼ 1.5, 90 °C) which are extreme for biological materials. Novel chitin–Fe2O3 three dimensional composites, which have been prepared for the first time using hydrothermal synthesis, were thoroughly characterized using numerous analytical methods including Raman spectroscopy, XPS, XRD, electron diffraction and HR-TEM. We demonstrate the growth of uniform Fe2O3 nanocrystals into the nanostructured chitin substrate and propose a possible mechanism of chitin–hematite interactions. Moreover, we show that composites made of sponge chitin–Fe2O3 hybrid materials with active carbon can be successfully used as electrode materials for electrochemical capacitors.

X-ray absorption fine structure study of short-range order of iron in Fe/Al multilayers

Results of quantitative analysis of fluorescence x-ray absorption fine structure (XAFS) experiments at the Fe–K absorption edge are presented for a 6*(4.3 nm Fe/10.4 nm Al) multilayer prepared by pulsed laser deposition. Fluorescence XAFS experiments have been combined with excitation of x-ray standing waves. This combination in one experiment allowed for a depth-controlled excitation of Fe fluorescence and hence for a depth-resolved analysis of short-range order. Depth-resolved analysis showed that instead of sharp Fe/Al or Al/Fe interfaces extended interlayer regions exist. The structure retained that of bulk α-Fe. In the upper half of the Fe layer 37 at. % Al as nearest and next nearest neighbors of Fe were found, whereas in the lower half 80 at. % Al atoms occur. Thus the Fe/Al interface (deposition of Fe on Al) should be characterized by an intermixing zone significantly larger in comparison to that of the Al/Fe interface (deposition of Al on Fe). By conventional XAFS measurement carried out at a fix...

Crystal structure of K1-xCsxBSi2O6 (x = 0.12, 0.50) boroleucite solid solutions and thermal behaviour of KBSi2O6 and K0.5Cs0.5BSi2O6

Abstract The crystal structures of two K1-xCsxBSi2O6 solid solutions have been refined at room temperature by the Rietveld method: x = 0.12, a = 12.6858(4) Å, Rwp = 7.66%, RF = 5.56% and x = 0.50, a = 12.8480(2) Å, Rwp = 7.64%, RF = 3.10%. They are isostructural to cubic KBSi2O6 with the space group I4̅3d. The structure is built up from (Si,B)O4 tetrahedra linked in four-, six- and eightfold rings which are forming a three-dimensional borosilicate framework. The framework contains large cavities that are placed in continuous channels along the [111] directions. The Cs and K atoms occupy the positions in the channels statistically. Thermal behaviour of KBSi2O6 and K0.5Cs0.5BSi2O6 has been studied by high-temperature powder X-ray diffraction within the temperature range of 293-1073 K. A new tetragonal polymorph of KBSi2O6 has been found in situ under heating. The new polymorphic I4̅3d (cubic) – Ia3̅d (cubic) transition and the new Ia3̅d cubic polymorphic phase has been proposed for K1-xCsxBSi2O6 from our experimental and literature data on crystal structures and thermal expansion of leucites. The structural relaxation under cationic (K, Cs) substitutions and under heating has been investigated.

Structural and magnetic phase transformation in metastable Fe-Cr alloys induced by ion irradiation

Unusual metastable paramagnetic phases have been observed in Fe–Cr thin films (thickness about 40 nm) fabricated by pulsed laser deposition. In the present article, x-ray diffraction and Mossbauer spectroscopy have been applied to follow the structural and magnetic phase transformation in these alloys induced by ion irradiation with a projected range positioned in the center of the films. It has been found that the critical dose for the transformation to the more stable body-centered cubic (bcc) structure depends on the initial phase of the film and the ion mass. The initial body-centered tetragonal phase, which forms in the alloys with low Cr content (∼30 at. %), can be completely transformed to the bcc phase already by a dose of 5×1015 Cr/cm2, whereas the primitive orthorhombic phase of roughly equiatomic Fe–Cr alloys is about four times more resistant against ion bombardment. A five times higher Ne ion dose is required to induce the same transformation as by the Cr bombardment. The observed effects are...