Magnetization and magnetic excitations in HoAl2

The magnetization of HoAl₂ single crystals parallel and perpendicular to the applied field for three crystallographic directions has been measured between 4.2 and 300 K in fields up to 8 T. Further the spin wave excitations were investigated by inelastic neutron scattering at 5.2 K along <100>, <110> and <111> directions in reciprocal space. The results are interpreted consistently in terms of a cubic crystal field using a simple molecular field to calculate the magnetization and an isotropic Heisenberg exchange interaction to obtain the magnetic excitations.     

Magnetization behaviour of DyAl2 single crystals

We report the theoretical interpretation of the magnetization and the magnetocrystalline anisotropy of ferromagnetic DyAl₂ single crystals between 4.2 and 60 K and magnetic fields up to 15 T. Good agreement between theory and experiment is obtained by using three temperature independent parameters: the two crystal field parameters B₄ = (?0.50 ± 0.05) × 10^?4 meV, B₆ = ? (0.51 ± 0.05) × 10^?6 meV and the Curie temperature T_c = (62 ± 2) K.     

Deposition of high-resolution Carbon/Carbon multilayers on large areas for X-ray optical applications

To synthesize X-ray optical multilayers showing both high resolution and high reflectivity spacer and absorber materials with low absorption coefficients for the desired spectral range are required. Simulations of C/C multilayers with different period thicknesses, d, and single layer densities, , show that a reflectance R([_Cu]K)>80% and a resolving power of about /600 can be achieved for C/C layer stacks with d=3 nm and N=1000 periods.An advanced large area PLD technique was used to deposit C/C single- and multilayers onto Si-substrates up to 6 in diameter. By variation of the laser parameters, we achieved densities of the carbon single layers in the range of _C=2.0...2.7 g/cm³ (measured by XRR) and surface roughnesses _C=0.13...0.19 nm (measured by AFM). Due to the interface intermixing and penetration depth of highly energetic ions, especially during the deposition of the absorber layers, the density contrast of multilayers with period thicknesses lower than 5 nm is noticeably reduced. C/C multilayers with period thicknesses d=1.1...7.0 nm, more than 500 periods and density contrasts of about 0.2 g/cm³ were deposited. PACS 81.15.Fg; 41.50+h; 68.55-a     

Point focusing with flat and wedged crossed multilayer Laue lenses

Point focusing measurements using pairs of directly bonded crossed multilayer Laue lenses (MLLs) are reported. Several flat and wedged MLLs have been fabricated out of a single deposition and assembled to realise point focusing devices. The wedged lenses have been manufactured by adding a stress layer onto flat lenses. Subsequent bending of the structure changes the relative orientation of the layer interfaces towards the stress‐wedged geometry. The characterization at ESRF beamline ID13 at a photon energy of 10.5 keV demonstrated a nearly diffraction‐limited focusing to a clean spot of 43 nm × 44 nm without significant side lobes with two wedged crossed MLLs using an illuminated aperture of approximately 17 µm × 17 µm to eliminate aberrations originating from layer placement errors in the full 52.7 µm × 52.7 µm aperture. These MLLs have an average individual diffraction efficiency of 44.5%. Scanning transmission X‐ray microscopy measurements with convenient working distances were performed to demonstrate that the lenses are suitable for user experiments. Also discussed are the diffraction and focusing properties of crossed flat lenses made from the same deposition, which have been used as a reference. Here a focal spot size of 28 nm × 33 nm was achieved and significant side lobes were noticed at an illuminated aperture of approximately 23 µm × 23 µm.     

Tailored internal coating of components by PLD and pulsed laser evaporation

An advanced PLD technique combining laser ablation and laser induced thermal evaporation was introduced to deposit thin films onto the inner surfaces of components.Beside the well known film properties of the classical PLD, like high reproducibility, smooth surface and high thickness precision, this novel combination of laser ablation and evaporation is characterized by improved or extended properties in terms of microstructure, deposition rate and possible layer thickness. The extension of the conventional PLD process allows for the co-deposition of dense, amorphous films as well as columnar grown or even porous films with thicknesses up to several tens of micrometers.In a first successful application of the novel process, tailored thermal barrier coatings (TBCs) for combustion chambers were realized. A remarkable result was that these coatings sustained very large strains of about 5% without notable delaminations. Under hot gas testing in model combustion chambers, the PLD-TBCs showed very promising behavior with excellent adhesion.Super hard, amorphous carbon films (DLC) deposited onto the inner surfaces of small components by this PLD technique are characterized by a Youngs modulus of about 400–500 GPa and a low friction coefficient of about 0.1. Due to its layered structure, with graded material density and hardness, this DLC exhibits relatively low internal compressive stresses of about -1...-2 GPa. PACS 81.15.Fg; 68.55-a; 46.50+a     

Molecular exchange through the vesicle membrane of siloxane surfactant in water/glycerol mixed solvents

The effect of glycerol on the permeability of vesicle membranes of a siloxane surfactant, the block copolymer polyethyleneoxide-b-polydimethylsiloxane-polyethyleneoxide, (EO)15-(DMS)15-(EO)15, was studied with freeze-fracture transmission electron microscopy (FF-TEM) and pulsed-field gradient nuclear magnetic resonance (PFG-NMR) spectroscopy. The FF-TEM results show that, in pure water, the surfactant can form small vesicles with diameters of less than 25 nm, as well as a few multilamellar vesicles with diameters larger than 250 nm. Gradual substitution of water with glycerol to a glycerol content of 40% leads to significant structural transformations: small vesicles are gradually swollen, and large multilamellar vesicles disappear. A glycerol content of 60% results in the complete disintegration of the vesicles into membrane fragments. PFG-NMR measurements indicate that the vesicle membrane does not represent an effective barrier for water molecules on the NMR time scale; hence, the average residence time of water in the encapsulated state is below tau b = 2 ms. In contrast, the average residence time of glycerol molecules in the encapsulated state can be as large as tau b = 910 ms. The permeability of the vesicle membrane increases with increasing glycerol concentration in the solvent: At a concentration of 40%, the residence time tau b is lowered to approximately 290 ms. After vesicle destruction at higher glycerol concentrations, a small glycerol fraction is still bound by membrane fragments that are formed after the disintegration of the vesicles.     

Laboratory LPP EUV reflectometer working with non-polarized radiation

A laboratory extreme ultraviolet reflectometer (EUVR) for the wavelength range from 10 to 16 nm was built at IWS Dresden using a gold target laser pulse plasma (Au-LPP) source. The peak reflectance and the center wavelength are reproduced in relative standard deviation of 0.2 and 0.02%, respectively. In contrast to measurements using linearly polarized s-adjusted synchrotron radiation at PTB, measurements with non-polarized radiation at the EUVR yield systematically lower values for the reflectance due to the smaller reflectance of the p-component at higher angles of incidence.     

A novel automated electrochemical ascorbic acid assay in the 24-well microtiter plate format

Automatic ascorbic acid (AA) voltammetry was established in 24-well microtiter plates. The assay used a movable assembly of a pencil rod working, an Ag/AgCl reference and a Pt counter electrode with differential pulse voltammetry (DPV) for concentration-dependent current generation. A computer was in command of electrode (z) and microtiter plate (x, y) positioning and timed potentiostat operation. Synchronization of these actions supported sequential approach of all wells and subsequent execution of electrode treatment procedures or AA voltammetry at defined intervals in a measuring cycle. DPV in well solutions offered a linear current/concentration range between 0.1 and 8.0 mM, a sensitivity of about 1 μA mM⁻¹ AA, and a detection limit of 50 μM. When used with a calibration curve or standard addition, automated voltammetry of samples with added known amounts of AA demonstrated good recovery rates. Also, the assay achieved the accurate determination of the AA content of vitamin C tablets, a fruit juice and an herbal tea extract. Robotic AA voltammetry has the advantage of conveniently handling multiple samples in a single measuring run without the continuous attention of laboratory personnel. It is a good option when the goal is cost-effective AA screening of sample libraries and has potential for applications in health care and the food processing, cosmetic and pharmaceutical industries.