Johannes Eisenmenger

Effect of annealing on the depth profile of hole concentration in (Ga,Mn)As

The effect of annealing at

Patterning of YBCO thin films by ion implantation and magneto-optical investigations

250\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}

Large area magneto-optical investigations of YBCO thin films

on the carrier depth profile, Mn distribution, electrical conductivity, and Curie temperature of (Ga,Mn)As layers with thicknesses

Structures in superconducting YBa2Cu3O7−δ thin films investigated by magneto-optic technique

\ensuremath{\geqslant}200\phantom{\rule{0.3em}{0ex}}\mathrm{nm}

Magnetic instability in YBa2Cu3O7−δ films

, grown by molecular-beam epitaxy at low temperatures, is studied by a variety of analytical methods. The vertical gradient in hole concentration, revealed by electrochemical capacitance-voltage profiling, is shown to play a key role in the understanding of conductivity and magnetization data. The gradient, basically already present in as-grown samples, is strongly influenced by post-growth annealing. From secondary ion mass spectroscopy it can be concluded that, at least in thick layers, the change in carrier depth profile and thus in conductivity is not primarily due to out-diffusion of Mn interstitials during annealing. Two alternative possible models are discussed.

Influence of ion induced amorphicity on the diffusion of gold into silicon

Abstract YBa 2 Cu 3 O 7− δ thin films deposited by pulsed laser deposition were patterned by ion implantation. The patterning technique is based on the local disordering of the crystal structure due to elastic collisions of the implanted O + -ions and thus on a strong breakdown of superconductivity in the irradiated areas. With this patterning method circular and meandering structures with a size of 1 mm were prepared for investigations regarding high current applications. O + -ions with an energy of 180 keV were used to avoid a contamination of the film. The achieved structures were investigated concerning a dependence on the dose by means of RBS, XRD, AFM and magneto-optical characterization. Using a fluence of 5×10 14 O + /cm 2 a fully planar and stable structure can be obtained. The patterning depth can be adjusted by varying the implantation energy. So this technique was also used successfully on YBCO thin films covered already with a 200 nm Au top layer.

Ultrafast Magneto-Optical Study of Flux Avalanches in High-Tc Superconductors

A new apparatus for magneto-optical investigations of high temperature superconducting (HTS) films as large as 20×20 cm2 is presented. With this equipment flux penetration of an external magnetic field into YBCO thin films has been studied by scanning the samples through an inhomogeneous magnetic field (magneto-optical scanning technique, MOST). The normal penetration of magnetic flux into a superconductor will be changed drastically in the presence of defects. The apparatus was constructed to realize an effective quality control of large area HTS thin films used for device fabrication. With this technique, a visualization of flux pattern in superconducting films larger than 1×1 cm2 is presented for the first time. The results are compared to inductive jc measurements as well as to micrographs [optical microscope (OM), scanning electron microscopy (SEM)] and show that also in the large area characterization the magneto-optical method is very sensitive to microstructural defects impairing the critical curr...

Microbridge on YBa2Cu3O7−δ thin film patterned by reversible laser annealing

Using a reflection magneto-optic technique we have investigated natural inhomogeneities and artificial structures in YBCO thin films exposed to an external magnetic field. The artificial structures were mechanically scratched by scanning a diamond tip with different loading over the film surface. Alternatively planar structures with reduced oxygen content could be patterned by heating the YBCO film with a focused laser beam in nitrogen atmosphere. Depending on the laser annealing parameters different screening properties concerning the applied magnetic field could be achieved.As a magneto-optically active layer we used EuS films evaporated on glass as well as bismuth- and gallium-doped lutetium-iron-garnet films grown onto (111) oriented gadolinium-gal lium-gar net substrates by liquid phase epitaxy. In contrast to measurements with EuS films that show only weak faraday rotation for temperatures higher than 20 K the magneto-optic studies have been expanded to about 60 K by using the garnet films.

Defect visualization in large area YBCO thin films by magneto-optical scanning technique

Abstract Using a magneto-optic technique we have investigated the magnetic flux propagation into and out of superconducting thin YBa 2 Cu 3 O 7− δ films. After field cooling below T c , the external magnetic field B ext perpendicular to the film is changed which gives rise to shielding currents in the sample. The current distribution is disturbed momentarily by heating with a focused laser pulse near the sample edge. This triggers a magnetic instability, in which a magnetic flux avalanche starts to propagate.

Kondo effect and local disorder in ion irradiated AuFe

It is experimentally demonstrated that, after ion irradiating 60nm thick Au films on Si substrates with 230keV Ar+ ions, annealing conditions can be found leading to strong diffusional contrasts between bombarded and unbombarded areas. While Au readily diffuses into the bombarded part of the sample at 310°C, its diffusion is still completely blocked under identical conditions in the unbombarded parts. Clear evidence is provided that this diffusional contrast is due to bombardment induced amorphization of the underlying Si substrate. The amorphous Silicon (a-Si), however, has to extend right to the Au∕Si interface, since any intermediate crystalline layer will suppress the diffusional contrast. An example for this latter situation is realized by performing the ion bombardment prior to the evaporation of the top Au layer leading to a still crystalline Si surface layer, which is found to act as a barrier against Au diffusion at 310°C. In accordance with the idea that a-Si, independent of its specific prepara...