U Hübner

On-line nanolithography using electron beam-induced deposition technique

Abstract A four-channel gas feeding was installed at a commercial e-beam lithography system. The gas system and the deposition technique were tested with a solid precursor (CpPtMe 3 ). With this material base we investigated the deposition behaviour on different substrates (Si, SiO x on Si), at different gas pressures and different beam energies ( E 0 =2.5 and 15 keV). In all cases a minimum feature size of 30 nm was obtained. The growth of simple point structures both in width and height shows a clear dependence on the pixeltime. The feature size can thus easily be controlled via the pixeltime of the e-beam. In addition to fundamental research, we have produced nanowires and other arrangements by using this technique. All deposition structures were found to be accurately placed in a given wiring by using mix&match-technique.

Planar gradiometers with high- DC SQUIDs for non-destructive testing

We investigated planar gradiometers on the basis of galvanically coupled high- DC SQUIDs for application in non-destructive testing (NDT). The stability of the sensor of better than 1% permits NDT investigations in unshielded environments. The layout of the gradiometer sensors and a corresponding determination of their effective areas and baselines will be discussed as well as the properties of the Josephson junctions in the DC SQUID based on step-edge and bicrystal grain boundaries. We show measurements with this type of sensor applied in a testing system for NDT to determine spatial and field gradient resolution as well as the influence of sensor position and experimental environment such as the dewar material on the performance of the sensor and the whole testing system. As an example first investigations of the permanent magnetization of hardened valves will be presented where we look for a correlation between hardening and magnetic field distribution.

One-dimensional intrinsic Josephson arrays based on HTS thin films

Abstract Mesa structures were produced from different highly anisotropic HTS thin films showing the intrinsic Josephson effect in c -direction. We observed clear dependencies of the critical current on both external magnetic field and microwave field. For the first time we were able to detect the modulation of the critical current of BSCCO thin film mesas in external magnetic field. For BSCCO as well as for TBCCO we found modulation periods in the Tesla range which is in good agreement with the lateral dimensions of the junctions. In the current-voltage characteristics of TBCCO mesas we found subgap structures and measured their dependence on temperature, external magnetic field and microwave irradiation.

Development of planar thin film HTSC–SQUID gradiometers for different applications

Abstract We investigated the main dependencies of the gradient resolution of planar galvanometer superconducting quantum interference device (SQUID) gradiometers made of YBa 2 Cu 3 O 7-x (YBCO). We focussed especially on the influence of antenna layout and the parameters of the galvanometer SQUID such as effective and parasitic areas on the performance of the gradiometer and the behavior in an unshielded environment. The efficiency (that is, the quotient of effective area to inductance) of different geometries of antennas will be compared. Some aspects of the layout of the galvanometer SQUIDs are discussed in terms of parasitic area and best current resolution. Special problems due to the use of bicrystal Josephson junctions in gradiometers for operation in highly disturbed environment are shown. Step-edge Josephson junctions can offer alternative concepts. Reached gradient sensitivity values in the white noise region are 0.46 pT/(cm/ H z) in the case of bicrystal junctions and 0.69 pT/(cm/ H z) for step-edge junctions.

High-Tc dc-SQUID gradiometers in flip-chip configuration

We describe a new design of a gradiometric flip-chip antenna, which is inductively coupled to a dc-SQUID gradiometer. Both components are patterned out of thin films of the high-Tc superconductor YBa2Cu3O7−x (YBCO). For the flip-chip antenna, a 40 mm × 10 mm SrTiO3 single crystalline substrate is used, while the gradiometer sensors are prepared on 10 mm × 10 mm SrTiO3 bicrystal substrates. Special attention is paid to the inductive coupling between the flip-chip antenna and the read-out gradiometer antenna. We investigate different designs of coupling loops in order to optimize the coupling inductance between both components of the sensor. With optimized coupling the sensor achieves a field-gradient resolution of 12 fT cm−1 Hz−1/2 in the white noise region and of 310 fT cm−1 Hz−1/2 at 1 Hz in the unshielded laboratory environment.

Thin film series arrays of intrinsic Josephson junctions

The intrinsic Josephson effect between the CuO2 sheets in Tl-2212 and Bi-2212 was used to prepare thin film mesa structures acting as series arrays of a number of junctions corresponding to the height of the mesa. We investigated the electrical properties of these arrays at various temperatures, in external magnetic fields, and under irradiation of microwaves. The results are discussed within simple theoretical models of 1-D Josephson arrays.

Several kinds of Josephson junctions based on BSCCO-2212 and TBCCO-2212 thin films

Abstract The properties of bicrystalline and biepitaxial BSCCO-2212 Josephson junctions prepared on SrTiO 3 substrates were investigated. Based on these junctions d.c. SQUIDs were prepared working up to about 75 K. By measuring the temperature dependence of the transfer function of bicrystal SQUIDs, we were able to determine the magnetic penetration depth for BSCCO-2212 in the temperature range from 30 to 75 K. Using BSCCO-2212 and TBCCO-2212 thin films, we prepared intrinsic Josephson junctions with mesas heights of about 50 nm and lateral dimensions down to 3 × 3 μm 2 . We will show the influence of external magnetic field and microwave radiation on the intrinsic Josephson junction behaviour.