NbN/MgO/NbN Josephson tunnel junctions have been prepared using various barrier preparation conditions. The energy of the sputtered MgO particles arriving at the substrate was found to be the most important parameter. Tunnel junctions (10*10 mu m2) with Vm values of up to 23 mV have been fabricated. The optimized NbN/MgO/NbN junction process is extended to a reliable whole-wafer process for DC SQUID fabrication.
O. Dössel, B. David, M. Fuchs, J. Krüger, W. H. Kullmann, and K. M. Ludeke. A modular approach to multichannel magnetometry. In Clinical Physics and Physiological Measurement : an Official Journal of the Hospital Physicists' Association, Deutsche Gesellschaft fur Medizinische Physik and the European Federation of Organisations for Medical Physics, vol. 12 Suppl B, pp. 75-79, 1991
A 19-channel SQUID system for biomagnetic measurements has been developed. This system differs from standard instruments in its modular approach. Various gradiometers can be coupled to the SQUIDs, the cryogenic system allows the exchange of single channels and the electronics is based on a cassette system. Problems with thermal insulation, vibrations of the gradiometers and tilted gradiometer geometries are discussed and solutions are presented.
G. Gauglitz, and W. Nahm. Observation of spectral interferences for the determination of volume and surface effects of thin films. In Fresenius Journal of Analytical Chemistry, vol. 341(3-4) , pp. 279 283, 1991
The application of a rapid scanning diode array spectrometer allows the time-resolved observation of the interferences caused by multiple reflections at the interfaces of thin films. This spectral interferometry enables the observation of changes in optical pathlengths and allows to separate volume-effects like polymer swelling from surface-effects like adsorption or deposition. Polymer/solvent interactions will give an example for an application of this method.
A modular low-noise seven-channel SQUID-magnetometer for biomagnetic measurements was developed. The DC-SQUIDs are prepared by thin film technology based on the materials NbN-MgO-NbN, and show a flux noise below 10 μΦ0/√Hz. The signal is picked up with first-order wire-wound gradiometers of 2-cm diameter and coupled to the SQUIDs by integrated coupling coils. Individual channels can be replaced from the system, and various gradiometers can be used giving a flexible modular system. The electronics are based on the flux-locked-loop method extended by a bias modulation technique to reduce 1/f noise. The overall system noise is below 20 fT/√Hz. Biomagnetic measurements on auditory evoked fields have been carried out