Angle-resolved X-ray photoelectron spectroscopy (ARXPS) and a modified Levenberg-Marquardt fit procedure: a new combination for modeling thin layers

The combination of angle-resolved X-ray photoelectron spectroscopy (ARXPS) and a modified Levenberg-Marquardt (LM) fit procedure has been used to study a native oxide layer on a clean Si(100) substrate. Numerical calculations show that with an aperture of 3° or 9° of the electron analyser, the photoelectron take-off angle should not exceed 80° or 70°, respectively, as compared to normal take-off angles. At larger photoelectron take-off angles, the effect of the aperture on the photoelectron energy distribution may not be neglected. We show how absolute ARXPS measurements in which the same XPS feature is considered at several electron take-off angles are an alternative for relative ARXPS film thickness measurements, avoiding large errors in the quantitative results. Models for the composition and thickness of the oxide layer have been developed. Also, the errors in the parameters of these models have been calculated. It can be concluded that the native oxide layer on silicon is 27 ± 1 (±-5%) Å thick and that the ratio of the silicon atom concentration in the substrate to that in the native oxide layer is 3.7 ±- 0.3 (±-8%), values that agree well with the literature. This report shows that the combination of ARXPS and a LM fit procedure is well suited to study ultra-thin layers and gives reliable results

High quality YBa2Cu3Ox ultra-thin films and Y/Pr/Y multilayers made by a modified RF-magnetron sputtering technique

High quality ĉ-axis oriented thin and ultra-thin films have been grown in situ on (100) surfaces of ZrO2, SrTiO3 and MgO. Sharp transitions were observed with Tc,zero of 87–91 K for films thicker than 70 Å. On atomically polished MgO substrates films as thin as 15 Å revealed a full transition to superconductivity above 45.5 K. The critical current density at 77 K was found to be strongly dependent on film thickness. A maximum value was found for a 100 Å film with 8 × 106A/cm2 at 77 K. Also, YBCO/PBCO/YBCO multilayer thin films have been fabricated in situ by the same technique. The epitaxy is maintained throughout the whole multilayer system. The superconducting properties of YBa2Cu3Ox layers do not change compared to single layers. Interdiffusion and possible chemical reaction close to the interfaces can be neglected.\ud \u

Controlled preparation of all high-Tc SNS-type edge junctions and DC SQUIDs

High-Tc SNS-type Josephson junctions and DC SQUIDs were successfully fabricated using hetero-epitaxially grown multilayers of YBa2Cu3Ox and PrBa2Cu3Ox. These layers are c-axis oriented and hence edges of the multilayers give rise to a current flow in the ab-plane between the electrodes of a Josephson junction. The necessary structuring was done by Ar ion beam etching. The individual junctions exhibit a supercurrent up to 80 K. The IcRn-product of these junctions usually has a lower limit of 8 mV at 4.2 K. Voltage modulation of the first DC SQUIDs can be observed up to 66 K. Details on the fabrication and measurements are presented

Preparation and properties of all high Tc SNS-type edge DC SQUIDs

High-Tc SNS-type Josephson junctions and DC SQUIDs were successfully fabricated using hetero-epitaxially grown multilayers of YBa2Cu3Ox and PrBa2 Cu3O. These layers are c-axis oriented, and hence edges of the multilayers give rise to a current flow in the ab-plane between the electrodes of a Josephson junction. The necessary structuring was done by Ar ion beam etching. The individual junctions exhibit a supercurrent up to 80 K. The IcRn product of these junctions usually has a lower limit of 8 mV at 4.2 K. Voltage modulation of the first DC SQUIDs can be observed up to 66 K. The voltage modulation for various bias currents investigated at 4.2 K noise measurements were performed. Details on the fabrication and measurements are presente

Epitaxial multilayers of YBa2Cu3Ox/PrBa2Cu3Ox/YBa2Cu3Ox

Heteroepitaxial multilayers of YBa2Cu3Ox/PrBa2Cu3Ox/YBa2Cu3Ox have been made by sputtering. No degradation of the transition temperature and the critical current density due to the presence of the PrBa2Cu3Ox layer could be observed. By using high-resolution transmission electron microscopy the atomic details of the interfaces and the defect structures have been studied. These films showed a perfectly stacked lattice just above the interface between film and substrate. The orientation of the c-axis perpendicular to the substrate was fairly perfect. The structural faults are mainly distributed in the middle and overlying layers. The dominant defects in our films seems to be stacking faults which give rise to nano-sized coherent anti-phase domains with the 1-2-3 structure. Rutherford backscattering spectroscopy, secondary ion mass spectroscopy, and scanning Auger microscopy were used to examine the interdiffusion between layers. Within the experimental resolution of 7 nm no interdiffusion is visible between YBa2Cu3Ox and PrBa2Cu3Ox layers

Vortex motion and Josephson effect in superconducting microbridges in (001) and (105) oriented YBaCuO thin films

Microbridges with dimensions smaller than the effective penetration depth have been prepared in epitaxially grown

Active noise compensation for multichannel magnetocardiography in an unshielded environment

A multichannel high-T/sub c/-SQUID-based heart scanner for unshielded environments is under development, Outside a magnetically shielded room, sensitive SQUID measurements are possible using gradiometers. However, it is difficult to realize large-baseline gradiometers in high-T/sub c/ materials, Therefore, the authors developed two active noise compensation techniques. In the Total Field Compensation technique, a Helmholtz type coil set is placed around the sensors. One magnetometer is used as a zero detector controlling the compensation current through the coil set. For Individual Flux Compensation, the reference signal is sent to the separate SQUIDs (or their flux transformer circuits) to compensate the local environmental noise fluxes, The latter technique was tested on low-T/sub c/ rf-SQUID magnetometers, each sensor set to a field resolution SQUID magnetometers, i.e. 0.1 pT/sub RMS///spl radic/Hz. The authors were able to suppress the environmental disturbances to such an extent that magnetocardiograms could be recorded in an ordinary environment. Here the two suppression techniques are described and experimental results are presente