Several earlier μg experiments have shown that time-dependent thermocapillary (Marangoni) convection is the major cause for the formation of dopant striations in floating-zone grown semiconductor crystals, at least in small-scale systems not employing RF heating. To quantify this correlation, a silicon floating-zone experiment was performed on the TEXUS36 flight (February 7, 1998) in a monoellipsoid mirror furnace to measure temperature fluctuations in the melt zone and the microscopic growth rate simultaneously. Fluctuations of 0.5K – 0.7K with main frequencies between 0.1Hz and 0.3Hz were detectable. The microscopic growth rate fluctuated considerably around the average growth rate of 1mm/min: rates from 4mm/min to negative values (backmelting) were observed. Dopant striations are clearly visible in the Sb-doped crystal. The frequencies associated with the dopant inhomogeneities correspond quite well with those of the temperature fluctuations and microscopic growth rates. 3D numerical simulations were performed to predict the optimum position of the temperature sensor, to evaluate characteristic temperature amplitudes and frequencies, and to give insight into the instability mechanisms of Marangoni convection in this configuration. The simulations were in good agreement with the experimental values, showing temperature fluctuations with frequencies f ≤ 0.25Hz and amplitudes up to 1.8K at a position equivalent to that of the sensor tip in the experiment. Future microgravity S-FZ experiments, currently scheduled for a MAXUS flight in 2001, will try to influence the formation of dopant striations by rotating magnetic fields or by vibrational convection.

Transverse rotating magnetic fields (Bmax=7.5 mT, frot=50 Hz) were applied to the floating zone growth of doped silicon. Non-periodic dopant fluctuations caused by time-dependent thermocapillary convection were considerably reduced by the rotating field. The radial segregation profiles (measured by a spreading resistance probe) became more homogeneous and more symmetric. The transition from a regime dominated by time-dependent thermocapillary convection to a flow state characterized by the rotating magnetic field was determined. This threshold depends on the height of the melt as well as the melt diameter (crystals between 8 and 14 mm have been investigated) and the efficiency of the applied field increases with larger melt zones. For a melt of 14 mm in diameter and an aspect ratio of 1 it is in the range of 2.5–3.75 mT/50 Hz (corresponding to a Taylor number of Ta=9.3×103–2.1×104). The change from a time-dependent 3D-flow without field to a quasi-axisymmetric 2D-flow with the magnetic field is corroborated by numerical simulations of the flow field: the thermocapillary driven irregular flow rolls are transformed to a nearly axisymmetric flow with high azimuthal flow velocities but reduced axial and radial components.

Mechatronical integration of power and control electronics directly into the actuators offers many advantages such as reduced costs, increased EMC, reduced volume or less weight. However mechatronical integration often is accompanied with undesired increase of thermal or mechanical loading of electronics. Computer-aided thermal/mechanical modelling and cosimulation of electronic housings for control and power electronics lead to optimised design of a mechatronical integrated solution for an engine cooling system. Thus critical temperatures for the devices can be avoided resulting in a reliable performance within the specifications. In addition total development time could be reduced considerably

An in situ observation setup for the growth process based on near-IR microscopic interferometry was modified for a short- duration low-gravity experiment. Subsequently the observation in the environments were performed to reveal the influence of strongly-damped fluid flow on the growth process using the parabolic flights of an airplane and the free-fall of a drop capsule. As result, the dissolution and growth rates were successfully obtained using the setup with a high accuracy. It was also found that the rates were strongly decelerated during the low gravity conditions.

The use of do-loops in connection with variables for the FIDAP mesh generation is demonstrated. Special focus is drawn on the advantage of labeling objects explicitly especially for more complicated meshes. These concepts are illustrated with the mesh generation for a three zone resistance furnace.

A silicon crystal growth experiment has been accomplished using the floating-zone technique under microgravity on a sounding rocket (TEXUS 36). Measurements of temperature fluctuations in the silicon melt zone due to time-dependent thermocapillary convection (Marangoni convection) and an observation of the microscopic growth rate were simultaneously performed during the experiment. Temperature fluctuations of about 0.5–0.7°C with a frequency range <0.5Hz were detectable. The microscopic growth rate fluctuates considerably around the average growth rate of 1mm/min: Growth rates up to 3–4mm/min, close to zero mm/min, as well as negative values (backmelting) were observed. Dopant striations are clearly visible in the Sb-doped crystal. They were characterized by spreading resistance measurements and differential interference contrast microscopy. The frequencies of temperature fluctuations, microscopic growth rates, and the dopant inhomogeneities correspond quite well, with main frequencies between 0.1 and 0.3Hz. 3D numerical simulations were performed to predict the optimum position of the temperature sensor, and the characteristic temperature amplitudes and frequencies. At a position 3.4mm above the interface and 1.4mm inside the melt, equivalent to the sensor tip position in the experiment, temperature fluctuations up to 1.8°C and frequencies ⩽0.25Hz were found in the simulations.

Epitaxial c-oriented YBCO films laser deposited onto 3 in diameter CeO2-buffered sapphire wafers and LaAlO3 cylinders as well as sputter deposited onto 2 in diameter LaAlO3 wafers were characterized by integral and spatially resolved measurements of the critical current density j(c) and the microwave surface resistance R-s, by microstructure investigations using optical and electron microscopy and by x-ray diffraction. Epitaxial misorientations of in-plane-rotated as well as of a-axis-oriented grains were found in amounts up to 10%. The in-plane rotation seriously degraded R-s while the a orientation mainly lowered j(c). Moreover, a degradation of R-s and of the microwave power handling could be clearly correlated with the density of microcracks occasionally found in YBCO films on sapphire. Inhomogeneities like a-axis-oriented grains were observed to 'disperse' microcracks, probably in favour of the electrical properties. The impact of further microstructure imperfections on R-s, in particular of the typical twin lamellae and their domains, is discussed in view of findings from transmission electron microscopy.

Phase-pure, large grained Nb/sub 3/Sn films on sapphire substrates have been prepared by a two-step process. The average grain size increased with the film thickness. Transport properties like the penetration depth, mean free path, and critical current density have been investigated in relation to the microstructure of the films. Measurements of the DC- and HF-magnetic field dependent surface impedance were performed. Nonlinear surface resistance occurred at field levels above B/sub s/=25 mT, and was related to extrinsic mechanisms. The relevance of weak coupling at grain boundaries decreased with increasing grain size. Thus heating at local defects was concluded to be the dominant limiting mechanism in large grained films. An intrinsic field limit of B/sub cl/=140 mT was found. The polycrystalline films showed a much lower residual resistance and comparable power handling compared to high-quality epitaxial YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta//-films.

We have developed and successfully operated a compact tunable one-pole filter at 2 GHz for transmitter combiners in mobile radio base stations. The concept is based on edge-current free modes in circular symmetric resonators. Unloaded quality factors Q/sub 0/>5.10/sup 5/ were achieved with double-sided 2''-diameter YBaCuO films on Czochralski-grown LaAlO/sub 3/. The dielectric loss tangent limited Q/sub 0/ around 60 K to values below 10/sup 5/. A circulating (transmitted) power of 800 kW (130 W), 700 kW (115 W) and 90 kW (15 W) could be handled in pulsed operation (pulse duration 10 ms, duty cycle 3%) at 23, 45 and 76 K, respectively, without measurable Q-degradation. These results approach the best microwave field performance measured so far with unpatterned films at 19 GHz. The power handling of the filter degraded in proportion to the duty cycle, indicating heating as the dominant limitation. The filter could be tuned by 3% by moving a plunger film by 36 /spl mu/m above the ring-shaped groundplane of the resonator. The CW power handling was not affected by the tuning, but the radiation losses and the maximum achievable power levels were degraded compared to the fixed-frequency filter.

The growth process of silicon crystals grown with the float- zone method is strongly influenced by convection in the melt zone. Crystal growth under microgravity (μg)offers the advantage to reduce the buoyancy related convection. The size restriction which we have under terrestrial conditions due to the hydrostatic pressure is also avoided. But due to the low Prandtl number of silicon (Pr=0.02) and the comparatively high temperature dependence of surface tension (δy/δT=-.28x10-3 N/mK) even small free melt zones exhibit time-dependent thermocapillary (Marangoni) convection. Thus irregular dopant inhomogeneities occurred in doped crystals grown under 1g conditions as well as in crystals grown under (mu) g. Attempts to enhance the dopant distribution by applying static magnetic fields resulted in most cases in either a reduced radial homogeneity, or in time-dependent thermoelectromagnetic convection (TEMC). A promising alternative are transverse rotating magnetic fields: the time-dependent thermocapillary convection is not damped as in the case of static fields, but a 2D-axisymmetric, azimuthal flow is superimposed. Several experiments performed under 1g demonstrated the positive effect of rotating magnetic fields on the microscopic dopant distribution as well as on the radial dopant profile homogeneity.

Physical mechanisms which limit the power handling of YBa 2 Cu 3 O 7− x films and devices are discussed in terms of a quantitative classification scheme. The possible limitations are devided into magnetic or thermal, and global or local in nature. Analytical estimations are compared with measurements of YBa 2 Cu 3 O 7− x films (Ø = 1″–2″) using a niobium-shielded sapphire resonator at 19 GHz, and disk resonators at 2 GHz. Magnetic effects are found to play an essential role in nonoptimized films in terms of weak-links, and in high-quality films if the lower critical field Bcl is reached. The majority of films and disk resonators appear to suffer from microwave heating. Global heating appears predominantly at CW operation. Local heating results mainly from defects in films of medium quality. Defect-induced quenches are observed at moderate field levels, sometimes resulting in an irreversible degradation of the power handling.

Surface impedance data at 19 and 87 GHz of high-quality epitaxial YBCO films on different substrates are compared with data for Nb 3 Sn films on sapphire in terms of pair and quasiparticle (qp) transport. Surface resistance R s and penetration depth λ of YBCO are strongly affected by temperature dependent qp scattering, which is depressed in films with enhanced lattice strain. All films showed a comparable residual resistance R res (19 GHz)∼90 μΩ constituting a qp reservoir which is likely to be caused by the electronic configuration and by impurities. Subtracting R res from R s (T) revealed activated behavior with a reduced energy gap Δ 0 / k B T c ∼0.9 for a film on sapphire, but power-law behavior for the other films. The penetration depth did not reveal power-law dependences at T ≤0.5 · T c , but was consistent with a reduced energy gap of 0.45 for a film on MgO. The increase of λ( T ) at T ≥0.5 · T c was related to qp scattering, which also caused an extremal conductivity σ 1 ( T ). A shoulder in λ( T ) at T =(0.6–0.7) · T c confirmed evidence for the existence of two superconducting bands. The magnetic-field induced recovery of λ( B ) of various YBCO films hinted for an important role of magnetic scattering. The results are in contradiction to a d -wave symmetry of the order parameter, at least for the chain band.

A comparative study of the microwave properties of YNi2B2C and ErNi2B2C superconducting films is reported. The measurements were performed using a microstrip resonator (f=2 GHz) and a microwave cavity (f=87 GHz). The analysis of the temperature dependence of the surface impedance Zs confirms that YNi2B2C compound is a conventional BCS (s-wave) superconductor. On the contrary, ErNi2B2C samples show an anomalous behaviour in both the surface resistance and penetration depth. This is tentatively ascribed to pair breaking effects on the superconducting density of states. A simplified generalisation of the Abrikosov–Gorkov theory, proposed by Machida, is successfully applied to describe the penetration depth data in the antiferromagnetic compound, while for the surface resistance granular effects cannot be ruled out.

Several earlier mu g experiments have shown that time-dependent thermocapillary (Marangoni) convection is the major cause for the formation of dopant striations in floating-zone grown semiconductor crystals, at least in small-scale systems not employing RF heating. To quantify this correlation, a silicon floating-zone experiment was performed on the TEXUS36 flight (February 7, 1998) in the monoellipsoid mirror furnace TEM02-ELLI. During the experiment, temperature fluctuations in the silicon melt zone and the microscopic growth rate were simultaneously measured. Temperature fluctuations of 0.5 degrees C - 0.7 degrees C with main frequencies between 0.1Hz and 0.3Hz were detectable. The microscopic growth rate fluctuated considerably around the average growth rate of 1mm/min: rates from 4mm/min to negative values (backmelting) were observed. Dopant striations are clearly visible in the Sb-doped crystal. The frequencies associated with the dopant inhomogeneities correspond quite well with those of the temperature fluctuations and microscopic growth rates. 3D numerical simulations were performed to predict the optimum position of the temperature sensor, to evaluate characteristic temperature amplitudes and frequencies, and to give insight into the instability mechanisms of Marangoni convection in this configuration. The simulations were in good agreement with the experimental values, showing temperature fluctuations with frequencies f less than or equal to 0.25Hz and amplitudes up to 1.8 degrees C at a position equivalent to that of the sensor tip in the experiment.

High-quality c-axis oriented YNi/sub 2/B/sub 2/C (transition temperature T/sub c/=15 K) and ErNi/sub 2/B/sub 2/C (T/sub c/=9.5 K) borocarbide superconducting thin films were grown "in-situ" on MgO and sapphire substrates by planar magnetron sputtering. Here we report data on the temperature, DC and RF magnetic field dependent surface impedance of the films and discuss them in view of possible applications. The YNi/sub 2/B/sub 2/C films displayed the behavior expected for BCS-like superconductors, while the microwave response of the antiferromagnetically ordering compound ErNi/sub 2/B/sub 2/C was distinctly different. The field dependent surface resistance of both types of films displayed granular effects.

Crack-free thick YBa/sub 2/Cu/sub 3/O/sub 7-x/ films are prepared on CeO/sub 2/ buffered r-cut sapphire (2 inch in diameter) with thickness up to 700 nm, smooth surfaces ('peak-to-valley' roughness <10 nm), high critical currents (J/sub c/>2 MA/cm/sup 2/ at 77 K and 0 T) and low microwave surface resistance (R/sub s/(77 K)/spl ap/1.4 m/spl Omega/ and R/sub s/(4.2 K)/spl ap/110 /spl mu//spl Omega/ at 19 GHz), comparable to the best values reported for YBCO films on structurally better matched substrates. The improvement of the critical thickness of YBa/sub 2/Cu/sub 3/O/sub 7-x/ on structurally poorly matched sapphire from typically d/sub c//spl ap/250-300 nm to d/sub c/>700 nm is achieved by introducing defects which do not hamper the superconducting properties of the films. The modified film growth was reflected by slightly broadened rocking curves and an altered temperature dependence of R/sub s/. The thick YBCO films were able to handle high microwave power corresponding to magnetic field amplitudes (B/sub HF/) of at least 54 and 37 mT at 4.2 and 50 K (limited by the available power), and 17 mT at 77 K (often limited by quenches). The excellent high-power performance was achieved without any degradation of the samples despite frequent thermal cycling.

Pulsed laser deposited (PLD) Ag-doped YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) thin films on both sides of 3-inch diameter sapphire wafers are used routinely for development of microwave filters for future communication systems. The reproducibly deposited YBCO:Ag films of about 250 nm thickness show critical current densities of 4 MA/cm/sup 2/ at 77 K and laterally homogeneous maps of microwave surface resistance R/sub s/ of about 45 m/spl Omega/ at 145 GHz and 77 K measured by an open resonator technique. The R/sub s/ at 8.4 GHz and 77 K determined in the center position of the YBCO:Ag films with a sapphire resonator technique remains constant at about 380 /spl mu//spl Omega/ up to a microwave surface magnetic field of 7-10 mT. Correlations of transport and microwave properties to the film microstructure are shown in terms of in-plane epitaxy, size of particulates on the films, and composition ratios Cu/O and Y/O, and growth defects like stacking faults as shown by Raman spectroscopy, SEM, and SNMS depth profiling, and TEM cross sections, respectively. The optimum Ag-content of the PLD-YBCO target was determined to be about 4 weight -%. The results demonstrate that Ag-doping supports the PLD process for YBCO in terms of reliability and cost effectiveness.

Diagnostic techniques to analyse the performance of superconducting surfaces in high-frequency fields were decisive for the development of superconducting particle accelerators. They also play an important role for the application of HTS films in emerging products. We describe experimental methods for the measurement of critical current, temperature, and microwave surface resistance of HTS films as used today, and give first results on the local analysis of these quantities using scanning hall and scanning laser probe techniques.

We have investigated the quality and the homogeneity of YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) films up to /spl phi/=2" diameter and t=360 nm in thickness with a scanning Hall probe. The YBCO films were grown by high oxygen pressure sputtering with heater temperature compensation up to T=1020/spl deg/C, resulting in a constant growth temperature for both film sides. Typical /spl phi/=1" double-sided films on LaAlO/sub 3/ substrates revealed inductively T/sub c/=87.8(88.2) K and J/sub c/=4(4.5) MA/cm/sup 2/ for the first (second) deposited side. Surface resistance measurements at 87 GHz resulted in R/sub s/(4.2 K)=2.6 (1.6) m/spl Omega/. At 19 GHz, R/sub s/(4.2 K)=0.2 m/spl Omega/ with moderate field dependence up to B/sub s/=15 mT was obtained for both sides. The scanning Hall probe measurements have been carried out after cooling the film in an external magnetic field and then switching it off. The local J/sub c/ values deduced from the measured remanent induction B were in good agreement with inductive data taken at corresponding positions. Different kinds of defects and inhomogeneities were investigated with a spatial resolution of 1 mm.