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It was found from plan-view transmission electron microscopy (TEM) observations that c-oriented YBa2Cu3O7−δ (YBCO) films on LaAlO3, prepared by the magnetron sputtering technique had a single crystalline-like YBCO matrix, but always contained some precipitates of impurity phases. A large number of highly defective twin boundaries were also observed in all of these epitaxial films. Such highly defective twin boundaries are thought to be flux pinning centres and also paths for the diffusion of water into YBCO films. Therefore the films need to be passivated against attack from humid air.

The properties of a sputtered film are strongly influenced by the deposition conditions. In this article we try to develop an understanding of the way in which the many parameters associated with sputtering process combine together to give only a few parameters which ultimately determine the film properties. In particular we consider the stresses in films and consider the conditions required to produce films with neutral stress, a state often required in films made in routine production. It is apparent that the product of the sputtering gas pressure and the substrate–target distance is a major factor in controlling the film stress, but also of relevance are the sputtering voltage and the substrate temperature. Many elemental and alloy films have been investigated, using variable argon pressures and substrate–target distances, at a low power and therefore a deposition temperature of approximately 20–40 °C. Detailed analyses have shown that a model of the total energy flux of particles bombarding the film i...

Microstructures of c-axis oriented YBCO thin films made by high-pressure d.c. sputtering on LaAlO3 and MgO substrates were examined by TEM. The a-axis oriented grains, second phases and micro-twins were frequently observed in the film. The a-axis oriented grains expanded along their c-axis directions during film growth. The a- and b-axis misorientations were observed in the film on MgO due to serious lattice mis-match between YBCO and MgO. The second phases were often accompanied with a-axis oriented grains suggesting they act as nuclei. These observed results were correlated with the measured T c and J c of the films.

A thin‐film sample of YBa2Cu3O7−δ on MgO was irradiated at room temperature with 50‐keV 2H+ (deuterium) to a dose of 1×1016 ions cm−2. The film was mainly c‐axis textured film, ∼360–420 nm thick, deposited by sputtering on 〈100〉 MgO substrate. The as‐implanted sample was divided into several pieces and annealed in a flowing oxygen ambient using (i) a rapid thermal annealing oven, at various temperatures between 450 and 940 °C, and (ii) a conventional annealing furnace, at various temperatures between 100 and 350 °C. Analysis by secondary‐ion mass spectroscopy shows that the implanted 2H is a fast diffuser in the 123 phase. The apparent activation temperature (energy) for 2H release from the initial traps within the YBCO film during the anneal is estimated to be ∼175 °C (∼0.97 eV), which is obviously lower than the apparent activation temperature (energy) for 2H release from the initial traps within the MgO substrate (∼550 °C, i.e., ∼1.78 eV). At 200 °C the diffusivity of 2H in the YBCO film is estimated t...

The dynamics of flux vortices in 0.7 mu m thick Nb films have been investigated using a linear array of 2*2 mu m2 Hall probes that can resolve single vortices. The flux vortices move into and out of the centre of the film in bundles. The flux bundle radius has been measured directly by a coincidence technique, and was found to decrease from 3.4 mu m to 1.6 mu m as temperature increased from 4.5 K to 6.5 K. We have observed the onset of flux creep driven by an applied DC current, thus determining the pinning force at individual pinning sites and establishing that pinning force fp alpha (1-T/Tc)n with n=0.52+or-0.05. The temperature dependence of the flux bundle radius can be described by the collective pinning theory of Larkin and Ovchinnikov, taking into account the measured temperature dependence of the pinning force.

A parallel plate resonator technique was employed to investigate changes in the microwave surface impedance between 20 K and 60 K, when d.c. magnetic fields up to 4 T were applied parallel to the YBCO film surface. By using a simple model to describe the observed behaviour, we can extract values for the vortex viscosity /spl eta/ and pinning constant /spl kappa//sub p/, as a function of temperature in three sets of films. As a result of low energy deuterium ion implantation in one of the films, the low field behaviour was degraded but at high fields the pinning properties improved quite drastically. A much smaller effect was observed in field dependence of the dc screening current as measured using vibrating sample magnetometry. >

The domain structure of sputtered Co‐Pd multilayer films of varying thickness has been investigated by magnetic force microscopy. The domains appear as stripe domains, typical of perpendicularly oriented films. The size of the domains was strongly influenced by the thickness of the film. The domain repetition lengths give an additional experimental parameter which has been used to provide a stronger test of a theoretical model developed for ferromagnetic multilayer films [H. J. G. Draaisma and W. J. M. de Jonge, J. Appl. Phys. 62, 3318 (1987)]. It is found that the experiment and theory are broadly in agreement provided that the increased magnetization of the multilayer caused by polarization of the Pd is accounted for. There is a noticeable difference between the variation of the measured and theoretical domain repetition lengths with film thickness. This is attributed to the effects of domain‐wall pinning which is not considered in the model. It is estimated that the characteristic length of the films i...

A Vibrating Sample Magnetometer (VSM) was used to study the magnetic properties of YBa2Cu3O7−x (YBCO) thin films sputtered onto LaAlO3, SrTiO3 and MgO substrates, before and after ion implantation with deuterium and 16O+. By applying the Bean model, the irreversible magnetisation M, was converted into a critical current density Jc, using a length scale Λ determined from a non-destructive technique, at each temperature. The implantation led to significant changes in the superconducting properties of the films. Most notably, for the deuterium implantation in lower Tc films (84K typically), Tc was enhanced by several degrees and M/Λ was enhanced by 1.1 – 1.25 times. In higher Tc films (92K), Tc and Jc were unaltered at the present fluencies used. A similar observation was made for films with a range of Tc values implanted with 16O+; when the Tc was unaltered after implantation, M/Λ was also unchanged, but where Tc was depressed M/Λ was enhanced by a factor of 2.3. Possible mechanisms are discussed.

Thin films of YBa 2 Cu 3 O 7−δ (YBCO) deposited by sputtering on LaAlO 3 and SrTiO 3 substrates have been implanted with 50 keV 2 H + (deuterium) ions at doses of 1 × 10 12 cm −2 and 1 × 10 16 cm −2 . Depth profiles of the high dose implants obtained by secondary ion mass spectrometry (SIMS) were compared with Monte Carlo simulations (TRIM90) and showed evidence of channelling in the substrates. The superconducting transition temperature, T c , measured by a.c. susceptibility (ACS) disappeared for the high dose implanted samples and X-ray diffractometry (XRD) showed that the YBCO c-axis length had increased, indicating a loss in oxygen content. After annealing the implanted samples with a rapid thermal annealer in O 2 and N 2 atmospheres, SIMS profiles indicated the fast diffusion of deuterium out of the films.

The angular dependence of Jc was investigated for c-axis oriented sputtered YBCO films. The observed features can be described neither by a 2D- nor by a 3D-anisotropic Ginzburg-Landau theory. An intrinsic pinning mechanism, effective only within a critical angle theta c between the applied magnetic field and the copper oxide planes, has to be considered in order to describe the sharp and narrow peaks of Jc at high fields and high temperatures. Neutron irradiation results also seem to be in favour of an intrinsic pinning model.

We have used ultrahigh vacuum dc magnetron sputtering to deposit cobalt–palladium multilayers on silicon substrates. The films have been characterized using vibrating‐sample magnetometry, x‐ray diffraction, and cross‐sectional transmission electron microscopy. We have observed ways in which the films’ microstructures and magnetic properties vary as the sputtering pressure is altered, and related the changes in magnetic properties to the changes in microstructure.

Measurements on current‐biased Nb/AlOx/Al/AlOx/Nb double tunnel junction devices with very thin central Al layers show a novel double hysteretic structure in the subgap region. Similar junction structures have previously exhibited very large nonequilibrium effects; the effects reported here appear close to and above the equilibrium critical temperature of Al. A model is presented in which the hysteresis is shown to arise from a transition from finite to zero voltage across one barrier on increasing current, due to the nucleation of an inhomogeneous state in the ultrathin central Al layer in which normal and superconducting states coexist. This reverse switching effect is shown to arise from the self‐shunting effect of low‐gap regions. Predictions of this model are shown to agree with the experimental data.

The range data and migration of Au in YBa2Cu3O7−δ film were studied with implanted 197Au (1.5 MeV 5×1015 Au+/cm2) as a tracer. The film was a c‐axis oriented film, ∼750 nm thick, deposited by high‐pressure planar dc sputtering on 〈100〉 LaAlO3. Analysis by secondary ion mass spectroscopy shows that the as‐implanted Au concentration distribution is essentially Gaussian‐like and the depth (Rp) of maximum Au concentration (∼1.2 wt %) is 201 nm. The projected range (Rp) and (Rp) are found to be in very good agreement with the simulated data by TRIM−95, whereas the measured ‘‘straggle’’ (ΔRp*) is about 20% larger than that by TRIM−95 simulation. It has also been found that the implanted 197Au starts to migrate within the film at a temperature between 650 and 700 °C, which is much higher than that for the implanted 2H (∼175 °C) and the implanted 18O (between 250 and 300 °C) in c‐oriented YBa2Cu3O7−δ films.

The paper discusses techniques for determining the complex conductivities of thin films of high-Tc superconductors at microwave frequencies. Preliminary results suggest that measured microwave conductivities are sensitive to defects extended normal to the microwave current, which also affect the normal conductivity and Jc.

A Materials Science overview of the deposition of ceramic superconductors is presented. Whilst in the last four years the major effort has gone into the deposition of YBa2Cu3O7-∂ (YBCO), the bismuth and the thallium compounds will also be considered. The two major techniques of laser ablation and “off axis” sputtering will be discussed as well as evaporation, molecular beam epitaxy (MBE) and metallo-organic chemical vapour deposition (MOCVD). Emphasis will be placed on the in-situ deposition technique for YBCO though some consideration will be given to the “post heat treatment” methods being used for the bismuth and thallium compounds. One of the fundamental issues to be addressed will be the relationship between the deposition conditions and the properties of the films produced. The key issues of nucleation will be discussed, aiming at an understanding of the outstanding problems of preparing smooth uniform films.

A parallel plate resonator technique is employed to investigate the microwave losses of YBCO thin films in applied magnetic fields up to 8 T parallel to the film surface. Changes of the surface impedance ( Z S = R S - iX S ) are observed due to various loss mechanisms induced by the magnetic field.

The overall aim of this work is to engineer YBCO films with well-characterised crystal structures, by selective patterning, amorphisation, and annealing. Thin films (80 – 400 nm) of YBa 2 Cu 3 O 7-δ , deposited by sputtering onto LaAlO 3 and MgO substrates, have been implanted at 200 keV with either 20 Ne + or 18 O + ions, to a dose of 5x10 14 ions cm −2 . Both implantations amorphise the film, in some cases totally. Oxygen implantation produces less damage than the inert gas. Rapid Thermal Annealing (20 seconds, about 870°C, in oxygen) can induce recrystallisation, leading to a recovery of the superconducting 123 phase under certain conditions. Results from T c , J c , XRD, and TEM investigations are presented.

Details are presented of the design of a small DC planar magnetron source and its use in a research-scale UHV getter sputter deposition system. The system has been used for depositing a range of refractory materials as well as some metal multilayer structures (single crystal, polycrystalline and amorphous). For some of these structures a relatively high sputtering pressure is required and a study has been made of the deposition rate as a function of pressure for a range of different elements. This illustrates the effect of the momentum and energy transfer of the sputtered atoms as they travel from the target to the substrate.

Measurements of the upper critical fieldB c2 (T) have been made on a range of high-transition-temperature A15 niobium germanium samples prepared by dc sputtering with varying additions of oxygen and differing sputtering conditions. An overview is presented on the formation of Nb3Ge with particular reference to lattice parameter, composition, and normal state residual resistivity. The problem of sample inhomogeneity and its effect onB c2 (T) measurements is discussed. Correlations of $${\text{dB}}_{{\text{c2}}} /{\text{dT|}}_{{\text{T}}_{\text{c}} } $$ are made withT cand resistivity, and the results compared with previous studies of neutron-irradiated and coevaporated material. Existing theories of $${\text{dB}}_{{\text{c2}}} /{\text{dT|}}_{{\text{T}}_{\text{c}} } $$ are summarized and the problem of comparison of theory and experiment is discussed. An analysis is presented that does not depend directly on assumptions about the Fermi surface structure. The data indicate thatB c2 has a fundamental dependence onT cand resistivity that is similar to that found in Nb3Sn. There is evidence that the mean Fermi velocity for clean Nb3Ge is about twice the value for Nb3Sn; the mean Fermi surface area is also about twice the value for Nb3Sn. This suggests that Nb3Ge is more strongly coupled than Nb3Sn.

We report results obtained from several hundred Nb/Al2O3/Nb tunnel junctions fabricated by the ‘‘whole‐wafer’’ process. These results indicate that one of the factors determining resistance and quality variations in such devices is the microstructure of the underlying base layer of niobium. We have further developed the technique of anodization spectroscopy to provide a quantitative measure of the variation in the thickness of the thin aluminum layers which contain the tunnel barrier and have related this to the temperature at which the niobium base layer is deposited. We show that at least two mechanisms are responsible for normal‐state resistance variations in such devices and that device quality is closely related to the integrity of the aluminum layer underlying the tunnel barrier.

A simple model calculation has been made of the upper critical field of A15 superconducting materials. This has been combined with ideas from work by Labbe, Friedel and van Reuth (1966-70) to explain some of the physical properties of disordered A15 materials in general and Nb3Al in particular.

Experimental results of kappa 1(t)/ kappa 1(1) are presented. The results of some model calculations of kappa 1(t)/ kappa 1(1) based on a theory of Hohenberg and Werthamer (1963) are also given. The theory takes account of the anisotropic Fermi velocity. The main conclusion is that this theory can explain kappa 1(t)/ kappa 1(1) in dilute niobium alloys. It appears that the approach to 'dirtiness' occurs at shorter mean free paths than previously thought in these alloys.

The available methods for measuring diffusion rates of various metalloids in metallic glasses are critically reviewed, and the advantages of studying boron diffusion by secondary-ion mass spectrometry (SIMS) set out.

A series of experiments designed to investigate the role of oxygen during the sputtering of the A15 superconductor Nb3Ge is reported. The overall trend found by other workers, of oxygen enhancing the Tc of ‘Nb3Ge’ in certain circumstances, is confirmed: however, two additional and associated effects are observed with our particular configuration of target and substrate. First, a tendency for the oxygen impurity to reduce the room temperature resistance ratio, and secondly, the appearance of two A 15 phases of slightly differing lattice parameter which are most discernible when oxygen impurity is present. A discussion of these effects and a detailed analysis of X-ray diffraction measurements is presented. It is concluded that oxygen, though beneficial for the formation of ‘Nb3Ge', is not necessarily the most critical parameter in the formation of stoichiometric Nb3Ge.

Over the last few years we have been involved with the fabrication of a range of metal multilayers, ranging from a series of single crystal multilayers, layers for amorphisation studies of mainly Ni/Zr and Co/Ti, some layers for diffusion studies such as a Si/Ge and finally some trial structures for potential X-ray mirror systems such as W/Si and W/C which we extended to W/Ti for modelling purposes. In this paper we will describe the role of the sputtering conditions on the properties of the films produced with particular reference to the problems of producing routine epitaxial films; the role of impurities on the surface mobility of surface atoms and finally the role of reflected neutrals (and sputtered) atoms and their thermalisation as they travel from the target to the substrate.