J. Greggi

Critical parameters in the single‐target sputtering of YBa2Cu3O7

The critical parameters in the single‐target magnetron sputtering of YBa2Cu3O7 have been identified and sufficiently optimized to allow the reproducible deposition of films with Tc’s of ≳90 K and Jc’s of ≫ 106 A/cm2 at 77 K. It was found that during film growth the bombardment of the YBa2Cu3O7 by energetic particles must be minimized and also a stronger oxidizing agent than molecular oxygen must be present to obtain films with these properties. Otherwise, films are deposited that, by x‐ray diffraction and energy dispersive x‐ray spectroscopy analyses, are indistinguishable from the highest‐Tc 1:2:3 stoichiometric material but which have critical temperatures of ≪90 K. Films need not have 1:2:3 overall stoichiometry to have optimum superconducting properties. In such cases the excess elements are present as second‐phase particles.The critical parameters in the single‐target magnetron sputtering of YBa2Cu3O7 have been identified and sufficiently optimized to allow the reproducible deposition of films with Tc’s of ≳90 K and Jc’s of ≫ 106 A/cm2 at 77 K. It was found that during film growth the bombardment of the YBa2Cu3O7 by energetic particles must be minimized and also a stronger oxidizing agent than molecular oxygen must be present to obtain films with these properties. Otherwise, films are deposited that, by x‐ray diffraction and energy dispersive x‐ray spectroscopy analyses, are indistinguishable from the highest‐Tc 1:2:3 stoichiometric material but which have critical temperatures of ≪90 K. Films need not have 1:2:3 overall stoichiometry to have optimum superconducting properties. In such cases the excess elements are present as second‐phase particles.

Microstructural studies of CdTe and InSb films grown by molecular beam epitaxy

Epitaxial thin films of CdTe (1–5 μm) have been grown directly onto (001) InSb substrates or onto intermediate buffer layers of InSb (0.25–0.5 μm) by molecular beam expitaxy. Cross‐sectional transmission electron microscopy and high‐resolution transmission electron microscopy have been used to characterize the film and interfacial microstructures. Inferences about film quality were also compared with single‐crystal x‐ray rocking curve data and agreed well. Resulting microstructural features were correlated with various experimental growth parameters and substrate cleaning procedures. Results show that near‐perfect CdTe films can be grown on InSb substrates, but film quality is critically dependent upon substrate cleaning. Other factors observed to influence defect formation in the films include growth rate, total growth time, or a change in growth rate during film growth. Extended defects which form include twins, line dislocations, or looplike defects. Lattice imaging has demonstrated the lattice matchin...

The upper critical field of NbN film

It is proposed and experimentally verified that the anomalously high superconducting critical field normal to the surface of NbN films possessing a column‐void microstructure is Hc3, the field appropriate for surface superconductivity. It is also proposed that because the coherence length is much less than the lateral column dimension that the resistivity of the column and not the film enters calculations of the Maki parameter α. A previously noted discrepancy in α is removed by these proposals.

Effects of hypophosphite contents and surface treatment on electroplated Co-Ni-P thin films

This article describes the effects of sodium hypophosphite (hypo) content in cobalt nickel sulfate bath, and the duration of surface treatment prior to electroplating, on the magnetic, structural, and electrical properties of Co‐Ni‐P thin films. The coercivity of the Co‐Ni‐P layer can be controlled independently either by hypo content or by surface treatment. Transmission electron microscopy microstructure indicates that the width of grain boundaries of Co‐Ni‐P films is influenced by hypo in the magnetic bath. The mechanism of the coercivity increase by hypo in the bath is thought to result from magnetostatic or exchange decoupling at phosphorus‐rich grain boundaries. Effects of these factors on media noise can be well‐explained by the microstructural change of Co‐Ni‐P layers.

Comparison of YBa/sub 2/Cu/sub 3/O/sub 7/ films grown by solid-state and vapor-phase epitaxy

Epitaxial films of YBa/sub 2/Cu/sub 3/O/sub 7/ (YBCO) have been grown on single-crystal SrTiO/sub 3/ and MgO substrates by two different routes using RF and DC magnetron cosputtering. In the first case, amorphous oxide films were deposited at a substrate temperature of 400 degrees C and the crystalline film grew by solid-state epitaxy in an in situ postanneal at approximately 850 degrees C. In the second case, a substrate temperature of 600-650 degrees C was used which was sufficient to crystallize the film as it was deposited from the vapor phase. Reaction with the substrate was less for the films grown by vapor-phase epitaxy-even when they were annealed at 850 degrees C-as shown by the transition temperatures of very thin films, Auger depth profile measurements, in situ XPS analysis, and transmission electron microscopy. XPS was used to show that segregation of Ba at the free surface can occur in either type of film. The relative merits of each growth process are discussed for microwave applications and tunnel junction fabrication. >

Growth and characterization of epitaxial silicon on heteroepitaxial CaF2/Si(111) structures

We report the epitaxial growth of silicon on a CaF2/Si(111) heteroepitaxial structure. The results show that contrary to previous reports, the room‐temperature predeposition of a very thin layer of silicon does not significantly affect the problem of calcium migration to the top surface of the silicon film, although it appears to improve the surface morphology of the film. Planar and cross‐sectional transmission electron microscope and x‐ray diffraction studies have shown that the silicon film, although single crystalline, is highly defective, the main defects being twins on both the inclined {111} planes and the parallel (111) planes.

Growth and characterization of lattice‐matched CaxSr1−xF2 on GaAs(100)

The epitaxial growth and characterization of the structural, morphological, interfacial, and electrical properties of lattice‐matched Ca0.43Sr0.57F2 on GaAs(100) are reported here. The ∼200 nm films were grown at 500 °C on the GaAs(100) substrates that had been cleaned by annealing at 600 °C. Nomarski optical microscopy, transmission electron microscopy (TEM), scanning electron microscopy, and reflection high‐energy electron diffraction results showed that the films were smooth and crackfree, with good crystalline quality. TEM showed evidence of two general types of extended defects in the film which occur at or near the film/substrate interface region. Film resistivity was found to be (3.6±0.75)×1013 Ω cm, and the breakdown field strength was (5.8±1.4)×105 V/cm. However, the breakdown in this case represented a nondestructive conduction process, as opposed to the catastrophic and irreversible change observed in previous studies. The dielectric constant of the films was measured to be 7.43±0.22. Capacitan...

Lorentz microscopy studies of magnetization patterns recorded on a real disk

In this paper we describe a new method for producing samples with large thin areas for Lorentz TEM observation of recorded magnetic domain patterns in production‐quality thin‐film rigid disks. In this method, as applied in this paper to the study of electroplated Co‐Ni‐P media, a strippable metal layer is introduced beneath the magnetic layer, along with plated Ni‐P which provides a sublayer for magnetic film growth comparable to the normal polished electroless nickel substrate. In this way one can produce a magnetic layer identical to that on a real disk, write data on the disk with a flying head, and then remove the magnetic layer for TEM analysis. We also describe some typical applications of the new method, including a comparison of magnetic domain structure at recorded transitions in high‐ and low‐noise media, and an illustration of the effect of head pole geometry on bit‐cell shape.

Formation of the A15 phase in thin‐film Nb‐Al diffusion couples

Single‐crystal and polycrystalline thin‐film Nb‐Al diffusion couples have been prepared by evaporation at pressures of 10−11–10−10 Torr. Sapphire, single‐crystal MgO, polycrystalline Al2O3, and polycrystalline Nb were used as substrates. These couples were annealed in situ at temperatures between T=780 and 950 °C for 30 min, in order to study the formation of the A15 phase. Based on resistivity data, between 800 and 880 °C, the A15 phase was formed only on oxide substrates. The relative A15 content was higher in polycrystalline couples than in single‐crystal couples. Between 880 and 950 °C the A15 phase was also obtained in couples deposited on Nb substrates. X‐ray data confirmed that the temperature of the A2 (bcc) to A15 structure transformation was lower in couples where the Nb‐Al solid solution was in contact with an oxide substrate. X‐ray photoelectron spectroscopy indicated the occurrence of surface reactions between the oxide substrate and Nb or Al. Auger depth profiles of the Nb/Al ratio were simi...

Interpretation of magnetic domain images and electron diffraction patterns in Lorentz microscopy

Lorentz TEM (transmission electron microscopy) images and associated electron diffraction patterns of magnetic domains recorded on thin-film media under various conditions are described. Various patterns of deflected diffraction spots are observed, depending on the state of magnetization of the specimen. Black and white contrast in Foucault images is controlled by the position of the aperture and results from both the magnetization distribution in the ferromagnetic thin-film specimen and the fringing fields above and below the specimen. Also shown is the effect of overwrite currents on the domain images. >