Introduction

Abstract: The microstructure of YBCO/SrRuO3/YBCO junctions in the edge geometry have been studied by high resolution electron microscopy. Various defects in the YBCO and SrRuO3 films are observed and analyzed. The most striking defects in the c-axis-oriented YBCO film are a-axis particles, which cause bending and interruption of lattice planes as well as high steps and cracks in the subsequent layers. The SrRuO3 layer in the ramp-edge junction region consists of small domains with slightly different orientations. This leads to the formation of steps on its surface and large variation in SrRuO3 thickness. Mechanisms for forming this defective layer are suggested based on the growth mode and the crystal structure of SrRuO3. We find evidence for strain fields at the SrRuO3/YBCO interface. The oxygen deficiency in YBCO caused by this interface strain may to a large part be responsible for the excess resistivity of this junction. In addition to the defective SrRuO3 layer, the occurrence of various defects in the junction area, including Y2O3 and a-axis YBCO particles, seem to be the cause for the wide scatter in the junction electrical characteristics. The formation of steps and large thickness variation in the barrier layer may be the reason for the rather large critical thickness of the SrRuO3 superconductor-normal-superconductor (SNS) junction. In addition to the junction interfaces, the microstructure of SrRuO3/LaAlO3 and SrRuO3/SrTiO3 interfaces have also been studied.

Abstract: Here we present our observations of an anomalous desorption of copper oxides from a thin copper film during annealing as observed in an in situ transmission electron microscope. The epitaxial cuprous oxide that formed in air was observed to disappear when the specimen was annealed at 300°C and 10−8 torr. However, removal of the cuprous oxide that formed during oxidation in the microscope required both heating at 300°C and simultaneous exposure to methanol vapor.

Abstract: Films of Fe3O4 were prepared by sputter deposition onto MgO substrates of both 〈100〉 and 〈110〉 orientations. The films used in this study were mainly 50 nm thick. X-ray diffraction, Mössbauer spectroscopy, and other techniques revealed that the films were stoichiometric single crystals. Electron microscopy showed that the films were essentially dislocation free. Despite this high degree of perfection, the magnetic properties of the films were inconsistent with bulk single crystal properties. For example, the magnetization of the films did not saturate in fields as large as 7 Tesla, while bulk single crystals saturate by 0.1 Tesla.

Abstract: Transient liquid phase (TLP) bonding is a joining process in which a liquid-forming interlayer is placed between the substrates to be joined. At the bonding temperature, the interlayer initially liquates. Subsequently, interdiffusion between the liquid interlayer and the adjacent substrates results in a change in the overall composition of the joint, such that isothermal resolidification of the joint takes place. Standard models of the TLP process assume the sequential occurrence of discrete dissolution, isothermal solidification, and homogenization processes. This study uses edge-on transmission electron microscopy investigations to challenge the general applicability of such standard models to the TLP bonding of a variety of systems involving the B2 type intermetallic compound NiAl as a substrate material. This article considers the formation of boride phases apparently at the bonding temperature in NiAl/Ni-Si-B/Ni bonds. The precipitation of repeating sequences of phases in NiAl/Cu/Ni joints and the reliquation of the NiTi substrate in NiAl/Cu/NiTi bonds after the completion of isothermal solidification are examined.

Abstract: This investigation presents the interaction of dislocations and semicoherent precipitates (Ω phase) in an Al-Cu-Mg-Ag alloy. The study shows that the semicoherent precipitate is cut by dislocations during deformation. Conventional transmission electron microscopy (TEM) and high resolution TEM (HRTEM) observations demonstrate that shearing of precipitates by dislocations occurs by multiple cutting in the precipitate. The step height caused by cutting on the Ω precipitate is only several atomic layers of the Ω phase. The Ω phase is strengthened after shearing by dislocations. A strengthening mechanism is proposed on the basis of this observation. The strengthening mechanism is not only applicable to the Ω precipitate in Al-Cu-Mg-Ag alloys but also to the other semicoherent precipitates in other alloys.

Abstract: The magnetic behavior of lithographically defined thin film elements of permalloy imaged by Lorentz microscopy is described. Elements of thickness <100 nm, with in-plane dimensions in the micron and sub-micron range and of varying shape, have been subjected to in situ fields using an electron microscope that has been optimized for magnetic imaging. The information provided from the imaging modes has identified the details of the magnetization reversal mechanisms in the elements during the course of a hysteresis cycle. In particular, domain wall clusters which form at the edges of the elements are observed prior to switching of the magnetization. Results are described from elements with near single and multidomain structures with different geometry.

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