It is demonstrated that a stepped (305) surface of a SrTi03 crystal can be used routinely to evaluate the probing profile of scanning-force-microscopy probes. This provides a means to select optimal surface probes, and to evaluate possible image distortions within the range of the atomic and nanometer scale. The scope and limitations of the resolution of structural defects are discussed as a criterion for a true atomic resolution.Scanning force microscopy (SFM), which is often also referred to as atomic force microscopy, ' currently is intensively used in various fields of material science in order to study surface interactions and surface structures. However, the image information often remains vague or ambiguous, due to the lack of insight of the actual imaging process.The resolution of a scanning microscope depends on the effective size of the probe which in the case of scanning force microscopy is determined by the probe

It is demonstrated that a high-temperature-treated (305) surface of a SrTiO 3 crystal can be used to evaluate the probing profile of AFM tips routinely, to provide a means of selecting perfect tips and to evaluate possible image distortions. This is important in order to recognize typical AFM artifacts which are caused by tips with truncated or twinned peaks which occur rather often in the case of microfabricated AFM needles. By means of selected needles, it is shown that also defective tips can give apparently rather perfect atomic resolution from flat crystal surfaces. Scope and limitations of the resolution of structural defects are discussed as the criterion for real atomic resolution.

The interface between yttria-stabilized zirc~nia (YSZ) substrate and YBazCu107 (YBCO) film was studied by high-resolution electron microscopy. In all specimens we have observed an intermediated layer of BaZQ located between the substrate YSZ and YBCO. The BaZrO, layer is composed of almost equally aligned domains being 4-8 nm in the lateral directions. Reaction products such as Y and Cu oxides were never observed in or close to the BaZrQ reaction layer but they do occur in the YBCO film.

We present a study of the electrical properties of insulating CeO 2 layers in combination with superconducting ͑Y/Dy͒ Ba 2 Cu 3 O 7Ϫ␦ ͑RBCO͒ films over ramps and in crossover structures. CeO 2 is frequently used as a buffer layer, or template layer for biepitaxial grain boundary junctions, but can also be used as an insulating layer in ramp-type junctions and other multilayer structures. Epitaxial thin films of CeO 2 were deposited by pulsed laser ablation using SrTiO 3 substrates. We characterized the insulating performance of CeO 2 thin films in terms of breakdown field E bd and the relative dielectric constant ⑀ r . For 80 nm thick CeO 2 at 77 K we found E bd ϭ1ϫ10 6 V/cm, using a 1 nA/100 m 2 breakdown criterion, which gives us a specific resistivity of у10 9 ⍀ cm up to breakdown. From capacitance measurements on planar RBCO/CeO 2 /RBCO structures we obtained for the dielectric constant: ⑀ r Ϸ15. The texture of CeO 2 in combination with RBCO on ramped surfaces, simulated by SrTiO 3 ͑STO͒ ͑103͒ substrates having their normal tilted by 18°away from the STO͓001͔ direction, has been studied by x-ray diffraction. © 1996 American Institute of Physics. ͓S0003-6951͑96͒02604-6͔High-quality heteroepitaxial multilayers of superconductors and insulators are required for high T c superconducting electronic devices, like ramp-type junctions and crossover structures in multiturn coils. For the use in highfrequency applications, an insulator having a low dielectric constant is preferred to reduce capacitive shunting. Materials often used as insulators in high T c superconducting devices are PrBa 2 Cu 3 O 7 ͑PBCO͒ 1 and SrTiO 3 ͑STO͒. 2 The use of PBCO has some disadvantages for its relatively low resistivity at 77 K and the anisotropic growth. The last property enhances the formation of granular films, and leaks are likely to occur at boundaries between a-and c-axis oriented grains. The main drawback of STO is its large dielectric constant ͓⑀ r Ϸ300 for thin films ͑Ref. 2͔͒, which severely limits its applicability in high-frequency devices. CeO 2 has been shown to be useful as a planar insulator. 3 It has a cubic crystal structure with lattice constant a 0 ϭ5.411 Å, and CeO 2 ͓100͔ is commensurate with YBCO͓110͔, corresponding to a relative rotation of 45°of the lattices. The very simple crystal structure, containing only one metal ion and oxygen, makes CeO 2 an easy material to grow by pulsed laser deposition, as no problems with the stoichiometry are to be expected. The use of CeO 2 in ramp-type junctions and crossover structures requires a nearly perfect heteroepitaxy with RBCO, both on top of flat surfaces and on artificially created ramped surfaces. The rotation of CeO 2 relative to RBCO, however, might induce grain boundaries or cracks when growing on a ramped surface. Reuvekamp et al. 4 showed that the preferential orientation of RBCO grown on YSZ is with the c-axis perpendicular to the local YSZ substrate surface. The difference in orientation in the upper YBCO layer on the ramp and on flat surfaces then caused cr...

Ramp-edge YBa2Cu3Ox/PrBa2CuaOx/YBa2Cu30,, Josephson junctions with PrBa2Cu30 . (PrBCO) or SrTiO 3 as a separating layer on different kinds of substrate have been studied by high-resolution electron microscopy. The bottom YBa2CuaO x (YBCO) layer and the separating layer (PrBCO or SrTiO 3) were epitaxially c oriented, irrespective of the substrate (yttria stabilized zirconia (YSZ), SrTiO 3 or NdGaO3, all in (001) orientation). The use of ion milling in the manufacturing of Josephson junctions was found to yield smooth slopes with an angle of about 20 °. The Josephson junction was facing away from the beam direction was found to have a dimple in the substrate near the base of the junction. The barrier layers were observed to have a homogeneous thickness. These layers as well as the top YBCO layers were oriented with their c-axes perpendicular to (001) plane of the substrate for perovskite substrates and perpendicular to the surface for YSZ substrates. In the case of a YSZ substrate, the dimple in the substrate as well as the slope of the substrate close to the base of the junction were found to lead to small-angle grain boundaries in the YBCO film as well as randomly oriented YBCO grains, which results in a poor ramp-edge junction. In the case of SrTiO 3 or NdGaO 3 substrate, all components of the device were fully epitaxial, thus resulting in good ramp-edge junctions.