A. Del Vecchio

The effect of deposition rate on the intrinsic stress in copper and silver thin films

The effect of changing the deposition rate on the development of stress in evaporated copper and silver thin films deposited on oxidized silicon was examined. In situ stress measurements were made during deposition in ultrahigh vacuum using a scanning laser curvature system. In some experiments, the deposition rate was alternated without interruption of deposition. For copper thin films, a change in deposition rate has no effect on the development of the tensile stress, while the magnitude of the postcoalescence compressive stress decreases with increasing deposition rate. In silver films, the film thickness at the tensile maximum increases slightly with increasing deposition rate, while the magnitude of the postcoalescence compressive stress again decreases with increasing deposition rate. Analysis of the heat flow during deposition shows that the radiative heating and condensation contribute roughly equally to the temperature rise of the sample.

Structural analysis of infinite layer superlattices grown by pulsed laser deposition

In this work we investigate the structural properties of SrCuO2/CaCuO2 infinite layer superlattices by high‐resolution x‐ray diffraction and x‐ray specular reflectivity measurements. The infinite layer superlattices are grown by pulsed laser deposition on slightly misoriented (001) SrTiO3 substrates. We demonstrate that good quality superlattices with few monolayers thick constituent SrCuO2 and CaCuO2 layers can be grown having an interface roughness of less than 3–4 A. A strain analysis of the epitaxial film shows that the SrCuO2 layers are completely relaxed with respect to the substrate. However, the CaCuO2 layers are elastically strained with respect to the SrCuO2 layer. The Poisson ratio of the CaCuO2 is estimated to be 0.40±0.08.

Modulated sputtering process for smooth surface YBCO film deposition

Abstract A method to fabricate high T c superconducting films exhibiting a small surface roughness has been developed, using conventional dc inverted cylindrical magnetron sputtering. The method is based on the periodic modulation of the sputtering power during the deposition process: accordingly, deposition rate periodically reaches values as low as the 25% of the full power value. YBCO films, fabricated following such a modulated deposition process, have been electrically characterized and structurally investigated by X-ray diffractometry. The surface morphology has been analyzed by atomic force and scanning electron microscopy. Surface roughness as low as 2 nm have been obtained by using a modulation period of 30 s.

Secondary ion mass spectrometry and x-ray analysis of superconducting Nb/Pd multilayers

We report on accurate structural investigations of sputtered Nb/Pd multilayers by means of high-resolution secondary ion mass spectrometry and x-ray reflectivity. The combined use of secondary ion mass spectrometry and x-ray specular reflectivity techniques allows us to study the chemical configuration of the interfaces and to relate it to the observed superconducting properties. Secondary ion mass spectrometry analyses reveal a distinct Nb and Pd modulation and very sharp profiles with abrupt interfaces indicating a negligible interdiffusion of Nb and Pd at the interfaces. Moreover, analyzing the features in the Nb and Pd profiles and correlating them to the oxygen distribution in the multilayers and to the low-angle x-ray patterns, thin layers (3–4 nm thick) of niobium oxide were noticed at the Nb/Pd interfaces, while no oxide layers at the Pd/Nb interfaces could be detected. The role of this oxide layer in the determination of the crossover between three- and two-dimensional superconducting behavior in...

Structural ordering and chemical configuration of Ba-based infinite-layer superlattices

In this work, we present a detailed structural and microanalytical study of BaCuO2/CaCuO2 superlattices grown on (001) SrTiO3 substrates by pulsed laser deposition technique. Our analyses were performed by using high-resolution x-ray diffraction, reciprocal space mapping, x-ray specular reflectivity, and x-ray photoelectron spectroscopy. We found that the BaCuO2/CaCuO2 superlattices are grown pseudomorphically on the SrTiO3 substrate. X-ray photoelectron spectroscopy measurements show that the Ca is partially oxidized having both Ca–O and Ca–Ca bonds, while Ba is completely oxidized (Ba–O bonds). The results of our analyses demonstrate that the pulsed laser deposition technique allows one to fabricate high quality infinite-layer superlattices of high structural and chemical ordering.

Glancing incidence X-ray characterization of ultrathin YBa2Cu3O7 − x films fabricated by modulated magnetron sputtering

Abstract In high- T c superconductor ultrathin films and multilayers the superconducting current flow is extremely sensitive to the structural quality of the interfaces and to any surface irregularities. In this work we present a microstructural and morphological study of ultrathin YBa 2 Cu 3 O 7 − x (YBCO) films grown on SrTiO 3 substrate. The films (thickness

Structural investigation of YBCO films and bicrystal grain boundary junctions

SummaryWe present a structural analysis of YBCO superconducting thin films fabricatedin situ by Inverted Cylindrical Magnetron (ICM) sputtering on commercial SrTiO3 single-crystal and bicrystal substrates. A detailed structural characterization of the superconductor films was performed by using single-crystal X-ray diffractometry confirming that YBCO films have a strongc-axis orientation of the grains with a small mosaic spread. In the films grown on bicrystal substrates we observed a strong correlation with the lattice structure of the substrate. In addition, a surface analysis of the region across the grain boundary edge has been performed by using scanning electron microscopy.

Glancing-incidence X-ray characterization of Nb/Pd multilayers

SummaryThe study of periodic metallic multilayers in which one of the two constituent layers is a superconductor has attracted considerable interest. The structural configuration and quality of the interfaces is of fundamental importance because it influences the phases of the superconductive wave function in the interface region and, hence, the coupling between the nearest superconductive layers. In this work we present a structural investigation of Nb/Pd multilayers by using high- and low-angle X-ray diffraction measurements. All the samples were grown on Si(100) substrates by de-triode sputtering. We investigated two samples consisting of 10 stacks of nominally 19 nm Nb, 4 nm Pd and 18 nm Nb, 8 nm Pd, respectively. The high-angle analyses reveal that the Nb layer is oriented in the [110] direction and the Pd in the [111] direction. Off-specular reflectivity measurements show the presence of a (partially) correlated roughness across the interfaces. From specular reflectivity it was found how the rms roughness increases from the substrate to the surface.

AC susceptibility measurements of films with different structural qualities

Abstract Superconducting ReBa 2 Cu 3 O 7 (R = Y, Er) epitaxial thin films were deposited by reactive laser ablation on YSZ (Yitria Stabilized Zirconia) and SrTiO 3 substrates under various conditions. The structural quality of the films were characterized by complete XRD measurements. The superconducting properties have been investigated by AC susceptibility in an extended AC fields range ( h AC ≤400 Oe). We focused our attention on the imaginary part χ ″( T ) (loss peak) for fields applied parallel and perpendicular to the film surface. The use of “high” parallel AC fields leads to a precise determination of the irreversibility lines (IL) in the ( h AC , T ) plane. The IL are weakly frequency dependent and exhibit a nearly linear behavior. The observation of fine structures of the loss peak are correlated to the presence of different phases and/or grain orientations.

Superconducting and structural properties of Nb/Pd(Mn) multilayers

Nb/Pd(Mn) multilayers have been fabricated by sputtering and Molecular Beam Epitaxy (MBE). The samples were characterized by X-Ray analyses which showed in the case of sputtered samples oxygen contamination at the Nb interfaces. The MBE films exhibited higher residual resistivity ratios (RRR) and superconducting critical temperatures versus the Pd thicknesses in agreement with the de Gennes-Werthamer theory. Critical magnetic field measurements were also performed on these samples. Nb/PdMn multilayers were analyzed to study the superconductivity and the magnetism interplay.