Massoud Badaye

High‐quality c‐axis oriented superconducting Nd1+xBa2−xCu3O7−d thin films deposited by the laser ablation method

High‐quality single phase Nd1+xBa2−xCu3O7−d thin films have been fabricated on SrTiO3 substrates by the laser ablation method. The resistivity of the deposited films are usually lower than that of the YBCO film. The Tc(onset) and Tc(R=0) in the optimized thin films are as high as 91 and 88 K, respectively. The crystallinity of our films are higher than the best YBCO films ever reported. The rocking curve FWHM of the (005) peaks in our thin films is typically 0.05°, which is superior to the best reported YBCO films.

Spatial resolved emission spectroscopic study on laser plume of Y1Ba2Cu3Ox at different oxygen pressures

To investigate the characteristics of the plume generated by the laser ablation of Y1Ba2Cu3Ox, emission spectra of the ejected species were observed at different distances from the target in an oxygen atmosphere. It was found that velocities of ejected species increased with the distance from the target. At 35 mm from the target the emission intensities of Y, Ba, O atoms, and YO molecules drastically increased to an order of magnitude larger beyond several tens mTorr of oxygen pressure. This increase of emission intensity was due to the increment of the plasma density by a shock front formed at ∼35 mm. Above 0.5 Torr of oxygen pressure, molecular YO was produced by the oxidation of Y atoms. The plasma temperature was also elevated by shock heating.

Velocity distributions of ions in the ablation plume of a Y1Ba2Cu3Ox target

The velocity distribution of ionic species in the plume was monitored by a time‐of‐flight mass spectrometer during laser ablation of Y1Ba2Cu3Ox. As oxygen pressure was raised, the velocity of Cu+ ions shifted to the slower side, and the width of the velocity distribution narrowed down to a minimum width at around 3×10−2 Torr. Beyond this pressure the width rapidly broadened. This change is qualitatively interpreted considering the dynamics in the flow of the supersonic expansion and thermal equilibrium, and is also discussed in connection with the surface morphology of ablated films.

Cross sections for 16O(He,He)16O resonant elastic scattering and application to elemental analysis of YBa2Cu4O8 and Nd1+xBa2−xCu3O7−δ films grown on SrTiO3

The differential cross sections for 16O(He,He)16O resonant elastic scattering at 3.034 and 3.078 MeV have been measured using stoichiometric thin (100 A) and thick (6000 A) SiO2 layers formed on Si(100) wafers by thermal oxidation at 900 °C under H2 and O2 flows. We have determined the resonance widths (Γ) and interaction radii (a), which are the parameters defining the cross sections in the partial wave analysis, by best fitting the angular and energy dependent scattering yields from oxygen. A computer simulation program for Rutherford backscattering including the 16O(He,He)16O resonant scattering has been synthesized and applied to the elemental analysis of thin YBa2Cu4O8 and Nd1+xBa2−xCu3O7−δ films grown on SrTiO3 substrates. The present elemental analysis is compared with the transition temperatures of superconductivity (Tc) in the context of the oxygen deficiency. The accuracy of oxygen content is estimated to be better than 0.1 (a few %). How to improve the accuracies of the elemental analysis, in p...

Recovery and recrystallization of SrTiO3(100) surface characterized by ion channeling

Abstract The surface crystallinity of SrTiO3(100) (STO) substrates and recovery of the damaged STO surfaces were investigated using Rutherford backscattering spectrometry in conjunction with channeling technique. We have found that STO single crystal substrates coated with an amorphous STO layer up to 80 A thick can be completely recrystallized by annealing at 1100°C in 1 atm O2 for 30 min, while those with an amorphous layer thicker than 260A cannot be fully recovered by this 30 min annealing process, nor by extending the annealing time to 3 hours.

Investigation of the physical and chemical interaction of a low energy oxygen ion beam with oxide superconducting films

Abstract The mono-valent O + ion is chemically highly reactive and when accelerated to 10s of electron volts it gains significant kinetic energy. We investigated the effect this species has on the surface of superconducting thin films in ultra high vacuum. We followed the interactions using an atomic force microscope, reflection high energy electron diffraction and X-ray diffraction. Using acceleration energies between 20 and 200 eV and comparing the effect of O + and Ar + ion beams, we were able to differentiate the chemical and physical effects induced by the O + ion. We found that O + improves the smoothness of the surface, but degrades the bulk properties of the films. Above 50 eV physical sputtering leading to a reduction in surface roughness was found to dominate. In the absence of the ion beam at 400°C, rectangular precipitates up to 50A˚in height were found to grow on the surface of these films. The O + ion beam inhibits the chemical reaction causing these precipitates. Also the O + ion beam caused significant expansion of the c -axislattice parameter of the films, greater then that expected for just oxygen loss. In all these cases the superconducting properties were lost.

Mass spectroscopic studies on outgrowth precipitates in laser ablated films

Abstract We have observed the velocity distribution of ionic species in the plume by a mass spectrometer during laser ablation of Y1Ba2Cu3Ox target. The velocity distribution of Cu+ ions is strongly influenced by ambient oxygen pressure. As an oxygen pressure is raised, thevelocity distribution of Cu+ ions becomes narrows up to 2x10−2 Torr, and then becomes broad again at higher pressures. This change in the velocity distribution reflects the conversion of the supersonic expansion into the thermal equilibrium flow of the ejected species in the plume. The surface morphology of films is crucially dependent on the velocity distributions.

Determination of the topmost atomic layer of NdBa2Cu3Oy thin films by developed total reflection angle X-ray spectroscopy (TRAXS)

Abstract The surface termination layer of c -axis oriented NdBa 2 Cu 3 O y thin films deposited by laser ablation process has been studied by a developed TRAXS method, described as glancing incidence-exit X-ray scattering (GIEXS). Using the SrTiO 3 substrate terminated with a well defined surface, coated with island-like gold layer, we have demonstrated the effectiveness of GIEXS to distinguish the surface atomic layer from their underlying layered bulk crystal. Applying this method to examine the surface atomic layer of NdBa 2 Cu 3 O y thin films cleaned with atomic oxygen beam, we have found that the surface of NdBa 2 Cu 3 O y thin films is predominantly terminated with CuO chain plane.

Surface characterization of superconductive Nd1Ba2Cu3Oy thin films using scanning probe microscopes

Recently, superconductive Nd1Ba2Cu3Oy (Nd123) thin films with high superconducting transition temperature (Tc) have been successfully fabricated at our institute employing the standard laser ablation method. In this paper, we report parts of the results of surface characterization of the Nd123 thin films using an ultrahigh vacuum scanning tunneling microscope/spectroscopy (UHV- STM/STS) and an atomic force microscope (AFM) system operated in air. Clear spiral pattern is observed on the surfaces of Nd123 thin films by STM and AFM, suggesting that films are formed by 2D island growth mode at the final growing stage. Contour plots of the spirals show that the step heights of the spirals are not always the integer or half integer numbers of the c-axis parameter of the structure. This implies that the surface natural termination layer of the films may not be unique. Surface atomic images of the as-prepared Nd123 thin films are obtained employing both STM and AFM. STS measurements show that most of the surfaces are semiconductive, or sometimes even metallic. The results of STS measurements together with the fact that we are able to see the surface atomic images using scanning probe microscopes suggest that exposure to air does not cause serious degradation to the as-prepared surfaces of Nd123 thin films.

Determination of Surface Atomic Layer of SrTiO 3 Single Crystal and RBa 2 Cu 3 O y Thin Films by Glancing Incident-Exiting X-Ray

The surface atomic layer of c-axis oriented RBa2Cu3Oy (R=Nd,Y) thin films deposited by laser ablation process has been studied by means of glancing incident and exiting x-ray(GI-EX). Utilizing the GI-EX method we have correctly identified the topmost layer of SrTiO3 (001) single crystal with a well defined surface. It demonstrated the effectiveness of GI-EX to distinguish the surface atomic layer from their underlying layered bulk crystal. GI-EX spectrum proved that the surface of NdBa2Cu3Oy thin films is predominantly terminated with a CuO chain plane, while a different layer covered the surface of YBa2Cu3Oy thin films.