Aboud H. Hamdi

Formation of thin‐film high Tc superconductors by metalorganic deposition

Metalorganic deposition (MOD) is a nonvacuum method of thin‐film deposition which allows easy alteration of chemical components and is compatible with thin‐film processing. We report the preparation of thin‐film superconductors by MOD. Rutherford backscattering spectrometry was used to determine film compositions and thicknesses. Films, approximately 500 nm thick, of YBa2Cu4Oz (z undetermined) were deposited on 〈100〉 single‐crystal SrTiO3. A superconducting onset temperature of 90 K was measured with 37 K the zero resistance temperature. Scanning electron microscopy revealed grain sizes approximately 250 nm in diameter.

Rapid thermal annealing of high Tc superconducting thin films formed by metalorganic deposition

Thin‐film superconductors of Y‐Ba‐Cu and Yb‐Ba‐Cu have been formed by the nonvacuum method of metalorganic deposition (MOD). The films produced in this manner were homogeneous and free of voids and cracks over large dimensions. A two‐step rapid thermal annealing of the MOD films, in oxygen, at 850 °C for 60 s followed by a second annealing at 920 °C for 30 s enhanced grain growth in the films and reduced the effects of substrate interaction. Preferred epitaxial grain growth, in the high Tc films, with the c axis both perpendicular and parallel to the substrate surface, occurred on 〈100〉 SrTiO3. Both the Y‐Ba‐Cu and Yb‐Ba‐Cu films showed superconducting onset temperatures above 90 K and zero resistance at 86 K.

Diamond-like carbon coating for aluminum 390 alloy — automotive applications

In an attempt to increase the wear resistance of automotive powertrain components, General Motors Research and Development Center initiated a study to determine the potential of surface modification as a means of improving the tribological properties of highly eutectic aluminum alloys, and to investigate feasibility of their mass production. In particular, plasma immersion ion implantation technique was employed to develop diamond-like hydrocarbon coating of aluminum 390 alloy and the coatings performance was verified both in a bench and, in an engine dynamometer test.

Use of ion beams to decompose metalorganics into patterned thin‐film superconductors

Ion implantation of 400 keV O+2 ions, at a dose of 5×1014 ions/cm2, was used to selectively decompose a high Tc superconductor‐forming metalorganic (MO). Implantation rendered the metal carboxylates insoluble in their solvent, xylene, permitting patterning of the MO prior to pyrolysis and annealing. Fine line superconductors were formed having 90 K onset temperatures and zero resistance at 68 K.

Microstructure and superconducting properties of Y–Ba–Cu–O and Yb–Ba–Cu–O thin films formed by metalorganic deposition

Thin films of Y--Ba--Cu--O and Yb--Ba--Cu--O, 0.5--1.5 {mu}m in thickness, were deposited onto {l angle}211{r angle} and {l angle}100{r angle} SrTiO{sub 3} single crystal substrates by metalorganic deposition (MOD). After deposition the samples were annealed by conventional furnace annealing or rapid thermal annealing (RTA). The microstructures of these films were then characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive x-ray spectrometry (EDS). Grain size of the annealed films varied from 0.25 to 1.0 {mu}m. Improved superconducting properties were found for the RTA samples, compared to furnace annealing, and were attributed to larger grain size, little strontium diffusion into the thin films from the substrate, and highly preferred orientation of the 1:2:3 phase.

Use of electron beam lithography to selectively decompose metalorganics into patterned thin‐film superconductors

Fine line superconductors, approximately 5 μm in width and 260 nm thick, were formed from Y‐Ba‐Cu on 〈100〉SrTiO3 by the combined methods of metalorganic deposition and selective area electron beam exposure. The lines were written in metal neodecanoates using an electron beam having a spot size of 0.25 μm and an energy of 25 kV. The dosage of the exposure was 1200 μC/cm2. Unexposed areas were removed with a 30 s xylene wash. A 500 °C pyrolysis in air for 300 s followed by rapid thermal annealing in oxygen produced lines having superconducting onsets above 90 K and zero resistance at 69 K.

Characterization of surface modified α-iron by nitrogen plasma immersion ion implantation: a microstructural study

Abstract This paper discusses the morphology of pure iron surfaces modified by nitrogen plasma immersion ion implantation and compares them to similar surfaces treated with conventional plasma nitriding. Analysis of the samples was performed with glancing angle X-ray diffraction and traditional Bragg–Brentano geometry X-ray diffraction, transmission electron microscopy, scanning electron microscopy, and depth profiling using X-ray photoelectron spectroscopy in combination with sputtering. The structures formed both by thermal nitriding and plasma ion implantation correlate very well with the Fe–N phase diagram, as the surface temperature and nitrogen concentration are decisive factors in developing specific crystalline phases. Only at lower temperatures, where chemical absorption and thermal diffusion effects are strongly limited, does the distribution of implanted nitrogen become substantially of the non-equilibrium type, and can almost be freely tailored. At low temperatures, however, the nitrided layer becomes extremely shallow (defined almost solely by the ballistic ion model), thereby limiting the applicability of this technology for iron-based materials. Hence, unless specific ferrous alloy materials are chosen which promote nitride formation and diffusion, e.g. chromium and iron-chromium alloys, the niche for nitrogen plasma ion implantation into ferrous materials seems to be limited to those cases where surface nitriding is desired, but where exposure of the workpiece to high temperature is forbidden.

Surface enhancement by shallow carbon implantation for improved adhesion of diamond-like coatings

A surface layer of metal carbides provides an excellent interface to achieve a highly adherent diamond-like carbon (DLC) coating. A plasma immersion ion implantation based procedure is described which delivers a high retained dose of implanted carbon at the surface of aluminum alloys. This proposed implantation procedure employs a low target bias of only 10–12 kV, a pulse repetition rate of around 5 kHz, and a duty cycle of 25%. The resultant shallow implantation profile, followed by an argon sputter cleaning, is continued until a saturated carbon matrix is brought to the surface providing an excellent interface for subsequent growth of DLC. At a carbon retained dose above 1018 atoms/cm2, the DLC adhesion exceeds the coating’s cohesion strength. Regardless of the silicon content in the aluminum, the coating produced by this method required tensile strengths typically exceeding 150 MPa to separate an epoxy coated stud from the coating in a standard pull test. Improved DLC adhesion was also observed on chro...

Grain growth of rapid-thermal-annealed Y-Ba-Cu oxide superconducting thin films

A study of the microstructure of Cu‐rich and stoichiometric Y‐Ba‐Cu oxide thin‐film superconductors is presented. The films were deposited on 〈100〉 SrTiO3 by the nonvacuum technique of metalorganic deposition followed by rapid thermal annealing in oxygen. Analysis showed that for annealing temperatures below 900 °C, grain size increased with increased annealing temperature, with an enhancement in grain growth for the Cu‐rich films. Annealing near or above the melting point of the 1‐2‐3 phase causes only a slight increase in the rate of grain growth and no detectable effects of the excess Cu. Annealing above 920 °C produces segregated CuO islands 5–10 μm in size in the Cu‐rich films. Oriented grain growth was found for the 1‐2‐3 grains with their c axis perpendicular and parallel to the SrTiO3 substrates. Sheet resistivity measurements were correlated with grain size, phase separation, and oriented grain growth. An anomalous behavior in the resistance‐temperature plot at 220–240 K of the Cu‐rich films is s...

Improved adhesion of diamondlike coatings using shallow carbon implantation

A surface layer of metal carbides provides an excellent interface to achieve a highly adherent diamondlike carbon (DLC) coating. A plasma immersion ion implantation (PIII)-based procedure is described, which delivers a high retained dose of implanted carbon at the surface of aluminum alloys. A shallow implantation profile, followed by argon sputter cleaning and continued until a saturated carbon matrix is brought to the surface, provides an excellent interface for subsequent growth of DLC. At a carbon retained dose above 10 18 atoms/cm 2 the DLC adhesion exceeds the coatings cohesion strength. Regardless of the silicon content in the aluminum, the coating produced by this method required tensile strengths typically exceeding 140 MPa to separate an epoxy-coated stud from the coating in a standard pull test. Improved DLC adhesion was also observed on chromium and titanium. The reported tensile strength is believed to substantially exceed performance of DLC coatings produced by any other method.