Peter Madakson

Processing of La1.8Sr0.2CuO4 and YBa2Cu3O7 superconducting thin films by dual‐ion‐beam sputtering

High quality La1.8Sr0.2CuO4 and YBa2Cu3O7 superconducting thin films, with zero resistance at 88 K, have been made by dual‐ion‐beam sputtering of metal and oxide targets at elevated temperatures. The films are about 1.0 μm thick and are single phase after annealing. The substrates investigated are Nd‐YAP, MgO, SrF2, Si, CaF2, ZrO2‐9% Y2O3, BaF2, Al2O3, and SrTiO3. Characterization of the films was carried out using Rutherford backscattering spectroscopy, resistivity measurements, transmission electron microscopy, x‐ray diffraction, and secondary ion mass spectroscopy. Substrate/film interaction was observed in every case. This generally involves diffusion of the substrate into the film, which is accompanied by, for example, the replacement of Ba by Sr in the YBa2Cu2O7 structure, in the case of SrTiO3 substrate. The best substrates were those that did not significantly diffuse into the film and which did not react chemically with the film. In general, the superconducting transition temperature is found to ...

Processing of La/sub 1. 8/Sr/sub 0. 2/CuO/sub 4/ and YBa/sub 2/Cu/sub 3/O/sub 7/ superconducting thin films by dual-ion-beam sputtering

High quality La1.8Sr0.2CuO4 and YBa2Cu3O7 superconducting thin films, with zero resistance at 88 K, have been made by dual‐ion‐beam sputtering of metal and oxide targets at elevated temperatures. The films are about 1.0 μm thick and are single phase after annealing. The substrates investigated are Nd‐YAP, MgO, SrF2, Si, CaF2, ZrO2‐9% Y2O3, BaF2, Al2O3, and SrTiO3. Characterization of the films was carried out using Rutherford backscattering spectroscopy, resistivity measurements, transmission electron microscopy, x‐ray diffraction, and secondary ion mass spectroscopy. Substrate/film interaction was observed in every case. This generally involves diffusion of the substrate into the film, which is accompanied by, for example, the replacement of Ba by Sr in the YBa2Cu2O7 structure, in the case of SrTiO3 substrate. The best substrates were those that did not significantly diffuse into the film and which did not react chemically with the film. In general, the superconducting transition temperature is found to ...

Interdiffusion and resistivity of Cu/Au, Cu/Co, Co/Au, and Cu/Co/Au thin films at 25–550 °C

The interdiffusion and resistivity of Cu/Au, Cu/Co, Co/Au, and Cu/Co/Au thin‐film structures were studied, at temperatures ranging from 25 to 550 °C, using Rutherford backscattering spectroscopy, Auger analysis, and four‐point probe resistance measurements. Intermetallic phase formation was studied by x‐ray diffraction and changes in microstructure were analyzed by scanning electron microscopy. Interdiffusion of Cu and Au in the Cu/Au structure is observed at temperatures as low as 150 °C and is accompanied by an increase in resistivity. No significant reactions occur in the Cu/Co, Co/Au, and Cu/Co/Au thin‐film structures up to 400 °C, after which the resistivity increases. The very rapid increase in resistivity observed at 250 °C for the Cu/Au system and at 450 °C for Cu/Co/Au, is associated with structural changes in the films which result in large grains and the formation of AuCu, Cu3Au, and Cu3Au2 compounds. The structural changes in the Cu/Co/Au system occur at a higher temperature because of the tim...

Substrate effect on the superconductivity of YBa2Cu3O7 thin films

The interaction between the substrate and YBa2Cu3O7 films made by ion beam sputtering and e‐beam evaporation is found to significantly influence the superconducting transition temperature, Tc. The substrates investigated are Al2O3, MgO, SrTiO3, ZrO2‐9% Y2O3 (YSZ), and BaF2. In the case of Al2O3, a spinel is formed at the interface and Al is found to be present in solution in the YBa2Cu3O7. This reaction significantly depresses Tc. For SrTiO3, both Sr and Ti are found in the film without severely depressing the Tc; this, however, depends on the annealing conditions. Although under similar conditions little interaction was observed for the MgO substrates, a moderate reduction in Tc was observed. An interaction zone of BaZrO3 perovskite is formed at the interface between the YSZ substate and the 123 structure. In addition, Zr is found in solution in the 123 film. The presence of Zr has little effect on the Tc. The films were characterized using Rutherford backscattering spectroscopy (RBS), transmission elect...

Characterization of CVD-hydrogenated diamondlike thin films on silicon by EELS, RBS/channeling and nuclear reaction analysis

Abstract Thin diamondlike films, deposited on (100) Si, have been examined by electron energy loss spectroscopy (EELS), Rutherford backscattering spectroscopy (RBS) and nuclear reaction analysis. Results indicate that films deposited at high partial pressures of H2, which have been found to be softer than those deposited at low partial pressures, have higher concentrations of oxygen but similar concentrations of hydrogen within their bulk. It is proposed that the oxygen is bound to the carbon matrix, thus modifying the extended sp2 network. Analysis of the substrate indicates a damaged region at the top surface of the Si.

As+ and Ga+ implantation and the formation of buried GaAs layers in silicon

A buried layer of GaAs was formed in single‐crystal silicon by dual implantation of extremely high doses of As+ plus Ga+ at 200 keV, followed by furnace annealing. The layer consists of polycrystalline grains with random orientation. Rapid thermal annealing, in the presence of oxygen, does not result in the formation of GaAs. Instead, Ga and As migrate to the surface to form an oxidized layer, which is separated from the underlying silicon by a thin layer of SiO2. Analysis of the samples with single implants of Ga+ or As+ indicates the oxides formed to be Ga2O3 and As2O2. Samples implanted with As+ alone have essentially dislocation loops after annealing, while those implanted with only Ga+ have mostly microtwins and precipitates. Up to 88% Ga and 62% As from the single implants and 31% As and Ga from the dual implants are lost during annealing. This is probably due to the migration of the implanted species to the surface and the subsequent formation of volatile oxides. However, such outward migration doe...

Stresses and radiation damage in Ar+ and Ti+ ion-implanted silicon

Comparative studies of stress and radiation damage in 〈111〉 silicon were carried out after ion implantation with 28‐keV Ar+ and 30‐keV Ti+ to doses ranging from 1012 to 1017 ions/cm2. The effect of annealing at 600 °C for 2 h was also investigated. Automatic x‐ray diffraction measurement of strains in the specimens shows that in the as‐implanted condition the stresses are compressive and they increase linearly with ion dose up to about 1016 ions/cm2, after which they relieve. This behavior was the same for both the ‘‘reactive’’ (Ti) and the ‘‘unreactive’’ (Ar) ion implantation. However, after annealing the stresses in the Ar+ implanted samples remain compressive and those in the samples implanted with Ti+ become tensile. The change from compressive to tensile stresses is associated with titanium‐silicide formation. X‐ray diffraction patterns show that the silicide consists of metastable and equilibrium phases. Sheet resistance measurements on the samples with a continuous TiSi2 layer show the resistivity ...

Effects of tin ion and nitrogen ion implantation on the oxidation of titanium

Abstract The high temperature oxidation of ion-implanted titanium was studied using the scanning electron microscopy, X-ray photoelectron spectroscopy and Rutherford back-scattering techniques. The specimens were implanted with either tin ions (Sn + ) or nitrogen ions (N 2 + ) or a combination of the two, to doses of between 10 15 and 10 17 ions cm −2 . The implantation energies were 200 keV for tin ions and 200 or 400 keV for nitrogen ions. The specimens, treated and untreated, were oxidized in air at 500 °C for 100 h. The combination of nitrogen and tin ions was found to increase the thickness of the nitride-oxide film on the titanium surface by four orders of magnitude and to increase the hardness significantly. Nitrogen ions alone produced a more uniform oxide layer but the thickness of the layer was unchanged. The implantation of tin ions alone led to a reduction in the oxidation of titanium by the formation of SnO 2 . The results are discussed in terms of well-established mechanisms of the oxidation of titanium, in which oxygen diffuses into the metal along anion vacancies of the rutile lattice.

Interdiffusion, hardness and resistivity of Cr/Cu/Co/Au thin films

The effects of interdiffusion and microstructure on the hardness and resistivity of Cr/Cu/Co/Au thin films were studied at temperatures ranging from 25 to 600 °C. Cobalt was found to be a very effective diffusion barrier between Cu and Au at temperatures of ≤400 °C for annealing times greater than 2 h. As a result, little or no change in hardness or resistivity of the Cr/Cu/Co/Au structure occurs. Above 400 °C, the Co layer breaks down, and there is massive interdiffusion of Cu and Au, which is associated with grain growth, grain boundary precipitation and surface roughening of the films. The observed changes in the hardness and resistivity correlate with the degree of interdiffusion of Cu and Au for temperatures ≤500 °C. The activation energy for interdiffusion is 1.65 eV and that for Au diffusion into Cu via the Co layer is 1.91 eV. These values are consistent with those reported for grain boundary diffusion in thin films.

Correlation between resistivity and diffusion in thin films

Empirical equations have been derived that relate resistivity to diffusivity and activation energies for thin films. Results for the Cr/Au structure agree with published data on the interdiffusion of Cr and Au thin films at temperatures ranging from 350 to 450 °C. The following relationships were determined: Δρ/ρ0C=λ exp(−Q/kT); Δρ/ρ0C=nDt/χ2; Δρ/ρ0C=ψ exp(−χ2/4Dt) and D=Nχ2 /t exp(−Q/kT), where Nχ2/t=D0(cm2/s) is the frequency factor; Δρ is the change in resistivity; ρ0 is the room temperature resistivity; χ is film thickness; T is temperature; t is time; C is concentration; k is Boltzman’s constant; D is diffusion coefficient; and n, ψ, N, and λ are constants. Analysis of the Cr/Au resistivity data using these equations gives D0=1.2×10−7 cm2/s and Q=1.00 eV for Cr diffusion in Au; and D0=1.0×10−7 cm2/s and Q=1.06 eV for Au diffusion in Cr. These values were verified by analysis using Rutherford backscattering spectroscopy and, they are consistent with those reported for grain boundary diffusion.