J.R. Tesmer

Transport‐magnetism correlations in the ferromagnetic oxide La0.7Ca0.3MnO3

We present results of temperature and magnetic field dependent resistivity ρ(H,T) and bulk magnetization M(H,T) measurements on post‐annealed La0.7Ca0.3MnO3 thin films that were grown via pulsed‐laser deposition. Both the resistivity and the anomalously large negative magnetoresistance peak near the ferromagnetic ordering temperature (Tc=250 K), with Δρ/ρ0=−85% at 50 kOe. A clear correlation is found between ρ and M that is described by the phenomenological expression ρ(H,T)∝exp[−M(H,T)/M0]. This correlation reflects the important interplay between transport and magnetism in this system, and suggests that the transport below Tc involves polaron hopping.

Effect of deposition rate on properties of YBa2Cu3O7−δ superconducting thin films

Superconducting thin films of YBa2Cu3O7−δ on (100) SrTiO3 are prepared in situ by a pulsed laser deposition technique at deposition rates from 1 to 145 A/s. Crystallinity of the films is examined by Rutherford backscattering in the channeling mode using a 2.2 MeV He+ ion beam. The backscattering minimum yield (χmin) increases with the deposition rate. A χmin of 3% is observed in the films deposited at the lowest deposition rate. Even at a deposition rate of 145 A/s, the films show good crystallinity with χmin of 15%, indicating epitaxial growth. The x‐ray diffraction measurements show that the films have strong c‐axis orientation normal to the substrates. The films have metallic resistance versus temperature behavior with zero resistance temperatures of 90 K. The results indicate that the pulsed laser deposition technique could be used to deposit large‐area films efficiently with adequate substrate movement.

Effect of particle‐induced displacements on the critical temperature of YBa2Cu3O7−δ

The particle‐induced depression of the superconducting critical temperature Tc of YBa2Cu3O7−δ is shown to be directly proportional, over seven orders of magnitude, to the nonionizing energy deposited in the lattice by primary knock‐on atoms displaced by incident electrons, protons, and heavy ions. It is concluded that ΔTc is proportional only to the average number of defects produced and can therefore be predicted for any particle, energy, and fluence from a calculation of the nonionizing energy loss.

High‐energy elastic backscattering of helium ions for compositional analysis of high‐temperature superconductor thin films

A thin‐film technique for measuring the chemical composition of Y‐Ba‐Cu‐O thin films to a few percent accuracy is described. This technique utilizes non‐Rutherford backscattering of 8.8 MeV helium ions, which has an increased sensitivity 16O by a factor of 25 over Rutherford backscattering spectrometry. The ratios of the cross sections for He++ scattered from oxygen, copper, and yttrium relative to barium are easily determined using thin‐film standards that can be fabricated in any deposition system capable of producing thin‐film superconductors. The technique does not require the constant use of standards or accurate charge determination.

DIAMONDLIKE CARBON DEPOSITION ON SILICON USING RADIO-FREQUENCY INDUCTIVE PLASMA OF AR AND C2H2 GAS MIXTURE IN PLASMA IMMERSION ION DEPOSITION

Diamondlike carbon (DLC) was deposited on silicon using a plasma immersion ion deposition (PIID) method. Inductive radio-frequency plasma sources were used to generate Ar and C2H2 plasmas at low gas pressures ranging from 0.04 to 0.93 Pa. The film stress and hardness were sharply dependent upon bias voltage at an operating pressure of 0.04 Pa. A maximum hardness of 30 GPa and compressive stress of 9 GPa was observed at a pulsed bias of −150 V bias (carbon energy of 80 eV). The mechanical properties of DLC films are correlated with UV Raman peak positions which infer sp3-bonded carbon contents.

Ultraviolet-Ozone Oxidation of Metal Films

Metal oxides such as zirconia and hafnia are being investigated as new materials for application as gate dielectrics in future complementary metal-oxide-semiconductor devices. In this paper, we present results on oxidation of metal films such as Zr, Hf, and Al by the ultraviolet (UV) ozone oxidation method. A nuclear reaction analysis technique, the 16 O(d,α) 14 N nuclear reaction, was used to quantify the oxygen concentration in the dielectric stacks. The method was found to be sensitive to monolayer levels of oxygen. It was found that the oxidation kinetics of the metals increased significantly due to the presence of UV light. The oxidation rate was also found to depend on the oxygen partial pressure. The oxidation rate of Zr was greater than that of Hf, while Al oxidized more slowly than Hf for the UV-ozone oxidation conditions investigated. Possible reasons for the observed oxidation behavior are discussed in detail.

Formation of YBa2Cu3O7 superconducting films by ion implantation

We have fabricated superconducting thin films by ion implanting Y into a base material formed by the coevaporation of BaF2 and Cu. The implantations were carried out at 77 K and resulted in the formation of an amorphous Y‐Ba‐Cu‐F surface layer. Oxygen annealing with the addition of water vapor renders the base material insulating with a room‐temperature resistance of 105 Ω. An identical annealing treatment on the Y‐implanted material produces a superconductor with an onset temperature of 85 K.

Effect of nitrogen implantation on the surface hardness of pure aluminum and alloy materials

Abstract Samples of high purity annealed aluminum and 6061-T6 aluminum alloy were implanted with N+ ions at 200 keV at doses of 5, 10, 18, and 28 × 1017 cm−2. Additionally a third sample was implanted with 15 × 1017 cm−2 at 200 keV followed by an implant of 11 × 1017 cm−2 at 100 keV. Implant profiles were analyzed using Rutherford backscattering (RBS). The surface hardness of these samples were measured using a nanoindenter. A substantial increase in surface hardness was observed in all the implanted samples. The thickness and peak hardness of the surface layer were enhanced by dual energy implantation. Beam heating during ion implantation resulted in annealing of the 6061-T6 samples. These effects were confirmed by annealing experiments which produced little change in overall hardness profiles. Large scale cracking of the hard surface layer was observed in low dose pure Al samples. This cracking behavior was altered by annealing.

In-situ capability of ion beam modification and characterization of materials at Los Alamos National Laboratory

Abstract The capability of in-situ ion beam modification and characterization of materials developed at Los Alamos National Laboratory is described. A beam-line from a 3 MV tandem accelerator and a beam-line from a 200 kV ion implanter are joined together in an in-situ target chamber. The chamber is equipped with a cold and hot sample stage with a temperature range from −100 to 500°C. The angular (sample spin and basal rotation) motions and translational motions of the sample stage are controlled by a multi-axis goniometer. This chamber provides a unique capability to conduct a temperature dependent experiment of ion irradiation and sequential backscattering and channeling analysis. The efficiency and reliability of in-situ ion beam techniques are demonstrated by two examples, irradiation damage in (100) MgAl 2 O 4 spinel crystals and ion-beam-induced densification of zirconia sol-gel thin films.

Ion beam mixing of U-based bilayers

Bilayer samples of U/Al, U/Ti, U/Si, and U/C have been ion beam mixed with 400 keV Ar and U/Al with Xe ions at doses from 2{times}10{sup 15} to 1{times}10{sup 17} ions/cm{sup 2}. Mixing experiments were performed at various temperatures between 77 and 420 K. The amount of interfacial mixing, 4{ital Dt}, follows a linear dose dependence below a critical temperature depending on the system studied. Below this temperature, the mixing efficiency, defined as {partial derivative}(4{ital Dt})/{partial derivative}{Phi} where 4{ital Dt} is the mixing and {Phi} is the dose, is temperature independent. Its value, as well as the value of the transition temperature, agrees well with the thermodynamical model of chemically biased diffusion in a thermal spike for the four systems tested. The transition between the thermal spike regime and the temperature enhanced mixing regime was interpreted on the basis of an intracascade mechanism. The formation of an intermetallic compound in the U/Al system was detected and interpreted on a qualitative basis by crystallographic considerations.