K.-H. Dahmen

Enhancement of thermal and electrical properties of carbon nanotube polymer composites by magnetic field processing

We show that the thermal and electrical properties of single wall carbon nanotube (CNT)-polymer composites are significantly enhanced by magnetic alignment during processing. The electrical transport properties of the composites are mainly governed by the hopping conduction with localization lengths comparable to bundle diameters. The bundling of nanotubes during the composite processing is an important factor for electrical, and in particular, for thermal transport properties. Better CNT isolation will be needed to reach the theoretical thermal conductivity limit for CNT composites.

Self-Standing Crystalline TiO2 Nanotubes/CNTs Heterojunction Membrane: Synthesis and Characterization

In the present study, we report for the first time synthesis of TiO(2) nanotubes/CNTs heterojunction membrane. Chemical vapor deposition (CVD) of CNTs at 650 °C in a mixture of H(2)/He atmosphere led to in situ detachment of the anodically fabricated TiO(2) nanotube layers from the Ti substrate underneath. Morphological and structural evolution of TiO(2) nanotubes after CNTs deposition were investigated by field- emission scanning electron microscopy (FESEM), glancing angle X-ray diffraction (GAXRD), and X-ray photoelectron spectroscopy (XPS) analyses.

MOCVD of HTS and GMR perovskites by aerosol and liquid delivery MOCVD

Abstract Aerosol and liquid delivery MOCVD are techniques that were developed to overcome the problems with thermally less stable alkaline earth metal precursors in the deposition of alkaline earth doped HTS and GMR perovskites. In this paper, we will discuss the advantages and disadvantages of these techniques compared to the conventional MOCVD process. The deposition of CeO 2 films as an intermediate buffer layer for the deposition of YBa 2 Cu 3 O 7 on (1102) sapphire with Aerosol MOCVD will be discussed, as well as the deposition of alkaline earth doped lanthanum manganites, La 1 − x M x MnO 3 (M=Ca, Sr) on LaAlO 3 , MgO and YSZ by liquid delivery MOCVD.

Microstructures of La 1− x A x (A = Ca or Sr)MnO 3−δ thin films by liquid-delivery metalorganic chemical vapor deposition

The microstructure of La 1– x A x (A = Ca or Sr)MnO 3–δ thin films grown by liquid-delivery metalorganic chemical vapor deposition on (001) MgO and (110) pseudo-cubic LaAlO 3 were studied by transmission electron microscopy. The La 1– x Ca x MnO 3–δ thin film on large lattice mismatched MgO exhibited very defective microstructures and consisted of two typical regions. The first region was close to the film–substrate interface and had an epitaxial relationship to the substrate with many differently oriented domains nucleated on the substrate surface. The second region consisted of columnar grains with some degree of texture. In contrast, the smaller lattice-mismatched La 1– x Sr x MnO 3–δ /(110) pseudo-cubic LaAlO 3 film had good crystalline quality with highly oriented columnar grains but exhibited complicated dislocation structures. Apart from the misfit dislocations formed at the film–substrate interface, two types of anomalous dislocations with limited contribution to relieving misfit stresses were also observed. One type of dislocation had extra planes in the film and some climbed into the substrate. These dislocations were considered to form from dislocation loops during nucleation of the film. The other type of dislocations had extra planes parallel to the film–substrate interface and glided into the substrate side resulting in a 2° tilt of the film with respect to the substrate. The complicated dislocation configurations present in the sample were related to the complex strain field in the film. The relative strains along the interface measured in the film were heterogeneous. The variations of the strains in the film were related to the local Curie temperature changes and second-order phase transitions of the film.

Texture Analysis in LD-MOCVD Processed Thin Film Giant Magnetoresistant (LaM)MnO3 Materials

Thin films of La0.67M0.33MnO3 (M=Sr), LSMO were deposited on three different substrates of LAO, Sapphire, and Y-ZrO2 (YSZ) using metal–organic chemical vapor deposition methods. The effect of texture and orientation on the resistance (0 and 6T) and magnetoresistance (MR) of (LSMO) thin films on various substrates has been investigated. X-ray pole figures were measured using Philips X’Pert X-ray diffractometer equipped with the PopLa analysis package. A direct correlation was observed between the lattice mismatch strain and the structure of the thin film growth. LSMO/LAO seems to be the most perfect system for epitaxial growth due to the negligible lattice-mismatch (∼2%). The dominant orientation changes for the films deposited on LAO [100] and LAO [110] substrates while the transition temperature from ferromagnetic to paramagnetic state of the film on LAO [100] is 50 K higher than that of the film on LAO [100]. The MR data and TMI temperature were measured using standard 4-point resistivity devices and SQUID.

Effects of thermal annealing on the texture of La0.67Sr0.33MnO3 thin films

Thin films of La 0.67 Sr 0.33 MnO 3 (LSMO) were prepared at 670 °C on LaAlO 3 (LAO) and SrTiO 3 (STO) substrates by liquid-delivery metalorganic chemical vapor deposition. X-ray diffraction analysis 2¸/¸ and pole figure scans showed that the films are epitaxial with (001) LSMO //(001) LAO and (001) LSMO //(001) STO . The crystal structure of LSMO/LAO was indexed as face-centered cubic with a double cell and LSMO/STO as simple cubic. Electron microscopy revealed square facets and elongated grain features. Films heat-treated between 700 and 800 °C on LAO resulted in a structural change, while those on STO showed an increase in texture.

Structure, Electrical and Magnetic Properties of Thin Films of La 1−x M x MnO 3 on Si

Thin films of lanthanum manganates doped with Ca 2+ , Sr 2+ , Ba 2+ and Pb 2+ have been deposited on Si(100) substrate and their electrical and magnetic properties were discussed with respect to the composition, structure and nature of the dopant. Buffer layers of YSZ and La 0.8 Al 0.2 O 3 were employed and their effect on the materials was studied. Interesting magnetotransport properties were found in some of the films, where there is a large difference between the insulator-metal transition temperature and a ferromagnetic transition temperature.

Dry Etching to form Submicron Features in CMR Oxides: (Pr,Ba,Ca)MnO 3 and (La,Sr)MnO 3

Effective pattern transfer into (Pr,Ba,Ca)MnO 3 and (La,Sr)MnO 3 has been achieved using Cl 2 /Ar discharges operated under Inductively Coupled Plasma conditions. Etch rates up to 900 A-min −1 for (La,Sr)MnO 3 and 300 A-min −1 for (Pr,Ba,Ca)MnO 3 were obtained, with these rates being a strong function of ion flux, ion energy and ion-to-neutral ratio. The etching is still physically-dominated under all conditions, leading to significant surface smoothing on initially rough samples. Sub-micron (0.35 μm) features have been produced in both materials using SiN x as the mask.

Grain Boundary Effets On Transport In MOCVD-Grown, Ca-Doped Lanthanum Manganites

THURSDAY AFTERNOON, JANUARY 8,1998 259 BAYVIEW, 2:OO TO 5:OO Session FD CMR MATERIALS AND THEIR PROPERTIES R. B. Van Dover, Cochair Bell Labs, ID-154, 600 Mountain Road, Murray Hill, NJ 07974 A. Gupta, Cochair IBM Research Center, P.O. Box 218, Yorktown Heights, NY 10598

Crystallinity and Magnetoresistance in Calcium Doped Lanthanum Manganites

Thin films of calcium doped lanthanum manganites La{sub 1{minus}x}Ca{sub x}MnO{sub 3} (LCMO) with x {approximately} 0.41 have been prepared on LaAlO{sub 3}(001) (LAO) Y-stabilized ZrO{sub 2}(001) (YSZ), and Al{sub 2}O{sub 3}(0001) (SAP) substrates by liquid delivery metal-organic chemical vapor deposition (LD-MOCVD). The films on YSZ and SAP substrates have a textured, polycrystalline morphology with a preferred orientation of (110). The films on LAO show a single-crystalline morphology and a (100) orientation. Transport measurements show the polycrystalline films have a resistance peak approximately 60 K lower than the films on LAO and, in general, have a much higher overall resistance. The magnetoresistance (MR) ratio ([R(H) - R(0)]/R(H)) is sharply peaked near the maximum in resistance for the films on LAO, while the polycrystalline films show a noticeable absence of this sharply peaked behavior and a flat, rather large ({approximately} 100%) MR ratio over a large temperature range. These results will be discussed in terms of grain boundary scattering, crystallite size, and magnetization.