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Room: 330C
Session Chairperson: Robert Shull, NIST, Bldg. 223, Rm B152, Gaithersburg, MD 20899
9:00 am INVITED
RESISTANCE BEHAVIOR OF Cr-Si-O THIN FILMS: Alan F. Jankowski, Jeffrey P. Hayes, Ronald Musket, Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, CA 94550; Frederic Cosandey, Chandrasekhar E. Gorla, Rutgers University - College of Engineering, P.O. Box 909, Piscataway, NJ 08855; Ronald S. Besser, Victor Westerlind and Gregory Cobai, Silicon Video Corporation, 6580 Via Del Oro, San Jose, CA 95119
Thin coatings of Cr-Si-O are assessed for use as a resistor. The submicron thick films are sputter deposited using a working gas mixture of (1-x)Ar-(x)O2. Several sintered-compacts of metal and oxide powders are commercially prepared for use as the sputter targets. The deposition process yields a range of film compositions which consist of 2-30 at.% Cr and 20-45 at.% Si as measured using Rutherford Back Scattering. A broad range of resistance values (101 to 1014 Ohm-cm) are found as measured by point contact with metal pads deposited onto the Cr-Si-O film surface. The film structure and morphology is characterized using transmission electron microscopy from which the resistance behavior can be correlated to the distribution of metallic-Cr. Thermal aging reveals metastability in the Cr-Si-O film morpholgy and resistance behavior.
9:30 am
MICROSTRUCTURE AND OPTICAL PROPERTIES OF GaN NANOCRYSTALS IMBEDDED IN A POLYMER MATRIX: M. Benaissa, Instituto Nacional de Investigaciones Nucleares, Mexico; M. José-Yacamán, Instituto de Fisica-UNAM, Mexico; K.E. Gonsalves, G. Carlson, University of Conneticut, Storrs, CT 06269
Presently, nanostructured GaN composite was prepared using a novel synthetic route. GaN nanocrystals were imbedded in a poly(methyl methacrylate) thin film matrix (GaN/PMMA) and then studied from structural and optical point of views. X-ray powder diffraction and high-resolution transmission electron microscopy were performed to analyze the microstructure while the optical properties were measured by optical absorption and photoluminescence. Microstructural analyses showed that the GaN nanocrystallites imbedded in the PMMA matrix have an average size of about 5.5 nm and crystallize in the zinc blende lattice (lattice constant a close to 0.45 nm) with some nitrogen vacancies and structural imperfections. Optical absorption measurements indicate that the band gap energy of the GaN/PMMA composite is approximately 3.51 eV.
9:50 am
ANELASTIC AND MAGNETOELASTIC BEHAVIOUR OF BULK NANOPHASE MATERIALS: E. Bonetti, L. Del Bianco, Dipartimento di Fisica and Istituto Nazionale per la Fisica della Materia, viale Berti Pichat 6/2 I-409128 Bologna, Italy
Mechanical spectroscopy techniques have been employed to investigate the anelastic and magnetoelastic behavior of bulk nanophase Fe and Fe-Al prepared by mechanical alloying and FeCuNbSiB granular alloys obtained starting from amorphous precursors through thermal treatments. The different magnetic states of the materials lead to strong modifications of the anelasticity spectra. The experimental results are presented and discussed with specific reference to the following to aspects : a) magnetoelastic coupling and giant DE effect in the FeCuNbSiB system occurring just below the nanocrystallization temperature, b) giant modulus enhancement in bulk iron and iron-aluminum alloys linked to changes of the magnetic behavior connected to grain size reduction and interfacial structure relaxation.
10:10 am BREAK
10:25 am
MAGNETIC PROPERTIES OF GRANULAR Co-Cu ULTRATHIN FILMS: A. Cabbibo, Y.D. Park, J.A. Caballero, J.R. Childress, Materials Science and Engineering, University of Florida, Gainesville, FL 32611-2066
Ultrathin (<10nm) films and multilayers of granular Co-Cu composites have been prepared by co-sputtering. Nanoscale Co particles are formed in Cu by depositing on heated substrates (TS>100C), with the usual increase in magnetic coercivity Hc, and superparamagnetic behavior above a critical blocking temperature (Tb) which depends on the partical size, shape, and local magnetic environment. We find that the confinement of the granular layer to thicknesses near the particle size induces variation in Hc and Tb due to changes in particle shape, magnetic anisotropy and inter-particle interactions. By varying the composition and thickness of both magnetic layer and interlayer, as well as the deposition conditions, one can identify conditions under which then magnetic granular layers can be fabricated with large anisotropy and therefore increased blocking temperature, without the need for post-deposition high-temperature processing. Such layers are designed to be used in magnetoresistive spin-valve multilayer structures.
10:45 am
ATOMIC STRUCTURE PECULIARITIES AND PHASE TRANSFORMATIONS IN HIGH-Tc SUPERCONDUCTING CERAMIC COMPOUNDS YBa(2)Cu(3)O(7-x): V.G. Pushin, L.I. Yurchenko, T.G. Koroleva, G.Ye. Vedernikov Institute of Metal Physics, Ural Division of Russian Academy of Sciences, S. Kovalevskaya 18, 620219 Ekaterinburg, Russia.
Recent results of high-resolution and in situ transmission and scanning electron microscopy, diffraction of X-rays and electrons, physical and mechanical tests on high T-c superconducting ceramic compounds of Yba (2)Cu(3)O(7-x), including thick ceramic films synthesided on ZrO(2), are presented. The main types of atomic structures, structural defects, secondary phase inclusions are systematized. It is shown that grain structure of ceramics in form of the polyhedral matrix crystallites divided by grain boundaries is characterized by a porosity and secondary phase inclusions, which exist inside grains and between them. In some cases the inclusions of amorphous phase were detected. The peculiarities of high-resolution TEM of investigated ceramic compounds are discussed. The pretransition phenomena and phase martensite-like transformations in high-Tc superconducting ceramics and classical high-Tc intermetallic compounds of type A15 (V(3)Si, Nb(3)Sn, V(3)Ge) and C15(V(2)Zr, V(2)Zr, V(2)Hf) are compared.
11:05 am
LOW FREQUENCY INTERNAL FRICTION STUDIES OF NANOCRYSTALLINE COPPER-IRON MATERIALS: W.N. Weins, J.D. Makinson, R.J. DeAngelis, Department of Mechanical Engineering, The Center for Materials Research and Analysis, University of Nebraska, Lincoln, NE 68588-0656
The low-frequency internal friction behavior of mechanically milled copper and copper-30 wt% iron alloys was studied over a temperature range of 100-700°K and a frequency range of approximately 1 to 3 Hz. Alloys were prepared by consolidating mechanically milled and alloyed powders using hot isostatic pressing to form compacts from which bars were machined for testing. Samples studied included unmilled copper, milled copper and milled copper-30 wt% iron. All powders were consolidated at 600°C and diffracting particle size of the consolidated material varied from 18-30 nm. The internal friction studies indicated the presence of a large grain boundary peak in all samples at approximately 300°C which increased with decreasing particle and grain size. The presence of iron appears to depress this peak and cause the occurrence of a second smaller high temperature peak in the range of 400-500°C, which is believed to be associated with iron in solid solution.
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