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  • 1
    Electronic Resource
    Electronic Resource
    Electric field forced phase switching in La-modified lead zirconate titanate stannate thin films (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 1699-1704 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electric field forced antiferroelectric to ferroelectric phase switching has been demonstrated in thin films of Pb0.97La0.02(Zr,Ti,Sn)O3 perovskites for the first time. Several compositions in the tetragonal antiferroelectric phase field of this system were prepared in thin film form by a sol-gel technique. Forward and reverse switching threshold fields of 27–103 kV/cm and 18–62 kV/cm, respectively, were determined from polarization-electric field hysteresis and incremental capacitance data. Switching times as fast as 300 ns were recorded for one of the antiferroelectric compositions. An electric field induced longitudinal strain of 0.16% was measured for a film of composition (Pb0.97La0.02)(Zr0.60Ti0.10Sn0.30)O3 using a laser ultradilatometer. These films are candidate materials for high charge storage integrated capacitors and microelectromechanical devices requiring large nonlinear strain response.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356357
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  • 2
    Electronic Resource
    Electronic Resource
    Ohmic contacts to n-GaAs with a Pt/Ge/Au contacting layer and a Ta-Si-N barrier: Electrical and metallurgical characteristics (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 7373-7381 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Pt/Ge/Au trilayers of various Pt:Ge compositions, overlaid with a Ta-Si-N barrier layer and an Au metallization layer, are investigated as ohmic contacts to n-type GaAs. After annealing in flowing argon at 450 °C for 15 min, a contact resistivity of 3.7×10−6 Ω cm2 is obtained for the sample of atomic ratio Pt/Ge=1. The contact resistivity of this sample degrades only slightly to 5.0×10−6 Ω cm2 upon aging at 450 °C for 60 h, while the surface stays smooth. Contact resistivities of samples with other Pt/Ge atomic ratios are in the range of 10−5–10−4 Ω cm2. To understand this electrical behavior, the contacts are characterized by backscattering spectrometry, x-ray diffraction, and transmission electron microscopy in conjunction with energy-dispersive analysis of x rays. The reaction products vary with the Pt:Ge compositions due to the difference of the chemical reactivity between Pt, Ge, and GaAs. The formation and distribution of a ternary PtGe:As phase are the determining factors for the contact resistivity. The outstanding thermal stability of the contact is due to the Ta-Si-N barrier layer which closes the GaAs-trilayer system and protects their chemical equilibria from being disrupted by an inflow of Au from the metallization layer. Without the barrier layer, the morphology of the contact degrades badly at 450 °C after 20 h or less.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356651
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  • 3
    Electronic Resource
    Electronic Resource
    Magnetization and ferromagnetic resonance studies on amorphous films of Fe2O3-Bi2O3-Li2O : 38th Annual Conference on Magnetism and Magnetic Materials (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 6828-6830 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This report is on magnetic properties of samples of 0.5 Fe2O3-(0.5−x)Bi2O3-xLi2O (x=0.1–0.4) prepared in oxygen atmospheres by rf sputtering techniques. The films develop a spontaneous moment M only when annealed in air at temperatures Ta≥675 K. The room-temperature M vs Ta data show a maximum in M for Ta=775–875 K even though x-ray diffraction data do not show the precipitation of any crystalline ferromagnetic or ferrimagnetic phases. The spontaneous moment could be attributed to the presence of ordered clusters in the amorphous film. The magnetization is found to be dependent on the concentration of nonmagnetic Li2O: M increases with increase in x. An in-plane anisotropy in the films is evident from ferromagnetic resonance studies (FMR) at x-band frequencies. The anisotropy field increases with increasing x. The room-temperature in-plane FMR linewidth decreases with increasing x.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356798
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  • 4
    Electronic Resource
    Electronic Resource
    Out-of-plane magnetoresistivity for fields parallel to the c axis in single-crystalline (La1−xSrx)2 CuO4 (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 1706-1710 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The c-axis magnetoresistivity as a function of temperature T and field H for fields parallel to the c axis is experimentally investigated for single-crystalline (La1−xSrx)2CuO4 (x=0.068). It is argued that the observed Lorentz force free magnetoresistive phenomena cannot be accounted for by previously considered mechanisms. By contrast, they can be explained by the extended Josephson coupling model, which takes into account both effective thermal energy and anisotropy. Based on this extended model, it is shown that all the magnetoresistivity curves obtained in H//I//c at various constant temperatures could be nicely scaled onto a single curve without any adjustable parameter in a wide transition region.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357685
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  • 5
    Electronic Resource
    Electronic Resource
    Interlayer coupling in antiferromagnetic EuTe/PbTe superlattices (abstract) : The 6th joint magnetism and magnetic materials (MMM)-intermag conference (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 6291-6291 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report neutron diffraction studies of magnetic correlations in MBE-grown (111) EuTe/PbTe multilayers. Bulk EuTe is a type-II fcc antiferromagnet. This structure consists of ferromagnetic (FM) sheets of spins on (111)-type planes which are coupled antiferromagnetically to one another. In EuTe/PbTe the lattice mismatch strain selects an arrangement of the FM sheets parallel to the multilayer plane. Thus, in the case of an odd number of EuTe monlayers, there should be a nonzero magnetic moment—in other words, such superlattices are expected to behave as ferrimagnets, not anitferromagnets. This has been confirmed by recent SQUID studies. As suggested by the above model, the dipolar fields arising from the lack of total moment compensation may introduce interlayer magnetic coupling, even though in this system there are no carriers that can transfer magnetic interactions across the nonmagnetic spacers through the RKKY mechanism, which is usually the case in coupled magnetic multilayered systems. Our experiments have indeed revealed clear magnetic superlattice peak patterns in several samples. The results of measurements in high external fields (up to 6 T) bring further support for the dipolar nature of the observed interlayer coupling. However, in some contrast to the expected scenario, the most pronounced coupling effects were seen in the case of an even number of monolayers. Possible explanations of this fact (e.g., higher-order terms in dipolar fields, or structural imperfections) are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358309
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  • 6
    Electronic Resource
    Electronic Resource
    Magnetic properties of nanophase cobalt particles synthesized in inversed micelles : The 6th joint magnetism and magnetic materials (MMM)-intermag conference (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 6316-6318 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Cobalt particles were prepared with the microemulsion method in the binary system of DDAB (didodecyldimethylammonium bromide)/toluene by reduction of CoCl2 with NaBH4. The average particle size of the as-prepared samples could be varied from 1.8 to 4.4 nm by controlling the concentration of CoCl2 in the solution of DDAB in toluene. TEM studies showed that the particles were quite uniform and well isolated. The particle sizes determined from magnetic data were consistent with those measured by TEM. The coercivity of the particles at 10 K increased from 640 to 1250 Oe as particle size increased from 1.8 to 4.4 nm. The blocking temperature of the particles increased from 19 to 50 K for the same size range. The saturation magnetization σs at 2 K increased with decreasing particle size. The value of σs of the particles with average size of 1.8 nm was about 200 emu/g, which is 20% higher than the bulk value. This implies that the magnetic moment per atom is enhanced in the nanoparticle system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358280
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  • 7
    Electronic Resource
    Electronic Resource
    Characterization of a-Ge:H with the steady-state photocarrier grating measurement (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 5191-5195 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The steady state photocarrier grating measurement technique has been used and is shown to be valid for the characterization of steady-state transport properties of minority carriers in undoped improved quality hydrogenated amorphous germanium (a-Ge:H). Deviations from the theoretically predicted behavior of the measurement have been observed on some a-Ge:H samples. At room temperature in a-Ge:H, the ratio of photoconductivity to dark conductivity is less than 1. The high density of thermally generated carrier is observed to affect the measurement by reducing its sensitivity. Whether it is also the cause of the observed deviation will be discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355716
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  • 8
    Electronic Resource
    Electronic Resource
    Magnetic properties of microemulsion synthesized cobalt fine particles : 38th Annual Conference on Magnetism and Magnetic Materials (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 5876-5878 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Two microemulsion systems, the ternary system H2O/AOT/isooctane and the binary system DDAB/toluene, were used to prepare metallic cobalt particles by borohydride reduction of a cobalt salt. The particles prepared in the AOT system were extremely small and superparamagnetic with magnetic moment per particle of 11.5μB, a blocking temperature of 2 K, and σs=146 emu/g at 1.7 K. The magnetic moment and σs combined imply a particle size of about 5.4 A(ring). However, the particles made in the DDAB system were relatively large, ∼10 nm. They were ferromagnetic at room temperature but with no coercivity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355546
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  • 9
    Electronic Resource
    Electronic Resource
    Stability of rhenium thin films on single crystal (001) β-SiC (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 897-901 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thermal reactions of Re thin films in contact with single crystalline (001) β-SiC at temperatures between 700 and 1100 °C for 30 min are investigated by MeV He++ backscattering spectrometry, x-ray diffraction, secondary ion mass spectrometry, and transmission electron microscopy (plan-view and cross-sectional). No reaction between Re and SiC is observed for any annealing conditions. The average grain size of the as-deposited Re film is 220 nm and increases to 280 nm after annealing at 1100 °C for 30 min. A strong {0001}Re fiber texture is also observed after annealing. The chemical stability of Re thin films on SiC is consistent with the earlier study of solid-phase stability in the ternary Re-Si-C system which shows that Re and its silicides have tie lines with SiC at 1600 °C. It also coincides with calculations of the free energy of reaction from assessed thermodynamic data for rhenium silicides and SiC. The implications of this Re stability with SiC for applications of Re as a metal for electrical contact to SiC-based devices are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356444
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  • 10
    Electronic Resource
    Electronic Resource
    Reaction of Ta thin film with single crystalline (001) β-SiC (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 2169-2175 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The reaction between a sputter-deposited Ta film (320 nm thick) and a single crystalline (001) β-SiC substrate induced by vacuum annealing at temperatures of 600–1200 °C for 1 h (30 min at 1100 °C) is investigated by 3 MeV He++ backscattering spectrometry, x-ray diffraction, secondary ion mass spectrometry, and transmission and scanning electron microscopies. No significant reaction is observed at 800 °C or at lower temperatures. At 900 °C, the main product phases are Ta2C and carbon-stabilized Ta5Si3. A minor amount of unreacted Ta is also present. After annealing at 1000 °C, all the tantalum has reacted; the reaction zone possesses a multilayered structure of β-SiC/TaC/carbon-stabilized Ta5Si3/α-Ta5Si3/Ta2C. The diffusion path at 1000 °C is plotted on the isothermal section of the Ta-Si-C phase diagram. At 1100 °C, the reacted layer has an interface with the SiC substrate that is still quite flat but has a rough surface due to the formation of macroscopic voids within the reacted layer. The equilibrium products predicted by the phase diagram are TaC and TaSi2. This final state is reached by annealing at 1200 °C for 1 h. At that point, the reacted layer has a laterally very uneven structure and morphology.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357629
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