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  • Artikel  (202)
  • 2000-2004  (97)
  • 1995-1999  (98)
  • 1980-1984  (7)
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  • 1
    Digitale Medien
    Digitale Medien
    Effect of Cu doping on the magnetoresistive behavior of double perovskite Sr2FeMoO6 polycrystals (2002)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 91 (2002), S. 4421-4425 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The electrical, magnetic, and transport properties of Cu-doped polycrystalline samples Sr2Fe1−xCuxMoO6 with ordered double perovskite structure have been investigated systematically. Analysis of the x-ray powder diffraction pattern based on the Rietveld analysis indicates that the substitution of Fe3+ ions by Cu2+ ions enhances the site location order of Fe, Cu, and Mo on the B site for the high-doping-level samples (x=0.20, 0.25, 0.30). With increasing doping level, a transition from semiconductor to metal behavior was also found to occur. Furthermore, the transition temperature was found to decrease either by the application of a magnetic field or by increasing the doping level. It can be concluded that the existence of Cu2+ ions induces the occurrence of Fe3+δ ions and the double exchange interaction in Fe3+–O–Mo–O–Fe3+δ. The transport mechanism in these samples can be attributed to the competition between the metal phase and the semiconductor phase arising from the doping of Cu2+ ions. Both the semiconductor-to-metal transition and the magnetoresistive behavior can be explained by the percolation threshold model. © 2002 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1454207
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  • 2
    Digitale Medien
    Digitale Medien
    Effect of Li substitution on the crystal structure and magnetoresistance of LaMnO3 (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 5915-5919 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The crystal structure and magnetoresistance of the polycrystalline La1−xLixMnO3 (x=0.10, 0.15, 0.20, 0.30) are investigated. The result of the Rietveld refinement of x-ray powder diffraction shows that the room temperature structural transition from rhombohedral (R3¯C) to orthorhombic (Pbnm) symmetry occurs at the Li-doped level x≥0.2. Accompanying the occurrence of the structural transition, the lattice distortion and the bending of the Mn–O–Mn bond increase and the ferromagnetic transition temperature TC decreases. For x=0.10 and 0.15 samples, double metal–insulator (M–I) transitions accompanying a single ferromagnetic transition and a negative magnetoresistance as high as 26% in a magnetic field of 0.8 T are observed. For x=0.20 and 0.30, the samples manifest nonmetallic behavior throughout the measured temperature range. We suggest that the double M–I transitions phenomena of low Li-doped samples originate from the magnetic inhomogeneity due to the formations of the Mn3+ and Mn4+-rich regions induced by partial substitution of the monovalent Li1+ ions for the trivalent La3+ ions. The transport property of high Li-doped samples (x=0.20 and 0.30) can be explained according to the additional localization of eg electrons induced by a static coherent Jahn–Teller distortion of the MnO6 octahedra stemming from the structural transition from rhombohedral (R3¯C) to orthorhombic (Pbnm) and the reduced bandwidth of eg electrons due to the increased bending of the Mn–O–Mn bond. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1319971
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  • 3
    Digitale Medien
    Digitale Medien
    Coexisting photoluminescence of Si and Ge nanocrystals in Ge/Si thin film (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 5318-5321 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Thin films of composite germanium/silicon (Ge/Si) were prepared by pulsed laser ablation alternately on Ge and Si materials on a rotary target, followed by vacuum deposition of the ablated materials on an ultraclean glass substrate. X-ray diffraction and atomic force microscopy phase analysis confirmed that the film structure consisted of a mixture of Si and Ge nanoparticles which could exist in two possible phases. Most of the particles are of less than 30 nm in diameter even after the sample was annealed at 500 °C for 6 h. With different excitation light of wavelengths 280 and 380 nm the composite film yielded independent photoluminescence emissions corresponding, respectively, to the Si and Ge nanoparticles which did not interfere with each other. These results demonstrate that there was very little interaction between the Si and Ge emissions arising from their coexisting mixture in the thin film, even after high temperature annealing of the film in the atmosphere. It opens up the possibility for application of the Si/Ge composite film in multiple function optoelectronic devices. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1412269
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  • 4
    Digitale Medien
    Digitale Medien
    Thermal stability of W ohmic contacts to n-type GaN (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 278-281 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: W was found to produce low specific contact resistance (ρc∼8.0×10−5 Ω cm2) ohmic contacts to n+-GaN (n=1.5×1019 cm−3) with limited reaction between the metal and semiconductor up to 1000 °C. The formation of the β–W2N and W–N interfacial phases were deemed responsible for the electrical integrity observed at these annealing temperatures. No Ga out-diffusion was observed on the surface of thin (500 A(ring)) W contacts even after 1000 °C, 1 min anneals. Thus, W appears to be a stable contact to n+-GaN for high temperature applications. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.362816
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  • 5
    Digitale Medien
    Digitale Medien
    Reduced temperature growth of crystalline 3C-SiC films on 6H-SiC by chemical vapor deposition from silacyclobutane (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 1271-1273 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: 3C- on 6H-SiC (0001) epitaxial growth from the single-source organosilane precursor silacylobutane (c-C3H6SiH2) has been investigated over the temperature range of 800–1100 °C. Spectrophotometry was used to determine an optical absorption edge of ∼2.27 eV for the films grown at 900 °C, corresponding approximately to the energy band gap of 3C-SiC. The crystallinity, structure, strain, and dislocation density in the 3C-SiC thin films were determined using double crystal x-ray diffractometry (DCXRD). The films grown at 800–1000 °C were found to be exclusively 3C-SiC. The films grown at 1100 °C were a mixture of 3C, 4H, and 6H polytypes of SiC. All films shown an excellent surface morphology. The optimum films are obtained at 900 °C, exhibiting structural properties nearly equal to those of the substrate: narrow DCXRD peak width (∼17 arcsec) and low dislocation density (∼3×106 cm2). © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.360368
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  • 6
    Digitale Medien
    Digitale Medien
    Reflectance studies of the tin(II) diphenylcarbazide solid monitoring reagent for atmospheric oxidants (1982)
    s.l. : American Chemical Society
    Analytical chemistry 54 (1982), S. 1227-1229 
    Details
    ISSN: 1520-6882
    Quelle: ACS Legacy Archives
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1021/ac00244a054
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  • 7
    Digitale Medien
    Digitale Medien
    Minority-carrier-enhanced reactivation of hydrogen-passivated Mg in GaN (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 2690-2692 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The influence of minority-carrier injection on the reactivation of hydrogen passivated Mg in GaN at 175 °C has been investigated in p-n junction diodes. The dissociation of the neutral MgH complexes is greatly enhanced in the presence of minority carrier and the reactivation process follows second-order kinetics. Conventional annealing under zero-bias conditions does not produce Mg-H dissociation until temperatures ≥450 °C. These results provide an explanation for the e-beam-induced reactivation of Mg acceptors in hydrogenated GaN. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.116310
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  • 8
    Digitale Medien
    Digitale Medien
    Ion implantation doping and isolation of GaN (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 1435-1437 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: N- and p-type regions have been produced in GaN using Si+ and Mg+/P+ implantation, respectively, and subsequent annealing at ∼1100 °C. Carrier activation percentages of 93% for Si and 62% for Mg were obtained for implant doses of 5×1014 cm−2 of each element. Conversely, highly resistive regions ((approximately-greater-than)5×109 Ω/(D'Alembertian)) can be produced in initially n- or p- type GaN by N+ implantation and subsequent annealing at ∼750 °C. The activation energy of the deep states controlling the resistivity of these implant-isolated materials is in the range 0.8–0.9 eV. These process modules are applicable to the fabrication of a variety of different GaN-based electronic and photonic devices. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.114518
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  • 9
    Digitale Medien
    Digitale Medien
    Cell-Type Specific and Ligand Specific Enhancement of Cellular Uptake of Oligodeoxynucleoside Methylphosphonates Covalently Linked with a Neoglycopeptide, YEE(ah-GalNAc)3 (1995)
    s.l. : American Chemical Society
    Bioconjugate chemistry 6 (1995), S. 695-701 
    Details
    ISSN: 1520-4812
    Quelle: ACS Legacy Archives
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1021/bc00036a006
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  • 10
    Digitale Medien
    Digitale Medien
    Enhanced intergrain tunneling magnetoresistance in double perovskite Sr2FeMoO6 polycrystals with nanometer-scale particles (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 3853-3855 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Polycrystalline ordered double perovskite Sr2FeMoO6 bulk samples with grain size in the range of 29–45 nm have been synthesized at temperatures from 900 to 1000 °C, using a sol-gel method. We find that the intergrain magnetoresistance is closely correlated with the grain size. The sample with the grain size of 29 nm shows large magnetoresistance Δρ/ρ0, 30%–20% at a low magnetic field of 4 kG over a wide temperature range from 20 to 300 K. The results can be explained in terms of spin-dependent intergrain tunneling model. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.125478
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