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  • 1
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Glass/ Fe50 A(ring)/Co11 A(ring)/Cut/Co11 A(ring)/Cu10 A(ring) structures were sputtered in a high-vacuum system with a base pressure of 5×10−8 Torr. The magnetoresistance (MR) reaches 8% at room temperature for tCu=10 A(ring) with a saturation field of 700 Oe. For tCu=22 A(ring) the MR reaches 6.4% for a 200 Oe field. Our results are analyzed in a semiclassical approach by solving the Boltzmann equation for the five-layer structure with λCo=76 A(ring) and λCu=420 A(ring) and using both interfacial and bulk spin-dependent scattering. Interlayer coupling was checked by magneto-optical measurements using the transverse Kerr-effect geometry. For tCu=10 A(ring) we observe zero-remanence magnetization curves with saturation fields around 1 kOe. For tCu=22 A(ring) no evidence for macroscopic antiferromagnetic coupling is observed since the hysteresis cycle is almost square.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 7370-7373 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Co-Re superlattices were prepared with nominal periodicities of 65–67 A(ring) and varying bilayer composition. The structural characterization was made by x-ray diffraction and Rutherford backscattering spectrometry (RBS). First, second, and third order satellites are observed in the x-ray diffractogram at 2θ values and with intensities close to those predicted by simulation. This confirms the coherence of the superlattice. RBS measurements combined with RUMP simulations give information on interface sharpness and the absolute thicknesses of the Co and Re layers. Discrepancies between the experimental and simulated diffractograms are found for Co thicknesses below 18 A(ring).
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 7067-7078 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effects of As doping, at concentrations CAs≤4.8×1018 cm−3, on the growth kinetics of Si(001):As layers deposited at temperatures Ts=575–900 °C by gas-source molecular-beam epitaxy from Si2H6 and AsH3 have been investigated. With constant AsH3 and Si2H6 fluxes, film deposition rates RSi increase while CAs decreases with increasing Ts. All incorporated As resides at substitutional electrically active sites for CAs up to 3.8×1018 cm−3 (Ts=800 °C), the highest value yet reported for Si(001):As growth from hydride source gases. Immediately following film growth or partial-monolayer As adsorption on clean Si(001), the samples were quenched to 300 °C and exposed to atomic deuterium (D) until saturation coverage. In situ D2 temperature-programmed desorption (TPD) spectra from both as-deposited Si(001):As and As-adsorbed Si(001) layers are composed of β1 and β2 peaks, due to D2 desorption from Si monodeuteride and dideuteride surface phases, together with a new peak β3 which we attribute to desorption from Si–As mixed dimers. Analyses of the TPD spectra show that, because of the lone-pair electrons associated with each As surface atom, the total dangling-bond coverage, and hence RSi, decreases with increasing incoming flux JAsH3 at constant Ts. From measurements of the steady-state As surface coverage θAs vs CAs and Ts, we obtain an As surface segregation enthalpy ΔHs=−0.92 eV. Dissociative AsH3 adsorption on Si(001) was found to follow second-order kinetics with a relatively Ts-independent reactive sticking probability of 0.3. Associative As2 desorption is also second order with a rate constant kd,As2=1×1013 exp(−3.0 eV/kTs). From the combined set of results, we develop a predictive model with no fitting parameters for CAs vs JAsH3, JSi2H6, and Ts. © 2000 American Institute of Physics.
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  • 4
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We use a combination of in situ and postdeposition experimental probes together with ab initio calculations of strain coefficients and formation energies associated with specific C configurations in the Si lattice to determine C incorporation pathways and lattice site distributions in fully coherent Si1−yCy alloy layers grown by molecular-beam epitaxy on Si(001) as a function of deposition temperature Ts (380 °C–680 °C) and C fraction y (0–0.026). Lattice strain and Raman spectroscopy measurements demonstrate that all C, irrespective of y, is incorporated into substitutional lattice sites in Si1−yCy(001) layers grown at Ts≤480 °C. Increasing Ts≥580 °C leads to strong C surface segregation, as shown by in situ angle-resolved x-ray photoelectron spectroscopy, yielding additional pathways for C incorporation. Photoluminescence measurements indicate that an increasing fraction of the incorporated C in the higher-temperature layers resides in dicarbon complexes. Reflection high-energy electron diffraction and cross sectional transmission electron microscopy reveal surface roughening at Ts≥580 °C with the formation of bulk planar structures, interconnected by {113} segments, that are periodic along [001] with a periodicity which decreases with increasing Ts. We interpret the planar structures as layers of C-rich Si1−yCy which form in the presence of excess surface C resulting from segregation. Our ab initio density functional calculations show that substitutional C arranged in an ordered Si4C phase is 0.34 eV per C atom more stable than isolated substitutional C atoms. © 2002 American Institute of Physics.
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 6183-6188 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Er-related luminescence near 1.54 μm (∼805 meV) is observed under below band gap excitation at 4.2 K in GaN:Er and GaN:Er,O implanted samples. The spectrum of the recovered damage samples is a multiline structure. So far, these lines are the sharpest ones reported for GaN. Well-resolved green and red luminescences are observed in implanted samples. The dependence of luminescence on the excitation energy as well as the influence of different nominal fluence and annealing conditions is discussed. Combining the results obtained from photoluminescence and Rutherford backscattering spectrometry, different lattice sites for the optical active Er-related centers are identified. © 2001 American Institute of Physics.
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 8210-8215 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Bi12(GaxBi1−x)O19.5 (BGaO) films with thickness in the range 100–1000 nm have been deposited on (100) Y-stabilized zirconia (YSZ) and (100) Bi12GeO20 (BGO) substrates using a KrF excimer pulsed laser and polycrystalline targets with composition x=0.63–0.72. The laser power density threshold for ablation of the targets has been determined to be J0=4.8 J/cm2. A deposition rate of 0.03 A(ring)/pulse was found for the substrate-target distance (6 cm) and laser fluence (J=7 J/cm2) used. Transparent and crystalline films were obtained heating the substrate in the 450–550 °C range under 1.5×10−1 mbar of oxygen pressure. Films deposited on hot substrates have a Ga stoichiometry x=0.5 but a Bi content slightly lower than that corresponding to sillenite. Films deposited on YSZ show preferential orientation. From the x-ray diffraction results and the comparison of the ionic distributions, it has been concluded that the most likely orientation between both lattices is 〈310〉{130}BGaO(parallel)〈011〉{100}YSZ. A {100}BGaO(parallel){100}BGO epitaxy has been inferred from Rutherford backscattering analysis. On both substrates the films behave as step waveguides with refractive index close to the value determined in bulk BGaO. © 1996 American Institute of Physics.
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  • 7
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The combined hyperfine interaction of mercury in a hexagonal close-packed cobalt single crystal was measured using the e−−γ perturbed angular correlation technique with the 197Hg and 199Hg probes, without applied magnetic field. The magnetic and quadrupole coupling constants of the 5/2− levels in both 197Hg and 199Hg were measured with extremely high precision, ωL( 197Hg)=951(9) Mrad/s, ωL (199Hg)=1039(10) Mrad/s, vQ (197Hg)=3.7(5) MHz and vQ (199Hg)=32(2) MHz. Using the well-known g factors and quadrupole moments of the respective levels, the magnetic hyperfine field, ||Hhf(HgCo)||=581(12) kG, and the electric field gradient, ||Vzz(HgCo)|| =2.0(3)×1017 V/cm2, were derived. The importance of using these hyperfine probes for studying the microscopic structure of cobalt-based multilayers is introduced and discussed.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 6480-6482 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Spin-valve structures, glass/NiFeI/Cu/NiFeII/a-TbCo/Cu, were prepared where the pinned Permalloy layer is exchanged biased by a 200 to 400 A(ring) thick a-Tb0.23Co0.77 layer. Exchange fields between 50 and 250 Oe were achieved with TbCo thicknesses below 400 A(ring), for a pinned Permalloy layer 150 A(ring) thick. The exchange fields are strongly dependent on substrate bias. The magnetoresistance of these structures reaches 4.5% when thin Co layers are added at the NiFe/Cu interfaces.
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  • 9
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: NiFe/oxide/Co junctions were fabricated by magnetron sputtering for studies of polarized electron transport across the insulating barrier. Al2O3, Al-Al2O3, and MgO insulating barriers were prepared with junction resistances from 0.5 to 116 Ω. The I-V characteristics at room temperature are linear. For low barrier resistance, the magnetoresistance of the structure is dominated by the anisotropic magnetoresistance of the ferromagnetic electrodes. For the higher barrier resistances, a different magnetoresistance effect is observed, which is tentatively related to tunneling or spin-valve effects across the insulating junction.
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 3164-3173 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The optoelectronic properties of hydrogenated amorphous silicon–carbon alloys (a-SiC:H) are studied over the entire compositional range of carbon content. The films are prepared using radio-frequency glow discharge and optimization was made with respect to deposition power and pressure, hydrogen dilution, and methane (or ethylene) -to-silane gas phase ratio. Regardless of the deposition conditions and source gases used, the optical, structural, and transport properties of the a-SiC:H alloys followed simple universal dependencies related to changes in the density of states associated with their structural disorder. The Urbach tail energy Eu and the B factor of the Tauc plot correlate with E04 (defined as the energy at which the absorption coefficient is equal to 104 cm−1) taken from photothermal deflection spectroscopy measurements. Up to E04pds≈2.6 eV, Eu increases monotonically from 50 up to ≈200 meV, while the B factor decreases from ≈800 down to ≈200 cm−1/2 eV−1/2. Above E04pds≈2.6 eV, both Eu and B remain approximately constant. The photoconductivity decreases exponentially with E04pds and is below 10−10 Ω−1 cm−1 for E04pds≥2.6 eV. Room-temperature photoluminescence is observed when E04pds≥2.6 eV. The photoluminescence peak position lies an average of 0.6 eV below the value of E04pds and increases linearly with decreasing value of the B factor of the Tauc plot. © 1995 American Institute of Physics.
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