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  • American Institute of Physics (AIP)  (50)
  • 2015-2019  (14)
  • 1990-1994  (36)
  • 1
    Electronic Resource
    Electronic Resource
    ErSb/GaSb(001) and GaSb/ErSb/GaSb(001) heterostructures and [ErSb,GaSb] superlattices: Molecular beam epitaxy growth and characterization (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 2876-2883 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Successful growth of ErSb(001) single crystal layers on GaSb(001) substrates has been demonstrated. The reflection high-energy electron diffraction patterns show a (4×4) surface reconstruction. Reflection high-energy electron diffraction oscillations, x-ray diffraction, and Rutherford backscattering with channeling indicate single crystal monolayer-by-monolayer growth and continuity of the Sb sublattice at the ErSb/GaSb interface. The ErSb has a low room temperature resistivity equal to 30 μΩ cm but may be used as a metallic reflector only for wavelengths greater than 2.4 μm. The overgrowth of GaSb on ErSb leads to mirrorlike surfaces but the overlayers contain symmetry-related defects. On the contrary, nearly perfect GaSb overlayers were grown on [ErSb,GaSb] superlattices which exhibit metallic behavior.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356181
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  • 2
    Electronic Resource
    Electronic Resource
    Small-angle x-ray scattering study of anodically oxidized porous silicon layers (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 780-784 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Small-angle x-ray scattering was used to investigate the microstructural change induced by electrochemical oxidation of porous silicon (PS) layers. It is shown that when the oxidation level increases, the size of the crystalline Si domains, which constitute the PS layer, decreases. This size reduction is correlated to the blue-shift observed in the photoluminescence spectra when the oxidation level is increased. Moreover, we found that a "fuzzy'' surface appears between pores (voids) and matter when the samples are electrochemically oxidized. This interface is found very sharp for the as-prepared and nonoxidized PS layers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356454
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  • 3
    Electronic Resource
    Electronic Resource
    Intra-4f-shell transitions at room temperature of Er3+ ions in Ca1−xErxF2+x thin films grown on Si(100) (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 1133-1137 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Intra-4f-shell transitions of Er3+ ions in Ca1−xErxF2+x thin films were studied by means of photoluminescence (PL) and cathodoluminescence (CL) measurements at room temperature. The samples, with x varying from 0.01 to 0.2, were epitaxially grown on Si(100) substrates by sublimation of solid solution powders. Using the 488-nm line of an Ar+-ion laser as the excitation source, it is shown that the films present strong PL lines corresponding to the internal transitions between the 4S3/2,4F9/2,4I11/2, and 4I13/2 excited levels and the 4I15/2 fundamental state of Er3+ (4f11) ions. Their centers of gravity were pointed out at λ=533, 650, 980, and 1530 nm, respectively. These electronic transitions were also evidenced by means of the CL technique. Moreover, this technique showed that the luminescence is uniform in all points of the layers. The PL intensities vary considerably as a function of the erbium substitution rate. In the visible range the strongest luminescence was found for x less than 0.01, while for the 1530-nm line (which presents evident potential applications for optical communications) the highest luminescence intensity corresponds to x close to 0.16. The refractive index (n) of the layers also varies with the erbium concentration. For a 1.3-μm incident radiation, n continuously increases from 1.425 to 1.466 when x varies from 0.035 to 0.19. This result shows that these structures can lead to the realization of plane optical waveguides.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356497
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  • 4
    Electronic Resource
    Electronic Resource
    Optical and electrical properties of rare earth (Yb,Er) doped GaAs grown by molecular beam epitaxy (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 4171-4175 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electrical and optical properties of erbium-doped and ytterbium-doped GaAs are reported in this article. The studied samples are semi-insulating and have been grown by molecular beam epitaxy. The Yb and Er concentrations in the GaAs epitaxial layers measured by secondary ion mass spectroscopy are 2–3×1017 cm−3. The photoluminescence of Yb intra-4f shell has not been observed, while that of Er has been widely reported. Photoinduced current transient spectroscopy measurements (PICTS) reveal that the Yb doping (Er doping) creates a level in the gap with an activation energy of 0.65 eV (0.67 eV). The depth of such levels may be responsible for the absence of Yb 4f photoluminescence in GaAs:Yb. Moreover, photoconductivity experiments show the presence of rare earth related traps. The energies of these traps correspond exactly to the difference between the gap energy and the corresponding activation energy found by PICTS. These observations confirm the excitation model based on the energy transfer from recombination to the rare earth transitions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356000
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  • 5
    Electronic Resource
    Electronic Resource
    Coadsorption of hydrogen and CO on Pt(335): Structure and vibrational Stark effect (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 4277-4287 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have studied CO and H coadsorbed on the stepped Pt(335) surface in vacuum to learn about their interaction at steps and to compare with previous electrochemical studies. Both electroreflectance and conventional reflectance absorption vibrational spectra were obtained of atop bonded CO. Its stretch vibrational frequency ν, Stark tuning rate (dν/dE), and integrated absorbance S were all studied as functions of CO and H coverage. With CO only on step edges, S for atop CO decreases to zero with increasing H coverage. The CO affected by H is in a mixed phase and is bridge bonded. Atop CO's (dν/dE) decreases with increasing CO coverage but is unaffected by coadsorbed H. In the low CO coverage limit (dν/dE)=88±9 cm−1/(V/A(ring)), in agreement with theory and with previous measurement. The standard model of dipole–dipole screening is unable to explain the CO coverage dependence of both (dν/dE) and S. The vibrational polarizability of CO increases with coverage. We also compare our results with spectroelectrochemical data from CO on Pt(335) in aqueous electrolyte. Our measured (dν/dE) is too small to explain the variation of CO's ν with electrode potential φ in the electrochemical experiments if (dE/dφ) in the double-layer is taken from conventional models. The effect of coadsorbed H is also different; in vacuum H has no effect on CO's (dν/dE) but in electrolyte, at low CO coverage, (dν/dφ) drops to zero at the potential where H adsorption begins.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467478
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  • 6
    Electronic Resource
    Electronic Resource
    Role of atomic mass of underlayer material in the transition noise of longitudinal media (abstract) : 35th annual conference on magnetism and magnetic materials (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 4749-4749 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Magnetic and recording properties of CoPtCr on Mo and W underlayers were investigated and compared to Cr underlayers over the sputtering pressure range of 3–24 mTorr. Normalized media transition noise decreases with increasing pressure in all cases, and the reduction can be attributed to a reduced intergrain exchange coupling due to isolation of the magnetic grains. In the low-pressure regime, the transition noise increases with increasing atomic mass of the underlayer, Cr〈Mo〈W. This trend can be attributed to the growth features of the underlayers which change from a partially coupled structure for Cr to closely coupled grains for W. We attribute this behavior in the low-pressure regime to increasing mobility with increasing atomic mass since the energy flux of the sputtered atoms and the back-reflected argon atoms increases with the atomic mass of the target. In the high-pressure regime, all underlayers produce an isolated grain morphology in the magnetic layer, which indicates sufficient thermalization of the atoms during the transport resulting in similarly low values of transition noise.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348269
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  • 7
    Electronic Resource
    Electronic Resource
    Characterization of Er3+-doped glasses by fluorescence line narrowing (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 6799-6811 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Stark levels of the 4I15/2 ground state manifold have been determined for Er3+-doped fluorozirconate, fluorophosphate, phosphate, and silicate bulk glasses from fluorescence-line-narrowing (FLN) measurements at 4.2 K. Splittings between adjacent Stark levels were observed to be 10–140 cm−1 and the total energy spread of the manifold was found to range from 335 to 400 cm−1. The position of a given Stark level varies up to 60 cm−1 depending on the particular Er3+ sites excited. Using the 4.2-K results, homogeneous broadening is found to be a reasonable approximation for the 300-K luminescence band of the glasses examined. Results are also presented for silica preforms as well as for a barium-zinc-lutetium-thorium fluoride composition. The FLN studies together with a Judd–Ofelt [Phys. Rev. 127, 750 (1962); J. Chem. Phys. 37, 511 (1962)] analysis of the absorption data suggest similarities in the local environment between the fluorozirconates and the high-fluorine fluorophosphates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347669
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  • 8
    Electronic Resource
    Electronic Resource
    The effect of Cr underlayer thickness on magnetic and structural properties of CoPtCr thin films (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 4686-4688 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thin Co-based alloy films have shown important recording, magnetic, and structural changes when grown on Cr underlayers of different thicknesses. We have investigated these properties using several different CoPtCr compositions on Cr underlayers ranging from 0 to 200 nm in thickness. We report epitaxial growth of the hcp Co (11.0) planes on the (100) planes of bcc Cr for the first time on a disk appropriate for magnetic recording. The 〈11.0〉 Co preferred orientation occurs only when the Cr underlayer has a 〈100〉 preferred orientation. The 〈100〉 preferred orientation in the Cr layer results from the use of sputtering rates above 150 nm/min and only persists to thicknesses of about 50 nm. The thin Cr underlayers (〈50 nm) with a 〈100〉 preferred orientation have fine well-packed grains. Thicker Cr underlayers have larger grains which are uncoupled and have a more random crystal orientation. The CoPtCr film morphologies follow these trends. The noise performance of these films improves with increasing Cr underlayer thickness and decreasing S* values. The CoPtCr films on thicker Cr (〉50 nm) show no evidence of epitaxy and develop uncoupled grain structures like the Cr. The uncoupling of grains or the lack of in-plane c-axis orientation could both explain the drop in S* that has been correlated to S0/N improvement. Our results suggest that for the CoPtCr/Cr system, both grain morphology and crystallography must be considered in interpreting the changes in magnetic and recording properties.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.344801
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  • 9
    Electronic Resource
    Electronic Resource
    Photoluminescence spectra in an applied magnetic field for excitons bound to ionized donors in high-purity, epitaxial GaAs (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 4909-4918 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The magnetic-field dependence (0–6.4 T) of the photoluminescence spectra of ionized donor-bound excitons [(D+, X)] has been studied for high-purity GaAs grown by organometallic vapor phase epitaxy. Detailed data were taken on circularly polarized emission, leading to an electron-hole-coupling model which yields total angular momentum values of J=1,2. The effective magnetic-moment g values describing the substate splittings between MJ = +1 and −1 are found to be 0.86 and ≈0.5 for the J=1 and 2 states, respectively. The studies were performed on material with background, donor impurities identified as Si and Ge, yielding a chemical shift between (D+Si, X) and (D+Ge, X) of 0.15 meV at 6.4 T. Well-resolved (D+, X) features were only observed in the highest-purity material (impurity concentrations ≈ low 1014 cm−3). Some results are also reported for a layer grown by molecular-beam epitaxy whose lack of neutral-donor-related features permits the high-energy (D+, X) components to be observed at high fields.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349036
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  • 10
    Electronic Resource
    Electronic Resource
    Correlation between the photoreflectance response at E1 and carrier concentration in n- and p-GaAs (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 2525-2531 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We investigated the photoreflectance (PR) response of metalorganic chemical vapor deposition-grown n- and p-type GaAs at the higher-energy transition E1(≈2.9 eV). The doping level range of interest was 2×1016–4×1018 cm−3 for Si:GaAs and 6×1016– 1×1019 cm−3 for Zn:GaAs. Both the position and the broadening parameter, Γ1, of the E1 transition within the doping concentration range were investigated. The evaluation of Γ1's, based on the curve fitting of the PR response and the Kramers–Kronig analyzed data reveal a nearly linear relation between Γ1 and the logarithm of the carrier concentration. This observation has the potential application for contactless determination of carrier concentration in moderate and heavily doped nanoscale films. Secondary-ion mass spectroscopy measurements show that there is relatively large compensation in Si:GaAs samples, but it does not correlate with the broadening of the E1 structure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348691
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