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  • 2000-2004  (26)
  • 1990-1994  (25)
  • 1
    Electronic Resource
    Electronic Resource
    Determination of the optical constants of ZnSe films by spectroscopic ellipsometry (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 514-517 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Spectroscopic ellipsometry was used to determine the real and imaginary parts of the dielectric function of ZnSe thin films grown on (001) GaAs substrates by molecular-beam epitaxy, for energies between 1.5 and 5.0 eV. A sum of harmonic oscillators is used to fit the dielectric function in order to determine the values of the threshold energies at the critical points. The fundamental energy gap was determined to be at 2.68 eV. The E0+Δ0 and E1 points were found to be equal to 3.126 and 4.75 eV, respectively. Below the fundamental absorption edge, a Sellmeir-type function was used to represent the refractive index. At the critical points, E0 and E0+Δ0, the fitting was improved by using an explicit function combining the contributions of these two points to the dielectric function.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358484
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  • 2
    Electronic Resource
    Electronic Resource
    Superconducting and structural properties of Nd2−xCexCuO4−y thin films on perovskite and fluorite substrates (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 2119-2124 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High quality epitaxial Nd2−xCexCuO4−y (NCCO) thin films were fabricated on various substrates by pulsed-laser deposition using N2O reactive gas. The similarities and dissimilarities of the superconducting and structural properties of NCCO films, on perovskite-type substrates such as LaAlO3, NdGaO3, and SrTiO3 and on a fluorite-type substrate of yttria-stabilized zirconia (YSZ), were investigated systematically as a function of film thickness by transport measurements and structural analysis. A remarkable reduction of Tc was observed when the film was thinner than a critical thickness, which strongly depends on the substrate. The critical thicknesses for which Tc is 80% of Tc max are 1200, 1000, 600, and 450 A(ring) for LaAlO3, NdGaO3, SrTiO3, and YSZ, respectively. YSZ turns out to be the best candidate for the growth of very thin NCCO films among the substrates studied. These results show a strong correlation between the strain and Tc in NCCO thin films and point the way to the fabrication of n-type superconducting electric field devices using ultrathin NCCO films.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356318
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  • 3
    Electronic Resource
    Electronic Resource
    Giant magnetoresistance peaks in CoNiCu/Cu multilayers grown by electrodeposition : 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. 6519-6521 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Giant magnetoresistance (GMR) of CoNiCu/Cu multilayers grown by electrodeposition was measured as a function of the copper layer thickness and effects of the order of 14% were obtained. The copper layer thickness ranged from 0.7 to 3.5 nm. Two peaks in the magnetoresistance were observed. One was centered at a copper thickness of ∼1.0 nm and the second was centered at ∼2.3 nm. Comparison of the field dependence of the magnetoresistance with the field dependence of the magnetization, as determined by vibrating-sample magnetometer, suggests that the saturation field for GMR and the magnetization are similar for the larger copper thicknesses, but are strikingly different near 1.0 nm copper thickness. This observation suggests that the GMR is affected by different factors depending on the thickness of the copper layer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358250
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  • 4
    Electronic Resource
    Electronic Resource
    Misfit dislocation nucleation in doped and undoped ZnSe/GaAs (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 63 (1993), S. 3197-3199 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have observed that undoped ZnSe films grown on GaAs substrates by molecular beam epitaxy show an irregular array of interfacial 60° misfit dislocations. However, N and Cl doping of the ZnSe thin films changes the interfacial dislocation structure. p-type ZnSe with N concentrations of ∼1018/cm3 shows a regular array of interfacial 60° misfit dislocations and a lower (∼1×106/cm2) density of threading dislocations compared to undoped films. However, samples with doping levels higher than 1019/cm3 show a density of threading dislocations of ∼108/cm2. These differences are explained in terms of Frank partial dislocations observed only in doped ZnSe. The Frank partial dislocations act as nucleation sites for the misfit dislocations. Thus, different mechanisms for the formation of misfit dislocations in doped and undoped films occur in this system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.110197
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  • 5
    Electronic Resource
    Electronic Resource
    Microstructure of laser-deposited superconducting Nd1.85Ce0.15CuO4−y films (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 62 (1993), S. 3022-3024 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The morphology and microstructure of Nd1.85Ce0.15CuO4−y (NCCO) films grown epitaxially on (100) LaAlO3 (LAO) by pulsed laser deposition were studied by selected-area electron diffraction and high-resolution electron microscopy. The films were composed primarily of c-axis oriented grains and did not contain any polytypoidic faulting. The in-plane epitaxial relationship of the films was found to be [100]NCCO //[001]LAO. The Nd1.85Ce0.15CuO4−y-LaAlO3 interface is sharp and free of defects. A weak peak around the (110) position of NCCO(T') structure in x-ray diffraction was observed. Using microdiffraction and energy-dispersive x-ray analysis, we confirmed that this peak corresponds to the (004) reflection of cubic Ce0.5Nd0.5O1.75.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.109177
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  • 6
    Electronic Resource
    Electronic Resource
    Chemical ordering in Zn1−xFexSe alloys (1992)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 61 (1992), S. 2302-2304 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have observed chemical ordering in Zn1−xFexSe (x≈0.5) epilayers as well as in nominal (ZnSe/FeSe) superlattices along the [001] growth direction and the [110] direction using transmission electron microscopy. The ordered structure consists of alternating ZnSe and FeSe layers along the [001] and [110] directions. In nominal (ZnSe/FeSe) superlattices grown on (001) GaAs substrates, strain-induced interdiffusion between the layers takes place followed by ordering of the resultant Zn1−xFexSe alloys. Computer simulated images for a Zn0.5Fe0.5Se compound were obtained and compared with experimental images. To our knowledge, this is the first observation of ordering in a II-VI alloy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.108271
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  • 7
    Electronic Resource
    Electronic Resource
    Strain effects on the energy bands of ZnSe films grown on GaAs substrates by spectroscopic ellipsometry (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 64 (1994), S. 3620-3622 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Room-temperature spectroscopic ellipsometry measurements were carried out on ZnSe thin films grown on (001)GaAs substrates by molecular-beam epitaxy for the study of the lattice mismatch-induced strain at the interface. The magnitude of the absorption coefficient at the E0+Δ0 critical point is very sensitive to the strain in the film. The variation in the magnitude of the absorption coefficient is used to estimate the critical thickness for the onset of dislocation generation. Almost complete relaxation of the films was obtained for thicknesses higher than 500 nm. Also, the strain-induced coupling between the valence subbands was found to cause additional shifting of the light-hole subband.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.111223
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  • 8
    Electronic Resource
    Electronic Resource
    Structural characterization and microwave loss of Nd1.85Ce0.15CuO4−y superconducting thin films on yttria-stabilized zirconia buffered sapphire (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 64 (1994), S. 375-377 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have grown superconducting Nd1.85Ce0.15CuO4−y (NCCO) thin films on (11¯02) sapphire using a yttria-stabilized zirconia (YSZ) buffer layer, which has been demonstrated to be the best material for the growth of n-type superconducting NCCO thin films. The films are c-axis oriented, epitaxially grown with a small mosaic spread of 0.2° and a Rutherford backscattering spectroscopy channeling yield of ∼9%. Cross-sectional transmission electron microscopy images reveal a sharp interface between NCCO and YSZ. The microwave surface resistance of NCCO films on YSZ buffered sapphire at 9.6 GHz is only 80 μΩ at 4.2 K in zero magnetic field, which is comparable to Y1Ba2Cu3O7−y films at similar reduced temperature, as a consequence of the decrease of structural imperfection in the film. The temperature dependence of the surface resistance and magnetic penetration depth in these films further confirms the s-wave BCS nature of NCCO.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.111152
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  • 9
    Electronic Resource
    Electronic Resource
    Composition modulation in lattice matched Zn1−xMgxSySe1−y/ZnSe buffer layer/GaAs heterostructures (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 65 (1994), S. 1230-1232 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: [100] composition modulation as well as [101] and [1¯01] tweed strain contrast were observed in lattice matched Zn1−xMgxSySe1−y epitaxial films grown on ZnSe buffer layers. The composition modulation corresponds to regions with different S and Mg concentration in a direction perpendicular to the growth direction. Very high quality lattice matched Zn1−xMgxSySe1−y films with a ZnSe quantum well were grown on As stabilized GaAs substrates exposed to Zn for a short time. The density of defects in these samples was less than 5×104/cm2. Other samples showed rough interfaces and high densities of Frank partial dislocations. The roughness is believed to result from an As-rich GaAs surface produced after the desorption of oxide under As overpressure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.112079
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  • 10
    Electronic Resource
    Electronic Resource
    Dependence of dielectric properties on internal stresses in epitaxial barium strontium titanate thin films (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 78 (2001), S. 2354-2356 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A series of heteroepitaxial BaxSr1−xTiO3 thin films with composition x=0.50 were deposited on (001) MgO substrates by pulsed-laser deposition. The thickness of the films was varied from 14 to 500 nm to produce a systematically decreasing level of in-plane tensile stresses. The microstructural and crystallographic features of the films were determined via transmission electron microscopy and x-ray diffraction. A theoretical treatment of the in-plane misfit strain as a function of film thickness is in agreement with the measured out-of-plane lattice parameters. Electrical measurements indicate a drop in the dielectric constant from 2350 for highly stressed thin films to 1700 for relaxed thicker films. The variation in the dielectric constant with the misfit strain is in accordance with a thermodynamic model developed. The relationship between the dielectric constant and electric field is also described by extending the thermodynamic model and taking the effect of electric field into account. A new definition of tunability is adopted to study the effect of strain on tunability. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1359141
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