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  • 1
    Electronic Resource
    Electronic Resource
    A theoretical and experimental study on subcooled flow boiling at high heat flux (1994)
    Springer
    Heat and mass transfer 29 (1994), S. 319-327 
    Details
    ISSN: 1432-1181
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Description / Table of Contents: Zusammenfassung In einem Fluidsystem, das bei hohem Wärmefluß den Effekt des unterkühlten Siedens zeigt, findet der wesentliche Wärmetransportmechanismus in einer sehr dünnen Schicht statt, die zwischen der beheizten Oberfläche und den Dampfpolstern liegt und als „Unterschicht“ bekannt ist. Basierend auf den Gesetzmäßigkeiten des konvektiven Siedens unter dominierendem Einfluß der Wärmeleitung durch die Flüssigkeits-Unterschicht wurde ein theoretisches Modell zu Beschreibung des Wärmeübergangs bei unterkühltem Sieden entwickelt. Um nützliche Daten für die Simulation der in Leichtwasserreaktoren (LWR) herrschenden Bedingungen zu gewinnen, erfolgten die Experimente bei Aufwärtsströmung siedenden Wassers in einem senkrechten Rohr im Druckbereich 6,9 bis 15,5 MPa. Diese experimentellen Ergebnisse werden mit Vorausberechnungen nach dem erstellten Theoriemodell, sowie jenen nach fünf der bekanntesten Korrelationen verglichen. Für unterkühltes Sieden in Leichtwasserreaktoren zeigte sich hierbei, daß die Experimente am besten durch das neuentwickelte Modell wiedergegeben werden.
    Notes: Abstract In a subcooled flow boiling system at high heat flux, the major heat transfer mechanism places emphasis on a very thin liquid layer, known as the ‘sublayer’ which is trapped between the heated surface and the vapor blankets. Base on the convective boiling heat transfer dominated by the heat conduction through the liquid sublayer, a theoretical model for subcooled flow boiling heat transfer has been developed. To provide useful data in the simulation of Light Water Reactors (LWRs) conditions, heat transfer experiments for up-flow boiling water through a vertical tube at the pressure ranging from 6.9 to 15.5 MPa have been conducted. The experimental results are compared with the predictions of the present model and other five famous correlations. For the LWRs subcooled flow boiling, the comparison reveals that the present model show the best agreement with the measured data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01578416
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  • 2
    Electronic Resource
    Electronic Resource
    Study of Ni as a barrier metal in AuSn soldering application for laser chip/submount assembly (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 3808-3815 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The possibility of replacing Pt in the Ti/Pt/Au base and traditionally used metallurgical structure by Ni, while bonding InP laser chip to a submount with AuSn (80% Au) solder, has been investigated. Various Ni-based metal alloys have been prepared by evaporation. Reflow experiments were conducted in a chamber under forming gas-controlled ambient. The Ti/Ni/AuSn system provided much longer surface local freezing duration compared to the Ti/Pt/AuSn system. Scanning electron microscopy analysis revealed a smoother surface morphology for the Ti/Ni/AuSn system after the metal refroze. Auger electron spectroscopy depth profiles indicated the formation of a Ni-Sn-Au interacted layer. The interaction took place in two steps: the first stage was the dissolution of Ni into the Au-Sn liquid followed by precipitation of a Ni-Sn-Au intermetallic compound; the second stage was a solid-state interdiffusion of Sn, Au, and Ni which occured in the interacted layer and in the original Ni layer. The latter step was a diffusion-controlled process, resulting in a very slow growth rate. Both Au and Sn reacted to form Ni alloy layers of almost equal thickness, regardless of the reaction duration (up to about 5 min). This intensive reaction, however, did not lead to full consumption of the Ti interfacial layer, which provided an excellent adhesion layer between the submount and the metallurgical structure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352279
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  • 3
    Electronic Resource
    Electronic Resource
    Magnetic anisotropy and lattice strain in Co/Pt multilayers : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 6198-6200 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The correlation is reported between perpendicular anisotropy and in-plane lattice strain in Co/Pt multilayers. (Cox/Pty)n samples, where x, y are the thickness of the individual Co and Pt layers and n is the number of repeats that were prepared by molecular beam epitaxy and studied by means of polar magneto-optic Kerr effect and transmission electron microscopy. Kerr rotation data and electron diffraction experiments show that the largest perpendicular anisotropy and square hysteresis loop occur when x=3 A(ring) while the Pt layers are subjected to about −2% in-plane strain. As Co thickness increases, Co and Pt layers gradually lose coherency and the magnetic anisotropy goes from perpendicular to planar. This is accompanied by a relaxation of lattice strain in both Co and Pt layers. The close relationship between magnetic anisotropy and lattice strain can be explained as magnetoelastic anisotropy or stress anisotropy effect due to lattice mismatch between the adjacent epitaxial layers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352696
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  • 4
    Electronic Resource
    Electronic Resource
    Interface analysis of (110)-oriented Co/Pt superlattices with large magnetic anisotropies using x-ray diffraction (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 908-913 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on studies of the profiles of the strain field components in epitaxially grown (110)-oriented Co/Pt superlattices with fixed Pt layer thickness (nominally 18 A(ring)) and varying Co layer thickness. The strain profiles in the growth direction as well as fluctuations in lattice parameters at the interfaces are obtained using a parameter refinement method for the quantitative analysis of high angle aitch-theta–2aitch-theta x-ray diffraction scans. We find that all strain components originate only from the Co-Pt interfaces. Off-axial x-ray scattering measurements provide for the in-plane strain components, which are found to increase with increasing Co layer thickness. From the obtained strain fields the in-plane uniaxial magnetic anisotropy contributions caused by magnetoelastic interactions are calculated, which agree well with experimentally observed values.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357768
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  • 5
    Electronic Resource
    Electronic Resource
    Au-Sn/W and Au-Sn/Cr metallized chemical vapor deposited diamond heat sinks for InP laser device applications (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 563-567 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An attempt to apply a more stable metallurgical soldering system than the traditionally used Ti/Pt/Au-Sn reactive system was explored by replacing the barrier metals in between the chemical vapor deposited diamond (CVDD) submount and the Au-Sn solder with either W or Cr layers. In the case of the W layer a thin layer of Ti was added to improve the adhesion of Au-Sn solder to the W layer. The CVDD/W(100 nm)/Ti(10 nm)/Au-Sn(1.5–2.2 μm) system was heat treated at 350 °C for durations of 5 s–5 min, simulating a bonding cycle, and the metallurgical interactions were analyzed. Some diffusion of the Ti was observed, but the W layer remained intact. Thus, due to the absence of interaction between the Sn or Au and the W barrier layer, the Au:Sn ratio was kept uniform for long duration heating ((approximately-greater-than)2 min). The Au-Sn solder tends to "ball up'' in local spots leading to the formation of local voids in the continuous solder layer over the W. In the case of the CVDD/Ti (100 nm)/Cr(200 nm)/AuSn(1.5–2.2 μm) structure a minimum interaction between the Au-Sn solder and the barrier was observed through a heating cycle at 350 °C for 5 min. This heat treatment, however, led to solder surface roughness in the order of about 5000 A(ring) between bump peak and valley, but the Au:Sn composition remained in the eutectic ratio of 70:30 at. %. Both soldering metallurgical systems gave a potential good bonding of InP laser diodes to CVDD heat sinks.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355840
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  • 6
    Electronic Resource
    Electronic Resource
    Influence of crystal structure on the magnetoresistance of Co/Cr multilayers : 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. 6516-6518 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Epitaxial Co/Cr multilayers, and single-crystal Co thin films etc. have been grown on MgO and Al2O3 substrates with Cr and Mo as buffer layers by molecular beam epitaxy technique. From the structure and magnetoresistance studies, we have found that the ferromagnetic anisotropy of resistance (AMR) is strongly influenced by the buffer layer, but with negligible effect due to the variation of the structure of Co films. The AMR of Co film on Cr buffer layer is quite small (0.1%); however, the MR of Co/Cr multilayers is almost one order larger than the AMR of Co film on Cr buffer layer. An enhancement factor of 4 for the MR in Co/Cr multilayers by the interface roughness has been observed. This suggests that the effect due to the spin dependent scattering at the interfacial regions of the superlattice is larger than that due to the spin dependent scattering in the ferromagnetic layers for the MR in the Co/Cr multilayer system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358247
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  • 7
    Electronic Resource
    Electronic Resource
    Interface anisotropy in cobalt-based epitaxial superlattices (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 5412-5414 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have measured the magnetic anisotropy in a series of Co-Au and Co-Cu superlattices prepared by molecular-beam epitaxy. Significant epitaxial strains give rise to a magnetoelastic contribution and a large crossover thickness (∼19 A(ring)) for perpendicular easy magnetization. The results are discussed in the context of a careful analysis of the interfacial strains and coherence determined by in situ time-resolved reflection high-energy electron diffraction techniques and x-ray scattering.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.344570
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  • 8
    Electronic Resource
    Electronic Resource
    Shape-memory properties in Ni-Ti sputter-deposited film (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 6224-6228 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The objective of this research is to establish a shape-memory effect in sputter-deposited films of nickel titanium. The alloy, generically called nitinol, was prepared from sputtering targets in two different compositions. Films were deposited up to 10 μm in thickness on glass substrates using a dc magnetron sputtering source. The as-deposited films were amorphous in structure and did not exhibit a shape memory. The amorphous films were crystallized with a suitable annealing process, and the transformation properties were measured using differential scanning calorimetry. The crystallized films showed transition temperatures that were much lower than those of the parent material. X-ray diffraction patterns indicated that the films were not a single phase but showed evidence of a second phase. However, the annealed films demonstrated a strong shape-memory effect. Stress/strain measurements and physical manipulation were used to evaluate the shape recovery. These tests demonstrated sustained tensile stresses of up to 480 MPa in the high-temperature phase, and a characteristic plastic deformation in the low-temperature phase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346914
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  • 9
    Electronic Resource
    Electronic Resource
    Magnetic anisotropy and structural characterization of Co/Pt superlattices grown along selected orientations by molecular-beam epitaxy : 35th annual conference on magentism and magnetic materials San Diego, California (USA) 29 Oct − 1 Nov 1990 (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 5646-5648 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this paper we report the molecular-beam epitaxial growth of Co/Pt superlattices on epitaxial Ag films on GaAs substrates. The growth axis of the superlattice was selected by seeded epitaxy to be along either the [001], [110], or [111] axis of Pt. The magnetic properties of the superlattices depend on the orientation of the growth axis. In situ x-ray photoelectron diffraction studies of the Co-Pt interfaces during their formation reveals that they are not atomically abrupt for any of the orientations. We conclude that models for magnetic anisotropy of Co/Pt superlattices should be based on a combination of magnetocrystalline anisotropy and strain in compositionally mixed interfaces.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347923
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  • 10
    Electronic Resource
    Electronic Resource
    Antiferromagnetic coupling between layers in Co/Cr multilayer (invited) (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 5925-5930 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: It has been shown by several groups that Fe layers in epitaxial Fe/Cr sandwiches or multilayers (MLFs) are coupled antiferromagnetically (AF) for very small Cr thicknesses. One way this is manifest in the MLF is that for a fixed Fe thickness (30 A(ring)) the hysteresis curves are progressively flatter as the Cr thickness decreases. This is the opposite behavior to that expected if the Fe layers were uncoupled or ferromagnetically coupled. We have observed the same type of behavior in a series of nominally 21-A(ring) Co/X Cr MLFs where X varies from 14 to 57 A(ring). These MLFs have been well characterized with both x-ray scattering and cross-sectional high-resolution electron microscopy. They are highly polycrystalline, nonideal MLFs with appreciable mixed interfaces. We have determined that Co/Cr MLF have an interface or exchange anisotropy with an average value of ∼7 kOe in a direction opposite to that of the in-plane magnetization. Such an AF interaction is expected from Cr layers having interface thicknesses comparable to that of the pure Cr regions. It provides a natural mechanism for the Cr layers to align the Co layers either AF or FM depending on the local structural details. Both types of alignment are likely to be present in a MLF and the regions having AF alignment will cause the observed flattening of the hysteresis loops. The magnetoresistance of these MLFs has a behavior similar to, but much smaller than, the "giant'' magnetoresistance seen in the epitaxial Fe/Cr MLF and single-crystal Fe whiskers. The magnetoresistance in pure Fe has been attributed to the domain structure and it is likely responsible for this effect in the Co/Cr MLF as well.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346016
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