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  • 1990-1994  (19)
  • 1
    Electronic Resource
    Electronic Resource
    Formation of amorphous interlayers in ultrahigh vacuum deposited yttrium thin films on (111)Si (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 5280-5282 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Formation of amorphous interlayers (a interlayers) has been observed in the interfacial reactions of ultrahigh vacuum deposited yttrium thin films on atomically clean (111)Si at low temperatures. The observation of the a interlayer in the Y/Si system represents the first report of solid-state amorphization for rare-earth metal/Si systems. The Y/Si system is also the only system found to date among all metal/Si systems in which the a interlayer can be grown to a thickness exceeding 10 nm during deposition at room temperature. A process involving significant diffusion of both Y and Si atoms is proposed to account for the dependence of amorphization on the thickness of deposited yttrium films.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353760
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  • 2
    Electronic Resource
    Electronic Resource
    Evolution of vacancy ordering and defect structure in epitaxial YSi2−x thin films on (111)Si (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 3307-3312 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The evolution of vacancy ordering and defect structure in epitaxial YSi2−x thin films on (111)Si have been studied by both conventional and high-resolution transmission electron microscopy. Epitaxial YSi2−x with an ordered vacancy structure was grown on (111)Si by rapid thermal annealing. In samples annealed at 500 °C for 120 s epitaxial YSi2−x was found to form. After annealing at 600 °C for 15 s, the appearance of additional diffraction spots is attributed to the formation of an ordered vacancy superstructure in the epitaxial YSi2−x thin films. In samples annealed at 600 °C for longer time or higher temperatures, the splitting of extra diffraction spots is correlated to the formation of an out-of-step structure. Streaking of the split diffraction spots in the diffraction pattern is attributed to the presence of an out-of-step structure with a range of M values. The M was found to settle down to 2 after high-temperature and/or long time annealing. Planar defects in YSi2−x films were analyzed to be stacking faults on {101¯0} planes with 1/6 〈1¯21¯3〉 displacement vectors. Computer simulation was carried out to determine the atomic structure of stacking fault. The simulated images are seen to match rather well with experimental images taken under two different values of defocus.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.350950
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  • 3
    Electronic Resource
    Electronic Resource
    Interfacial reactions of ultrahigh vacuum deposited yttrium thin films on (111)Si at low temperatures (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 8258-8266 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Interfacial reactions of ultrahigh vacuum deposited yttrium thin films on atomically clean (111)Si at low temperatures have been studied by both conventional and high-resolution transmission electron microscopy, Auger electron spectroscopy, and x-ray diffraction. A 10-nm-thick yttrium thin film, deposited onto (111)Si at room temperature, was found to completely intermix with Si to form an 11-nm-thick amorphous interlayer. Crystalline Y5Si3 and Si were observed to nucleate first within the amorphous interlayer in samples annealed at temperatures lower than 200 °C. Epitaxial YSi2−x was found to be the only phase formed at the interface of amorphous interlayer and crystalline Si in samples annealed at temperatures higher than 250 °C. In as deposited 20- to 60-nm-thick Y thin films on silicon samples, crystalline Y5Si3, Si, and YSi and a 2.5-nm-thick amorphous layer were found to be present simultaneously. Good correlations were found among difference in atomic size between metal and Si atoms, the calculated free energy of mixing as well as the critical and maximum amorphous interlayer thickness for the Y/Si and a number of refractory metal/Si systems. The Y/Si system is the only system found up to date among all metal/Si systems that the a interlayer can be grown to a thickness exceeding 10 nm during deposition at room temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353444
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  • 4
    Electronic Resource
    Electronic Resource
    Nanometer thick Si/SiGe strained-layer superlattices grown by an ultrahigh vacuum/chemical vapor deposition technique (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 3441-3445 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High quality Si/Si1−xGex superlattices having layers as thin as 1.5 nm have been grown by an ultrahigh vacuum/chemical vapor deposition system. High-resolution double-crystal x-ray diffraction, and conventional and high-resolution cross-sectional transmission electron microscopy were used to evaluate the crystalline quality of these superlattices. A dynamical x-ray simulation program was employed to analyze the experimental rocking curves. Excellent matches between experimental rocking curves and simulated ones were obtained for all superlattices with various periodicity. A cross-sectional transmission electron micrograph of an 80 period Si(4.2 nm)/Si0.878Ge0.122 (1.5 nm) superlattice, in which each individual layers was clearly resolved, demonstrated the capability of this growth technique for nanometer thick layer deposition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356104
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  • 5
    Electronic Resource
    Electronic Resource
    Interfacial reactions in ultrahigh vacuum deposited Y-Si multilayer thin films (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 2007-2014 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Interfacial reactions of ultrahigh vacuum deposited Y-Si multilayer thin films have been studied by both conventional and high-resolution transmission electron microscopy, Auger electron spectroscopy, and x-ray diffraction. An amorphous Y-Si intermixing layer with a composition approximately equal to YSi2 was found to form in multilayer films with a composition ratio of 1Y:2Si at room temperature. Homogenization in atomic composition in the amorphous phase proceeded in samples annealed at 250–350 °C. In samples annealed at 400 °C for 30 min, the amorphous layer was completely transformed to crystalline YSi2. The formation of crystalline Y5Si3 and YSi was detected in as-deposited samples with concentration ratios 1Y:1Si and 5Y:3Si as well as in samples prepared with excess Y. Y5Si3 was the only silicide phase present in 5Y:3Si films after 400 °C annealing. The results indicated that the phase formation and stability in Y-Si multilayers depend critically on the composition. Based on the prediction of a growth control model, it was concluded that the formation of amorphous layer at room temperature is controlled by nucleation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356300
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  • 6
    Electronic Resource
    Electronic Resource
    Direct observation of Si delta-doped GaAs by transmission electron microscopy (1992)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 60 (1992), S. 2628-2630 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Direct observation of the Si delta-doped layer in GaAs has been achieved by high resolution transmission electron microscopy. Samples with different Si doses, from half a monolayer to two monolayers, were studied. The observed spreading of the delta-doped layer showed that Si atoms are largely confined in five monolayers at most (in the highest dose case), indicating excellent confinements of dopants in GaAs. From the images, the Si atoms were uniformly distributed in the doped layer, no cluster formation was observed. For delta-doped GaAs grown at low temperature (480 °C), stacking faults originated from the doped layers were observed. These faults were thought to be caused by the large unrelaxed strain in the low-temperature grown GaAs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.106902
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  • 7
    Electronic Resource
    Electronic Resource
    Photoreflectance study of surface Fermi level in molecular beam epitaxial grown InAlAs heterostructures (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 64 (1994), S. 3314-3316 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have studied the band gaps and the surface Fermi level positions of a series of In1−xAlxAs surface-intrinsic-n+ structures at room temperature by photoreflectance. Experiments demonstrated that over aluminum concentrations of 0.42–0.57, the surface Fermi level is not pinned at midgap, as commonly believed, but instead varies, respectively, from 0.50±0.01 to 0.81±0.01 eV below the conduction band edge.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.111294
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  • 8
    Electronic Resource
    Electronic Resource
    Transient oscillatory conjugate natural convection in a tall water cavity (1993)
    Springer
    Heat and mass transfer 29 (1993), S. 95-105 
    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 einer zweidimensionalen numerischen Simulationsrechnung wurde der Einfluß der Wärmekapazität einer beheizten Wand auf die nichtstationäre oszillatorische Konvektion in einem großen Behälter untersucht. Die Resultate beziehen sich speziell auf Wasser (Pr=6), einen tiefen Behälter (H/W=6) und konstanten Wärmezufluß auf der einen und isotherme Kühlung auf der anderen Wandseite. Es traten signifikante Effekte in Abhängigkeit von der Wandwärmekapazität auf. Insbesondere vermag eine beheizte Wand begrenzter Wärmekapazität bei niedrigen Rayleigh-Zahlen die Entwicklung des Strömungsprozesses bis zum Stationärzustand abzubremsen und bei hohen Rayleigh-Zahlen die Strömungsoszillationen während der Einschwingphase zu dämpfen. Bei periodischem Strömungszustand undRa* H =4,4·1010 verringert die Wandkapazität die Amplitude der Temperaturschwingung beträchtlich. Es zeigte sich ferner, daß ein quasiperiodischer Strömungszustand beiRa* H =4,8·1010 periodisch wird, wenn die Wandkapazität Einfluß nimmt. Letztere hatte keine nachweisbaren Wirkungen bei chaotischem Strömungszustand mitRa* H =6,0·1010.
    Notes: Abstract A two-dimensional numerical simulation was conducted to investigate the effects of the heat capacity of the heated wall on the transient oscillatory convection in a tall cavity. Results were particularly obtained for water (Pr=6) in a tall cavity (A=6) with constant-heat-flux heating on one side and isothermal cooling on the opposing side. Significant wall heat capacity effects were found. Specifically, a heated wall of finite heat capacity can slow down the flow evolution process to steady state at low Rayleigh number and damp the flow oscillation during the initial developing period at high Rayleigh number. In periodic flow atRa* H =4.4×1010 the wall heat capacity significantly reduces the amplitude of the temperature oscillation. A quasi-periodic flow atRa* H =4.8×1010 was found to become periodic when the wall heat capacity was included. The wall heat capacity does not shown noticeable effect when the flow is chaotic forRa* H =6.0×1010.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01560078
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  • 9
    Electronic Resource
    Electronic Resource
    Steady conjugate heat transfer in turbulent channel flows (1990)
    Springer
    Heat and mass transfer 25 (1990), S. 215-220 
    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 einer numerischen Studie werden die Eigenschaften der stetig konjugierten Wärmeübertragung in einer turbulenten Kanalströmung, die über eine endliche Länge gleichmäßig beheizt wird, untersucht. Der Einfluß der Wandstärke, des Wärmeleitfähigkeitsverhältnisses von Wand zu Fluid und der Prandtl-Zahl auf den dimensionslosen Wärmestrom und auf die Entwicklung des Temperaturfeldes sind detailliert besprochen worden. Besondere Aufmerksamkeit wird der Untersuchung des Einflusses der Wandwärmeleitung bei niedrigen Reynolds-Zahlen auf die Wärmeübertragung bei turbulenter Zwangskonvektion gewidmet. Die Ergebnisse zeigen, daß der Einfluß der Wandwärmeleitung auf die turbulente Zwangskonvektion bei Kanalströmung sehr bedeutend ist. Dies gilt besonders für den Fall, daß größere Wanddicken und ein hohes Wärmeleitfähigkeitsverhältnis von Wand zu Fluid vorliegen.
    Notes: Abstract The characteristics of steady conjugate heat transfer in turbulent channel flow which is uniformly heated over a finite length are numerically studied. The influences of wall thickness, wall-to-fluid conductivity ratio, and Prandtl number on the nondimensional heat flux and the evolution of temperature field are discussed in great detail. Particular attention is paid to study the wall conduction effects on low-Reynolds number turbulent forced convection heat transfer. The results show that the effects of wall conduction on turbulent forced convection channel flow are significant, especially for the cases with larger wall thickness and wall-to-fluid conductivity ratio.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01785408
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  • 10
    Electronic Resource
    Electronic Resource
    Molecular dynamics simulation of a leucine zipper motif predicted for the integrase of human immunodeficiency virus type I (1994)
    New York : Wiley-Blackwell
    Biopolymers 34 (1994), S. 1027-1036 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We have used the molecular dynamics (MD) simulation package AMBER4 to search the conformation of a peptide predicted as a leucine zipper motif for the human immunodeficiency virus type I integrase protein (HIV IN-LZM). The peptide is composed of 22 amino acid residues and its location is from Val 151 to Leu 172. The searching procedure also includes two known α-helices that served as positive controls - namely, a 22-residue GCN4-p1 (LZM) and a 20-residue poly(L-alanine) (PLA). A 21-residue peptide extracted from a cytochrome C crystal (CCC-t) with determined conformation as a β-turn is also included as a negative control. At the beginning of the search, two starting conformations - namely, the standard right-handed α-helix and the fully stretched conformations - are generated for each peptide. Structures generated as standard α-helix are equilibrated at room temperature for 90 ps while structures generated as a fully stretched one are equilibrated at 600 K for 120 ps. The CCC-t and PLA helices are nearly destroyed from the beginning of equilibration. However, for both the HIV IN-LZM and the GCN4-p1 LZM structures, there is substantial helicity being retained throughout the entire course of equilibration. Although helix propagation profiles calculated indicate that both peptides possess about the same propensity to form an α-helix, the HIV IN-LZM helix appears to be more stable than the GCN4-p1 one as judged by a variety of analyses on both structures generated during the equilibration course. The fact that predicted HIV IN-LZM can exist as an α-helix is also supported by the results of high temperature equilibration run on the fully stretched structures generated. In this run, the RMS deviations between the backbone atoms of the structures with the lowest potential energy (PE) identified within every 2 ps and the structure with the lowest PE searched in the same course of simulation are calculated. For both the HIV IN-LZM and the GCN4-p1 LZM, these rms values decrease with the decrease of PE, which indicates that both structures are closer in conformations as their PEs are moved deeper into the PE well. © 1994 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360340806
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