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  • 1
    Electronic Resource
    Electronic Resource
    Native defects in low-temperature GaAs and the effect of hydrogenation (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 2411-2422 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A range of experimental techniques has been used to measure point defect concentrations in GaAs layers grown at low temperatures (250 °C) by molecular-beam epitaxy (LT-GaAs). The effects of doping on these concentrations has been investigated by studying samples containing shallow acceptors (Be) or shallow donors (Si) in concentrations of ∼1019 cm−3. Material grown under As-rich conditions and doped with Be was completely compensated and the simultaneous detection of As0Ga by near-band-edge infrared absorption and As+Ga by electron paramagnetic resonance confirmed that the Fermi level was near the midgap position and that compensation was partly related to AsGa defects. There was no evidence for the incorporation of VGa in this layer from positron annihilation measurements. For LT-GaAs grown under As-rich conditions and doped with Si, more than 80% of the donors were compensated and the detection of SiGa–VGa pairs by infrared localized vibrational mode (LVM) spectroscopy indicated that compensating VGa defects were at least partly responsible. The presence of vacancy defects was confirmed by positron annihilation measurements. Increasing the Si doping level suppressed the incorporation of AsGa. Exposure of the Be-doped layer to a radio-frequency hydrogen plasma, generated a LVM at 1997 cm−1 and it is proposed that this line is a stretch mode of a AsGa–H–VAs defect complex. For the Si-doped layer, two stretch modes at 1764 and 1773 cm−1 and a wag mode at 779 cm−1 relating to a H-defect complex were detected and we argue that the complex could be a passivated As antisite. The detection of characteristic hydrogen-native defect LVMs may provide a new method for the identification of intrinsic defects. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360163
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  • 2
    Electronic Resource
    Electronic Resource
    Stiffness of compressed fiber mats (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 5056-5061 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We investigate, using an analytical and a numerical model, the in-plane stiffness of fiber mats. A mat is modeled by randomly depositing thin linear-elastic fibers on top of each other under the influence of an external pressure. The external pressure has the effect of bending the fibers over each other. The fibers are assumed rigidly bonded at contacts. For a low external pressure the stiffness of the mat deviates from that of its two-dimensional projection only by a geometrical factor, and the effective Poisson contraction is close to zero. For higher pressures, stiffness is governed by two competing effects and a maximum appears in the stiffness. The effective Poisson ratio is clearly negative in this range. An approximative analytical description is developed for the stiffness of mats formed under low external pressure. The stiffness is given as a function of only a few parameters: the degree of bonding, the dimensions of the fibers, the elastic constants of the fiber material, and the density of fibers. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1315622
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  • 3
    Electronic Resource
    Electronic Resource
    Defect formation in implantation of crystalline Si by MeV Si ions (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 990-995 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The distributions of vacancy-type defects and displaced Si atoms in Si(100) produced by the room-temperature implantation of 1014–1016 12-MeV 28Si+ ions/cm2 are measured with low-energy positron- and ion-beam techniques. The observed damage regions are reproduced by computer simulations. The distribution of displaced Si atoms coincides with the deposited energy distribution in elastic collisions. At the fluence of 1×1016 Si+/cm2, no crystalline structure was found in the peak region of the deposited energy at the depth of z=6 μm. Saturation of the divacancy concentration was observed at the ion fluences 3×1015 Si+/cm2 close to the surface (z〈0.7 μm) and 3×1014 Si+/cm2 deeper in the sample (z〉1 μm). In the region z〈0.7 μm, the divacancy concentration is a factor of 4 higher than that in the region z〉1 μm. This is also found in the simulated spatial structure of collision cascades.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345709
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  • 4
    Electronic Resource
    Electronic Resource
    Modeling multilayer woven fabrics (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 79 (2001), S. 180-181 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A numerical algorithm for nonlinear elastic relaxation of a multilayer woven fabric is introduced and tested. The equilibrium solutions are compared with real samples. An excellent result is obtained in spite of two simplifications: Bending stiffness of the fibers and friction between the fibers are both neglected. The numerical simulation is very fast and cost efficient in the search for optimal fabrics. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1385350
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  • 5
    Electronic Resource
    Electronic Resource
    Observation of Ga vacancies in silicon δ-doping superlattices in (001) GaAs (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 1843-1845 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Positron annihilation experiments have been performed to investigate the compensating defects in silicon δ-doping superlattices in (001) GaAs. The results reveal vacancies and ion-type defects, which are located between the delta planes in undoped GaAs. The vacancy defect is identified as the Ga vacancy and the negative ion is attributed to the Ga antisite. The concentrations of these defects increase strongly, when the areal concentrations of free carriers are reduced at the delta planes. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.119417
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  • 6
    Electronic Resource
    Electronic Resource
    On the calibration of a superconducting gravimeter using absolute gravity measurements (1991)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 106 (1991), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: A 24 hr continuous parallel registration between an absolute free-fall gravimeter and a relative cryogenic gravimeter is analysed. Different adjustment procedures (L1, L2 norms) are applied to the sets of absolute and relative readings in order to estimate the value of the calibration factor of the superconducting meter, as well as its uncertainty. In addition, a sensitivity test is performed to investigate the influence of some parameters (like the laser frequency and its short-term drift) upon this factor. The precision in the calibration factor is found to be better than 1 per cent, but systematic effects related to the short time interval may add another one and half per cent uncertainty. From preliminary results, it appears that this calibration experiment leads to a close agreement between the values of the gravimetric factor for the reference tidal wave O1 observed with the superconducting meter and the theoretical value (Dehant–Wahr body tide + ocean loading).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1991.tb03907.x
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  • 7
    Electronic Resource
    Electronic Resource
    LTCC technology for cost-effective packaging of photonic modules (2005)
    Bradford : Emerald
    Assembly automation 25 (2005), S. 30-37 
    Details
    ISSN: 0144-5154
    Source: Emerald Fulltext Archive Database 1994-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Purpose - The aim of the research was to evaluate the concept that utilizes structured planar substrates based on low temperature co-fired ceramics (LTCC) as a precision platform for the passive alignment of a multimode fiber and wide-stripe diode laser. Design/methodology/approach - Presents the manufacturing process for realisation of 3D precision structures, heat dissipation structures and a cooling channel into the LTCC substrate. The developed methodology for 3D modelling and simulation of the system was used to optimize structures, materials and components in order to achieve optimal performance for the final product and still maintain reasonably low fabrication costs. The simulated optical coupling efficiency and alignment tolerances were verified by prototype realization and characterization. Findings - The achieved passive alignment accuracy allows high coupling efficiency realisations of multimode fiber pigtailed laser modules and is suitable for mass production. Research limitations/implications - Provides guidance in the design of LTCC precision platforms for passive alignment and presents a hybrid simulation method for photonics module concept analysis. Practical implications - The three-dimensional shape of the laminated and fired ceramic substrate provides the necessary alignment structures including holes, grooves and cavities for the laser to fiber coupling. Thick-film printing and via punching can be incorporated in order to integrate electronic assemblies directly into the opto-mechanical platform. Originality/value - Introduces the LTCC 3D precision structures for photonics modules enabling passive alignment of multimode fiber pigtailed laser with high efficiency optical coupling. Demonstrates the hybrid simulation methodology for concept analysis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1108/01445150510578987
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  • 8
    Electronic Resource
    Electronic Resource
    Determination of post-glacial land uplift from the three precise levellings in Finland (1998)
    Springer
    Journal of geodesy 72 (1998), S. 516-529 
    Details
    ISSN: 1432-1394
    Keywords: Key words. Deformation analysis ; Fennoscandia ; Postglacial rebound ; Precise levelling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying
    Notes: Abstract. We have calculated vertical velocities and their change in time from three precise levellings in Finland, with central epochs 1902, 1946, and 1986. Models with and without simultaneous determination of heights give the same results for velocities. Evidence for velocity change in time appears at first sight strong but on closer examination turns out to be inconclusive. We offer an alternative explanation in terms of levelling errors and estimate them. A new uplift map closely reproduces main features of earlier maps from partial data, but does not support some details in them.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001900050191
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  • 9
    Electronic Resource
    Electronic Resource
    Positron Mobility and Trapping in Semiconductors (1992)
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 105-110 (Jan. 1992), p. 369-376 
    Details
    ISSN: 1662-9752
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/01/59/transtech_doi~10.4028%252Fwww.scientific.net%252FMSF.105-110.369.pdf
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  • 10
    Electronic Resource
    Electronic Resource
    High Temperature Positron Diffusion in Si, Ge and GaAs (1992)
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 105-110 (Jan. 1992), p. 837-840 
    Details
    ISSN: 1662-9752
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/01/59/transtech_doi~10.4028%252Fwww.scientific.net%252FMSF.105-110.837.pdf
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