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  • 1
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    Adaptive regridding in 3D reflection tomography (2006)
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    Publication Date: 2020-07-08
    Description: 3D reflection tomography allows the macro-model of complex geological structures to be reconstructed. In the usual approach, the spatial distribution of the velocity field is discretized by regular grids. This choice simplifies the development of the related software, but introduces two serious drawbacks: various domains of the model may be poorly covered, and a relevant mismatch between the grid and a complex velocity field may occur. So the tomographic inversion becomes unstable, unreliable and necessarily blurred. In this paper we introduce an algorithm to adapt the grid to the available ray paths and to the velocity field in sequence: so we get irregular grids with a locally variable resolution. We can guide the grid fitting procedure interactively, if we are going to introduce some geological a priori information; otherwise, we define a fully automatic approach, which exploits the Delauny triangles and Voronoi polygons.
    Description: JCR Journal
    Description: open
    Keywords: reflection tomography ; irregular grids ; automatic regridding ; travel time inversion ; 04. Solid Earth::04.06. Seismology::04.06.07. Tomography and anisotropy
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
    Format: 4496891 bytes
    Format: application/pdf
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  • 2
    Electronic Resource
    Electronic Resource
    Franz–Keldysh effect in lateral GaAs/AlGaAs based npn structures (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 70 (1997), S. 2876-2878 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Lateral npn structures, fabricated by focused laser beam-induced doping, combine large potential modulations with a small width of the p-doped regions. This results in strong lateral electric fields, which can be tuned by applying a bias voltage. Photon absorption for energies below the band gap is allowed due to the Franz–Keldysh effect. We estimate the value of the electric fields by analyzing wavelength-dependent photocurrent measurements. The fields are comparable to attainable fields in existing vertical modulator structures. The spatially resolved photocurrent measurements reveal the location of the highest lateral electric field, which is at the edges of the p-doped region. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.119204
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  • 3
    Electronic Resource
    Electronic Resource
    Double wavelength selective GaAs/AlGaAs infrared detector device (1992)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 60 (1992), S. 2011-2013 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We demonstrate the first GaAs/AlGaAs multiquantum well infrared detector device with double wavelength selectivity and high wavelength resolution. By applying an efficient light coupling mechanism, which is based upon the excitation and emission of surface plasmons, we have achieved a responsivity R of 2.20 A/W and a detectivity D* of 2.2×1011 cm (square root of)Hz/W for λ=7.38 μm at a temperature T=5 K for a 300 K background irradiance and a 90° field of view, which are one of the highest values reported to date.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.107127
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  • 4
    Electronic Resource
    Electronic Resource
    Sharp-line photoluminescence of excitons localized at GaAs/AlGaAs quantum well inhomogeneities (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 64 (1994), S. 3320-3322 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: GaAs/AlGaAs single quantum well samples have been investigated by photoluminescence spectroscopy using a probe size of about a micron at low temperature. Thin quantum wells fabricated by molecular beam epitaxy with growth interruptions at the interfaces reveal intense photoluminescence lines with spectral widths below 0.1 meV at the low-energy side of the main luminescence. Mapping the quantum well by scanning the probe shows local emission of these sharp lines, which change in number and in energy with lateral probe position. The local source of the sharp lines, as well as their temperature and saturation behavior shows that they are caused by single excitons localized at sample inhomogeneities, like GaAs well width fluctuations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.111265
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  • 5
    Electronic Resource
    Electronic Resource
    Pressure studies of tunneling processes through a doped barrier (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 59 (1991), S. 2436-2438 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have investigated the influence of hydrostatic pressure on the tunneling processes between two independently contacted two-dimensional electron gas systems which are separated by a doped AlGaAs barrier. For magnetotunneling data, the pressure dependence of the GaAs effective mass m* was determined between p=0 and 10 kbar. In this range, we find a linear pressure dependence of d(m*/me)/dp=8×10−4 kbar−1 for the electrons in the two-dimensional channels. At higher pressures several new resonances are observed, which correspond to transition energies in the order of 4 meV. These effects are most probably explained by local phonon modes related to the DX centers inside the barrier.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.106013
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  • 6
    Electronic Resource
    Electronic Resource
    Fabrication of lateral npn-phototransistors with high gain and sub-μm spatial resolution (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 66 (1995), S. 751-753 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A novel kind of phototransistor with high gain and sub-μm spatial resolution is fabricated by focused laser beam-induced Zn doping of an n-modulation doped GaAs/Al0.4Ga0.6As quantum well structure. To produce this lateral npn-structure, p-doped lines are directly written over a mesa without degrading the quality of the sample. The local Zn doping causes an effective potential barrier for electrons. Photogenerated holes reduce this barrier and amplify the thermionic electron current. Spatially resolved photocurrent measurements show typical responsivities above 103 A/W and linewidths as small as 605 nm. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.114082
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  • 7
    Electronic Resource
    Electronic Resource
    Electric-field-induced exciton transport in coupled quantum well structures (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 232-234 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report a conceptionally new approach to achieve electrostatically induced transport and confinement for spatially indirect excitons. Experimentally, exciton transport is demonstrated in an electric-field-tunable GaAs/AlAs coupled quantum well structure, which is configured as a three-terminal device. In spatially resolved photoluminescence experiments, it is shown that indirect excitons experience a drift field, which is given by an electrostatically induced band-gap gradient in the plane of the coupled quantum well structure. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.114677
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  • 8
    Electronic Resource
    Electronic Resource
    Fabrication of in-plane-gate transistor structures by focused laser beam-induced Zn doping of modulation-doped GaAs/AlGaAs quantum wells (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 64 (1994), S. 592-594 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Local Zn doping of n-modulation-doped GaAs/AlGaAs quantum well samples induced by absorption of a focused laser beam has been used to fabricate in-plane-gate transistor structures. Laser-induced thermal Zn diffusion from a highly doped SiO2 emulsion into the sample surface layers allows direct writing of lateral npn structures with sub-μm resolution. The p-doped lines form lateral potential barriers which are efficiently isolating the gate electrodes for large applied voltages at room temperature. Transistor structures with a 3-μm-wide electron channel in between V-shaped gates yield a transconductance of about 50 μS and are pinched-off at gate voltages UG≤−2.0 V.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.111087
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  • 9
    Electronic Resource
    Electronic Resource
    Polarization dependent photocurrent spectroscopy of InAs/GaAs quantum dots (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 2247-2249 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have performed interband photocurrent spectroscopy on self-assembled InAs/GaAs quantum dots using a graded index separate confinement heterostructure in waveguide geometry. The photocurrent spectrum of the quantum dots is found to be shifted to higher energies in comparison to the photoluminescence spectrum. The polarization dependent measurements show that the valence band ground states of strained InAs islands have heavy hole character. In a structure with seven vertically stacked quantum dot layers separated by 10 nm GaAs spacers, we find a change in the photocurrent spectra which is evidence for vertical coupling. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.124979
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  • 10
    Electronic Resource
    Electronic Resource
    Low temperature current imaging tunneling spectroscopy on wet chemically etched quantum wires (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 52-54 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this letter, low temperature current imaging tunneling spectroscopy studies on wet chemically etched quantum wires are reported. On the wires, symmetric current voltage curves are observed. Between the wires, however, significant current is only observed for negative sample bias. Through this behavior, topographic and current imaging profiles of quantum wires are obtained. In liquid helium, the current profiles of the wires are clearly smaller than the topographic profiles, which is used to determined the edge depletion width directly. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.118116
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