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  • 2000-2004  (6)
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Year
  • 1
    Electronic Resource
    Electronic Resource
    Independent contacts to a double-electron gas using mesoscopic surface gates (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 4036-4038 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We demonstrate how two two-dimensional electron gases can be independently contacted using only surface gates defined by electron-beam lithography: macroscopic bar gates to contact the lower layer, and mesoscopic split gates to contact the upper layer. When the technique is applied to a sample consisting of two 150 Å GaAs wells separated by 300 Å Al0.33Ga0.67As barrier, there is more than 30 MΩ isolation at 5 K for interlayer voltages up to ±30 mV; the interlayer isolation operates up to 30 K. The independent contacts are used for a preliminary investigation of two parallel one-dimensional quantum wires. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.372451
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  • 2
    Electronic Resource
    Electronic Resource
    Transport properties of two-dimensional electron gases containing linear ordering InAs self-assembled quantum dots (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 78 (2001), S. 3896-3898 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present a study of the anisotropic properties of two-dimensional electron gases formed in GaAs/AlGaAs heterostructures in which InAs self-assembled quantum dots have been inserted into the center of a GaAs quantum well. We observe an anisotropic mobility for the orthogonal [1¯10] and [110] directions. The mobility in the [1¯10] direction was found to be up to approximately twice that in the [110] direction. It is suggested that the interface roughness scattering due to the inserted InAs material could be a cause for the large anisotropies in mobility. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1378801
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  • 3
    Electronic Resource
    Electronic Resource
    Ballistic transport in a GaAs/AlxGa1−xAs one-dimensional channel fabricated using an atomic force microscope (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 78 (2001), S. 3466-3468 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We fabricate a one-dimensional constriction in a shallow, δ-doped GaAs/AlxGa1−xAs two-dimensional electron gas, by locally oxidizing the surface using an atomic force microscope. The channel exhibits ballistic conduction with up to seven conductance plateaus, quantized in units of 2e2/h. The dependence of the device conductance on dc bias voltage reveals the energy separation of the first two subbands to be ΔE1,2=5.5(±0.3) meV, which allows ballistic conduction to be observed up to a temperature of 20 K. A lateral electric field, combined with the hard-walled confinement due to the insulating lines, allows manipulation of the electron wave function in a way which is not possible with surface-gated devices. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1374225
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  • 4
    Electronic Resource
    Electronic Resource
    Multilayered gated lateral quantum dot devices (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 1134-1136 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We describe a detailed device fabrication technique for the formation of a lateral quantum dot using a multilayered gated design. In our versatile system, a quantum dot is electrostatically defined by a split gate and two overlaying finger gates which introduce entrance and exit barriers to the dot. Periodic and continuous conductance oscillations arising from Coulomb charging effects are clearly observed in the transport properties at low temperatures. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.125961
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  • 5
    Electronic Resource
    Electronic Resource
    Scanning noninvasive voltage probe operating at 4.2 K (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 2100-2105 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A noninvasive voltage probe, consisting of a one-dimensional channel, has been fabricated within a modulation doped GaAs/AlGaAs heterostructure. With precision piezoelectric scanning equipment this probe has been brought to within 14 nm of a semiconductor device which includes surface gates and a 300 nm deep two-dimensional electron gas. Measurements of voltages applied to these conducting layers have been made at room temperature and at 4.2 K using the sensitive conductance of the one-dimensional channel. A voltage resolution of 0.48 mV has been observed at 4.2 K. Probe conductance measurements have also been made as a function of probe–sample separation. The conductance–separation data were fitted using a simple parallel plate capacitor model and a height resolution of 4 nm was calculated. Images of the sample layers have been obtained and a lateral resolution of 760 nm observed. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1351839
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  • 6
    Electronic Resource
    Electronic Resource
    The effect of elevated atmospheric carbon dioxide levels on soil bacterial communities (2000)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 6 (2000), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: The effect of elevated carbon dioxide levels on total bacterial communities was studied in a series of controlled and replicated model terrestrial ecosystems over a period of 38 weeks. The bacterial community was profiled using Denaturing Gradient Gel Electrophoresis (DGGE) analysis of bacterial 16S rRNA gene fragments amplified by the Polymerase Chain Reaction from DNA extracted directly from soil. Bacterial community DGGE profiles provided three major findings: (i) there was a high degree of profile similarity after ≈ 12 weeks (one plant generation); (ii) whilst overall DGGE profile was maintained over the 38 weeks (three plant generations), the banding patterns became more diverse with time; (iii) DGGE data provided no evidence for a shift in bacterial community structure resulting from exposure of the ecosystem to an increased atmospheric CO2 level.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2486.2000.00320.x
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