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  • 1
    Digitale Medien
    Digitale Medien
    Structural and optical studies of vertically aligned InAs/GaAs self-assembled quantum dots (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 6374-6378 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We report a structural and optical spectroscopic investigation of multiple layer InAs/GaAs self-assembled quantum dots, studied as a function of the GaAs thickness between the quantum dot layers. With decreasing GaAs thickness the positions of dots in different layers exhibit a transition from no correlation to full correlation. Optically the dots in uncorrelated and fully correlated structures are found to exhibit very distinct and different properties. With increasing laser power the photoluminescence of the correlated structure exhibits a high energy, asymmetrical broadening, an effect absent in the uncorrelated structure. In photoluminescence excitation multiple-LO-phonon carrier relaxation features are observed in the spectra of the uncorrelated structure but not in the spectra of the correlated structure. These differences are explained in terms of nonresonant carrier tunneling between the dots in the correlated dot structures. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1418003
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  • 2
    Digitale Medien
    Digitale Medien
    Spectroscopic determination of the electron distribution in a quantum cascade structure (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 2079-2081 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Complementary intersubband and interband optical measurements have been employed in order to study the bias dependence of the carrier distribution and energy level alignment within a GaAs–AlGaAs quantum cascade structure. Using these techniques, we have measured the redistribution of electrons throughout the bridging regions and upper states in the active regions with increasing bias. The high quality of the sample gives very narrow linewidths in the optical spectra, permitting the resolution of transitions involving closely spaced energy levels. This has allowed the direct observation of level alignment at the onset of current flow through the device. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.124922
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  • 3
    Digitale Medien
    Digitale Medien
    Decreasing the emission wavelength of GaAs–AlGaAs quantum cascade lasers by the incorporation of ultrathin InGaAs layers (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 78 (2001), S. 413-415 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We demonstrate that the emission wavelength of GaAs–Al0.33Ga0.67As quantum cascade lasers can be decreased significantly by incorporating InGaAs layers within the active regions. InAs monolayers are deposited during growth, with segregation effects resulting in the formation of thin InGaAs layers within the GaAs active region quantum wells of the laser. The InGaAs layers are positioned close to the antinodes of the lower laser level wave function, thus decreasing its confinement energy. The small spatial overlap of the InGaAs layers with the upper laser level minimizes the perturbation of the upper state. Consequently, the energy separation between the upper and lower laser levels increases, reducing the emission wavelength. The measured operating wavelength of 7.4 μm is the shortest reported for a GaAs–AlGaAs quantum cascade laser and is approximately 2 μm less than for an identical structure without InGaAs layers in the active regions. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1343841
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  • 4
    Digitale Medien
    Digitale Medien
    Electric-field-dependent carrier capture and escape in self-assembled InAs/GaAs quantum dots (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 4344-4346 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Photoluminescence and complementary photocurrent spectroscopy, both as a function of electric field, are used to probe carrier capture and escape mechanisms in InAs/GaAs quantum dots. Carrier capture from the GaAs matrix is found to be highly field sensitive, being fully quenched in fields of only 15 kV/cm. For fields less than 20 kV/cm, carriers excited in the wetting layer are shown to be captured by the dots very effectively, whereas for fields in excess of 50 kV/cm tunnel escape from the wetting layer into the GaAs continuum is dominant. For excitation directly into the dots, radiative recombination dominates up to 100 kV/cm. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1334363
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  • 5
    Digitale Medien
    Digitale Medien
    Controlling the performance of GaAs–AlGaAs quantum-cascade lasers via barrier height modifications (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 801-803 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A series of GaAs/AlGaAs quantum-cascade lasers has been studied in which the confinement of the upper lasing level is systematically varied. This is achieved by modifying the aluminum composition, and hence the height, of a single barrier in each active region. Increasing the height of the barrier increases the upper laser level lifetime, while decreasing the optical transition matrix element. We find an optimum barrier composition (Al0.4Ga0.6As), with the sample containing this barrier exhibiting a significantly improved low-temperature threshold current density (3.8 kA/cm2) and peak power output (∼800 mW) relative to previously reported GaAs-based quantum-cascade lasers. The temperature performance of all the samples is very similar, indicating that thermal activation of electrons from the upper laser level is not the dominant factor limiting high-temperature operation. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.125589
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  • 6
    facet.materialart.
    Unbekannt
    The Use of Books and Libraries in North Carolina. (1922)
    Chapel Hill, N.C. : Periodicals Archive Online (PAO)
    Social Forces. 1:1/5 (1922/1923) 78 
    Details
    ISSN: 0037-7732
    Thema: Sociologie
    URL: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pao:&rft_dat=xri:pao:article:1203-1922-001-00-000157
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  • 7
    facet.materialart.
    Unbekannt
    Reading Maketh the Full Man. (1922)
    Chapel Hill, N.C. : Periodicals Archive Online (PAO)
    Social Forces. 1:1/5 (1922/1923) 62 
    Details
    ISSN: 0037-7732
    Thema: Sociologie
    URL: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pao:&rft_dat=xri:pao:article:1203-1922-001-00-000156
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  • 8
    Digitale Medien
    Digitale Medien
    Methyl tert-Butyl Ether (MTBE) Contamination in Private Wells near Gasoline Stations in Upstate New York (1998)
    Springer
    Bulletin of environmental contamination and toxicology 61 (1998), S. 484-488 
    Details
    ISSN: 1432-0800
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Energietechnik , Medizin
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s001289900788
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  • 9
    Digitale Medien
    Digitale Medien
    Terpene-anhydride resins as coating materials (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 58 (1995), S. 69-76 
    Details
    ISSN: 0021-8995
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Low to moderate molecular weight terpene-anhydride resins were synthesized and evaluated in coatings applications. The terpenes used were terepinolene, β-pinene, and alloocimene. The comononmers used were maleic or itaconic anhydride. The terpene-anhydride resins were used to formulate solvent-borne coatings with an epoxy or diol as a coreactant. The coatings were evaluated as films over aluminum or steel panels. When a diol was used as a coreactant, the film properties were relatively poor. When epoxy was used as a coreactant, the properties of the films were much improved in terms of resistance to solvent and hardness. © 1995 John Wiley & Sons, Inc.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/app.1995.070580107
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  • 10
    Digitale Medien
    Digitale Medien
    High shear rheology and shear degradation of aqueous polymer solutions (1986)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 32 (1986), S. 5399-5413 
    Details
    ISSN: 0021-8995
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: We have investigated the possibility of replacing hydraulic oils with aqueous polymer solutions having the same rheological properties. We measured the low and high shear rate viscosities of polymer solutions at several moderate concentrations and compared the results to the predictions of a molecular model. We found that viscosities measured at shear rates near 1 million reciprocal seconds are in good agreement with those calculated using the model of Mochimaru.6 Shear degradation studies were also conducted using higher molecular weight versions of some of the polymers. Exposure of these to very high shear rate caused a permanent decrease in viscosity and a corresponding change in the molecular weight and molecular weight distribution. Taken together, these results show that very low molecular weight polymers at moderate concentrations are necessary to formulate an aqueous hydraulic fluid with approximately Newtonian behavior at shear rates near 1 million reciprocal seconds, and without long-term polymer degradation.
    Zusätzliches Material: 13 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/app.1986.070320613
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