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  • 1
    Digitale Medien
    Digitale Medien
    Geographical variations of trace elements in sediments of the major rivers in eastern China (2000)
    Springer
    Environmental geology 39 (2000), S. 1334-1340 
    Details
    ISSN: 1432-0495
    Schlagwort(e): Keywords China ; Geochemistry ; River ; Sediment ; Trace metals
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie
    Notizen: Abstract  A total of 26 geographically and hydrologically diverse sediment samples were collected from 12 major rivers in eastern China. The 〈63-μm fraction of the sediments was analysed for both total concentrations of Cu, Zn, Pb and Cd, and their associations with various geochemical phases. The geographical variations of sediment-bound trace metals can be related to the bedrock types and weathering processes in the corresponding river basins. The rivers in southern China had notably higher concentrations of trace metals in sediments because of abundant non-ferrous mineral deposits and stronger weathering process in the region. A large proportion of trace metals in these sediments was associated with iron and manganese oxides and organic matter. Relative low levels of trace metals were found in river sediments in northern China, and a significant proportion of the metals was bound to organic matter, carbonates, and the residual fraction. The sediments in the Yellow River, originating from special loess, had the lowest concentrations of trace metals. Most of the trace metals were associated with the carbonates and residual phases.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002540000224
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  • 2
    Digitale Medien
    Digitale Medien
    Characterization of exposure and processing of thick PMMA for deep x-ray lithography using hard x-rays (1998)
    Springer
    Microsystem technologies 4 (1998), S. 86-88 
    Details
    ISSN: 1432-1858
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Technik allgemein
    Notizen: Abstract  The first step for the fabrication of microstructures using deep x-ray lithography (DXRL) is the radiation of a sensitive polymer like poly(methyl methacrylate) (PMMA) by hard x-ray. At the Advanced Photon Source a dedicated beamline1 allowed the proper exposure of very thick resist (several mm). In this work we give a characterization of the PMMA/development system. As a result the resist dissolution rate (μm/min) of the exposed PMMA in different developer is calculated. We also analyze the conditions that produce bubbles and cracks in the thick exposed resist and investigate the scanning parameters that reduce them.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s005420050102
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  • 3
    Digitale Medien
    Digitale Medien
    Interband transitions in InAsxP1−x/InP strained multiple quantum wells (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 1645-1647 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We report the optical study of the interband transitions in InAsxP1−x/InP strained-layer multiple quantum wells grown by gas-source molecular beam epitaxy. Low-temperature photoluminescence, photoluminescence excitation, and room temperature photomodulated transmission measurements were performed to investigate optical interband transitions. In addition to transitions associated with the heavy-hole and the light-hole bands, a transition involved with the spin-orbit split-off band was observed. We also observed spectral linewidth broadening due to compositional inhomogeneity and layer-thickness fluctuations from the sample using short-period superlattices as the well materials. Calculations based on the envelope-function approximation and phenomenological deformation potential theory, including both band nonparabolicity and strain-induced valence-band mixing, were compared with experimental data to identify the optical transitions between quantized states in the wells. We found good agreement between theory and experiment.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.351683
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  • 4
    Digitale Medien
    Digitale Medien
    Laser action in GaN pyramids grown on (111) silicon by selective lateral overgrowth (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 2242-2244 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Laser action was observed in GaN pyramids under strong optical pumping at room temperature. The pyramids were laterally overgrown on a patterned GaN/AlN seeding layer grown on a (111) silicon substrate by metal–organic chemical vapor deposition. Each pyramid had a 15-μm-wide hexagonal base and was on average 15 μm in height. The pyramids were individually pumped, imaged, and spectrally analyzed through a high-magnification telescope system using a high-density pulsed excitation source. Under high levels of optical pumping, multimode laser at room temperature was observed. The integrated emission intensity for both spontaneous and lasing peaks was studied as a function of excitation power density. The effects of pyramid geometry and short-pulse excitation on the multimode nature of laser oscillations inside of the pyramids is discussed. This study suggests that GaN microstructures could potentially be used as pixel elements and high-density two-dimensional laser arrays. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.121689
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  • 5
    Digitale Medien
    Digitale Medien
    Erratum: "Recombination dynamics in n-AlxGa1−xAs/n-In0.5Ga0.5P type-II heterostructures" [Appl. Phys. Lett. 73, 1245 (1998)] (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 2219-2219 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.122431
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  • 6
    Digitale Medien
    Digitale Medien
    Pump-probe spectroscopy of band tail states in metalorganic chemical vapor deposition-grown InGaN (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 1892-1894 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Nanosecond nondegenerate optical pump-probe experiments have been performed on InGaN thin films and InGaN/GaN multiple quantum wells. Bleaching of absorption of the localized band tail states was observed with increasing excitation density (Iexc) of the pump pulse. The dynamics of the bleaching was found to depend on the localization depth of the band tail states and on Iexc. With high Iexc, large blueshifts in the spontaneous emission luminescence peaks were also observed, the magnitude of which was again found to depend on the localization depth of the band tail states. Stimulated emission is observed from the samples with increasing Iexc and correlates with significant changes in the behavior of the absorption bleaching. The observed bleaching dynamics of the band tail states are well explained by considering the effective lifetime of the band tail states as measured by time-resolved photoluminescence experiments. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.122317
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  • 7
    Digitale Medien
    Digitale Medien
    "S-shaped" temperature-dependent emission shift and carrier dynamics in InGaN/GaN multiple quantum wells (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 1370-1372 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We report temperature-dependent time-integrated and time-resolved photoluminescence (PL) studies of InGaN/GaN multiple quantum wells (MQWs) grown by metalorganic chemical vapor deposition. We observed anomalous emission behavior, specifically an S-shaped (decrease–increase–decrease) temperature dependence of the peak energy (Ep) for InGaN-related PL with increasing temperature: Ep redshifts in the temperature range of 10–70 K, blueshifts for 70–150 K, and redshifts again for 150–300 K with increasing temperature. In addition, when Ep redshifts, the spectral width is observed to narrow, while when Ep blueshifts, it broadens. From a study of the integrated PL intensity as a function of temperature, it is found that thermionic emission of photocarriers out of local potential minima into higher energy states within the wells is the dominant mechanism leading to the thermal quenching of the InGaN-related PL. We demonstrate that the temperature-induced S-shaped PL shift is caused by a change in the carrier dynamics with increasing temperature due to inhomogeneity and carrier localization in the InGaN/GaN MQWs. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.122164
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  • 8
    Digitale Medien
    Digitale Medien
    Femtosecond wave mixing experiments in ZnCdSe/ZnSe quantum wells (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 65 (1994), S. 1534-1536 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Extreme high order nonlinear diffracted signals are found in ZnCdSe/ZnSe quantum wells in two beam, self-diffraction geometry. Diffracted signals of all observed orders are shown to originate predominantly from excitonic resonances. Using four-wave mixing, an indication of hole-longitudinal optical phonon scattering between the heavy and the light hole states is found, and exciton-phonon interaction is studied.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.112034
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  • 9
    Digitale Medien
    Digitale Medien
    Optical properties of wurtzite GaN grown by low-pressure metalorganic chemical-vapor deposition (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 3691-3696 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We present the results of optical studies on the properties of GaN grown by low-pressure metalorganic chemical-vapor deposition, with emphasis on the issues vital to device applications such as stimulated emission and laser action as well as carrier relaxation dynamics. By optical pumping, stimulated emission and lasing were investigated over a wide temperature range up to 420 K. Using a picosecond streak camera, the free and bound exciton emission decay times were examined. In addition, the effects of temperature and pressure on the optical interband transitions and the transitions associated with impurity/defect states were studied using a variety of spectroscopic methods, including photoluminescence and photoreflectance. The fundamental band gap of GaN was mapped out as a function of temperature using the empirical Varshni relation. The pressure coefficient of the gap was determined using diamond-anvil pressure-cell technique. The hydrostatic deformation potential for the direct Γ band gap was also derived from the experimental results. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.361200
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  • 10
    Digitale Medien
    Digitale Medien
    Optical properties of highly strained CdSe/ZnSe quantum wells (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 5699-5704 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We present a study of the optical properties of highly strained CdSe/ZnSe quantum well system. A variety of CdSe/ZnSe samples containing single quantum well or multiple quantum wells grown by molecular beam epitaxy has been studied by using low-temperature photoluminescence (PL), photoluminescence excitation, and photoreflectance measurements. The strong PL signals associated with excitonic emissions from the samples show that the CdSe/ZnSe heterostructure system is promising in the development of laser diodes and light-emitting diodes operating in the blue-green range. Linewidth narrowing of PL spectra with decreasing well width is observed and attributed to alloy formation at the interface due to lateral interdiffusion. The PL signal intensities and the pressure coefficients of interband transitions are also found to depend on the well width, which can be explained in terms of strain relaxation induced misfit dislocations and the critical thickness in the heterostructure system. Our results suggest that the critical thickness for a CdSe layer coherently grown on ZnSe is less than four monolayers.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.354185
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