Bibliothek

feed icon rss

Ihre E-Mail wurde erfolgreich gesendet. Bitte prüfen Sie Ihren Maileingang.

Leider ist ein Fehler beim E-Mail-Versand aufgetreten. Bitte versuchen Sie es erneut.

Vorgang fortführen?

Exportieren
  • 1
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 4920-4922 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Magnetophotoluminescence excitation spectroscopy has been employed to study GaAs-AlGaAs coupled double quantum wells. The investigations were undertaken at liquid helium temperatures and in magnetic fields up to 15 T applied parallel to the growth direction. In zero magnetic field, under flat-band conditions, the spectrum is dominated by ground-state excitonic transitions between electron and hole states with envelope functions of the same symmetry. In a magnetic field, the oscillator strengths of excited excitonic states are enhanced and four series of transitions are observed. The spectral features corresponding to the ground state and the excited states have been analyzed and these results were utilized to determine the exciton binding energies for several excitonic transitions of different subbands in this coupled double quantum-well structure. A number of additional features are visible at higher magnetic fields; some of these peaks are believed to be associated with 2p exciton transitions between hole and electron states with envelope functions of opposite parity due to exciton mixing. A comparison is made between the experimental results and theoretical calculations which include these effects.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 2
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 4095-4102 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Ferroelectric twin-domain structures in epitaxial Pb(Zr, Ti)O3 (PZT) thin films grown on various single-crystal substrates such as MgO(001), KTaO3(001), and SrTiO3(001) were investigated by two-dimensional reciprocal space mapping using synchrotron x-ray diffraction. Each system showed a characteristic domain structure. PbTiO3 thin films grown on MgO(001) showed highly c-axis oriented domain structures consisting of a periodic array of 90° twinlike domains. Perfectly c-axis oriented films were obtained on SrTiO3(001), while the films grown on KTaO3(001) showed a-domain dominant structures with a small amount of c domains embedded in matrix a domains. Contributions of net elastic strain stored in each heteroepitaxial layer and its relaxation to the final domain structures were evaluated considering thermodynamic equilibrium relief of coherency strain by misfit dislocation generation at the film growth temperature. A comparison between theoretical consideration and experimental results clearly demonstrates that the nature of effective misfit strain and its relaxation during film growth play a critical role in the formation of domain structures in epitaxial PZT thin films. Moreover, it was verified that the control of such critical strain factors by changing film composition could modify dominant domain structures in a drastic way. In addition, it was found that the crystalline quality of the films is closely correlated to the tilting nature of the domain structure in each system and coherency strain across the 90° domain boundary is accommodated mainly by the domain tilt of the minor domain. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 3
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 8035-8038 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Strain relaxation and its effect on domain formation of epitaxial PbTiO3 thin films grown on MgO (001) substrates were investigated as a function of film thickness by two-dimensional reciprocal space mapping using synchrotron x-ray diffraction. Within a few hundreds of angstrom region, it was observed that c-domain abundance, α, was critically dependent on film thickness. As the film thickness increased further, α was saturated at a value of ∼0.75. The HK mesh scan on PbTiO3 (100) reflections revealed that directional tilting of a domains with four-fold symmetry began to develop as the film thickness exceeded 650 Å. Thermodynamic equilibrium relief of the coherency strain was evaluated based on Mattews–Blakslee criteria that determine thickness dependent misfit accommodation. This theoretical consideration with experimental results led us to conclude that the unrelaxed residual misfit strain has a significant effect on the domain formation, particularly in the region below the thickness of 1000 Å. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 4
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 6327-6329 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We have measured the diamagnetic shift of band-edge luminescence, no-phonon peak, and phonon sideband from a pseudomorphic, undoped Si0.83Ge0.17/Si quantum well using high-field magnetoluminescence spectroscopy. The quadratic dependence of the diamagnetic shift of the no-phonon luminescence peak suggests that the luminescence originates from excitons. Using a variational calculation, we determine the effective heavy-hole mass and the exciton binding energy to be 0.27m0 and 14.8 meV, respectively, and compare these results with reported values obtained from other measurement techniques. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 5
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 2863-2867 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Shubnikov–de Haas and Van der Pauw Hall effect measurements at 1.5 K have been carried out to investigate the existence of a two-dimensional electron gas and to determine subband energies in a Si-delta-doped Al0.27Ga0.73As/GaAs single quantum well. The fast Fourier transformation results for the S-dH data indicate clearly the occupation of two subbands in edge delta-doped Al0.27Ga0.73As/GaAs quantum wells. Capacitance-voltage profiling and temperature-dependent photoluminescence measurements have been performed to characterize the properties of edge delta-doped Al0.27Ga0.73As/GaAs quantum wells. Using these experimental results and a self-consistent numerical method which took into account the exchange-correlation effects, the electron subband energies were determined. These results indicate that edge delta-doped Al0.27Ga0.73As/GaAs single quantum wells are similar to the asymmetrical potential wells occupied by relatively high electron carrier densities.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 6
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 3528-3530 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A scheme to generate an optical matrix from a mode-locked Nd:YAG laser has been theoretically explored and experimentally demonstrated. The matrix consists of highly synchronized and sequentially delayed optical pulses suitable for use with two-dimensional array optoelectronic devices and clock distribution system. The output pulses have the same state of polarization and no timing jitter is produced among the elements. Encoded outputs have been generated from the matrix using a set of photomasks. This technique can be applied to high-speed optical parallel processing. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 7
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 72 (1998), S. 412-414 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: An all fiberoptic configuration to generate multi-wavelength picosecond optical pulses by self-seeding of a gain-switched 1.53 μm semiconductor laser has been proposed and experimentally demonstrated. The configuration consists of a 600 m highly dispersive fiber and an optical loop mirror multiplexer. Four-wavelength optical pulses with a spectral separation of 2.6 nm, a side-mode-suppression ratio of 16 to 20 dB, and a pulse width of 75 ps have been generated. The repetition rate of these pulses has been multiplied to 3.4 GHz, and totally 13.6 Gb/s (4×3.4 Gb/s) pulse signals have been produced. With the optical bit patterns generated from the multiplexer, output pulses with one, two, or four wavelengths at different combinations can be obtained. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 8
    Digitale Medien
    Digitale Medien
    s.l. : American Chemical Society
    Biochemistry 17 (1978), S. 4525-4533 
    ISSN: 1520-4995
    Quelle: ACS Legacy Archives
    Thema: Biologie , Chemie und Pharmazie
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 9
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 1995-1997 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Phase transformation in epitaxial PbTiO3 thin films grown on MgO(001) substrates was studied and quantified by two-dimensional reciprocal space mapping technique using synchrotron x-ray diffraction equipped with an in situ high temperature stage. Just below the Curie temperature, a twin-like domain structure was formed with an initial value of c-domain abundance, α∼0.3, and the value increased continuously during cooling, and eventually the c-domain dominant structure (α∼0.72) was achieved at room temperature through continuous expansion of the c domains. By investigating the intensity distribution of contour maps, domain tilting and mosaicity were characterized along the q[h00] direction and the presence of a strain gradient along the growth direction q[001] was also confirmed from the asymmetric distribution of the contour maps. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 10
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Science Ltd
    Clinical & experimental allergy 34 (2004), S. 0 
    ISSN: 1365-2222
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Medizin
    Notizen: Background Toluene diisocyanate (TDI)-induced asthma is an inflammatory disease of the airways characterized by airway remodelling due, at least in part, to an excess of extracellular matrix deposition in the airway wall. The ratio of matrix metalloproteinase-9 (MMP-9) and its inhibitor, tissue inhibitor of metalloproteinase-1 (TIMP-1) may be a marker of the balance between airway tissue destruction and repair.Objective We determined whether an imbalance of the MMP-9 : TIMP-1 molar ratio is present before and/or after challenge with TDI.Methods We used a murine model of TDI-induced asthma to evaluate the MMP-9 and TIMP-1 balance in the lung.Results The expression of MMP-9 and TIMP-1 mRNAs and proteins in the lungs increased at 7 h after TDI inhalation and continued for up to 72 h. Immunohistochemical and immunocytological analyses in the lungs of TDI-exposed mice revealed increases of immunoreactive MMP-9 and TIMP-1. There were significant correlations between the levels of MMP-9 or TIMP-1 and the number of neutrophils, lymphocytes, or eosinophils. The molar ratio of MMP-9/TIMP-1 significantly decreased at 7 h after TDI inhalation and continued up to 72 h.Conclusion These data suggest that TDI-induced asthma may be associated with an imbalance between MMP-9 and TIMP-1, which could be useful as a marker of airway inflammation and airway remodelling in this disease.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
Schließen ⊗
Diese Webseite nutzt Cookies und das Analyse-Tool Matomo. Weitere Informationen finden Sie hier...