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  • 11
    Digitale Medien
    Digitale Medien
    Operation of a quasi-optical gyrotron with a Gaussian output coupler (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 3492-3500 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The operation of a 92 GHz quasi-optical gyrotron having a resonator formed by a spherical mirror and a diffraction grating placed in −1 order Littrow mount is presented. A power of 150 kW with a Gaussian output pattern was measured. The Gaussian content in the output was 98% with less than 1% of depolarization. By optimizing the magnetic field at fixed frequency, a maximum efficiency of 15% was reached.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.871499
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  • 12
    Digitale Medien
    Digitale Medien
    Quantitative two-dimensional carrier profiling of a 400 nm complementary metal–oxide–semiconductor device by Schottky scanning capacitance microscopy (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 6752-6757 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Carrier profiling of a 400 nm complementary metal–oxide–semiconductor device has been accomplished by combining metal–semiconductor capacitance–voltage profiling techniques with two-dimensional scanning probe microscopy. When a metal probe is brought into contact with a semiconductor, a space-charged depletion region and therefore a capacitor is formed at the junction. By applying a small ac voltage, the voltage derivative of the contact capacitance can be measured with a lock-in amplifier. The amplitude of the derivative signal is a function of the carrier concentration, and the sign gives the type of carrier. The present work concentrates on the two dimensional (2D) carrier profiling of a 400 nm metal–oxide–semiconductor field effect transistor. The results demonstrate that this technique is capable of quantitative 2D characterization of semiconductor devices. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1322380
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  • 13
    Digitale Medien
    Digitale Medien
    Photoluminescence properties of ZnGa2O4:Mn powder phosphors (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 5691-5695 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The results of a systematic photoluminescence study of ZnGa2O4:Mn powder phosphor are reported. At room temperature this phosphor exhibits bright green luminescence with a spectral peak at 2.46 eV and Commission International de l'Eclairage chromaticity coordinates of x=0.073 and y=0.696. At low temperatures the luminescence was found to consist of three components assigned to the 4T1–6A1 inner transition of the 3d electrons of Mn2+ ions located on three different sites of the host crystal. Selective excitation and lifetime measurements were used to investigate the assignment of these features. The photoluminescence lifetime showed a single exponential decay of about 4 ms and at T=1.6 K an optical-phonon-related fine structure [Ephonon=(8.2±0.2) meV] of the main photoluminescence line was observed. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.359627
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  • 14
    Digitale Medien
    Digitale Medien
    Photoluminescence properties of ZnS epilayers (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 2803-2809 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A comprehensive study is reported of the photoluminescence properties of ZnS thin films between 1.6 and 320 K grown by metalorganic molecular beam epitaxy and chemical beam epitaxy on GaAs substrates. Both heavy- and light-hole free excitons were observed at low temperatures with linewidths of 7.0 and 5.3 meV, respectively, as well as donor- and acceptor-bound excitons and free-to-bound recombination along with their longitudinal optical (LO) phonon replicas. The free exciton emission was observed up to 320 K, and enabled the room temperature band gap of ZnS to be unambiguously determined as 3.723 eV. The temperature dependence of the peak position, intensity, and linewidth was well described by the conventional empirical relations and by Toyozawa's exciton line shape theory. The bound exciton peak positions were found to follow the temperature dependence of the band gap whereas the free-to-bound recombination feature was displaced by (1/2)kT above the band gap energy. Thermal quenching of the donor-bound exciton was described by a one-step quenching process with an activation energy of 14.4 meV. The self-activation (SA) center was also observed at 2.846 eV with a linewidth of 410 meV. The temperature dependence of the SA emission was well described by the configuration coordinate model. From the thermal broadening of the SA emission, an average phonon energy of 47.5 meV was determined, in good agreement with the LO phonon energy. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.363937
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  • 15
    Digitale Medien
    Digitale Medien
    Isotopic study of metalorganic chemical vapor deposition of (Ba, Sr)TiO3 films on Pt (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 415-417 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Isotopic labeling experiments (18O2) have been carried out to understand the film-formation reactions in the metalorganic chemical vapor deposition of (Ba, Sr)TiO3 (BST) films. Time-of-flight secondary ion mass spectrometry reveals both M 18O and M 16O (M=Ba, Sr, Ti) in the BST films, indicating that the oxygen in the BST films originates from both the gas phase oxidants (18O), and the precursor ligands (16O). Use of a 50% 18O2-50% N2 16O mixture results in a reduction of 18O incorporation in the BST film, indicating direct involvement of N2O in the film-formation reactions. Addition of N2O in O2 also appears to improve film surface morphology and step coverage. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.124393
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  • 16
    Digitale Medien
    Digitale Medien
    Dependence of dielectric properties on internal stresses in epitaxial barium strontium titanate thin films (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 78 (2001), S. 2354-2356 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A series of heteroepitaxial BaxSr1−xTiO3 thin films with composition x=0.50 were deposited on (001) MgO substrates by pulsed-laser deposition. The thickness of the films was varied from 14 to 500 nm to produce a systematically decreasing level of in-plane tensile stresses. The microstructural and crystallographic features of the films were determined via transmission electron microscopy and x-ray diffraction. A theoretical treatment of the in-plane misfit strain as a function of film thickness is in agreement with the measured out-of-plane lattice parameters. Electrical measurements indicate a drop in the dielectric constant from 2350 for highly stressed thin films to 1700 for relaxed thicker films. The variation in the dielectric constant with the misfit strain is in accordance with a thermodynamic model developed. The relationship between the dielectric constant and electric field is also described by extending the thermodynamic model and taking the effect of electric field into account. A new definition of tunability is adopted to study the effect of strain on tunability. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1359141
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  • 17
    Digitale Medien
    Digitale Medien
    Self-consistent theory of a harmonic gyroklystron with a minimum Q cavity (1986)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 29 (1986), S. 3858-3863 
    Details
    ISSN: 1089-7666
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: In this paper, the energy extraction stage of the gyroklystron [in Advances in Electronics and Electron Physics, edited by C. Marton (Academic, New York, 1979), Vol. 1, pp. 1–54], with a minimum Q cavity is investigated by using a self-consistent radio-frequency (rf) field model. In the low-field, low-current limit, expressions for the self-consistent field and the resulting energy extraction efficiency are derived analytically for an arbitrary cyclotron harmonic number. To our knowledge, these are the first analytic results for the self-consistent field structure and efficiency of a gyrotron device. The large signal regime analysis is carried out by numerically integrating the coupled self-consistent equations. Several examples in this regime are presented.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.865769
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  • 18
    Digitale Medien
    Digitale Medien
    Experimental measurements of competition between fundamental and second harmonic emission in a quasi-optical gyrotron (1990)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 2 (1990), S. 2544-2546 
    Details
    ISSN: 1089-7666
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A quasi-optical gyrotron (QOG) designed for operation at the fundamental ( fce(approximately-equal-to)100 GHz) exhibits simultaneous emission at fce and 2fce (second harmonic). For a beam current of 4 A, 20% of the total rf power is emitted at the second harmonic. The experimental measurements show that the excitation of the second harmonic is only possible when the fundamental is present. The frequency of the second harmonic is locked by the frequency of the fundamental. Experimental evidence shows that when the second harmonic is not excited, total efficiency is enhanced.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.859377
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  • 19
    Digitale Medien
    Digitale Medien
    Optimization of gyroklystron efficiency (1986)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 29 (1986), S. 1274-1281 
    Details
    ISSN: 1089-7666
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: In this article, the optimization of gyroklystron efficiency is investigated by employing a two–step procedure. As a first step, the prebuncher is analyzed using a small signal approximation, since the cavity(ies) here serve mainly to modulate the velocities of the electrons slightly, which will be bunched in the field-free drift section(s). It is found that the electrons entering the energy extraction cavity can be characterized entirely by only two dimensionless parameters: a bunching parameter q and a relative phase ψ. The numerical simulation of the extraction cavity, based on the nonlinear pendulum equations describing the interaction between the electrons and the rf field, supplemented by the initial conditions specified by q and ψ, constitutes the second step. The final result of this two-step analysis is the efficiency, η⊥,opt optimized with respect to q, ψ, and the magnetic detuning parameter Δ. This efficiency depends only on the normalized cavity length μ and the normalized rf field F of the energy extraction section. The efficiency as well as the conditions required to attain this optimum (qopt,Δopt, and qopt) are presented as contour plots on the (F,μ) plane and can be used efficiently to design gyroklystrons of any frequency and output power.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.865876
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  • 20
    Digitale Medien
    Digitale Medien
    "Zeptofarad" (10−21 F) resolution capacitance sensor for scanning capacitance microscopy (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 2618-2623 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: We describe a sensor for use in a scanning capacitance microscope (SCM) that is capable of "zeptofarad" (10−21 F) capacitance measurement resolution in a 1 Hz bandwidth with a peak-to-peak sense voltage on the probe tip of no more than 300 mV. This sensitivity is based on experimental data and simulation results that are in excellent agreement. The complete sensor incorporates an oscillator (phase locked to a 10 MHz crystal oscillator), a coupled transmission line resonator, an amplifier, and a peak detector. The resonator is fabricated from copper-clad, low-loss dielectric material and its size is such that it is easily incorporated with a scanning probe microscope. The sensor's use in the SCM enables capacitance resolution that has not previously been possible while retaining the instrumental advantages of imaging at low sense voltages. The performance of this sensor is discussed and compared to alternative scanning capacitance microscopy methodologies. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1369637
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