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  • American Institute of Physics (AIP)  (18)
  • 2000-2004  (18)
  • 2002  (5)
  • 2001  (13)
  • 1
    Electronic Resource
    Electronic Resource
    Efficient energy upconversion emission in Tm3+/Yb3+-codoped TeO2-based optical glasses excited at 1.064 μm (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 6550-6552 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Efficient energy upconversion of cw radiation at 1.064 μm into blue, red, and near infrared emission in Tm3+-doped Yb3+-sensitized 60TeO2-10GeO2-10K2O-10Li2O-10Nb2O5 glasses is reported. Intense blue upconversion luminescence at 485 nm corresponding to the Tm3+ 1G4→3H6 transition with a measured absolute power of 0.1 μW for 800 mW excitation power at room temperature is observed. The experimental results also revealed a sevenfold enhancement in the upconversion efficiency when the sample was heated from room temperature to 235 °C yielding 0.7 μW of blue absolute fluorescence power for 800 mW pump power. High brightness emission around 800 nm (3F4→3H6) in addition to a less intense 655 nm (1G4→3H4 and 3F2,3→3H6) fluorescence is also recorded. The energy upconversion excitation mechanism for thulium emitting levels is assigned to multiphonon-assisted anti-Stokes excitation of the ytterbium-sensitizer followed by multiphonon-assisted sequential energy-transfer processes. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1413489
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  • 2
    Electronic Resource
    Electronic Resource
    Laser interference structuring of a-Ge films on GaAs (2002)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 91 (2002), S. 2916-2920 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have investigated the laser interference crystallization (LIC) of amorphous germanium films on (100)-oriented GaAs substrates using nanosecond laser pulses. We demonstrate that LIC can produce periodic arrays of epitaxially crystallized Ge lines on GaAs with submicrometer widths. The gratings display a surface undulation with faceted surfaces, which depends on laser fluency. The undulation is attributed to the lateral solidification process induced by the temperature gradients created during the LIC process. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1448674
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  • 3
    Electronic Resource
    Electronic Resource
    Monte Carlo simulation study of the Fano factor, w value, and energy resolution for the absorption of soft x rays in xenon–neon gas mixtures (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 8202-8213 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Xenon gas proportional-scintillation counters (GPSC) have many applications in the detection of soft x rays where their energy resolution, R, is comparable to solid-state detectors when large window areas are required. However, R is known to deteriorate for energies Exr below 2–3 keV due to electron loss to the entrance window. Since the addition of a lighter noble gas increases the absorption depth, we have investigated the use of Xe–Ne gas mixtures at atmospheric pressure as detector fillings. The results of a Monte Carlo simulation study of the Fano factor, F, the w value, and the intrinsic energy resolution, R=2.36(Fw/Exr)1/2, are presented for Xe–Ne mixtures and pure Xe and Ne. The results show that the addition of Ne to Xe reduces the intrinsic energy resolution R but this never compensates for the reduction in scintillation yield in GPSC applications, implying that the instrumental energy resolution R will only improve with the addition of Ne when electron loss to the window in pure Xe is significant. The simulation reproduces the photoionization process of the Xe and Ne atoms, the vacancy cascade decay of the residual ions, and the elastic and inelastic scattering of electrons by the gas atoms. The contribution of energy and charge transfer mechanisms such as Penning, associative, and transfer ionization is discussed in detail. It is shown that Penning and associative ionization are the crucial indirect ionization processes which determine the behavior of F and w at low concentrations of Xe. The importance of the nonmetastable Ne states is also assessed. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1371281
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  • 4
    Electronic Resource
    Electronic Resource
    Epitaxial pulsed laser crystallization of amorphous germanium on GaAs (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 2575-2581 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have investigated the crystallization of amorphous germanium films on GaAs crystals using nanosecond laser pulses. The structure and composition of the crystallized layers is dominated by nonequilibrium effects induced by the fast cooling process following laser irradiation. Perfect epitaxial films are obtained for fluencies that completely melt the Ge film, but not the substrate. For higher fluencies, partial melting of the substrate leads to the formation of a (GaAs)1−xGe2x epitaxial alloy with a graded composition profile at the interface with the substrate. Since Ge and GaAs are thermodynamically immiscible in the solid phase, the formation of the alloy is attributed to the suppression of phase separation during the fast cooling process. Lower laser fluencies lead to polycrystalline layers with a patterned surface structure. The latter is attributed to the freeze-in of instabilities in the melt during the fast solidification process. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1390312
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  • 5
    Electronic Resource
    Electronic Resource
    Evidence for the precipitation of the Fe2Pr phase in the Fe–Pr binary system (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 2934-2938 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Directional solidification experiments were employed on Fe–Pr alloys at several low cooling rates in order to observe the solidification sequence displayed along the length of the samples. Measurements of the transition temperatures around the eutectic temperature of this system were also performed using a Calvet-type calorimeter. The results show the precipitation of the Fe2Pr phase and its peritectic formation, described as Fe17Pr2+L→Fe2Pr. The calorimetric measurements give the temperature of this reaction as being 669 °C. The system presents only one eutectic reaction at 664 °C, described as L→Fe2Pr+Pr, with a feathered morphology under metallographic analysis. Thermomagnetic measurements give the Curie temperature of the Fe2Pr phase as 44 °C. A sequence of reactions during solidification of the alloys around the eutectic point for the Fe–Pr binary system is proposed. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1394155
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  • 6
    Electronic Resource
    Electronic Resource
    Collinear light modulation by surface acoustic waves in laterally structured semiconductors (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 5060-5066 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The modulation of light beams by surface acoustic waves (SAW) in periodically modulated photonic materials is investigated. The periodic modulation allows for new scattering processes which can improve the efficiency of SAW-based modulators, as proposed by P. St. J. Russell [Phys. Rev. Lett. 56, 596 (1986)]. In particular, scattering geometries with collinear propagation paths for the SAW and the light beam become possible using SAW wavelengths much larger than the light wavelength. We analyze the performance of such modulators based on semiconductor materials and examine the role of random fluctuations in structure dimensions on their operation. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1359753
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  • 7
    Electronic Resource
    Electronic Resource
    Structural properties of hydrogenated carbon-nitride films produced by ion-beam-assisted evaporation of the molecular precursor C4N6H4 (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 7852-7859 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Hydrogenated carbon-nitride films (CNx:H) were deposited by evaporation of aza-adenine (8-aza-6-aminopurine, C4N6H4) and irradiated during film growth by a nitrogen ion beam with energies of 25, 50, and 100 eV. The relationship between the deposition conditions and the chemical bonding structure was investigated by x-ray photoelectron and infrared spectroscopies. The mass density of the films was estimated from the C 1s plasmon energy and the optical properties were examined by ultraviolet–visible spectroscopy. The infrared spectra indicate that in the case of evaporated films, the molecular structure of aza-adenine is preserved without substantial nitrogen loss (N/C(approximate)1.3). With increasing energy of the assisting nitrogen ion beam, the structure is subsequently transformed into an amorphous phase. This transition is accompanied by an increasing nitrogen loss down to N/C(approximate)0.8, a decrease of the optical band gap, and an increase of the film density. The known molecular structure of aza-adenine permits the reconstruction of the C 1s and N 1s core-level spectra with deconvoluted spectral components representing the different bonding environments of C and N atoms present in the molecule. The spectral components are identified by comparing the experimental data with theoretical calculations of the corresponding binding energies. By analysis of the spectral changes induced by the nitrogen ion beam with increasing energies, it is possible to study the microstructural modifications of the material. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1372371
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  • 8
    Electronic Resource
    Electronic Resource
    Radiative recombination during ambipolar carrier transport by surface acoustic waves in GaAs quantum wells (2002)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 80 (2002), S. 2320-2322 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on the defect-assisted radiative recombination of photogenerated electrons and holes in GaAs quantum wells (QWs) during the transport by surface acoustic waves (SAWs). The studies were performed by detecting the spatial distribution of the photoluminescence (PL) with a resolution of a few micrometers. Under a SAW, a high PL intensity is observed on spatially localized spots along the SAW propagation path. This high PL intensity is attributed to recombination of the carriers, which are transported by the SAW, induced by charged defects located on or close to the QW plane. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1463706
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  • 9
    Electronic Resource
    Electronic Resource
    Field-induced sharp ferroelectric phase transition in Sr0.66Ba0.34Nb2O6 relaxor ferroelectric (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 79 (2001), S. 2800-2802 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Field-induced sharp ferroelectric phase transition was observed in Sr0.66Ba0.34Nb2O6 single crystals. The peaks of the real and imaginary parts of dielectric permittivity arise upon cooling under weak dc bias electric fields and subsequently heating under zero fields or upon cooling under zero fields and subsequently heating under weak electric fields. The applied electric field cancels the random fields that destroy the phase transition and give rise to low temperature domain state if E=0. These results strongly suggest that the SBN system belongs to the random field Ising universality class, a rare case among structural phase transitions. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1413727
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  • 10
    Electronic Resource
    Electronic Resource
    Mobility anisotropy in InSb/AlxIn1−xSb single quantum wells (2002)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 80 (2002), S. 2138-2140 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Three types of defects at the surface of InSb quantum well samples are identified: hillocks, square mounds, and oriented abrupt steps. The electron mobility in the quantum well correlates to the density of abrupt features, such that samples with a high density of anisotropic defects show anisotropy in the mobility. We propose that the dominant scattering mechanism associated with these abrupt features is a fluctuation in the quantum well morphology. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1463206
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