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  • Articles: DFG German National Licenses  (54)
  • 1995-1999  (33)
  • 1985-1989  (21)
  • 1
    Electronic Resource
    Electronic Resource
    Measurements of charged particles in the laser ablation plume of polymers (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 3401-3407 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Charged particles in organic polymer plumes photoablated by ultraviolet lasers are measured with a Faraday cup assembly. In spite of a relatively low F2 laser (157 nm) fluence 〈1 J/cm2, relative charged fragment concentrations measured for polyimide, polytetrafluoroethylene, and polyethyleneterephthalate targets are (approximately-greater-than)10−3. Charged particle concentrations in the ablation plumes generated by an F2 laser with polyethyleneterephthalate and polyimide targets are always higher than those in KrF laser (248 nm) ablation plumes at the same specific laser energy deposited on the target. Charged fragments have also higher velocities in the F2 laser ablation plumes. An exponential increase in the charged fragment concentration with increasing laser fluence suggests that the ions are mainly produced through electron-neutral collisions in the hot material core close to the target surface. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359968
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  • 2
    Electronic Resource
    Electronic Resource
    Localization and hopping of magnetoelastic waves in highly magnetostrictive strings with random chain structures (abstract) : The 41st annual conference on magnetism and magnetic materials (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 5692-5692 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Analogous to the localization of the wave function of an electron in a random potential (Anderson localization), in the macroscopic system of magnetoelastic waves (MEWs) propagating in a highly magnetostrictive string exhibiting the giant ΔE effect, the piling-up of MEWs into a wave-packet in a restricted small region of the string is expected. This wave-packet is subject to hopping in a discontinuous wave by applying a magnetic field due to the change in the local elastic states caused by the ΔE effect. From this expectation, a theoretical analysis was performed focusing on the derivation of localization conditions of MEWs. The analysis was carried out using a one-dimensional string model having high magnetostriction. The string is assumed to be composed of random chains with (1) alloy-type disorder (random weights of masses with equal spacings) and (2) liquid-type disorder (random spacings of masses with equal weights). For the elastic and magnetoelastic constants of the string, the value of Fe78Si10B12 amorphous wire (Unitika) were used in the calculations. No substantial changes in the localization states were not recognized in both modes. The analysis revealed that, when the change of the apparent Young's modulus with magnetic field ΔE is 28%, the localized MEWs are subject to hopping conserving their wave identities (eigenfrequencies and eigenstates). This result in considered to originate from the changes in the disorder conditions to support the localization of MEWs. To confirm the above theoretical prediction experimentally, MEW properties have been measured by using Fe78Si10B12 amorphous wires connecting weights made of leads to form the random chain structure. The localized MEWs are, indeed, observed by detecting the local vibrations of the wires. Theoretical and experimental results will be presented in detail at the conference. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.364639
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  • 3
    Electronic Resource
    Electronic Resource
    Organic electroluminescence cells based on thin films deposited by ultraviolet laser ablation (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 2469-2471 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Organic thin films of copper-phthalocyanine (CuPc) and aluminum tris-8-hydroxyquinline (Alq3) were fabricated via KrF laser ablation. In spite of poor crystallinity exhibited in the reconstructed organic films, the CuPc film still works as a hole-transport layer in electroluminescence cells based on the CuPc and Alq3 layers. Electroluminescence at ∼500 nm was obtained with a low initiation voltage of ∼12 V. There is no significant difference in electroluminescence performance for devices fabricated via laser ablation and thermal evaporation. Emission at ∼600 nm caused by energy transfer from Alq3 to 4-(Dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM) is also observed from a DCM-doped Alq3 emission layer. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.120114
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  • 4
    Electronic Resource
    Electronic Resource
    Very high speed GaInAs metal-semiconductor-metal photodiode incorporating an AlInAs/GaInAs graded superlattice (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 54 (1989), S. 16-17 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A lateral structure metal-semiconductor-metal photodiode has been fabricated on GaInAs, in which an AlInAs/GaInAs graded superlattice has been incorporated. This photodiode has exhibited a dark current lower than 100 nA, an internal quantum efficiency of greater than 80% at a wavelength of 1.3 μm, and a capacitance of 40 fF, all at the bias voltage of 10 V. The response speed of this photodiode has been characterized by electro-optic sampling to exhibit a full width at half maximum of 14.7 ps.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.100822
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  • 5
    Electronic Resource
    Electronic Resource
    Room-temperature exciton optical absorption peaks in InGaAsP/InP multiple quantum wells (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 54 (1989), S. 1353-1355 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We grew In1−xGaxAsyP1−y/InP quantum wells (QWs) by low-pressure metalorganic vapor phase epitaxy. The In1−xGaxAsyP1−y layer was closely lattice matched to InP with a composition of y=0.9 (x=0.47y). We investigated structural imperfections such as composition fluctuations, interface roughness, and nonperiodicity analyzing the low-temperature photoluminescence linewidth. We found that the InGaAsP layer composition fluctuated, causing about 5 meV inhomogeneity in the exciton energy level in QWs wider than about 3 nm. Since we obtained very smooth interfaces with less than one monolayer of fluctuation and excellent periodicity by lowering growth temperature to 570 °C, the inhomogeneity of the exciton energy level could be held at 6 meV for 20-period 10-nm multiple QWs. As a result, despite composition fluctuations, a clear room-temperature exciton optical absorption peak was observed at 1.5 μm for the first time to our knowledge.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.100713
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  • 6
    Electronic Resource
    Electronic Resource
    Evaluation of exciton absorption peak broadening factors in InGaAsP/InP multiple quantum wells (1988)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 53 (1988), S. 2290-2292 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We evaluated the magnitude of broadening factors of ground-state exciton absorption peaks in In1−xGaxAsyP1−y/InP (x=0.47y) multiple quantum wells (MQW's) with about 10 nm wells. The absorption peaks broadened with a decrease of y. Analyzing the absorption peak broadening with increasing temperature, the thermal broadening factor at 300 K was found to be about 9 meV and composition independent. Analyzing the photoluminescence linewidth at 4.2 K, it was found that composition fluctuations in the well caused an inhomogeneity of the exciton energy level of 4.4 meV for the y=1.0 MQW and 7.5 meV for the y=0.6 MQW, being the greatest contributors to inhomogeneous broadening. We conclude that the exciton absorption peak broadening with a decrease of y is primarily due to the increase of composition fluctuations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.100256
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  • 7
    Electronic Resource
    Electronic Resource
    Study of Au-n-type GaAs Schottky contacts on a single-crystal part of large-grained polycrystalline GaAs (1986)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 59 (1986), S. 2507-2510 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Gold-n-type GaAs Schottky contacts have been fabricated on a single-crystal part of polycrystalline GaAs with grain size of about 1 cm. The current-voltage (I-V) characteristic has been measured over the temperature range 120–380 K. The barrier height is evaluated from the Richardson plot as 0.57 eV, and discussed by taking account of the effects of an interfacial layer between the metal and semiconductor. The capacitance-voltage (C-V) characteristic has been measured at 0.1, 1, and 100 kHz over the temperature range 120–500 K. A frequency dispersion is observed in the C-V characteristic. It is explained by the frequency dispersion in the dielectric constant of the interfacial layer and the capacitive response of trapping states in the interfacial layer and single-crystal parts of polycrystalline GaAs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.336997
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  • 8
    Electronic Resource
    Electronic Resource
    Effects of deep Fe acceptors on the impedance of a semi-insulating n-type Fe-doped InP Schottky barrier (1985)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 58 (1985), S. 4626-4632 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The capacitive response of deep Fe acceptors in a semi-insulating n-type Fe-doped InP Schottky barrier has been investigated. The capacitance-voltage (C-V) and conductance-voltage (G-V) characteristics over the frequency range 0.06–100 kHz are measured at 300, 317, and 335 K. Great frequency dispersion is observed in C and G. The reverse bias dependencies of C and (G−G0) are shown to be very weak at high frequencies, where G0 is the dc conductance. As measuring frequency is lowered, (G−G0) decreases but C increases considerably. At low frequencies, the bias dependencies of C and (G−G0) are observed and measured 1/C2 versus reverse bias curves are found to be straight lines. It is shown that at low frequencies, C and (G−G0) take maxima near zero bias and rapidly decrease in a forward bias region. As temperature increases, the frequency region in which such low-frequency characteristics are found extends more widely into a high-frequency range. Theoretical calculations of C and (G−G0) are also carried out. The results are compared with experimental ones. Observed variations of C and G with frequency, bias voltage, and temperature are well explained in terms of the delayed response of deep Fe acceptors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.336232
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  • 9
    Electronic Resource
    Electronic Resource
    Magnetic properties of BiFeO3-BaTiO3 and BiFeO3-PbTi(Zr)O3 glassy sputtered films (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 5434-5436 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Magnetic properties of glassy oxide films which exhibit ferromagnetism and ferroelectricity simultaneously above room temperature prepared by reactive rf sputtering are presented. Nominal film composition is the solid solution compound system expressed by (1−x)BiFeO3-x ABO3, x=0–1 where ABO3 denotes ferro- (antiferro-) electric perovskites, such as BaTiO3, PbTiO3, and PbZrO3. Spontaneous magnetization 4πMs for as-deposited films is small behaving paramagnetically and does not show the compositional dependence. After annealing at temperatures of 600–700 °C in either air or PbO atmosphere, considerably large 4πMs exceeding 1 kG appears at the solid solution composition. All samples with large 4πMs are x-ray amorphous and a rapid decrease in 4πMs takes place after annealing at higher temperatures ((approximately-greater-than)800 °C), where still unidentified crystallites are precipitated. Mössbauer absorption spectra were done to understand the origin of ferromagnetism. Besides pronounced magnetic (and/or dielectric) properties, these films have a high transmittance from visible through near-infrared regions, so that they are expected to be useful as optoelectronic device materials.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.342338
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  • 10
    Electronic Resource
    Electronic Resource
    Fabrication of transparent iron-oxide films by means of sol-gel synthesis (abstract) (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 5452-5452 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Transparent iron-oxide films were fabricated by sol-gel synthesis using a solution of ferric nitrate (III) dissolved in ethylene glycol.1 The solution was kept at 80 °C and stirred constantly in a nitrogen atmosphere. The gel with an appropriate viscosity was spin coated on soft glass plates, then dried and heated in air at various temperatures for 5 h. The films thus prepared are about 0.2 μm thick, amber colored, and especially transparent in the near-infrared region, whose transmittance exceeds 90%. Maximum saturation magnetization 4πMs=0.74 kG [curve (a)] was obtained by annealing at 450 °C, which is still insufficient to use practical application. Reduction heat treatment in a hydrogen atmosphere is found to be very effective to improve magnetic properties: 4πMs is increased to 3 kG [curve (b)], which is about four times as large as the previous one, but the films become semitransparent due to formation of magnetite particles. Original high transmittance recovers by successive annealing in air at 400 °C without any degradation of magnetic properties [curve (c)], where diffraction peaks of maghemite were observed. This strongly suggests that magnetic anisotropy may be arbitrarily controlled by forming linear chains of ferromagnetic particle clusters through reduction heat treatment in a magnetic field. Faraday rotation θF of the samples was also measured. These films are promising as a new type magneto-optic material.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.342345
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