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  • 1
    Digitale Medien
    Digitale Medien
    Strahlenwirkungen (1938)
    Springer
    Journal of cancer research and clinical oncology 47 (1938), S. 86-96 
    Details
    ISSN: 1432-1335
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01636029
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  • 2
    Digitale Medien
    Digitale Medien
    Laser generation and detection of surface acoustic waves: Elastic properties of surface layers (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 227-238 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A noncontact all-optical method for surface photoacoustics is described. The surface acoustic waves (SAWs) were excited employing a KrF laser and detected with a Michelson interferometer using a 633-nm HeNe laser. Due to an active stabilization scheme developed for the interferometer a surface displacement of 0.2 A(ring) could be detected. The materials investigated included pure materials such as polycrystalline aluminum, and crystalline silicon; films of gold, silver, aluminum, iron, and nickel on fused silica; and a-Si:H on Si(100). In the case of pure materials the shape of the acoustic pulse and the phase velocity were determined. The dispersion of the SAW phase velocity observed for the film systems was used to extract information on the film thickness, density, and transverse and longitudinal sound velocity. Models for the theoretical treatment of film systems and the calculation of dispersion curves are presented.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.350747
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  • 3
    Digitale Medien
    Digitale Medien
    High precision study of chemical relaxation in the system N2O4=2NO2 by photoacoustic resonance spectroscopy (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 8693-8702 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The chemical relaxation of the N2O4 dissociation was studied using Ar+ laser excited acoustic resonances of a cylindrical cavity. The resonance profiles of the first radial mode were measured as a function of pressure and temperature by a computer controlled setup. The N2O4 dissociation rate constant and the mean rotational and vibrational relaxation time of the N2O4–NO2 mixture were obtained for temperatures between 273 and 317 K by fitting a detailed theoretical model of the resonator to the measured values for frequency dispersion, resonance broadening, and strength of the photoacoustic signal. Excellent agreement between theory and experiment was obtained for the frequency dispersion and the photoacoustic signal. An empirical correction function had to be introduced to account for discrepancies between the theoretically predicted and measured values of the resonance broadening which was in the percent region. A value of 6.1×10−15 cm3/molecule s was determined for the rate constant of N2O4 dissociation in the low pressure limit at 298 K. The activation energy of the N2O4 dissociation for 20 mbar pressure was determined to be EA=36 kJ/mol. A comparison of the measured low-pressure limit of the unimolecular rate constant with theoretical predictions of RRKM theory yielded values for the mean collision efficiency of N2O4 and NO2 between 0.95 and 0.5 in the temperature range 273–317 K.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.459256
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  • 4
    Digitale Medien
    Digitale Medien
    Time-of-flight investigation of infrared laser-induced multilayer desorption of benzene (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 8330-8340 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Infrared (IR) laser-induced resonant desorption/ablation of benzene layers condensed on liquid-nitrogen-cooled substrates has been investigated using the time-of-flight (TOF) technique. Adsorbates of up to 5 μm thickness were irradiated with a line-tuned TEA CO2 laser. Time-resolved detection of desorbed particles was performed with a quadrupole mass spectrometer (QMS). Measured TOF spectra can usually be well fitted with a stream-modified Maxwell–Boltzmann distribution. Systematic deviations from these fits were observed depending on film thickness, laser fluence, and angle of detection. Spectroscopic data of the adsorbate–substrate system needed for model calculations were measured in situ. The absorption coefficients were found to be fluence dependent. Measurements of the desorption yield and kinetic energy of the desorbed particles were performed with the P932 and P934-CO2 laser lines as a function of film thickness and laser fluence. The solid–liquid phase transition could clearly be observed in these experiments. Average kinetic energies of up to 0.8 eV were measured in the TOF spectra, where the adsorbate temperature could be estimated to be less than 600 K. IR multilayer laser-induced desorption (LID) exhibits features very similar to those reported for UV multilayer LID. A mechanism based on the sudden rise of the adsorbate vapor pressure due to fast energy deposition by the laser pulse is discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.465606
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  • 5
    Digitale Medien
    Digitale Medien
    Collectivity and geometry. VI. Spectra and shapes in the three-dimensional case (1989)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 30 (1989), S. 970-980 
    Details
    ISSN: 1089-7658
    Quelle: AIP Digital Archive
    Thema: Mathematik , Physik
    Notizen: In this paper the reports on collectivity and geometry are concluded, where the microscopic description of many-body collective motions and their relation with the symplectic geometry of the n-particle system are reexamined. In the present paper it is shown that, modulo linear canonical transformations, the symplectic algebra sp(6,R) admits only three maximal subalgebras sp(2,R)⊕o(3), u(3), and cm(3), which contain the rotation algebra o(3). The objective is to discuss the spectra and shapes of "pure'' many-body systems for which the Hamiltonian is associated with a Casimir operator up to the second degree in the generators of a given maximal subalgebra, as well as those of "transitional'' systems, where the Hamiltonian is a function of the generators and Casimir operators of several of the maximal subalgebras.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.528342
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  • 6
    Digitale Medien
    Digitale Medien
    Excitation of elastic surface pulses by fiber optics and near-field optical devices (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 5090-5096 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Elastic surface pulses or surface acoustic wave (SAW) pulses were launched at the surface by confining pulsed laser radiation with single-mode fibers and tapered fiber tips, produced by the focused ion beam technique, in near-field configuration. The propagation of the elastic surface pulses was studied in a point-source point-probe experiment. The transient surface displacements of the propagating SAW pulses were detected by an actively stabilized Michelson interferometer with sub-angstrom resolution. For tip aperture sizes in the micrometer range confinement effects could be observed, extending the frequency spectrum of the launched SAW pulses to approximately 800 MHz. The actual frequency spectrum was limited by the applied detection method. An inverse square root dependence of the SAW amplitude with propagation distance was confirmed experimentally, as expected for the excitation geometry employed. Results are presented for layered systems with dispersion of the ultrasonic surface pulses. The relevance of the frequency spectrum of the SAW pulse for the determination of elastic and mechanical film properties in dispersive media is discussed. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1412583
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  • 7
    Digitale Medien
    Digitale Medien
    Investigation of phase transition thresholds by nonlinear transient laser gratings on silicon surfaces (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 3505-3510 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Nonlinear transient laser gratings were excited by crossing two 180 ps Nd:YAG laser pulses (355 nm) at the silicon surface. The launched counterpropagating surface acoustic wave trains were detected outside the source with a cw laser probe-beam-deflection setup. Phase transitions occurring within the Gaussian fluence distribution of the grating induced characteristic changes in the amplitude of the corresponding grating oscillations involved and higher harmonics were found in the frequency spectrum. In the molten surface region, the amplitude decreased compared to the thermoelastic excitation, and second-harmonic generation was observed, whereas ablation generated an asymmetric profile with higher amplitudes and even the third harmonic could be detected. An accurate method is introduced to determine the ablation threshold (340 mJ/cm2 for silicon) from the transition of linear to nonlinear behavior in the distorted non-Gaussian amplitude distribution. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.372373
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  • 8
    Digitale Medien
    Digitale Medien
    Density of glow discharge amorphous silicon films determined by spectroscopic ellipsometry (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4894-4896 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The dielectric function of thin-film hydrogenated amorphous silicon (a-Si:H) grown on fused silica at different substrate temperatures has been investigated by spectroscopic ellipsometry. An improved interpretation of the ellipsometric data is based on a tetrahedron model that takes into account the influence of hydrogen incorporation in the amorphous network. It is shown that the film density can be derived from an accurate data interpretation, whereas the maximum value of the imaginary part of the dielectric function ε2max and the void volume fraction are not proportional to the density of a-Si:H films.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.357267
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  • 9
    Digitale Medien
    Digitale Medien
    Excitation of higher harmonics in transient laser gratings by an ablative mechanism (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 1640-1642 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Laser-induced transient gratings were excited at the surface of an aluminum film by picosecond laser pulses. The counterpropagating surface acoustic waves with a fundamental frequency of 70 MHz that were launched were monitored outside the source region by laser probe beam deflection. The second and third harmonics were observed for ablative interaction of the laser radiation with the aluminum surface. A simple model is presented that describes the effects on the basis of nonlinear photoacoustic signal generation at the source due to a nonsinusoidal driving force. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.122231
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  • 10
    Digitale Medien
    Digitale Medien
    In situ Fourier transform infrared spectroscopy and stochastic modeling of surface chemistry of amorphous silicon growth (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 6096-6105 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We present a combined experimental and theoretical study of the formation of silicon hydride surface species during the F2 laser (157 nm) chemical vapor deposition of amorphous hydrogenated silicon (a-Si:H). A one-dimensional stochastic model has been applied to simulate the growing surface. The predictions of the model were compared to the results of Fourier transform infrared transmission spectroscopy providing submonolayer resolution. We present a qualitative analysis of the bonding configuration in the initial stage of film growth on H-terminated Si(111). The high sensitivity and resolution of the spectroscopic method allowed us to distinguish between four surface species by a deconvolution of the observed feature around 2100 cm−1 during the deposition process. The theoretical results for the evolution of the different surface species and bulk hydrogen are in close agreement with these spectra. Consistence between mass spectrometric data and simulation was also achieved for the growth rate and bulk hydrogen content as a function of disilane partial pressure and laser intensity. The good agreement between experiment and simulation obtained in this work indicates that it is possible to describe the main features of the complex chemical system of the growing film with a model based on a few dominant surface reactions. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.367503
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