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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 5314-5316 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Modulated thermoreflectance microscopy is applied to a complete thermal characterization of a thin film of gold (78 nm) or YBaCuO (300 nm) on a LaAlO3 substrate. The phase profile, measured at several modulation frequencies covering an appropriate range, is fitted with a rigorous thermal diffusion model. This leads to a simultaneous estimation of the thermal diffusivities of the film and the substrate, as well as of the thermal film/substrate boundary resistance. The estimated values for the gold film sample are, respectively, 4.3×10−6 m2 s−1 (substrate diffusivity), 1.0×10−4 m2 s−1 (film diffusivity), and 1.0×10−8 m2 KW−1 (thermal boundary resistance), while for the thermally anisotropic YBaCuO film sample are, 4.1×10−6 m2 s−1, 3.5×10−6 m2 s−1 (in-plane diffusivity), and 8.0×10−8 m2 KW−1, respectively. © 1999 American Institute of Physics.
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 3344-3350 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A theoretical and experimental study of the influence of planar thermal barriers on photothermal reflectance microscopy signals is presented. An analytical solution is developed for the problem of vertical barriers in a semi-infinite solid and the signal contrast obtained when scanning through the barrier is discussed as a function of the thermal resistance, the thermal diffusion length, and the pump and probe beam dimensions. The shape and the width of the signal perturbation introduced by the barrier is also analyzed. For the case of slanted barriers results of finite-element calculations are presented, and the main feature of the signal when going from vertical to slanted barriers is thus shown. Finally, the theoretical predictions are compared with measurements made on Fe sintered samples. Scanning through grain interfaces revealed different signal shapes and contrast. Good agreement between theory and experiment was found when the optical contrast at the interface is negligible. Examples are shown where the thermal barrier model is no longer valid and an extended model seems to be necessary.
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  • 3
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present a quantitative and comparative study of three different photothermal techniques based on the signal produced on vertical/slanted thermal barriers under a variety of barrier/sample conditions. Models based on integral methods are developed to calculate the amplitude and phase of the sample surface temperature and mirage deflection in surrounding air. The geometries studied include: vertical, tilted, buried, and finite size barriers separating identical or different media. The models incorporate the probe and pump beam sizes, the thermal resistance of the barrier and the optothermal characteristics of the sample. Experimental measurements are performed on a variety of fabricated barriers with three modulated photothermal techniques: the thermoreflectance, infrared radiometry, and mirage detection. We discuss in a comparative way the limits, drawbacks and the applicability of each technique. Model fits to the experimental results allow characterization of the thermal barrier (spatial localization, geometry, orientation, and size) and provide an accurate determination of its thermal resistance. © 1996 American Institute of Physics.
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 3984-3993 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this paper we analyze the possibility of extending the photothermal methods developed for thermal diffusivity measurements of isotropic materials [A. Salazar and A. Sánchez-Lavega, Rev. Sci. Instrum. 65, 2896 (1994)] to the case of anisotropic specimens. A full theoretical treatment of the photothermal signal generation for the case of an anisotropic sample with its principal axes aligned with the sample surface is presented. Three photothermal detection schemes have been studied: infrared radiometry, photothermal reflectance, and optical beam deflection (mirage effect). The fundamental result we have obtained is that when using infrared radiometry, photothermal reflectance and collinear mirage setups, the thermal magnitude retrieved is the resistivity to heat diffusion (a tensor defined as the inverse of the thermal diffusivity tensor). Only the perpendicular mirage experiment allows one to directly retrieve the thermal diffusivity along any direction of the material. Experimental measurements performed on two highly anisotropic materials confirm the above-mentioned results. © 1996 American Institute of Physics.
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 1036-1042 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We consider a photothermal microscope using infrared detection for local thermal diffusivity measurements. In order to extract a reliable thermal diffusivity estimate from the recorded temperature profile, we show that diffraction arising from the Cassegrain objective of the microscope must be taken into account. Indeed, the apparent temperature profile is deformed significantly when the thermal diffusion length approaches the size of the diffraction pattern. This is especially a problem for low diffusivity samples because avoiding high-noise figures at very low modulation frequencies implies small thermal diffusion length measurements. The measurement of the impulse response of the microscope allows us to correct the recorded profile for diffraction and detector size effects. In particular, whereas the amplitude profile is smoothed only in the excitation beam area, the phase profile is globally distorted, yielding up to a 60% thermal diffusivity overestimate if neglected. Furthermore, nonlinear infrared emission contributes to enhance the impact of diffraction. Validation of our model is done with a Y2O3-doped ZrO2 sample by comparing the estimation at different modulation frequencies and also with the well-established photothermal beam deflection technique. © 1998 American Institute of Physics.
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  • 6
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 56 (1990), S. 1749-1751 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using a scanning photothermal reflectance microscope we have observed a large enhancement of the modulated reflectance signal accompanied by a phase change of π in the region of a copper-decorated grain boundary in silicon. A preliminary analysis of the data is given in terms of the thermal and plasma waves generated in the specimen. Orders of magnitude of recombination velocities of the surface and the boundary are determined in reasonable agreement with electrical measurements.
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 84 (1998), S. 38-43 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We consider the influence of sample heating on spatially resolved thermal diffusivity measurements with a photothermal microscope using infrared detection. The continuous component of temperature induced by an intensity modulated focused laser beam results in a sensitivity amplification in the laser beam area and contributes to enhance the effect of diffraction on the phase profile, yielding a thermal diffusivity overestimate if it is not considered. A model including diffraction and nonlinear infrared emission is presented. For moderate heating, the influence of sample heating on the phase shift and on the amplitude of the infrared signal as seen by the detector is calculated. By using this model for fitting successively the amplitude and the phase data, no significant change in thermal diffusivity value is found on a homogeneous Y2O3-doped ZrO2 sample when the modulation frequency is changed. Validation of our model is done by comparing experimental amplitude data with the expected profiles obtained with the experimental absorbed power and with the reference thermal conductivity estimate for cubic zirconia. © 1998 American Institute of Physics.
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2154-2160 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Computer simulations are performed in this article to show the feasibility of simultaneous determination of the film diffusivity, the substrate diffusivity, and the thermal boundary resistance of film-on-substrate systems by modulated thermoreflectance microscopy and multiparameter fitting. The dependences of the phase on the probe-to-pump beam separation, measured at four different modulation frequencies, are simultaneously fitted to an appropriate thermal diffusion model to extract the three thermal parameters. The selection of the optimal frequency combination is analyzed. Three samples: an 80 nm gold film on LaAlO3 and diamond substrates, and a 300 nm YBaCuO film on LaAlO3 substrate, are simulated. Experimental results are also presented to discuss the influence of the shape and irregularity of the beam on the fitting. The simulation results show that the statistical mean values of the three thermal parameters are very close to the input values, and the statistical errors of the film diffusivity and substrate diffusivity are comparable to the overall experimental error. However, the error of the thermal boundary resistance depends largely on the absolute thermal resistance value and the diffusivity difference between the film and the substrate. Under typical experiment conditions, the measurement errors of the two diffusivities are ∼5%, and error of the thermal boundary resistance is 10%–20%. © 2000 American Institute of Physics.
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 57 (1986), S. 1126-1128 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We describe a new design for a mirage cell which is much more compact than the previously described setup and whose sensitivity has been improved by an order of magnitude. This cell has been successfully coupled to Fourier transform infrared spectrometers, visible spectrometers, and a thermal wave imaging setup.
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  • 10
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 64 (1994), S. 4-6 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Photothermal microscopy was used for absolute temperature determination of InGaAsP/InP lasers. High modulation frequencies were employed in order to improve spatial contrast. The strong thermal mismatch between InGaAsP and InP induces a heat confinement in the active region as shown experimentally and confirmed by finite element calculations. Facet temperature was found to be 10 K/mW for a 2-μm-wide active layer, which is low compared to those reported for GaAlAs/GaAs and GaInP. Moreover, measurements along the cavity do not show differences in temperature when approaching the facets. Both results indicate a weak nonradiative recombination process at the facets, in agreement with the higher mirror reliability of this type of laser.
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