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  • 1
    Electronic Resource
    Electronic Resource
    Thermal recovery and spectral diffusion of photochemical holes in polymorphic systems (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 9262-9270 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present comparative investigations of doped benzophenone in its glass and crystal phases by using thermal cycling hole burning techniques. Chlorin and s-tetrazine were used as probe molecules. We measured the distribution of reactive barriers and the spectral diffusion behavior in both phases. The distribution in the glass is broad and is well described by a Gaussian. In the crystal, there are rather well-defined barriers, yet they are different for different sites. The respective kinetics is exponential and its temperature dependence is Arrhenius-like in contrast to the glass phase. Thermally induced spectral diffusion broadening in the glass phase is strong and shows the pattern well known from other organic glasses. In the crystal, it is much weaker, yet it is not completely absent. The experiments seem to indicate a threshold temperature ∼40 K. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468018
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  • 2
    Electronic Resource
    Electronic Resource
    Proton implantation into GaAs: Transmission electron microscopy results (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 2206-2210 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Semi-insulating liquid-encapsulated Czochralski grown GaAs wafers were implanted at room temperature with protons at energies of 2, 4, and 30 keV at doses up to 1×1018 cm−2. Without using further annealing treatments the samples were inspected, also using cross-sectional techniques, by transmission electron microscopy. Surface amorphization of the bombarded GaAs was found. Excess hydrogen precipitates in the form of large bubbles in the amorphous layer. Nearly spherical hydrogen bubbles were detected in the crystalline layer below the amorphous zone. At 30 keV, pressurized bubble rafts, where a certain number of bubbles are located in the plane of a microcrack, were detected. The recent observations of similar bubble rafts by Neethling and Snyman [J. Mater. Sci. 23, 2697 (1988)] and the present rafts are discussed in the light of the theoretical treatment by d'Olieslaeger et al. [Philos. Mag. B 63, 1321 (1991)]. The bubble rafts have presumably been produced by the collapse of pressurized hydrogen-filled microcracks.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351118
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  • 3
    Electronic Resource
    Electronic Resource
    Hot implantation of protons into GaAs: Transmission electron microscopy (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 4371-4374 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Implantation of hydrogen at 600 °C into GaAs at 8 keV and at high doses resulted in the formation of a two-layer structure. The topmost layer roughly extended in depth to the range of the protons and exhibited a high concentration of loops, hydrogen bubbles, decorated dislocations, and faults. Occasional microsplits on {110} were observed. The deeper layer contained pressurized hydrogen platelets on {111}. These results are critically compared with previous results obtained with cold implanted and subsequently annealed GaAs. The present observations are also discussed in relation to the theoretical treatment by d'Olieslaeger [J. Mater. Sci. 23, 2697 (1988)]. Estimates of the importance of arsine production are also presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.354404
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  • 4
    Electronic Resource
    Electronic Resource
    Structural disorder and spin-lattice relaxation (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 605-609 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We measured the spin-lattice relaxation of the photoexcited triplet state of quinoxaline in variety of organic glasses and polymers as a function of temperature. The experiment covered the temperature range from a few K close to the glass transition. The remarkable thing is that the temperature dependence of the spin-lattice relaxation seems to be uniform for the various glassy and polymeric materials within the whole temperature range and seems to follow a quadratic temperature dependence. The only exception in polyethylene. There, the temperature dependence is much steeper but levels off above 40 K.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465732
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  • 5
    Electronic Resource
    Electronic Resource
    A comparative pressure tuning hole burning study of protoporphyrin IX in myoglobin and in a glassy host (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 2478-2486 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We measured the behavior of spectral holes under isotropic pressure changes as a function of burn frequency. We compared a protein sample, namely protoporphyrin IX substituted myoglobin in a glycerol/water glass with a sample where the protoporphyrin IX was directly dissolved in a host glass. The differences are remarkable—holes in the pure glass behave as expected for a homogeneous isotropic material. It is the nonlinear frequency dependence of the pressure shift where the deviation of the protein sample is most obvious. These observations signal a correlation between the structures of the dye probe and the structures of the apoprotein. They further show that global parameters of the apoprotein, such as the isothermal compressibility, depend strongly on the associated conformational substates and are subject to unexpected large variations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465210
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  • 6
    Electronic Resource
    Electronic Resource
    Spin-conversion relaxation in dimethyl-s-tetrazine doped n-octane: Deuteration and symmetry breaking (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 1-6 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Spectral hole burning is used to measure spin-conversion relaxation of methyl groups attached to a dye probe. The dye is dimethyl-s-tetrazine, the host is n-octane, which is, at low temperatures, a Shpol'skii-matrix. The temperature dependence of the spin-conversion relaxation follows the same pattern for the protonated and the perdeuterated methyl-rotor. However, the relaxation rates of the perdeuterated rotor are higher by almost two orders of magnitude. Partial deuteration destroys the rotor symmetry and leads to a breakdown of the correlation between nuclear spin and rotational wave function.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465798
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  • 7
    Electronic Resource
    Electronic Resource
    Spectral diffusion and thermal recovery of spectral holes burnt into a phthalocyanine doped Shpol'skii system (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 8586-8590 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We measured thermally irreversible line broadening features of photochemical holes burnt into a phthalocyanine doped Shpol'skii crystal. The broadening, as obtained from temperature cycling hole burning experiments is significant, indicating that irreversible structural changes do occur in Shpol'skii matrices. Different sites show a different behavior. As far as line broadening is concerned, the observed features are similar to glasses. The thermal recovery curve of the holes, however, differs very much from glasses. It can be fitted by a bimodal Gaussian distribution. This bimodal distribution is interpreted in terms of two categories of photoproduct states, which the phthalocyanine molecule can possibly occupy: In category one, the two inner protons are neighbors in category two, they are diagonal.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459245
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  • 8
    Electronic Resource
    Electronic Resource
    Proteins and glasses: A comparative study of spectral diffusion phenomena (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 3134-3136 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We compare the spectral diffusion broadening of mesoporphyrin substituted horseradish peroxidase with the chromophore doped host glass. Whereas the broadening in the glass is smooth and follows a power law with an exponent close to (3)/(2) , there is a a steplike broadening in the protein which occurs around 14 K. The observed phenomena are interpreted on the basis of a two domain interaction of the chromophore with its environment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461780
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  • 9
    Electronic Resource
    Electronic Resource
    Color effects in pressure-tuned hole-burned spectra (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 7619-7624 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We applied hydrostatic pressure to spectral holes burned into a resorufin doped ethanol/methanol glass. We found that the line shift is perfectly linear with pressure and showed a pronounced dependence on the burn frequency as predicted by theory [J. Chem. Phys. 90, 3274 (1989)]. We exploited the burn frequency dependence to determine the solvent shift of the dye probe and the compressibility of the alcohol glass used. On the other hand, the behavior of the hole width under pressure shows features not predicted by theory: The broadening is, like the line shift, dependent on the burn frequency within the inhomogeneous band, yet in a nonlinear fashion. We attribute the color effect in the pressure induced broadening of the hole to a breakdown of the Gaussian approximation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460148
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  • 10
    Electronic Resource
    Electronic Resource
    Photochemical holes under pressure: Compressibility and volume fluctuations of a protein (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 8600-8603 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: From the pressure induced frequency shift of photochemical holes burnt into mesomorphyrin substituted horseradish peroxidase, we determined the compressibility of the protein and the vacuum frequency of the chromophore. From the compressibility, an estimation of the volume fluctuations of the biomolecule is possible.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460042
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