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  • American Institute of Physics (AIP)  (33)
  • American Geophysical Union (AGU)
  • 2000-2004  (33)
  • 1
    Electronic Resource
    Electronic Resource
    Solvation dynamics of nile blue in ethanol confined in porous sol–gel glasses (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 5781-5791 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report on solvation dynamics measurements of the chromophore nile blue in ethanol confined to sol–gel glasses with 50 Å and 75 Å average pore size and compare them with the dynamics of the respective bulk solution. Both the amplitude of the dynamic Stokes shift as well as the dynamics of the solvation process are drastically changed upon confinement. In both confined solutions the dynamic Stokes shift is reduced by a factor of about 2. As the large majority of the chromophores is adsorbed at the inner pore surfaces the solute molecules interact with only a "half-space" of solvent molecules. In a first approximation this decreases the stabilization energy by a factor of 2. The solvation dynamics in the confined solutions show nonexponential behavior comparable to the bulk. However, the whole solvation process slows down and the single decay time constants characterizing it increase with decreasing pore size of the sol–gel glass. We have introduced two phenomenological models to rationalize this behavior. The enhanced polarization field model takes into account the confinement and predicts a strengthening of the solvent's polarization field in an extended solvation cage induced by the electrical field of the chromophore. The steric hindrance model focuses on the interaction of the liquid with the surface reducing molecular mobility resulting in longer relaxation times. Probably both effects are of relevance in the confined solutions investigated. Confinement affects the steady-state spectra as well leading to a redshift of the absorption and a blueshift of the fluorescence. Additional data on the reorientational dynamics of the chromophore are consistent with the fact that the molecules are predominantly adsorbed at the pore surfaces. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1309151
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  • 2
    Electronic Resource
    Electronic Resource
    Magnetic rotation molecular spectroscopy using an oscillating field (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 8594-8607 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The high resolution magnetic rotation spectrum of a diatomic molecule is considered. A procedure is described for calculation of the magnetic rotation signal in both first and second harmonic for an oscillating magnetic field in the low-field limit. The procedure is simpler than other methods available in the literature, and a more complete account is taken of the various possible contributions to the signal. Perturbations between electronic states that make it possible to observe magnetic rotation signals for high-J transitions are discussed, along with the associated evolution of line shape that complicates frequency measurements from magnetic rotation spectra. Examples are given from a recent magnetic rotation study of the A 3Π1u–X 1Σg+ system of 79Br2. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1318747
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  • 3
    Electronic Resource
    Electronic Resource
    Properties of atoms in molecules: Transition probabilities (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 10095-10105 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The transition probability for electric dipole transitions is a measurable property of a system and is therefore, partitionable into atomic contributions using the physics of a proper open system. The derivation of the dressed property density, whose averaging over an atomic basin yields the atomic contribution to a given oscillator strength, is achieved through the development of perturbation theory for an open system. A dressed density describes the local contribution resulting from the interaction of a single electron at some position r, as determined by the relevant observable, averaged over the motions of all of the remaining particles in the system. In the present work, the transition probability density expressed in terms of the relevant transition density, yields a local measure of the associated oscillator strength resulting from the interaction of the entire molecule with a radiation field. The definition of the atomic contributions to the oscillator strength enables one to determine the extent to which a given electronic or vibrational transition is spatially localized to a given atom or functional group. The concepts introduced in this article are applied to the Rydberg-type transitions observed in the electronic excitation of a nonbonding electron in formaldehyde and ammonia. The atomic partitioning of the molecular density distribution and of the molecular properties by surfaces of zero flux in the gradient vector field of the electron density, the boundary condition defining the physics of a proper open system, is found to apply to the density distributions of the excited, Rydberg states. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481651
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  • 4
    Electronic Resource
    Electronic Resource
    Generation of plasma rotation in a tokamak by ion-cyclotron absorption of fast Alfvén waves : The 42nd annual meeting of the division of plasma physics of the American Physical Society and the 10th international congress on plasma physics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 2181-2187 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A mechanism is proposed and evaluated for driving rotation in tokamak plasmas by minority ion-cyclotron heating, even though this heating introduces negligible angular momentum. The mechanism has two elements: First, angular momentum transport is governed by a diffusion equation with a boundary condition at the separatrix. Second, Monte Carlo calculations show that ion-cyclotron energized particles will provide a torque density source which has a zero volume integral but separated positive and negative regions. With such a source, a solution of the diffusion equation predicts that ion-cyclotron heating will cause a rotational shear layer to develop. The corresponding jump in plasma rotation ΔΩ is found to be negative outwards when the ion-cyclotron surface lies on the low-field side of the magnetic axis and positive outwards with the resonance on the high-field side. The magnitude of the jump ΔΩ=(4qmaxWJ2*) (eBR3a2ne(2π)2)−1(τM/τE) where |J2*|(approximate)2–4 is a nondimensional rotation frequency calculated by the Monte Carlo ORBIT code [R. B. White and M. S. Chance, Phys. Fluids 27, 2455 (1984)]. For a no-slip boundary condition when the resonance lies on the low-field side of the magnetic axis, the sense of predicted axial rotation is co-current and overall agreement with experiment is good. When the resonance lies on the high-field side, the predicted rotation becomes countercurrent for a no-slip boundary while the observed rotation remains co-current. The rotational shear layer position is controllable and of sufficient magnitude to affect microinstabilities. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1362535
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  • 5
    Electronic Resource
    Electronic Resource
    On plasma rotation induced by traveling fast Alfvén waves (2002)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 9 (2002), S. 511-516 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Absorption of fast Alfvén waves by the minority fundamental ion–cyclotron resonance, coupled with finite banana width physics, generates torque distributions, and ultimately rotational shear layers in the bulk plasma, even when the toroidal wave number kφ=n/R of the fast wave vanishes (n=0) and cyclotron absorption introduces no angular momentum nor canonical angular momentum [F. W. Perkins, R. B. White, P. T. Bonoli, and V. S. Chan, Phys. Plasmas 8, 2181 (2001)]. The present work extends these results to traveling waves with nonzero n where heating directly introduces angular momentum. Since tokamak fast-wave antennas have approximately one wavelength per toroidal field coil, the toroidal mode number n lies in the range n=10–30, independent of machine size. A zero-dimensional analysis shows that the rotation rate arising from direct torque is comparable to that of the rotational shear layer and has the same scaling. Nondimensional rotation profiles for n=(−10, 10) show modest changes from the n=0 case in the expected direction. For a balanced antenna spectrum, the nondimensional rotational profile (averaged over n=−10, 10) lies quite close to the n=0 profile. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1415751
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  • 6
    Electronic Resource
    Electronic Resource
    Diffusion of ion-implanted boron in germanium (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 4293-4295 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The diffusion of boron (B) in germanium (Ge) is studied. B was introduced in Ge wafers by ion implantation, and concentration profiles after furnace annealing were obtained using secondary ion mass spectroscopy. The diffusion coefficient and solid solubility of B in Ge has been calculated to be 1.5(±0.3)×10−16 cm2/s and 5.5(±1.0)×1018/cm3, respectively, at 850 °C by fitting experimentally obtained profiles. This value of diffusion coefficient is at least two orders of magnitude lower than the minimum value reported in the literature for B diffusion in Ge. The results are significant as they question the general agreement about vacancy diffusion as the mechanism responsible for diffusion of B in Ge. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1402664
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  • 7
    Electronic Resource
    Electronic Resource
    Interlayer segregation of Cu atoms in Ta/NiFe/Cu/NiFe/FeMn/Ta spin-valve multilayers and its influence on magnetic properties (2002)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 91 (2002), S. 3759-3763 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Experimental results show that the exchange coupling field (Hex) of NiFe/FeMn for Ta/NiFe/FeMn/Ta multilayers is higher than that for spin-valve multilayers Ta/NiFe/Cu/NiFe/FeMn/Ta. In order to find out the reason, the composition and chemical states at the surface of Ta(12 nm)/NiFe(7 nm), Ta(12 nm)/NiFe(7 nm)/Cu(4 nm), and Ta(12 nm)/NiFe(7 nm)/Cu(3 nm)/NiFe(5 nm) were studied using x-ray photoelectron spectroscopy. The results show that no elements from lower layers float out or segregate to the surface in the first and second samples. However, Cu atoms segregate to the surface of Ta(12 nm)/NiFe(7 nm)/Cu(3 nm)/NiFe(5 nm) multilayers, i.e., Cu atoms segregate to the NiFe/FeMn interface for Ta/NiFe/Cu/NiFe/FeMn/Ta multilayers. We believe that the presence of Cu atoms at the interface of NiFe/FeMn is one of the important factors which causes the exchange coupling field (Hex) of Ta/NiFe/Cu/NiFe/FeMn/Ta to be weaker than that of Ta/NiFe/FeMn/Ta. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1450033
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  • 8
    Electronic Resource
    Electronic Resource
    Metallic ferromagnetism in Ni-doped La0.7Sr0.3CoO3 (2002)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 91 (2002), S. 519-521 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The structure, magnetization, and electrical transport of perovskite cobaltites La0.7Sr0.3Co1−yNiyO3 have been studied. It is found that the substitution of Ni for Co induces no apparent changes in bond length and angle in the Co(Ni)–O network, and only moderately suppresses the ferromagnetism. Moreover, a retention of the metallic conduction has been observed from y=0 to 0.2, which is in strong contrast to the reported insulating state of the other Co site doped La0.7Sr0.3CoO3. A double-exchange-like interaction between Ni ion and its neighboring Co ion is suggested to explain the experimental results. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1416131
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  • 9
    Electronic Resource
    Electronic Resource
    Interface reaction of Ta/Ni81Fe19 or Ni81Fe19/Ta and its suppression (2002)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 80 (2002), S. 455-457 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ta/Ni81Fe19 and Ni81Fe19/Ta structures are commonly used in the magnetic multilayers with giant magnetoresistance. For a Ta/Ni81Fe19/Ta fundamental structure, Ta seed and Ta cap layers resulted in a loss of moment equivalent to a magnetically dead layer of thickness 1.6±0.2 nm. In order to find out the reason, the composition and chemical states at the interface regions of Ta/Ni81Fe19 and Ni81Fe19/Ta were studied using the x-ray photoelectron spectroscopy and peak decomposition technique. The results show that there are thermodynamically favorable reactions at the Ta/Ni81Fe19 and Ni81Fe19/Ta interfaces: 2Ta+Ni=NiTa2. However, the thickness of a magnetically dead layer was significantly reduced by the insertion of a small amount of Bi in the Ta/Ni81Fe19/Ta structure. This result indicates that a surfactant Bi can suppress the interface reaction in multilayers. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1433913
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  • 10
    Electronic Resource
    Electronic Resource
    Interface reaction of NiO/NiFe and its influence on magnetic properties (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 78 (2001), S. 1706-1708 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ta/NiO/NiFe/Ta multilayers were prepared by rf reactive and dc magnetron sputtering. The exchange coupling field between NiO and NiFe reached 120 Oe. The composition and chemical states at the interface region of NiO/NiFe were studied using the x-ray photoelectron spectroscopy (XPS) and peak decomposition technique. The results show that there are two thermodynamically favorable reactions at NiO/NiFe interface: NiO+Fe=Ni+FeO and 3NiO+2Fe=3Ni+Fe2O3. The thickness of the chemical reaction as estimated by angle-resolved XPS was about 1–1.5 nm. These interface reaction products are magnetic defects, and we believe that the exchange coupling field Hex and the coercivity Hc of NiO/NiFe are affected by these defects. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1343474
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