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  • American Institute of Physics (AIP)  (7)
  • 1
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The systematic variation of anomalous Pr antiferromagnetic ordering temperature TN(Pr) for the two-CuO2-layer cuprate system MA2PrCu2Oy (M=Cu, Hg, Tl, Pb; A=Ba, Sr) was verified through the observation of a new Hg-1212 HgSr2PrCu2O6+δ tetragonal compound with a TN(Pr) of 6 K and a Pr—O bond length of 2.492 A(ring) between Pr and oxygen in the adjacent CuO2 layers. For the tetragonal/orthorhombic 1212 compounds including the PrBa2Cu3O7−y system, TN(Pr) was found to decrease monotonically with increasing Pr—O distance. The importance of Pr-O-Pr superexchange magnetic coupling is expected for all two-CuO2-layer MmA2PrCu2Oy m212-type (m=1, 2, 3) compounds. A similar Pr anomaly in the 2212-type system was first observed on the new tetragonal (Pb0.5Cu0.5)2(Ba0.5Sr0.5)2PrCu2O8 compound with a high TN(Pr) of 9 K. © 1996 American Institute of Physics.
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 6403-6407 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We observed a violation of the normal Raman selection rule in the resonant Raman spectra of interface (IF) phonon modes of the ultrathin (GaAs)4/(AlAs)2 superlattice. Contrary to the prediction of conventional theories, all four IF modes were observed in both (XX) and (XY) geometries. The result can be interpreted as a consequence of the deep penetration of the electron wave function in the GaAs wells into the AlAs barriers and a lack of definite parity of the electron wave function. Furthermore, our result indicates that conventional theory for bulk (thicker) systems may need to be modified and further developed to be applicable to ultrathin systems. © 2000 American Institute of Physics.
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 4489-4493 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Optical properties of ZnO quantum dots (QDs) capped with polyvinyl pyrrolidone (PVP) molecules have been investigated. It is demonstrated that surface modification by PVP can dramatically change the emission spectra of the ZnO QDs. At the optimized condition with a PVP/Zn2+ ratio of 3:5, the photoluminescence (PL) spectrum of ZnO QDs shows a strong ultraviolet (UV) emission while the low energy green emission is fully quenched. This is a result of the surface passivation of the ZnO QDs by the PVP molecules. The origin of the green emission is attributed to the surface states associated with oxygen vacancies. Temperature and excitation power dependent PL studies suggest that the UV emission is associated with localized states. © 2001 American Institute of Physics.
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  • 4
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Until now, the origin of hard magnetic properties of rapidly quenched Nd-Fe-B alloys with lower Nd concentration is not clear. In this paper, the phase compositions of rapidly quenched Nd4Fe77.5B18.5 alloys annealed under different conditions have been studied by using zero-field spin-echo nuclear magnetic resonance (NMR) and Mössbauer effect (ME) techniques. It is found that there exists a certain amount of Nd2Fe14B phase in the samples annealed at 960 °C and ingot alloy, which have poor hard magnetic properties; while, the sample annealed under optimal condition consists only of bct-Fe3B as the main phase and a small amount of a-Fe. However, the ME result indicates that about 5 at. % Fe atoms in FeIII (8 g) site of bct-Fe3B have been replaced by Nd atoms; the NMR result demonstrates that 11B NMR spectrum is the characteristic peak of bct-Fe3B, but it broadens asymmetrically to the high frequency side, which is due to the bct-Fe3B influenced by Nd atoms. The amplitude of radio frequency (rf) excitation field required to get the maximum 11B spin-echo signal from bct-Fe3B in the sample annealed at 839 °C is only about one third as much as that required to excite the 11B in the bct-Fe3B influenced by Nd atoms in the sample annealed at 670 °C for a short time, which implies the latter has a larger coercivity field than the former. It is concluded that the origin of hard magnetic properties of Nd4Fe77.5B18.5 alloy is not related to the 2:14:1 phase, but to the change of bct-Fe3B itself.
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 116 (2002), S. 6656-6659 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The ab initio quadratic CI calculation method and the effective-core-potential basis set have been used to calculate the equilibrium geometries, potential energy curves, dissociation energies of the ground state, and low-lying electronic states of Lu2 for the first time. The symmetries of these states are determined by analyzing the potential energy curves and optimization calculations at the same time. The analytical potential energy functions of these states have been fitted with the Murrell–Sorbie potential energy function from the calculated values with the ab initio method. The spectroscopic parameters of each state are calculated through the relationship equations between analytical potential energy function and spectroscopic parameters, and are compared with some other theoretical and experimental data available from the experiment at present. For the ground state, we obtain the symmetry is X 3Σg, ωe=113.3 cm−1 with ωeχe=0.16 cm−1, leading to a spectroscopic dissociation energy of 1.79 eV. They are in agreement with the recent experiments. © 2002 American Institute of Physics.
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  • 6
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 78 (2001), S. 760-762 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Chemically hybridized CdS-poly(N-vinylcarbazole) (PVK) nanocomposites with different molar ratios of CdS to PVK were prepared. A variety of techniques including optical absorption, photoluminescence (PL), photocurrent spectroscopy, and time-resolved PL were employed to investigate the properties of CdS–PVK nanocomposites. A significant enhancement of photoconductivity was observed in CdS–PVK nanocomposites as compared to pure PVK and CdS/PVK nanoblends. We interpret this result as the improved interface quality between CdS and PVK in CdS–PVK nanocomposites, which facilitates fast interfacial carrier transfer and thus increases the charge generation efficiency. © 2001 American Institute of Physics.
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  • 7
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 2837-2839 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: InAs quantum dots (QDs) grown on GaAs surface are investigated. The observed abnormal photoluminescence (PL) properties, including extremely sharp high-energy peaks, almost temperature-independent linewidth, and fast thermal quenching, are discussed in terms of the strong quantum confinement effects due to the absence of a cap layer and the lack of carrier redistribution channel caused by the small number of QDs capable of contributing to PL and the high-density surface defects. © 2000 American Institute of Physics.
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