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1

Digitale Medien

Ab initio calculation of band structure, x-ray emission, quantum yield, and electron-energy-loss spectra of hexagonal boron nitride (1993)

Ma, H. ; Lin, S. H. ; Carpenter, R. W. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 73 (1993), S. 7422-7426

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: The band structure of hexagonal boron nitride (BN) has been calculated using an ab initio linear combination of pseudoatomic-orbitals method. The calculated band structure confirms a previous finding that this material is an indirect band-gap insulator and has two empty interlayer bands. Projected densities of states are compared with the experimental x-ray emission spectra of B and N K edges and the agreement is good. This good agreement between the present ground-state calculation and the experimental x-ray emission spectra supports our previous finding that there should be very little valence electron relaxation effect on x-ray emission spectra. A real-space Green's function technique and the Z+1 approximation have been used to calculate the exciton spectra of B and N K edges. The first peak at 192 eV in B K edge is found to be a bound exciton with a binding energy of 1.7±0.4 eV. Only resonance is found for the N K edge. The calculated exciton spectra agree very well with the experimental quantum-yield and electron-energy-loss spectra.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.353983

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2

Digitale Medien

Theoretical study of laser heating and dissociation reactions in solids using ultrafast time-resolved x-ray diffraction (1992)

Ma, H. ; Lin, S. H. ; Rentzepis, P.

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 72 (1992), S. 2174-2178

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: A theory of ultrafast time-resolved x-ray diffraction is presented. We show that for the case in which vibrational relaxation is fast, the x-ray diffraction intensities in pulse laser heating are determined by the Debye–Waller factor. We also show how the scattering intensities of the diffraction spots change with the position of the dissociating atoms in a time-resolved x-ray diffraction experiment studying dissociation reactions in solids. Our results show that the scattering intensities change in both the fully dissociated and the partially dissociated cases, and that time-resolved x-ray diffraction could be a useful tool in probing dissociation reactions in solids.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.351607

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3

Digitale Medien

Theoretical comparison of electron energy-loss and x-ray absorption near-edge fine structure of the Si L2,3 edge (1990)

Ma, H. ; Lin, S. H. ; Carpenter, R. W. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 68 (1990), S. 288-290

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: Various approximations in the calculations of electron energy-loss cross section and x-ray absorption coefficient have been evaluated using the Si L2,3 edge as an example. It was found that the random phase approximation, for which the cross terms are neglected in the expressions of electron energy-loss cross section and x-ray absorption coefficient, is a very good approximation. The dipole approximation in the calculation of the electron energy-loss cross section was found to begin to break down even at small acceptance half angles, such as 12.5 mrad. For energy losses larger than that of the Si L2,3 edge the dipole approximation will break down faster. This approximation also fails for a large scattering angle even at a small energy loss. The electron energy-loss cross section and x-ray absorption coefficient of the Si L2,3 edge has been calculated and compared. The large difference in relative intensity reported experimentally between the two spectra is not confirmed in this study. More experimental comparisons between electron energy loss and x-ray absorption spectra are recommended for Si and other compounds.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.347129

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4

Digitale Medien

A modified parametrization scheme for the complete neglect of differential overlap method with relativistic correction of orbital exponents and energy levels with particular applications to rare earth compounds (1992)

Wu, G. S. ; Ma, H. ; Lin, S. H.

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 96 (1992), S. 4518-4525

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ISSN: 1089-7690

Quelle: AIP Digital Archive

Thema: Physik , Chemie und Pharmazie

Notizen: A new unified parametrization scheme for the complete neglect of differential overlap method, applicable to heavy atom systems is formulated. The exponents ζμ and electronegativities X(μ) of atomic orbitals are corrected by the relativistic Dirac–Fock expectation values of atomic orbital radii and energy levels. This leads to the possibility of calibrating the β0 parameters directly by the equilibrium geometric configuration of molecules. The parametrization for hydrogen, halides, and rare earth series, as well as some test calculations for compounds of these elements, have been carried out to show the utility of the scheme. The results demonstrate that the present scheme can give satisfactory MO levels and ionization potentials as well as correct molecular geometry.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.462813

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5

Digitale Medien

Effects of exchange bond disorder on transport measurements : 38th Annual Conference on Magnetism and Magnetic Materials (1994)

Stampe, P. A. ; Ma, H. ; Kunkel, H. P. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 75 (1994), S. 6510-6512

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: Measurements of the low field resistive anisotropy (LFRA) in amorphous Fe91Zr9 with and without hydrogen loading are presented. The temperature dependence of these data is compared with model calculations of the quadrupolar term [〈〈S2Z〉T〉J−S(S+1)/3], from which it is concluded that the model calculations reproduce both the temperature and the exchange bond dependence of this transport coefficient.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.356931

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6

Digitale Medien

Measurements of nondegenerate optical nonlinearity using a two-color single beam method (1991)

Ma, H. ; Gomes, A. S. L. ; de Araujo, Cid B.

Woodbury, NY : American Institute of Physics (AIP)

Applied Physics Letters 59 (1991), S. 2666-2668

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ISSN: 1077-3118

Quelle: AIP Digital Archive

Thema: Physik

Notizen: A two-color "z'' scan method is introduced to characterize the nonlinear refraction of optical materials in their absorptive region. We demonstrate the method by measuring the sign and the magnitude of the frequency nondegenerate nonlinearity in the absorptive region of semiconductor doped glasses.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.105933

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7

Digitale Medien

Light-controlled beam deflector in semiconductor doped glasses (1993)

Ma, H. ; de Araújo, Cid B.

Woodbury, NY : American Institute of Physics (AIP)

Applied Physics Letters 63 (1993), S. 3553-3555

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ISSN: 1077-3118

Quelle: AIP Digital Archive

Thema: Physik

Notizen: We report on the operation of an all-optical beam deflector whereby the deflected signal beam can be more powerful than the driving beam. Therefore, we have transferred the modulation of the driving beam to the signal beam with power gain and angular deflection rate of 10 mrad/kW. The main component of our deflector is a sample of Cd(S,Se) doped glass and its operation is based on the cross-bending effect.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.110094

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8

Digitale Medien

The spontaneous resistive anisotropy in amorphous and hydrogenated FeZr (1990)

Ma, H. ; Wang, Z. ; Kunkel, H. P. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 67 (1990), S. 5964-5966

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: Measurements of the spontaneous resistive anisotropy(SRA)—basically the difference between the longitudinal and transverse magnetoresistance extrapolated to zero induction—in amorphous FeZr as a function of field (0–1 T) and temperature (1.5–300 K) are presented. The Fe concentrations investigated range from 89 to 92 at. % and the effects of hydrogenation have also been studied. For the hydrogen-free samples a nonzero SRA develops at the ferromagnetic ordering (Curie) temperature Tc and persists to the lowest attainable temperature, with no obvious anomaly in the vicinity of the proposed transverse-spin freezing temperature Txy. With the inclusion of hydrogen, both Tc and the magnitude of the SRA increase, and attempts are made to correlate such increases with the changes in band structure and mean iron moment.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.346029

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