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  • 1
    Electronic Resource
    Electronic Resource
    Semiconducting iron disilicide films on Si(111): A high resolution electron energy loss spectroscopy study (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 5905-5911 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thin films of β-FeSi2 on Si(111) have been studied by low energy electron diffraction (LEED) and high resolution electron energy loss spectroscopy (HREELS). The observed LEED pattern is consistent with two possible epitaxial orientations. HREELS measurements demonstrate the semiconducting character of the films. The energy gap is determined to Eg(approximately-equal-to)0.92 eV–0.33 meV/K T(K). Additionally a number of optical phonons is found in the range between 200 and 500 cm−1. Theoretical spectra are calculated with optical phonon parameters obtained from infrared data and are compared with the measured spectra.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351898
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  • 2
    Electronic Resource
    Electronic Resource
    Laves-phase pseudobinaries A(Fe1−xBx)2 (A=Zr, Hf; B=Al, Si): Some structural and magnetic properties : The 5th Joint MMM−Intermag Conference (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 6553-6555 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The lattice parameters and the saturation magnetization are measured for the series of intermetallic compounds A(Fe,B)2, A=Zr, Hf and B=Si and Al, with concentrations less than 15%. The magnetization measurements and the lattice parameter behavior are qualitatively discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349907
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  • 3
    Electronic Resource
    Electronic Resource
    Barkhausen noise in the re-entrant system Ni1−xMnx: A study of the power spectra : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 5497-5499 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this article, the power spectra of the Barkhausen noise of Ni1−xMnx is presented. The measurements were made in the ferromagnetic phase at several temperatures and manganese concentrations in order to map the effects of the degree of disorder and of the temperature on domain wall dynamics. Measurements in standard ferromagnetic materials were also made to compare the dynamics in both cases.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353678
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  • 4
    Electronic Resource
    Electronic Resource
    An electron–nuclear double resonance study of the lowest triplet state of pyrimidine (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 99-109 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Optically-detected electron–nuclear double resonance was employed to measure the entire hyperfine and quadrupole tensors of the two nitrogen nuclei and the hyperfine tensors of the four hydrogen nuclei in the lowest triplet state T0 of pyrimidine-h4 as a guest in a single crystal of benzene-d6. The electron-spin-density distribution and the molecular geometry in the lowest triplet state have been determined as well as the orientation of the molecule in the benzene crystal. It is found that upon excitation into T0, pyrimidine remains a planar molecule of approximately C2v symmetry; the C–N–C angles, which are 115.5° in the ground state, and the angle between the directions of the nonbonding nitrogen orbitals both become 〉120°. Nearly 60% of the total electron-spin density is located at the two nitrogen atoms, the two nonbonding orbitals each carrying a spin density of 0.21, and the π orbitals a spin density of 0.08. We conclude that the lowest triplet state of pyrimidine is appropriately described in terms of an nπ* excitation; we find no evidence for vibronic coupling of this state with higher lying 3ππ* states.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463529
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  • 5
    Electronic Resource
    Electronic Resource
    An electron spin-echo envelope modulation study of the lowest triplet state of pyridine-d5: Spin-density distribution and structure (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 6549-6565 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Recently we have shown that the lowest triplet state (T0) of pyridine, incorporated in a single crystal of benzene, may be studied by electron spin-echo (ESE) spectroscopy. From the nitrogen hyperfine structure in the ESE detected electron paramagnetic resonance (EPR) spectra, we were able to conclude that pyridine, a planar molecule in the ground state, becomes nonplanar upon excitation into T0. Here we report the results of a detailed investigation of this distortion and of the electronic nature of the lowest triplet state of pyridine-d5. We have performed electron spin–echo envelope modulation (ESEEM) spectroscopy. From the modulation spectra, the electron-nuclear double resonance (ENDOR) frequencies corresponding to the various deuterium nuclei are obtained. Analysis of the dependence of these frequencies on the orientation of the magnetic field with respect to the triplet fine-structure axes system allows for a determination of the deuterium hyperfine and quadrupole tensors. From these tensors and the known nitrogen hyperfine tensor, the structure and spin-density distribution of pyridine in its lowest triplet state are deduced. Pyridine adopts upon excitation into T0 a boatlike structure, in which the nitrogen atom is tilted by about 40° with respect to the plane through the ortho- and meta-carbon atoms and the para-carbon/para-deuterium fragment by about 10° with respect to this plane. Thereby the hybridization of the ortho-carbon atomic orbitals strongly deviates from that for aromatic hydrocarbons and becomes almost sp3; the hybridization of the atomic orbitals on the other carbon atoms changes much less, while the nitrogen atomic orbitals remain sp2 hybridized. Approximately half of the spin density is found to be localized on the nitrogen atom with a remarkable distribution over the atomic orbitals: the π orbital carries 40%, the n orbital 10%. The rest of the spin density is distributed over the para- (30%) and ortho-carbon atoms (10% each). The lowest triplet state of pyridine is neither an nπ* state nor a ππ* state, but a state of mixed character as the result of a strong vibronic coupling between the 3B1 (nπ*) and 3A1 (ππ*) states.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457374
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  • 6
    Electronic Resource
    Electronic Resource
    An electron–nuclear double resonance study of the lowest triplet state of pyrazine (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 110-117 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The hyperfine and quadrupole tensors of the two nitrogen atoms and the hyperfine tensors of the four hydrogen atoms of pyrazine in the lowest triplet state T0 are obtained from optically-detected electron–nuclear double resonance (ENDOR) experiments on pyrazine-h4 in a single crystal of benzene-d6 at 1.2 K. Analysis of these tensors shows that pyrazine is in good approximation a planar molecule of D2h symmetry in the lowest triplet state. The in-plane structure changes significantly upon excitation into T0. An increase of the C–N–C angles is observed and a reduction of the C–N bond lengths. From the hyperfine tensors the distribution of the electron-spin density is derived. The nitrogen nonbonding orbitals together carry 36% of the total spin density and it is shown that the lowest triplet state of pyrazine is appropriately described in terms of a 3nπ* excitation. The results of the optically-detected ENDOR experiments give no indication of vibronic coupling of the lowest 3nπ* state with nearby 3ππ* states.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463609
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  • 7
    Electronic Resource
    Electronic Resource
    Absorption cross sections, saturated vapor pressures, sublimation energies, and evaporation energies of some organic laser dye vapors (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 1403-1409 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A new technique of transmission measurement of overheated dye vapors is applied to determine absolute absorption cross-section spectra of three active dyes for vapor phase dye lasers. The investigated compounds are 1,4-di[2-(5-phenyloxazolyl)]-benzene (POPOP), 1,4-di[2-(4-methyl-5-phenyl-oxazolyl)]-benzene (dimethyl-POPOP), and 2,5-diphenylfuran (PPF). The vapor absorption spectra are compared with liquid solution spectra in order to obtain information on the dye–solvent interaction. The saturated vapor densities are determined by transmission measurements after knowing the absolute absorption cross-section spectra. The latent heats of sublimation, evaporation, and melting are derived by analyzing the dependences of the saturated vapor densities on the vapor temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457152
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  • 8
    Electronic Resource
    Electronic Resource
    Magnetic and optical properties of triplet excitons and traps in 1,4-dibromobenzene (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 1521-1527 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An optical and magnetic resonance study on neat 1,4-dibromobenzene crystals shows that the molecules in their lowest triplet state are distorted into a chair-like shape and confirms previous conclusions about the one-dimensional character of the triplet excitons. From a study of the phosphorescence spectrum at various temperatures it is found that the band width of the triplet excitons is (−1.0±0.15) cm−1 and that the k=0 state is at the bottom of the band.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457112
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  • 9
    Electronic Resource
    Electronic Resource
    Vibron band structure in chlorinated benzene crystals: Lattice dynamics calculations and Raman spectra of 1,2,4,5-tetrachlorobenzene (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 4023-4034 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: From a combined theoretical and experimental study of 1,2,4,5-tetrachlorobenzene (TCB) we conclude that this crystal shows many interesting effects. In agreement with earlier optical measurements, which probe the complete vibron band structure of TCB, we calculate that several of the vibron modes have the dispersion of a one-dimensional crystal with stacks of molecules along the a axis. The inclusion of fractional atomic charges in the atom–atom potential used in the calculations is absolutely necessary to obtain the correct vibron bandwidths. Also the sign of the vibrational coupling matrix elements, which is given correctly by the calculations, is determined by these charges. For other properties, such as the crystal stability, the phonon frequencies, the site splitting in the vibron bands, and also the dispersion of the lower frequency vibrations, the interactions between the "one-dimensional'' stacks are essential, however. The calculations predict further, in qualitative agreement with the Raman spectra, that the splitting between the pairs of inequivalent vibron bands in α-TCB (the site splitting) is significantly larger than the factor group splitting in β-TCB. Finally we have found that, for those vibrations where the conditions are shown by the calculations to be favorable, the 35Cl/37Cl isotope effects are clearly visible in the Raman spectra.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454835
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  • 10
    Electronic Resource
    Electronic Resource
    Microwave-mixing scanning capacitance microscopy of pn junctions (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 7094-7099 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We describe an approach to scanning capacitance microscopy. A mixing technique is employed for imaging local capacitance variations simultaneously with the sample topography using an atomic force microscope (AFM) with a conductive tip. A SiO2/Si sample with lateral pn junctions formed by ion implantation has been investigated. Microwave signals incident on the metal–oxide–semiconductor (MOS) structure formed by the AFM tip and the sample give rise to mixing signals due to the nonlinear voltage dependence of the space charge capacitance in the Si. In our experiments two microwave input signals with frequencies f1 and f2 and a variable dc bias voltage were applied to the tip-sample MOS structure. The dependence of the generated sum frequency and third harmonic signals on the dc sample voltage shows that the f1+f2 and 3 f signals are proportional to dC/dV and d2C/dV2, respectively. Images of the sum frequency and third harmonic signals delineating the pn junctions on our model sample are presented and the dc bias voltage dependence of the images is discussed. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371797
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