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Author: Büchner, Bernd × Type: Article ×

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    Optical Anisotropy and Momentum-Dependent Excitons in Dibenzopentacene Single Crystals
    (Washington, DC : ACS Publications, 2022) Graf, Lukas; Liu, Fupin; Naumann, Marco; Roth, Friedrich; Debnath, Bipasha; Büchner, Bernd; Krupskaya, Yulia; Popov, Alexey A.; Knupfer, Martin
    High-quality single crystals of the organic semiconductor (1,2;8,9)-dibenzopentacene were grown via physical vapor transport. The crystal structure─unknown before─was determined by single-crystal X-ray diffraction; polarization-dependent optical absorption measurements display a large anisotropy in the ac plane of the crystals. The overall Davydov splitting is ∼110 meV, which is slightly lower than that in the close relative pentacene (120 meV). Momentum-dependent electron energy-loss spectroscopy measurements show a clear exciton dispersion of the Davydov components. An analysis of the dispersion using a simple 1D model indicates smaller electron- and hole-transfer integrals in dibenzopentacene as compared to pentacene. The spectral weight distribution of the excitation spectra is strongly momentum-dependent and demonstrates a strong momentum-dependent admixture of Frenkel excitons, charge-transfer excitons, and vibrational modes.
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    Growth of LiCoO2 Single Crystals by the TSFZ Method
    (Washington, DC : ACS Publ., 2018) Nakamura, Shigenobu; Maljuk, Andrey; Maruyama, Yuki; Nagao, Masanori; Watauchi, Satoshi; Hayashi, Takeshi; Anzai, Yutaka; Furukawa, Yasunori; Ling, Chris D.; Deng, Guochu; Avdeev, Maxim; Büchner, Bernd; Tanaka, Isao
    We have grown LiCoO2 single crystals by the traveling solvent floating zone (TSFZ) growth with Li-rich solvent, having observed the incongruent melting behavior of LiCoO2 between 1100 and 1300 °C. The optimum growth conditions in terms of atmosphere and solvent composition were determined to be Ar flow and an atomic ratio Li/Co 85:15, respectively. The crystals grown using a conventional-mirror-type furnace contained periodic inclusions of a Co-O phase due to the influence of Co-O phase segregation on the stability of the molten zone during growth. By using a tilted-mirror FZ furnace, inclusion-free LiCoO2 crystals of about 5 mm in diameter and 70 mm long were obtained at a tilting angle Î = 10°. The grown crystals were confirmed to be single-domain by neutron Laue diffraction. © 2018 American Chemical Society.