139 research outputs found
Structure and photoluminescence of helium-intercalated fullerite C₆₀
Intercalation of C₆₀ single crystals with helium was studied by powder x-ray diffractometry. It was established that the intercalation is a two-stage process, octahedral cavities are filled first and then tetrahedral ones, the chemical pressure being negative during both stages. For the first time low-temperature (5 K) photoluminescence spectra of helium-intercalated fullerite C₆₀ were studied. The presence of helium in lattice voids was shown to reduce that part of the luminescent intensity which is due to the emission of covalently bound pairs of C₆₀ molecules, the socalled "deep traps" with the 0-0 transition energy close to 1.69 eV. The mechanism of the effect of the intercalation with helium on the pair formation in fullerite C₆₀ is discussed
On spectral minimal partitions: the case of the sphere
We consider spectral minimal partitions. Continuing work of the the present
authors about problems for planar domains, [23], we focus on the sphere and
obtain a sharp result for 3-partitions which is related to questions from
harmonic analysis, in particular to a conjecture of Bishop
Thermodynamic Treatment of Undercooled Cu-Mg Liquid and the Limits for Partitionless Crystallization
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