Mixture films of Co and C60 with various compositions were fabricated by co-evaporation under UHV condition. As for the saturation composition with C60-based phase, Co5C60 is deduced from the systematic Raman analysis. It is reasonably interpreted that the C60-based phase can be realized by less than one electron transfer per a Co atom into C60 and the contribution of a covalent bonding which induces a differently coordinated structure of the C60 molecules from the fcc-C60. The electrical conduction features are dependent on the Co content. In the C60-based phase up to Co5C60, the conduction mechanism seems to be described by the band concept modified with the disorder, followed by the hopping conduction through the precipitated Co clusters or particles and then, by the metallic one with increasing Co content.
We report on the establishing of an exclusive magnetic effect in air-exposed CoC nanocomposites (x > 2) created through self-assembling in the depositing mixture. In order to verify the influence of ambient air on the CoC mixture film, we have studied in detail the film magnetization at rather low temperatures, which provides their ferromagnetic behavior. Tracing the possible exchange bias effect, we distinguished a clear vertical shift of the hysteresis loops recorded for the air-exposed CoC films in the field cooling (FC) regime. The detected vertical shift of the FC loops is caused by an uncompensated magnetic moment M induced by exchange coupling of the Co spins at the Co/CoO interface. This interface arises due to the oxidation of small Co clusters distributed in a C-based matrix of self-assembled composite films, which occurs during air exposure. The core-shell structure of the Co/CoO magnetic clusters (about 2-3 nm in size) consisting of a ε-Co core and fcc-CoO shell was confirmed by means of transmission electron microscopy. Established interface magnetism testifies to a composite nanostructure in the CoC mixture film with x > 2 and explains the influence of air exposure on the film structure. The discovered magnetic effect implies a new application potential for cobalt-fullerene composites in sensors and catalysis.
Driving by interplay between plasmonic and magnetic effects in organic composite semiconductors is a challenging task with a huge potential for practical applications. Here, we present evidence of a quantum plasmon excited in the self-assembled Co C nanocomposite films with x > 15 (interval of the Co cluster coalescence) and analyse it using the optical absorption (OA) spectra. In the case of Co C film with x = 16 (LF sample), the quantum plasmon generated by the Co/CoO clusters is found as the 1.5 eV-centred OA peak. This finding is supported by the establishment of four specific C-related OA lines detected at the photon energies E > 2.5 eV. Increase of the Co content up to x = 29 (HF sample) leads to pronounced enhancement of OA intensity in the energy range of E > 2.5 eV and to plasmonic peak downshift of 0.2 eV with respect to the peak position in the LF spectrum. Four pairs of the OA peaks evaluated in the HF spectrum at E > 2.5 eV reflect splitting of the C-related lines, suggesting great change in the microscopic conditions with increasing x. Analysis of the film nanostructure and the plasmon-induced conditions allows us to propose a Rashba-like spin splitting effect that suggests valuable sources for spin polarization.
The structure of noncrystalline regions of HDPE oriented filaments prepared by two different techniques with various degrees of orientation X has been studied by density measurements, small-angle X-ray scattering and DTA. It is shown that at A > 10 the noncrystalline regions of the oriented structure prepared from a crystallized material have 80 nrn voids (pores) in addition to an amorphous phase. The volume fraction of pores grows with increasing A. If a sample is prepared by crystallization from apre-orientedmelt, it does not contain discontinuities, and its noncrystalline regions consist of the amorphous material alone. In this case the density of the amorphous phasedoes not depend on the degree of sample orientation and has a constant magnitude typical of highly oriented PE samples.
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