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Temperature dependence of Fano resonance in nanodiamonds synthesized at high static pressures

Temperature dependence of Fano resonance, recently discovered in infra-red (IR spectra of nanodiamonds synthesized from chloroadamantane at high static pressures, is investigated. For the first time, marked variations of the resonance parameteres are observed. On heating, the shape of the Fano resonance changes considerably; the effect completely disappears above 350 C, but is recovered after cooling to ambient conditions. Such behaviour implies that assignment of the Fano effect to the surface transfer doping mechanism is not very plausible for the studied samples. The resonance shape varies due to strong temperature dependence of the difference of frequencies of IR-active "bright" and Raman-active "dark" modes of nanodiamond. The frequency of the Raman "dark" mode is only weakly temperature-dependent.