Temperature Dependence of the Fano Resonance in Nanodiamonds Synthesized at High Static Pressures

The temperature dependence of the Fano resonance recently discovered in infrared spectra of nanodiamonds synthesized from chloroadamantane at high static pressures is investigated. For the first time, marked variations of the resonance parameters are observed. On heating, the shape of the Fano resonance changes considerably; the effect completely disappears above 350 degrees C, but is recovered after cooling to ambient conditions. Such behavior 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 a strong temperature dependence of the difference between the frequencies of infrared-active "bright" and Raman-active "dark" modes of nanodiamond. The frequency of the Raman dark mode is only weakly temperature-dependent.