Features of resonant Raman scattering in superhard amorphous carbon

The resonant Raman scattering phenomena in carbon nanoclusters formed by $sp^3$ bonds have been investigated. Such structures have been synthesized from fullerite C$_{60}$ at pressures of 20–25 GPa at room temperature and under heating to 1400 K. Two types of Raman resonance are observed. The first type is associated with the resonant enhancement of the Raman spectra near the absorption edge and has been observed for the prepared samples under laser excitation at wavelengths of 1064 and 532 nm. In such spectra, high-frequency $sp^3$ modes of all nanoclusters from 1388 to 1640 cm$^{-1}$ are observed. The second type of resonance manifests itself in the activation of one of the modes in the range of 1388–1640 cm$^{-1}$ of the Raman spectrum, depending on the exciting-radiation wavelength. The frequency of the active mode is a linear function of the exciting-radiation wavelength. The piezospectroscopy method has been used to show that under the excitation with a shorter wavelength, clusters with a larger bulk compression modulus are involved in the Raman scattering processes.