Doomed Couple of Diamond with Terahertz Frequency: Hyperfine Quality Discrimination and Complex Dielectric Responses of Diamond in the Terahertz Waveband

The technology age of terahertz (THz) frequency is coming, with tremendous features and astonishing applications in various fields of science. Using THz time domain spectroscopy, we demonstrate experimentally, for the first time, the fingerprint absorption peaks and the complex dielectric response trends in a 0.1–3 THz frequency waveband, on intentionally synthesized and processed chemical vapor deposition polycrystalline and single-crystal diamond films with systematic quality difference. The two absorption signatures within the 0.1–3 THz frequency band, in which the atomic vibration is material-independent, are attributed to the sp2 phonon vibration modes of as-grown graphitic phases and/or defects. Regarding the complex dielectric responses of diamond in the THz waveband, the scattering effect resulting from the extended grain boundaries associated with concomitant pores (even gaps) (and/or extended crystal cleavage faults associated with amorphous carbon), as well as intrinsic lattice absorption resulting from increased sp2 impurities, have been taken into account. Especially the defect size comparable with the wavelength is also found to have a significant effect on the loss at a higher-frequency electromagnetic wave. These findings are expected to promote not only ultra-sensitive quality diagnosis for diamond but also verification of an ideal transmission material for THz waveband applications.