COMPLEX DIELECTRIC FUNCTION OF AMORPHOUS DIAMOND FILMS DEPOSITED BY PULSED-EXCIMER-LASER ABLATION OF GRAPHITE

Amorphous diamond films have been synthesized by pulsed excimer- (ArF) -laser ablation of graphite at room temperature. Detailed studies of the energy-dependent complex dielectric function in the energy range up to 40 eV have been carried out by Kramers-Kronig dispersion analysis of transmission electron-energy-loss spectroscopy and spectroscopic ellipsometry. Distinct from those of graphitic amorphous carbon and diamondlike carbon, the optical constants of amorphous diamond films are closely related to those of crystalline diamond, but with a smooth structure, a decrease in strength, and band shift towards lower energies. The variation of the dielectric function from crystalline diamond to amorphous diamond is analogous to that of crystalline and amorphous semiconductors such as Si and Ge. The extracted optical energy band gap reaches 2.6 eV, the highest value among the reported results for amorphous carbon films. The study of the dielectric function and its relation to the band structure of amorphous diamond films has also confirmed their diamond character. All of this information provides further evidence of the existence of amorphous diamond.