Complex Dielectric Function of Amorphous Diamond Films Deposited by Pulsed Excimer (ArF) 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 diamond-like carbon, the optical constants of amorphous diamond films are closely related to that of crystalline diamond, but with a smooth band structure, a decrease in the magnitude strength, and band shift towards lower energies. The variation of dielectric function from crystalline diamond to amorphous diamond is analogue to those 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 of amorphous carbon films. The implication of dielectric function to the bond structure analysis of a-D films has also confirmed its diamond character. All of these provide further evidence of the existence of amorphous diamond....Dielectric function, Amorphous diamond, Laser ablation.