Cu-DLC films are prepared by cathode arc technique with double-excitation source.
Cu doping increases the size, ordering and amount of sp2-C clusters of Cu-DLC films.
A lower Cu content induces a nanostructure surface with finer particles.
The Eg and refractive index (n) of Cu-DLC composite films decrease with Cu content.
The n of Cu-DLC films is proportional to Eg but extinction coefficient is inversely.